JP3968070B2 - Zinc-based plated steel for laser welding, method for producing the same, and laser welding method - Google Patents

Description

  The present invention relates to a zinc-based plated steel material, a manufacturing method thereof, and a laser welding method.

  Laser lap welding is performed on the galvanized steel materials or between the galvanized steel materials and other metal materials so that the zinc-based plating layer is sandwiched between the galvanized steel materials or between the galvanized steel materials and other metal materials. At this time, if the gap between the overlapping portions is zero or very small, a large number of welding defects (for example, pits, through holes, blow holes, etc.) may occur in the bead portion. The mechanical strength is reduced. The reason for this is that the low melting point and low boiling point zinc present in the zinc-based plating layer evaporates prior to the base material due to laser irradiation heat, and the gap between the overlapping parts is insufficient and there is no escape space for zinc vapor. As the zinc vapor passes through the molten pool as the matrix melts, the molten matrix explodes, creating pits and through holes, or zinc vapor is trapped in the molten matrix and blowholes are generated. is there. Here, “exploding” refers to a phenomenon in which the molten base material is blown off violently when zinc vapor passes through the molten pool of the base material.

  In order to secure a gap in the overlapped portion that serves as a escape path for zinc vapor and suppress the occurrence of welding defects, the overlapping is performed so that the tip of the protrusion provided on the plated steel plate a is in contact with the plated steel plate b, and then the steel plate a A method of forming a gradually narrowing gap between both contact portions (protrusions and clamps) by pressing and clamping a part slightly away from the protrusions of b against steel plates a and b is disclosed. (For example, see Patent Document 1). Further, a method of forming a gap when a convex punch is pushed into the rust-proof steel plate c, the periphery thereof is raised in an annular shape, and superimposed with the rust-proof steel plate d is disclosed (for example, Patent Document 2). reference). However, in any case, a process of providing protrusions and bulges on the steel material is necessary before welding, and there has been a problem of cost increase due to the introduction of new equipment and the increase of processes.

  Also, as a method to remove the zinc in the welded part before welding and suppress the generation of zinc vapor, the laser light is separated into two beams, and the zinc in the welded part is evaporated and separated by a preceding beam with a low energy density, followed by A method of welding with a high energy density beam is disclosed (see, for example, Patent Document 3). However, this method has a drawback in that the removal of zinc in the portion sandwiched between the galvanized steel plates that are overlapped becomes insufficient, and it is not an effective suppression measure for welding defects.

As a method of making zinc hard to evaporate and suppressing the generation of zinc vapor, oxide powders of elements whose standard free energy of formation ΔG ° of oxide is smaller than iron and larger than zinc are used as welds of galvanized steel sheets. Discloses a method of welding while supplying to (see, for example, Patent Document 4). The oxide of such an element does not oxidize iron in the welded portion, but oxidizes zinc to generate zinc oxide and suppresses evaporation of zinc. An element having a smaller standard free energy of formation ΔG ° of oxide is more easily oxidized, and the oxide is more stable. Therefore, the idea in Patent Document 4 is reasonable. However, as is apparent from the so-called Ellingham diagram (for example, see Non-Patent Document 1) in which the standard free energy of formation is plotted against the temperature, the standard free energy of formation of iron oxide in the temperature range from room temperature to about 1300 ° C. ΔG ° (Fe → Fe ₃ O ₄ or Fe → FeO) (hereinafter referred to as ΔG _Fe ) is larger than the standard free energy of formation of zinc oxide G ° (Zn → ZnO) (hereinafter referred to as ΔG _Zn ), but the difference between the two (| ΔG _Fe Since −ΔG _Zn |) is small, the ΔG ° difference (| ΔG _M −ΔG _Zn |) between the element M having the standard free energy of formation of oxide and zinc is even smaller between the two. Therefore, it is difficult for such an element oxide to oxidize zinc, and generation of zinc vapor cannot be effectively prevented. Further, if the temperature exceeds 1300 ° C., .DELTA.G _Fe is smaller than .DELTA.G _Zn, .DELTA.G ° is less than .DELTA.G _Fe, and large element improbable than .DELTA.G _Zn. Furthermore, in the example of Patent Document 4 described above, MnO (manganese (II) oxide) is used as the oxide powder, but the standard free energy of formation of MnO is ΔG _{Zn in} a wide temperature range from room temperature to about 1700 ° C. Since it is smaller, MnO cannot oxidize zinc (see, for example, Non-Patent Document 1). Accordingly, it is considered that zinc oxide, which is supposed to be generated by laser welding in the coexistence of galvanizing and MnO supplied to the weld, is not generated by the action of MnO. Further, with respect to the technique in Patent Document 4, the cost increase due to the introduction of equipment for accurately supplying an appropriate amount of oxide to the welded part has also been a problem. Furthermore, Mn compounds fall under the category of first-class designated chemical substances that are subject to the “Law Concerning Determination of Emissions of Specific Chemical Substances to the Environment and Promotion of Improvement of Management” (hereinafter referred to as the PRTR Law) When handling, it is required to notify the environment of emissions and issue a product safety data sheet (MSDS). It was.

  As another example, a method of fixing zinc to zinc oxide with a shielding gas containing carbon dioxide has been disclosed (see, for example, Patent Document 5 and Patent Document 6). In this case as well, an appropriate amount of gas is accurately welded. The cost increase due to the introduction of equipment to be supplied to the department and the use of gas was a problem.

  On the other hand, as a method of providing a cavity for first evaporating a compound having a boiling point lower than that of zinc during welding and releasing the zinc vapor pressure, a thin insert material made of organic material such as resin or cellophane tape is applied to the overlapping portion of the galvanized steel sheet. A method of welding after interposing is disclosed (for example, see Patent Document 7). During welding, organic substances such as resin with a lower boiling point than zinc evaporate first, and some of the zinc vapor escapes into the gaps formed, reducing not only the zinc vapor entering the molten steel, but also part of the organic carbon. It is said that zinc vapor easily escapes from the surface because it enters the molten steel and lowers its viscosity. However, many organic substances such as resins generate a large amount of hydrocarbon group decomposition gas at a temperature much lower than the boiling point of zinc (approximately 300 to 600 ° C) during welding, and the internal pressure around the weld zone increases rapidly. . Therefore, depending on the amount of galvanization, the type of organic insert material and the insertion method, in the case of resin coating (coating film), when the film thickness is approximately 5 to 25 μm, a large amount of decomposition gas is generated in a short time. There is a drawback that the molten base material is blown away or is easily trapped in the molten base material. Similar defects were found in the case of organic adhesive tapes. Furthermore, in the method using the organic insert material, there is a concern that a bad odor is generated by the above-described decomposition gas during welding, thereby deteriorating the working environment. In addition, since the organic insert material is more expensive than the galvanized steel sheet as the base material, the use of a thick organic insert material of 10 to 200 μm recommended by this technology has been a problem in terms of cost.

Japanese Patent Laid-Open No. 2001-162388 JP 2001-162387 A JP-A-4-231190 JP-A-8-215882 JP-A-6-328279 Japanese Unexamined Patent Publication No. 7-232293 Japanese Unexamined Patent Publication No. 6-7978 The Metallurgical Society of Japan, Introduction to Metal Chemistry, Volume 1, "Metal Physics", 1st edition, The Japan Institute of Metals, 81 (1996)

  The present invention has been made in order to solve the above-mentioned problems related to the laser lap welding technology of zinc-based plated steel materials, and does not require the introduction of new welding incidental equipment. Without using insert materials or PRTR-designated chemical substances that have an impact on the environment, the occurrence of welding defects is minimized, and the galvanized steel material for laser welding that does not deteriorate the appearance of the welded part, and its manufacturing method, It is another object of the present invention to provide a laser welding method using the zinc-based plated steel material.

  As a result of repeated studies to achieve the above-mentioned object, the inventors of the present invention have a specific melting point of 1500 ° C or lower and a boiling point or decomposition temperature of 1700 ° C or higher under normal pressure on a zinc-based plated steel material to be laser lap welded. A coating containing a metal oxide or a specific metal oxide that is oxidized or reduced when heated under normal pressure and can be converted into a metal oxide having a melting point of 1500 ° C. or lower and a boiling point or decomposition temperature of 1700 ° C. or higher is provided. If the laser welding is performed by sandwiching the film between the zinc-based plated steel materials or the overlapped portion of the zinc-based plated steel material and another metal material, the occurrence of welding defects can be minimized. And it discovered that a welded part external appearance was not reduced.

The present invention has been completed based on such knowledge, and the gist thereof is as follows.
(1) Film thickness containing 2 to 50% by volume of binder and metal oxide on at least part of the surface of the steel material coated with zinc or zinc-based alloy plating with a zinc adhesion amount of 20 g / m ² or more per side A zinc-based plated steel material having a film of 0.5 to 50 μm ,
The binder is one or more selected from organic-inorganic composites, inorganic sols, surfactants,
Wherein the metal oxide is a metal oxide having a SnO _2, Bi ₂ O ₃ or al one or two 1500 ° C. below the melting point and 1700 ° C. or higher boiling point or decomposition temperature at normal pressure is selected, SnO, BiO, When heated under normal pressure of one or more selected from Bi ₂ O ₄ and Bi ₂ O ₅ , it is oxidized or reduced to a metal oxide having a melting point of 1500 ° C. or lower and a boiling point or decomposition temperature of 1700 ° C. or higher. A zinc-based plated steel material for laser welding, which is a changeable metal oxide, or a mixture or composite oxide of a plurality of the metal oxides.
( 2 ) The zinc-based plated steel material for laser welding according to (1), wherein the metal oxide content in the film is 10% by volume or more.
( 3 ) The zinc-based plated steel material for laser welding according to (1), wherein 90% by volume or more of the metal oxide is fine particles having a particle size of 10 μm or less.
( 4 ) The surfactant is a branched alkylbenzene sulfonate (structure formula C _a H _{2a + 1} -C ₆ H ₄ -SO ₃ M, M ⁺ is a branched alkylbenzene sulfonate ion C _a H _{2a + 1-} Counter ion of C ₆ H ₄ —SO ₃ ^— , M = Na, NH ₄ , NH (C ₂ H ₄ OH) ₃ , or NH ₂ (C ₂ H ₄ OH) ₂ , and the carbon of the branched alkyl group the number a is 10 to 16), saturated alcohol sulfate (structural formula _{C b H 2b + 1 -OSO 3} M, M + is a saturated alcohol sulfate ion _{C b H 2b + 1 -OSO 3} - counterion M = Na, NH ₄ , NH (C ₂ H ₄ OH) ₃ , or NH ₂ (C ₂ H ₄ OH) ₂ , and the alkyl group has a carbon number b of 12 to 16), an unsaturated alcohol Sulfate salt (Structural formula C _c H _2c-1 -OSO ₃ M, C _c H _2c-3 -OSO ₃ M or C _c H _2c-5 -OSO ₃ M, M ⁺ is unsaturated alcohol sulfate ion C _{c ^{H 2c-1 -OSO 3 -,}} C c H 2c-3 - OSO 3 - or _{C c H 2c-5 -OSO 3} - in the counter _{ion, M = Na, NH 4,} NH (C 2 H 4 OH) ₃ or NH ₂ (C ₂ H ₄ OH) ₂ The carbon number c of the nyl group is 16 to 18), polyoxyethylene alkyl ether sulfate ester salt (structural formula C _d H _{2d + 1} O- (CH ₂ CH ₂ O) _m -SO ₃ M, M ⁺ is poly polyoxyethylene alkyl ether sulfate ion _{C d H 2d + 1 O- (} CH 2 CH 2 O) m -SO 3 - in the counter _{ion, M = Na, NH 4,} NH (C 2 H 4 OH) 3, or NH ₂ (C ₂ H ₄ OH) ₂ , wherein the alkyl group has a carbon number d of 12 to 18 and an ethylene oxide unit repeating number m of 2 to 4, and an α-olefin sulfonate (structural formula C _{e H 2e + 1 -CH = CH- (} CH 2) x -SO 3 M and _{C e H 2e + 1 -CH (} OH) - (CH 2) a mixture of _y -SO ₃ M, M ⁺ alkene sulfonate ion _{C e H 2e + 1 -CH =} CH- (CH 2) x -SO 3 - and hydroxy alkane sulfonic acid ion _{C e H 2e + 1 -CH (} OH) - (CH 2) y -SO 3 - counterion M = Na, NH ₄ , NH (C ₂ H ₄ OH) ₃ , or NH ₂ (C ₂ H ₄ OH) ₂ , the carbon number e of the alkyl group is 13 to 16, and the number of repetitions of the methylene group x , Y is 1-4), soap (structural formula C _f H _{2f + 1} -COOMe or C ₁₇ H ₃₃ -COOMe, Me ⁺ is a saturated fatty acid ion C _f H _{2f + 1} -COO ^- or oleic acid ion C ₁₇ H ₃₃ -COO ^- at the counter ion, Me = Na, K, NH ₄ , NH (C ₂ H ₄ OH) ₃ , or NH ₂ (C ₂ H ₄ OH) ₂ , and the alkyl group has a carbon number f of 11 to 17), polyoxyethylene alkyl ether (structure One selected from the formula C _g H _{2g + 1} O— (CH ₂ CH ₂ O) _n —H, the alkyl group carbon number g is 12 to 18, and the ethylene oxide unit repeat number n is 4 to 10. Or a zinc-based plated steel material for laser welding as described in ( 1 ), which is 2 or more types.
( 5 ) The surfactant is a branched alkylbenzene sulfonate sodium (structural formula C _a H _{2a + 1} -C ₆ H ₄ -SO ₃ Na, the branched alkyl group has a carbon number a of 10 to 16), saturated alcohol Sodium sulfate ester (structural formula C _b H _{2b + 1} -OSO ₃ Na, alkyl group carbon number b is 12-16), unsaturated alcohol sodium sulfate ester (structural formula C _c H _2c-1 -OSO ₃ Na, C _c H _2c-3 -OSO ₃ Na or C _c H _2c-5 -OSO ₃ Na, the carbon number c of the alkenyl group is 16 to 18), polyoxyethylene alkyl ether sulfate sodium (structure formula C _d H _{2d + 1 O- (CH 2 CH 2 O)} m -SO 3 Na, 12~18 carbon number d of the alkyl group, the repeating number m of the ethylene oxide units 2 to 4), alpha-olefin sodium sulfonate (formula C _e H _{2e + 1} -CH = CH- (CH ₂ ) _x -SO ₃ Na, a mixture of C _e H _{2e + 1} -CH (OH)-(CH ₂ ) _y -SO ₃ Na, the carbon number e of the alkyl group is 13 to 16, methylene group repeat number x, y is 1 to 4), sodium soap (structural formula C _f H _{2f + 1} -COONa or C ₁₇ H ₃₃ -COONa, carbon number f of the alkyl group is 11 to 17), polyoxyethylene alkyl ether (structural formula C _g H _{2g + 1} O- (CH ₂ CH ₂ O) _The zinc-based plated steel material for laser welding according to ( 4 ), wherein _n- H, the carbon number g of the alkyl group is 12 to 18, and the ethylene oxide unit repeating number n is one or more selected from 4 to 10) .
(6) at least a metal oxide having a SnO _2, Bi ₂ O ₃ or al least one of 1500 ° C. below the melting point and 1700 ° C. or higher boiling point or decomposition temperature at normal pressure is selected, SnO, BiO Metal oxide having a melting point of 1500 ° C. and a boiling point or decomposition temperature of 1700 ° C. or more that is oxidized or reduced when heated under normal pressure of one or more selected from Bi ₂ O ₄ and Bi ₂ O ₅ A treatment liquid in which one or both of metal oxides that can be changed into one and both and one or more binder components selected from organic-inorganic composites, inorganic sols, and surfactants are dispersed in a solvent, zinc Alternatively, it is characterized in that a coating containing metal oxide is formed by applying and drying at least part of the surface of a steel material obtained by coating zinc-based alloy plating with a zinc adhesion amount of 20 g / m ² or more per side. A method for producing galvanized steel for laser welding.
( 7 ) The method for producing a zinc-plated steel material for laser welding according to ( 6 ), wherein the film is formed only on a laser welded portion of the steel material.
( 8 ) The surfactant is a branched alkylbenzene sulfonate (structure formula C _a H _{2a + 1} -C ₆ H ₄ -SO ₃ M, M ⁺ is a branched alkylbenzene sulfonate ion C _a H _{2a + 1-} Counter ion of C ₆ H ₄ —SO ₃ ^— , M = Na, NH ₄ , NH (C ₂ H ₄ OH) ₃ , or NH ₂ (C ₂ H ₄ OH) ₂ , and the carbon of the branched alkyl group the number a is 10 to 16), saturated alcohol sulfate (structural formula _{C b H 2b + 1 -OSO 3} M, M + is a saturated alcohol sulfate ion _{C b H 2b + 1 -OSO 3} - counterion M = Na, NH ₄ , NH (C ₂ H ₄ OH) ₃ , or NH ₂ (C ₂ H ₄ OH) ₂ , and the alkyl group has a carbon number b of 12 to 16), an unsaturated alcohol Sulfate salt (Structural formula C _c H _2c-1 -OSO ₃ M, C _c H _2c-3 -OSO ₃ M or C _c H _2c-5 -OSO ₃ M, M ⁺ is unsaturated alcohol sulfate ion C _{c ^{H 2c-1 -OSO 3 -,}} C c H 2c-3 - OSO 3 - or _{C c H 2c-5 -OSO 3} - in the counter _{ion, M = Na, NH 4,} NH (C 2 H 4 OH) ₃ or NH ₂ (C ₂ H ₄ OH) ₂ The carbon number c of the nyl group is 16 to 18), polyoxyethylene alkyl ether sulfate ester salt (structural formula C _d H _{2d + 1} O- (CH ₂ CH ₂ O) _m -SO ₃ M, M ⁺ is poly polyoxyethylene alkyl ether sulfate ion _{C d H 2d + 1 O- (} CH 2 CH 2 O) m -SO 3 - in the counter _{ion, M = Na, NH 4,} NH (C 2 H 4 OH) 3, or NH ₂ (C ₂ H ₄ OH) ₂ , wherein the alkyl group has a carbon number d of 12 to 18 and an ethylene oxide unit repeating number m of 2 to 4, and an α-olefin sulfonate (structural formula C _{e H 2e + 1 -CH = CH- (} CH 2) x -SO 3 M and _{C e H 2e + 1 -CH (} OH) - (CH 2) a mixture of _y -SO ₃ M, M ⁺ alkene sulfonate ion _{C e H 2e + 1 -CH =} CH- (CH 2) x -SO 3 - and hydroxy alkane sulfonic acid ion _{C e H 2e + 1 -CH (} OH) - (CH 2) y -SO 3 - counterion M = Na, NH ₄ , NH (C ₂ H ₄ OH) ₃ , or NH ₂ (C ₂ H ₄ OH) ₂ , the carbon number e of the alkyl group is 13 to 16, and the number of repetitions of the methylene group x , Y is 1-4), soap (structural formula C _f H _{2f + 1} -COOMe or C ₁₇ H ₃₃ -COOMe, Me ⁺ is a saturated fatty acid ion C _f H _{2f + 1} -COO ^- or oleic acid ion C ₁₇ H ₃₃ -COO ^- at the counter ion, Me = Na, K, NH ₄ , NH (C ₂ H ₄ OH) ₃ , or NH ₂ (C ₂ H ₄ OH) ₂ , and the alkyl group has a carbon number f of 11 to 17), polyoxyethylene alkyl ether (structure One selected from the formula C _g H _{2g + 1} O— (CH ₂ CH ₂ O) _n —H, the alkyl group carbon number g is 12 to 18, and the ethylene oxide unit repeat number n is 4 to 10. Or the manufacturing method of the galvanized steel material for laser welding of ( 6 ) description which is 2 or more types.
( 9 ) The surfactant is a branched alkylbenzene sulfonate sodium (structural formula C _a H _{2a + 1} -C ₆ H ₄ -SO ₃ Na, the branched alkyl group has a carbon number a of 10 to 16), saturated alcohol Sodium sulfate ester (structural formula C _b H _{2b + 1} -OSO ₃ Na, alkyl group carbon number b is 12-16), unsaturated alcohol sodium sulfate ester (structural formula C _c H _2c-1 -OSO ₃ Na, C _c H _2c-3 -OSO ₃ Na or C _c H _2c-5 -OSO ₃ Na, the carbon number c of the alkenyl group is 16 to 18), polyoxyethylene alkyl ether sulfate sodium (structure formula C _d H _{2d + 1 O- (CH 2 CH 2 O)} m -SO 3 Na, 12~18 carbon number d of the alkyl group, the repeating number m of the ethylene oxide units 2 to 4), alpha-olefin sodium sulfonate (formula C _e H _{2e + 1} -CH = CH- (CH ₂ ) _x -SO ₃ Na, a mixture of C _e H _{2e + 1} -CH (OH)-(CH ₂ ) _y -SO ₃ Na, the carbon number e of the alkyl group is 13 to 16, methylene group repeat number x, y is 1 to 4), sodium soap (structural formula C _f H _{2f + 1} -COONa or C ₁₇ H ₃₃ -COONa, carbon number f of the alkyl group is 11 to 17), polyoxyethylene alkyl ether (structural formula C _g H _{2g + 1} O- (CH ₂ CH ₂ O) _The zinc-based plated steel material for laser welding according to ( 8 ), wherein _n- H, the carbon number g of the alkyl group is 12 to 18, and the ethylene oxide unit repetition number n is one or more selected from 4 to 10) Manufacturing method.
( 10 ) In the laser welding method for welding the overlapping portion of two metal materials using a laser beam, the zinc-based plating for laser welding according to any one of (1) to ( 3 ) on at least one metal material A laser welding method characterized by using a steel material and disposing the coating containing the metal oxide of the plated steel material so as to be sandwiched between the overlapping portions.

  The zinc-plated steel material for laser welding of the present invention only has to be provided with a functional film containing a specific metal oxide that enhances laser weldability and is environmentally friendly on a normal zinc-based plated steel material. The introduction of welding incidental equipment is unnecessary, and furthermore, as a binder for the metal oxide, if a cleaning agent suitable for organic soils such as fats and fats and inorganic soils such as inorganic salts and minerals is selected, Since the coating can be directly provided on the zinc-plated steel material contaminated with these materials without going through the process of removing these stains, the field of assembling of outer plates, structural materials, parts, etc. of automobiles and various vehicles As a steel material for laser lap welding with low cost and low environmental impact, the industrial value is extremely high.

  Hereinafter, embodiments of the present invention will be described in detail.

  In the present invention, a metal oxide having a melting point of 1500 ° C. or lower and a boiling point or decomposition temperature of 1700 ° C. or higher under normal pressure, or oxidized or reduced when heated under normal pressure to have a melting point of 1500 ° C. or lower and 1700 ° C. or higher. A metal material that can be converted into a metal oxide having a boiling point or a decomposition temperature, or a metal material that is laser-welded by providing a coating containing a plurality of mixtures or composite oxides of the metal oxides on the plating surface of a zinc-based plated steel material It is a major technical point to laser-weld the film in between the overlapping parts. When such a superposition part is irradiated with a laser, the metal oxide melts before and after the evaporation of zinc (boiling point 907 ° C.) in the plating layer as the temperature rises due to the heat of irradiation. Before the vapor pressure increases, the zinc vapor escapes through the molten pool of metal oxide, and the internal pressure of the overlapping portion is released smoothly. At this point, the base metal (melting point of steel at about 1540 ° C) at the laser irradiation site is not yet melted, so zinc vapor cannot pass through the base metal and does not create a weld defect. When the temperature rises above the melting point of the steel, the base metal at the laser irradiation site also melts, but since a considerable amount of zinc vapor has already been released, there is little zinc vapor passing through the molten pool of the base metal, and welding at the bead part The occurrence of defects can be minimized. When the temperature of the laser irradiation site rises above the boiling point of the metal oxide, the evaporation of the metal oxide begins, but since the boiling point is as high as 1700 ° C or higher, the vapor pressure is lower than that of zinc, and the molten base material is blown off violently. The internal pressure is not so high. Furthermore, the present inventors have analyzed the cross-section of the bead part after laser welding and confirmed that the metal oxide or its constituent elements are distributed throughout the bead part. It is considered that the metal oxide enters the molten base material, lowers its viscosity or surface tension, and makes it difficult for explosion of the molten base material and blowholes to occur. If the viscosity of the molten base material decreases, even if the zinc vapor pressure is relatively low, the melt easily deforms when subjected to pressure. As it is pushed, the steam is released smoothly without passing through with vigor. If the surface tension of the molten base material is lowered, the surrounding unmelted portion is easily wetted, and the melt is difficult to peel off from the solid surface and is difficult to explode.

The zinc-based plated steel material used in the present invention is a zinc-based plated steel material coated with zinc or zinc-based alloy plating having a zinc adhesion amount of 20 g / m ² or more per side. In the conventional plated steel material that does not have the coating film of the present invention, the present inventors may have a total zinc amount in the plating layer in a portion sandwiched between two metal materials of the overlapped portion of 20 g / m ² or more. For example, weld defects created by zinc vapor during laser welding have an adverse effect on the surface appearance, etc.Further, if the total zinc content in the plating layer in the overlapped portion is 40 g / m ² or more, weld defects caused by zinc vapor It becomes prominent and reveals that practical problems arise. The plating layer only needs to be in a portion sandwiched between the two metal materials of the overlapped portion to be laser welded. If such a requirement is satisfied, the plating layer may be only on one side of the zinc-based plated steel material. Even on both surfaces, there may be a portion that is not partially plated on at least one surface.

The steel used as the base material for the zinc-based plated steel used in the present invention is not particularly limited in its components, and may be plain steel or Cr-containing steel. In addition, the zinc-based plating coated on the surface of the zinc-based plated steel material is not particularly limited as long as it has a zinc adhesion amount of 20 g / m ² or more per side, and as an applicable plating layer, For example, zinc plating, zinc-based alloy plating made of zinc and further at least one of iron, aluminum, cobalt, tin, nickel, or zinc-based alloy plating containing a metal element or non-metal element other than these. It is done. The method for forming the plating layer is not particularly limited, and for example, electroplating, electroless plating, hot dipping, vapor phase plating, or the like can be used. The plating method may be either a continuous type or a batch type. For example, in hot dipping, the continuous type is mainly used for thin plate materials and wire materials, and the batch type plating is used for pipes, rolled materials, processed products, This is so-called post-plating by forming in a final product such as bolts / nuts, cast forgings, etc. and then dipping in a hot dipping bath.

  In addition, as the treatment after plating on the zinc-based plated steel material used in the present invention, zero spangle treatment that is uniform appearance after hot dipping, annealing treatment that is modification treatment of the plating layer, surface condition and material adjustment There may be temper rolling, but in the present invention, these are not particularly limited, and any of them can be applied.

  The metal oxide used in the present invention has a melting point of 1500 ° C. or lower under normal pressure and a boiling point or decomposition temperature of 1700 ° C. or higher, or is oxidized or reduced when heated under normal pressure, and has a melting point of 1500 ° C. or lower. It must be a metal oxide that can be converted into a metal oxide having a boiling point or decomposition temperature of 1700 ° C. or higher, or a mixture or complex oxide of said metal oxides. A metal oxide that can be converted into a metal oxide having a melting point of 1500 ° C. or lower and a boiling point or decomposition temperature of 1700 ° C. or higher is a metal oxide that forms the oxide in the air at 1500 ° C. or lower when heated under normal pressure. It refers to a substance that is oxidized by oxygen or reduced by oxygen desorption and changes to a metal oxide having a melting point of 1500 ° C. or lower and a boiling point or decomposition temperature of 1700 ° C. or higher.

  When the metal oxide is heated under normal pressure, the melting point of the metal oxide, or the melting point of the metal oxide obtained after oxidation or reduction of the metal oxide exceeds 1500 ° C, The metal oxide does not melt easily, and the metal oxide and the steel melt almost simultaneously, or the steel melts faster, so the high-pressure zinc vapor exceeding 1500 ° C passes through the steel molten pool vigorously. And significant welding defects occur. When the metal oxide is heated under normal pressure, the boiling point or decomposition temperature of the metal oxide, or the boiling point or decomposition temperature of the metal oxide obtained after oxidation or reduction of the metal oxide is below 1700 ° C, laser welding In this case, since the bead portion is heated to a temperature higher than 2000 ° C., the vapor pressure of the metal oxide in the overlapped portion is increased, and it passes through the molten pool of steel vigorously, resulting in significant welding defects. Further, due to the intense movement of the metal oxide vapor, the metal oxide is not efficiently dissolved in the molten steel, and the effect of lowering the viscosity or surface tension of the molten steel is reduced.

  In the present invention, the average film thickness of the film is preferably in the range of 0.5 to 50 μm. When the film thickness is less than 0.5 μm, the content of metal oxide in the film is small, and the molten pool is not sufficiently formed, so the zinc vapor is not released smoothly while the temperature is low, and the steel melts. Then, a large amount of zinc vapor passes through the molten steel at once, and a remarkable welding defect occurs. If it exceeds 50 μm, not only is the excellent effect of smoothly releasing zinc vapor within a low zinc vapor pressure saturated, but also the coating cost increases, so this is not suitable.

  In the present invention, the film coated on the surface of the galvanized steel material preferably contains 10% by volume or more of the metal oxide according to the present invention. If it is less than 10% by volume, the content of the metal oxide in the film is small and the molten pool is not sufficiently formed, so that a remarkable welding defect occurs for the same reason as described above. The entire film may be formed of only metal oxide.

  The metal oxide used in the present invention is preferably fine particles having a particle size of 90 μ% or more and a particle size of 10 μm or less, and more preferably 90% by volume or more is a particle having a particle size of 5 μm or less. When fine particles with a particle size of 10 μm or less are contained in less than 90% by volume (that is, the content of large particles having a particle size of more than 10 μm exceeds 10% by volume), the average film thickness of the film mainly composed of a metal oxide Particles having a size equal to or exceeding (0.5 to 50 μm) are increased, fine particles are unevenly distributed in the film, and surface unevenness is increased, resulting in a non-uniform film.

  The metal oxide fine particles used in the present invention may be produced by any method. For example, the metal oxide fine particles may be produced by mechanically pulverizing mineral lumps or particles of oxidized metal, synthesized by a vapor phase method, a wet method, or the like. The thing etc. which were granulated can be used.

  In the present invention, in order to determine whether 90% by volume or more of the metal oxide fine particles have a particle size of 10 μm or less, an aggregate of metal oxide particles to be used (a mixture of particles of various sizes). ) Plots the relationship between the particle size and the cumulative volume ratio in order from the smallest particle size, and reads `` d90 (90% particle size) '' where the cumulative volume ratio is 90%. Investigate. The measurement method at that time is to obtain d90 and particle size distribution by irradiating laser light in a state where powder is dispersed in a solvent and analyzing the interference fringes generated at that time, , Shimadzu SALD, CILAS CILAS, Horiba LA etc.

The metal oxide used in the present invention is not a designated chemical substance of the PRTR method . That is, oxides of Be, B, V, Cr, Mn, Co, Ni, As, Se, Mo, Cd, Sb, Hg or Pb (PRTR method first-class designated chemical substances), In, Te or Tl Oxides (same type 2 specified chemical substances) or complex oxides (1st class or 2nd class specified chemical substances) composed of two or more metal elements containing at least one of these metal elements in may have a 1500 ° C. below the melting point and 1700 ° C. or higher boiling point or decomposition temperature, is not used as the metal oxide in the present invention. For example, divanadium pentoxide (vanadium oxide (V), V ₂ O ₅ ; melting point 690 ° C., decomposition temperature 1750 ° C.), selenium oxide (SeO; melting point 1102 ° C., boiling point 1802 ° C.), indium (II) oxide (InO; melting point 1052 ° C, boiling point 1727 ° C), etc. ₂ (melting point 1470 ° C., boiling point> 1700 ° C.) composite oxides, etc., not used as the metal oxide of the present invention. The composite oxide referred to here is a neutral multicomponent oxide containing two or more kinds of metal ions. In the case of a two-component oxide, it is also called a double oxide.

In the present invention, a metal oxide having a melting point of 1500 ° C. or lower and a boiling point or decomposition temperature of 1700 ° C. or higher under normal pressure is selected from stannic oxide (tin oxide (IV ), SnO _2; mp 1127 ° C., decomposition temperature ≧ 1800 ° C.), bismuth oxide _{(III) (Bi 2 O 3} ; mp 820 ° C., one or a mixture of boiling point 1900 ° C.), cost, and, It is used from the point of performance expression that almost no weld defects are generated during laser welding. In the present invention, the metal oxide that can be converted to a metal oxide having a melting point of 1500 ° C. or lower and a boiling point or decomposition temperature of 1700 ° C. or higher when heated under normal pressure is a substance other than a PRTR-designated chemical substance. Among these oxides, stannous oxide (tin (II) oxide (SnO; becomes SnO ₂ when heated in air) ) , bismuth (II) oxide (BiO; Bi ₂ O ₃ when heated in air) Bismuth oxide (IV) (Bi ₂ O ₄ ; when heated, oxygen is desorbed at 305 ° C to become Bi ₂ O ₃ ), bismuth oxide (V) (Bi ₂ O ₅ ; when heated, oxygen is desorbed at 357 ° C and Bi One or a mixture of two or more of ( ₂ O ₃ ) is used from the viewpoint of cost and performance manifesting that almost no weld defects are generated during laser welding.

In the present invention, a binder is used because only a metal oxide is insufficient in film formability and adhesion to a zinc-based plated steel material. At that time, to coatings that zinc-plated steel, you containing 2 to 50% by volume binder to hold the metal oxide fine particles. When the film is formed on the plating surface, the binder binds the metal oxide fine particles and uniformly disperses them in the film, thereby causing the film to adhere to the plating surface. 2% by volume less than if the binder film, the kind of the metal oxide fine particles, and the force to bind the fine particles, you insufficient adhesion to the plated surface of the film. The effect that the binder binds the metal oxide fine particles is fully manifested in 2 to 50% by volume of the film, and the effect is saturated when it exceeds 50% by volume. It is not preferable to unnecessarily increase the volume%.

The binder, organic - inorganic composite, inorganic sol is one or a mixture of two or more of surfactants, from the environmental impact of the point of view, respectively, of water soluble organic - inorganic composite, aqueous inorganic Sol and aqueous surfactants are more preferred, and it is particularly preferred that each is not a designated chemical substance of the PRTR method. Water soluble organic - inorganic composite is coated on the plated surface, after drying, the form of such an emulsion or suspension water-soluble resin or water dispersible resin (water-insoluble resin to form a uniform film by the following peak metal temperature 250 ° C. And finely dispersed in water) is the main component and is not particularly limited as long as it is capable of binding the metal oxide fine particles to each other and improving the adhesion of the coating to the plating surface. Structures commonly found in such aqueous resins include, for example, those in which various hydrophilic groups are introduced into the molecular chain so that they can be dissolved or dispersed in water, and emulsions formed by emulsion polymerization or emulsion treatment after polymerization. Can be illustrated. Such water-soluble organic - Examples of the resin which can be used as the organic component of the inorganic composite, polyolefin resins, acrylic resins, polyurethane resins, polycarbonate resins, polyester resins, epoxy resins, phenol resins, other The thermosetting resin can be exemplified, and a crosslinkable resin is more preferable. However, it is better not to use PRTR-designated resins such as water-soluble or water-dispersible bisphenol A type epoxy resins . Water soluble organic - Inorganic composite, organopolysiloxanes modified with the aqueous organic resin or other organic components, the organic modified silicone and the like. Examples of the aqueous inorganic sol include those in which various hydrophilic groups are introduced on the surface of the colloid so that they can be dispersed in water. Examples of such colloid include various oxidations such as silica, alumina, ceria, titania, yttria, zirconia, and the like. The thing can be illustrated.

The aqueous surfactant is not particularly limited as long as it enhances the ability to bind the metal oxide fine particles to each other and the film adhesion to the plating surface. However, fats and oils such as animal and vegetable oils and mineral oils, human fats A cleaning agent capable of cleaning a plating surface contaminated with various organic substances such as fingerprints, sweat stains, carbohydrates, proteins, organic solvents, resins and pigments, and various inorganic substances such as inorganic salts and minerals is preferable. Such a cleaning agent is not particularly limited as long as it has an excellent detergency against organic soils and inorganic soils, but preferably an anionic surfactant or a nonionic surfactant having a strong ability to clean organic soils. Surfactant, or one or a mixture of two or more of these, having excellent ability to remove these from the plating surface even if the plating surface is heavily soiled, and relatively good wetting to the plating surface It is preferable to exhibit properties, film formability, adhesion between the metal oxide fine particles and the binder, and film adhesion to the plating surface. The main anionic surfactant that can be used in the present invention as such a detergent is a branched alkylbenzene sulfonate (hereinafter abbreviated as ABS. Structural formula C _a H _{2a + 1} -C ₆ H ₄ -SO ₃ M, M ⁺ branched alkylbenzene sulfonate ion _{C a H 2a + 1 -C 6} H 4 -SO 3 - in the counter ion, (constituting the sodium salt of branched alkylbenzenesulfonate) M = Na, NH ₄ (constituting ammonium salt), NH (C ₂ H ₄ OH) ₃ (constituting triethanolamine salt), or NH ₂ (C ₂ H ₄ OH) ₂ (constituting diethanolamine salt). Carbon number a is 10 to 16.), saturated alcohol sulfate ester salt (hereinafter abbreviated as saturated AS. Structural formula C _b H _{2b + 1} -OSO ₃ M, M ⁺ is saturated alcohol sulfate ion C _b H _{2b + 1} -OSO ₃ ^- in the counter ion, M = Na (constituting the sodium salts of saturated alcohol sulfates), (constituting the ammonium _{salt) NH 4, NH (C 2} H 4 OH) 3 ( Torietano Ruamine salt), or NH ₂ (C ₂ H ₄ OH) ₂ (diethanolamine salt) .Alkyl group carbon number b is 12 to 16), unsaturated alcohol sulfate ester salt (hereinafter abbreviated as unsaturated AS) Structural formula C _c H _2c-1 -OSO ₃ M, C _c H _2c-3 -OSO ₃ M or C _c H _2c-5 -OSO ₃ M, M ⁺ is unsaturated alcohol sulfate ion C _c H _{2c- ^{1 -OSO 3 -, C c H}} 2c-3 - OSO 3 - or _{C c H 2c-5 -OSO 3} - in the counter ion, (constituting the sodium salt of an unsaturated alcohol sulfate) M = Na, NH ₄ (Constituting ammonium salt), NH (C ₂ H ₄ OH) ₃ (constituting triethanolamine salt), or NH ₂ (C ₂ H ₄ OH) ₂ (constituting diethanolamine salt) The carbon number c of the alkenyl group is 16 to 18.), polyoxyethylene alkyl ether sulfate ester salt (hereinafter abbreviated as AES. Structural formula C _d H _{2d + 1} O— (CH ₂ CH ₂ O) _m —SO ₃ M, M ⁺ represents polyoxyethylene alkyl Ether sulfate ion C _d H _{2d + 1} O- (CH ₂ CH ₂ O) _m -SO ₃ ^- in the counter ion, (constituting the sodium salt of polyoxyethylene alkyl ether sulfuric acid esters) M = Na, (constituting the ammonium _{salt) NH 4, NH (C 2} H 4 OH) 3 ( triethanolamine salt Or NH ₂ (C ₂ H ₄ OH) ₂ (constituting a diethanolamine salt). The carbon number d of the alkyl group is 12 to 18, and the repeating number m of the ethylene oxide unit is 2 to 4. ), Α-olefin sulfonate (hereinafter abbreviated as AOS. Structural formula C _e H _{2e + 1} -CH = CH- (CH ₂ ) _x -SO ₃ M and C _e H _{2e + 1} -CH (OH)-( CH ₂ ) _y -SO ₃ M mixture, M ⁺ is alkene sulfonate ion C _e H _{2e + 1} -CH = CH- (CH ₂ ) _x -SO ₃ ^- and hydroxyalkane sulfonate ion C _e H _{2e + 1 -CH (OH) - (CH 2} ) y -SO 3 - in the counter ion, (constituting the sodium salt) M = Na, (constituting the ammonium _{salt) NH 4, NH (C 2} H 4 OH) 3 ( tri (Constitutes ethanolamine salt) or NH ₂ (C ₂ H ₄ OH) ₂ (constituts diethanolamine salt). The carbon number e of the alkyl group is 13 to 16, and the repeat number x and y of the methylene group are 1 to 4.) soap (structural formula C _f H _{2f + 1} -COOMe or C ₁₇ H ₃₃ -COOMe, Me ⁺ is a saturated fatty acid ion C _f H _{2f + 1} -COO ^- or oleic acid ion C ₁₇ H ₃₃ -COO ^- counterion in (constituting the sodium salts of fatty acids) Me = Na, (constituting the potassium salt) K, (constituting the ammonium _{salt) NH 4, NH (C 2} H 4 OH) 3 ( structure triethanolamine salt ), Or _{NH 2 (C 2 H 4 OH} ) 2 ( constituting a diethanolamine salt). Carbon number f of alkyl group is 11 to 17.), Also, non-ionic, which can be used in the present invention as a detergent The main surfactant is polyoxyethylene alkyl ether (hereinafter abbreviated as AE. Structural formula C _g H _{2g + 1} O— (CH ₂ CH ₂ O) _n —H, alkyl group carbon number g is 12 to 18. The number of repeating n of ethylene oxide units is 4 to 10.), and one or a mixture of two or more selected from these surfactants is used.

Since the sodium salt of the anionic surfactant has better detergency and degreasing power than the corresponding ammonium salt and triethanolamine salt, the sodium salt is preferable as the anionic surfactant used in the present invention. That is, sodium branched alkylbenzene sulfonate (structure formula C _a H _{2a + 1} -C ₆ H ₄ -SO ₃ Na, carbon number a of the branched alkyl group is 10 to 16), saturated alcohol sulfate sodium (structure formula C _b H _{2b + 1} -OSO ₃ Na, alkyl group carbon number b is 12-16), unsaturated alcohol sodium sulfate ester (structure formula C _c H _2c-1 -OSO ₃ Na, C _c H _2c-3 -OSO ₃ Na or C _c H _2c-5 -OSO ₃ Na, the carbon number c of the alkenyl group is 16-18, sodium polyoxyethylene alkyl ether sulfate ester (structure C _d H _{2d + 1} O- (CH ₂ CH ₂ O) _m -SO ₃ Na, carbon number d of the alkyl group is 12 to 18, repeating number m of ethylene oxide unit is 2 to 4), sodium α-olefin sulfonate (structural formula C _e H _{2e + 1} -CH = _{CH- (CH 2) x -SO 3} Na, C e H 2e + 1 -CH (OH) - (CH 2) a mixture of _y -SO ₃ Na, the number of carbon atoms e alkyl groups 13-16, the methylene group Repeat number x, y is 1 to 4), sodium soap (structural formula C _f H _{2f + 1} -COONa or C ₁₇ H ₃₃ -COONa, the alkyl group preferably has a carbon number f of 11 to 17). Of the branched sodium sodium alkylbenzene sulfonates, branched sodium dodecylbenzene sulfonate having 12 alkyl groups is particularly preferred.

  In addition to the above, monoethanolamine salts are also commonly used as detersive anionic surfactants. However, since monoethanolamine is a type 1 designated chemical substance in the PRTR method, it is not used in the present invention. Is good.

In addition, linear alkyl benzene sulfonate (hereinafter abbreviated as LAS, which is an anionic surfactant. Structural formulas C _h H _{2h + 1} -C ₆ H ₄ -SO ₃ M, M ⁺ are linear alkyl benzene sulfonate ions C _{h H 2h + 1 -C 6 H} 4 -SO 3 -. counterion carbon number h of straight chain alkyl groups of 10 to 14) has a detergency similar to the ABS, and inexpensive because, household It is widely used as a synthetic detergent and can be used as a binder for metal oxides in the present invention. However, LAS, unlike ABS, falls under the first-class designated chemical substance of the PRTR method, so it is better not to use it in the present invention as much as possible.

The anionic surfactant includes lauric acid ethanolamide, lauric acid diethanolamide, coconut oil fatty acid diethanolamide, as a nonionic surfactant that can enhance detergency by the combined use with an anionic surfactant. Fatty acid alkanolamides such as palm kernel oil fatty acid diethanolamide (Structural Formula C _i H _{2i + 1} -CONH-CH ₂ CH ₂ OH or C _i H _{2i + 1} -CON (CH ₂ CH ₂ OH) ₂ , carbon of alkyl group The number i may add 11 to 17). In addition, other anionic surfactants, nonionic surfactants, and amphoteric surfactants may be added as long as the detergency of the anionic surfactant and nonionic surfactant is not impaired. Good.

In the present invention, the water-soluble organic - inorganic composite, the aqueous inorganic sol, as well as single use of aqueous surfactant, may be used as a mixture of two or more, or modified to a binder.

  In the present invention, even when plating oxide or the like is attached to the surface of the zinc-based plated steel material, the film reacts with the plating oxide so that the film adheres to the plating coating surface of the zinc-based plated steel material. An agent, an etching agent, or the like may be included.

  The film comprising the metal oxide fine particles and the binder is formed by dispersing these in a solvent to prepare a treatment liquid, and applying and drying on at least a part of the surface of the galvanized steel material. It is preferable from the viewpoints of improving the dispersibility of the solid components therein and optimizing the viscosity of the processing solution. The solvent used in the present invention exerts an active action such as swelling, dissolution, modification, chemical reaction, etc. on the solvent inert to both the metal oxide fine particles and the binder, or at least one of the metal oxide fine particles and the binder. However, any solvent may be used as long as it does not cause a significant change in properties so as to impair the purpose of the present invention. However, it is a low environmental impact solvent and is not a dangerous substance defined by the Fire Service Act, in particular an aqueous solvent. Is preferred. Examples of the aqueous solvent include water, water adjusted to pH with various weak acids and weak alkalis, or water containing a small amount of a polar organic solvent such as ethanol, isopropyl alcohol, and methyl ethyl ketone. The method for dispersing the metal oxide fine particles and the binder in the solvent is not particularly limited, but in order to prepare a stable and uniform dispersion, a wetting agent is used to improve the wettability between the metal oxide fine particles and the binder and water. (Surfactant for the purpose of wetting), using a dispersing agent (surfactant for the purpose of dispersing) to increase the dispersibility of the fine particles and the binder, using a wetting agent and a dispersing agent together, the fine particles and the binder In order to prevent sedimentation, it is preferable to take measures such as adding a thickener, or chemically bonding acid groups to the surface of the fine particles by surface modification or the like to form an aqueous dispersion emulsion (emulsification). As an example of a specific dispersion method using a dispersing agent, a method in which an anionic or cationic surfactant is adsorbed on metal oxide fine particles or a binder, an electrostatic charge is applied to the particle surface, and particles are repelled. There is a method in which a nonionic surfactant having a relatively large molecular weight is supported on metal oxide fine particles or a binder to increase the apparent particle size and prevent aggregation by a steric hindrance effect. Wetting agents, dispersants and thickeners used to prepare dispersions provide uniform and stable particle dispersion, and good adhesion effect between metal oxide fine particles and binder, and plating surface after film formation. If it is a thing, it will not specifically limit. Such a dispersion is, for example, a colloidal dispersion if the fine particles are colloids, or a suspension if the particle size is approximately 0.1 μm or more, or an emulsion when the particles are emulsified.

  In the present invention, as a method of applying and drying a treatment liquid in which metal oxide fine particles and a binder are dispersed in a solvent on the surface of a zinc-based plated steel material, the treatment liquid is applied, dried, and then uniformly obtained at a final plate temperature of 250 ° C or less. There is no particular limitation as long as it is a method capable of forming a film. For example, metal dip to treatment bath, roll coating of treatment liquid, bar coating, brush coating, brush coating, spraying, etc., followed by heat drying or reaction with hot air, etc. The method may be formed and is not limited to the method described here.

  In the present invention, the film may be composed of 10% by volume or more of a dry solid of the aqueous sol of the metal oxide. The particle size of such an aqueous sol before drying is generally 0.0005 to 0.05 μm (0.5 to 50 nm), and a metal oxide treatment liquid mainly composed of an aqueous sol is applied to the surface of the zinc-based plated steel material and dried. As a method, as in the case of the treatment liquid in which the metal oxide fine particles and the binder are dispersed in a solvent, a uniform film can be formed at a final plate temperature of 250 ° C. or less after the treatment liquid is applied and dried. If there is, it does not specifically limit.

  In the zinc-based plated steel material for laser welding of the present invention, the coating may be provided only in a region where the plated steel material is irradiated with laser light. For example, after forming a part made of the plated steel material into a desired shape and then assembling each part by welding, the film is provided only on the part irradiated with laser light for welding after the forming process, and then overlapped When welding together, the coating cost is greatly reduced.

  The zinc-based plated steel material for laser welding of the present invention can be laser lap welded by overlapping the plated steel materials or the plated steel material and another metal material that can be laser welded. In the method, laser welding may be performed by arranging the overlapped portion so as to sandwich the coating provided on the plating coating surface of the plated steel material. At this time, it is preferable not to provide a gap between the surface of the film and the surface of the metal material to be overlap welded in order to prevent poor welding.

  In the present invention, in the case of having a base treatment film at the interface between the film and the plated steel material, the film composition is not particularly limited, but is not subject to legal regulations as a dangerous substance or a deleterious substance, or a designated chemical substance of the PRTR Law, and It is preferably formed of a compound that improves the adhesion between the film and the plated steel material. For example, zirconium, tungsten, titanium, aluminum, or a metal compound containing one or more rare earth elements, phosphate other than the metal compound, phosphite, hypophosphite, silica, Examples thereof include one or more compounds selected from a compound having a siloxane bond, a silane coupling agent, a titanium coupling agent, an organic resin, and the like.

  In the present invention, the film may contain various organic or inorganic compounds as long as the purpose is not impaired. Examples of such additives include various corrosion inhibitors, organic or inorganic pigments, dyes, crosslinking agents, solid and liquid lubricants, and the like.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited by these Examples.

[Zinc-based plated steel]
An alloyed hot-dip galvanized steel sheet having a thickness of 0.8 mm and an adhesion amount of 50 g / m ^{2 on} one side (coated with anti-rust oil so that the plating surface layer does not oxidize or rust) was used.

[Metal oxide]
(1) Tin oxide (tin oxide (IV), SnO ₂ ) fine particles (NanoTek manufactured by Kanto Chemical Co., Ltd., particle size range 17-122 nm)
(2) Bismuth (III) oxide (Bi ₂ O ₃ ) fine particles (NanoTek, manufactured by Kanto Chemical Co., Ltd., particle size range: 23 to 135 nm)
(3) stannic oxide sol (manufactured by Taki Chemical Co., Ltd., SnO ₂ , average diameter 8 nm, 10 mass% aqueous colloidal solution)
( 4 ) stannous oxide (tin (II) oxide, SnO) fine particles (mechanically pulverized granular reagent manufactured by Kanto Chemical Co., Ltd., particle size range 0.4 to 8.8 μm)
[binder]
(Non-machine-based sol)
( i ) Silica slurry (Dokai Chemical Industries, Ltd. Sun Lovely LFS, leaf-like SiO ₂ thickness 0.01-0.5 μm, leaf surface diameter 2-5 μm, 15 mass% aqueous dispersion)
( ii ) Alumina sol (Alumina sol-200 manufactured by Nissan Chemical Industries, Ltd., average length 100 nm, average width 10 nm, 10% by weight aqueous colloidal solution of feather-like Al ₂ O ₃ )
(Surfactant)
( iii ) Branched sodium dodecylbenzenesulfonate solution (branched sodium dodecylbenzenesulfonate 90% by weight, which is a reagent manufactured by Kanto Chemical Co., Ltd.) (Branched sodium dodecylbenzenesulfonate is one of the above-mentioned detergent ABS and has 12 carbon atoms in the alkyl group.)
( iv ) Sodium dioxyethylene lauryl ether sulfate solution (Emul E-27C manufactured by Kao Corporation, an aqueous solution of 27% by mass of sodium dioxyethylene lauryl ether sulfate. 1 with 12 carbon atoms in the alkyl group and 2 repeats of ethylene oxide units.)
( v ) Hexaoxyethylene lauryl ether solution (Emulgen 108 manufactured by Kao Corporation, 100% by mass of hexaoxyethylene lauryl ether, liquid at room temperature. Hexaoxyethylene lauryl ether is one of the above-mentioned cleaning agents AE and is an alkyl group containing carbon 12 , Number of ethylene oxide unit repeats 6.)
[Formation of film satisfying the requirements of the present invention]
(A) When surfactants ( iii ) to ( v ) are not used as binders After the zinc-based plated steel material is degreased with alkali, rust preventive oil is removed, and the surface is cleaned, the metal oxide fine particles (the metal An aqueous slurry in which an appropriate amount of binder (any one of the binders (i) to ( ii )) and distilled water are added to the oxide (1), (2), ( 4 )) and uniformly mixed, or The aqueous sol of metal oxide ( 3 ) was applied by a bar coater, dried in a hot air oven (about 80 ° C.), allowed to cool, and a dry film was formed on one side of the zinc-based plated steel material. A plated steel material was used. The film thickness after drying was any of 2 μm, 5 μm, 10 μm, and 20 μm.
(B) In the case where surfactants ( iii ) to ( v ) are used as binders, the surface of the galvanized steel was left as rust-preventive oil or other dirt, and was used as a test material without degreasing. An appropriate amount of binder ( iii ) and distilled water were added to the metal oxide fine particles (any one of the metal oxides (1) and (2)) and mixed uniformly to the steel material to which such dirt adhered. When the aqueous slurry was applied with a bar coater, the steel material surface was uniformly covered with the aqueous slurry regardless of the amount of rust preventive oil remaining on the surface of the test steel material, and no repelling occurred. When this was dried in a hot air oven (about 80 ° C.) and allowed to cool, the steel material surface was uniformly covered with a dry film, and almost no defective parts such as film peeling and cracking were found. Such a dry film was formed on one surface of a zinc-based plated steel material to obtain a zinc-based plated steel material for laser welding. The film thickness after drying was any of 2 μm, 5 μm, 10 μm, and 20 μm.

When using a binder (iv) or (v), the binder (iv), made of a non-for volatile content of the liquid, the metal oxide fine particles, an appropriate amount of binder (iv) or (v) and distilled water (v) Even if water is evaporated in a hot air furnace after applying the aqueous slurry to the steel material, a soft film that does not dry out is obtained. Since it is difficult to cut the coated steel material to the size of the material to be welded without impairing such a soft film, the film was formed by the following procedure when using the binder ( iv ) or ( v ). After cutting the zinc-based plated steel material with the rust-preventive oil into the size of the material to be welded (rectangular piece with a length of 120 mm and a width of 40 mm), aqueous slurry is applied with a bar coater, and the entire surface of the rectangular piece is aqueous. It was confirmed to get wet with the slurry. This is dried in a hot air oven (about 80 ° C), and the surface of the rectangular piece is uniformly covered with a film, and it is confirmed that there is no defect such as film peeling or cracking. For laser welding with a soft film A zinc-based plated steel material was used. The film thickness after moisture drying was 2 μm, 5 μm, 10 μm, or 20 μm.

[Formation of comparative material film]
As a comparative material, colloidal silica which is a metal oxide other than the metal oxide that satisfies the requirements of the present invention (Nissan Chemical Industry Co., Ltd. Snowtex ST-N, SiO ₂ particle size range 10-20 nm, 20% by weight aqueous Colloid solution: Melting point of dried solid film: 1710 ° C, boiling point: 2230 ° C, Alumina sol (Nissan Chemical Industry Co., Ltd. Alumina Sol-200, Feather Al ₂ O ₃ average length 100nm, average width 10nm, 10% by weight aqueous colloid Solution: Melting point of dry film 2055 ° C, boiling point 2980 ° C), Zirconia sol (ZSL-10A made by Nutex Co., Ltd., ZrO ₂ particle size range 3-5nm, 10% by weight aqueous colloidal solution. Melting point of dry film. The film was formed on one side of the galvanized steel material which had been degreased with alkali in the same manner as in the case of film formation (A) satisfying the requirements of the present invention using a temperature of about 2700 ° C. and a boiling point of about 4300 ° C.

  The constituent components of each film, their volume% in the film, and the film thickness are shown in Table 1, Table 2 (Continuation 1 of Table 1), and Table 3 (Continuation 2 of Table 1).

[Create welded material]
The zinc-based plated steel material provided with the above-mentioned film on one side and the zinc-based plated steel material not provided with a film containing no metal oxide containing alkali degreasing are cut into rectangular pieces each having a length of 120 mm and a width of 40 mm, and the film is sandwiched between them. In this way, the rectangular pieces were overlapped, and the plating surface was leveled and fixed with a clamp torque of 1470 N · cm. At this time, depending on the combination of the rectangular pieces to be overlaid, the film thickness after superposition (= distance between the plating surfaces of the steel materials facing each other through the film) is 0 μm (no film), 2 μm, 4 μm, 5 μm, 10 μm, 15 μm, 20 μm 40 μm was prepared. In the case of a rectangular piece provided with a soft film containing binder ( iv ) or ( v ), a metal foil with a thickness of 2 to 40 μm is inserted as a spacer between the two rectangular pieces, and the soft film is crushed when the clamp is pressed. I tried not to be. This metal foil was inserted at a position sufficiently away from the position where the weld bead was generated by receiving the laser beam.

[Laser welding conditions]
Using a continuous wave YAG laser, a laser beam is irradiated from directly above the workpiece (length 120mm, width 40mm), the center of the workpiece is scanned in the longitudinal direction from one end to the other, and welding is performed. Went.

Laser output: 4.0kW
Welding speed: 3, 4, 5, or 6 m / min Condensing position: Steel sheet surface Condensing diameter: 0.6 mm
Shielding gas: Nitrogen (Flow rate 30L / min)
[Evaluation of laser weldability]
The explosive dissipation (mass loss) of the welded material during welding, the amount of pits generated in the weld bead, and the blowhole occurrence rate were used as indicators of weldability. If the mass loss is large, in most cases, the bead portion will be thin, welding defects (pits, through-holes, blowholes, etc.) will occur frequently, the joint strength will decrease, and the welded portion surface appearance will deteriorate. The smaller the better. The amount of pits and blowhole occurrence rate correlate with joint strength, and the smaller the better.
(A) Evaluation by Explosion Dissipation Amount (Mass Loss) The mass difference before and after laser welding of the work piece was measured to determine the mass loss (g / 100 mm) per 100 mm weld bead length. By comparing the mass loss of the welded material with no coating at the overlapped part (superimposition of galvanized steel materials with no coating on the surface) and the material to be welded with the coating sandwiched at the same welding speed The weldability was determined. Assume that the mass loss of the material to be welded with the film sandwiched and the material to be welded without the film on the overlapped part is X and Y (g / 100 mm), respectively, and evaluated according to the following criteria.

Grade 4: X <0.3Y
3: 0.3Y ≦ X <0.5Y
2: 0.5Y ≦ X <0.8Y
1: 0.8Y ≦ X
(B) Evaluation by pit amount and blow hole occurrence rate Using a low-magnification (20x or 50x) magnifying glass, the occurrence of pits seen in the weld bead and blow-off inside the weld bead by X-ray transmission test The occurrence of holes was investigated. The blowhole generation rate was determined by the following formula, and the weldability was evaluated according to the following criteria.

Blow hole occurrence rate (%) = (total blow hole length along welding direction / weld length 120 mm) x 100
Score 5: There is no pit with a diameter of 0.1mm or more on the appearance, and no blowholes are generated.

      4: There are no pits with a diameter of 0.1mm or more on the appearance, and 0% <blow hole occurrence rate <3%.

      3: Appearance has 1 to 3 pits with a diameter of 0.1mm or more, and 0% ≤ blowhole generation rate <3%.

      2: Appearance has 1 to 3 pits with a diameter of 0.1 mm or more, and 3% ≤ blow hole generation rate <20%.

      1: Appearance has 4 or more pits with a diameter of 0.1 mm or more, or 20% ≦ blow hole occurrence rate.

  The above evaluation results are summarized in Table 4, Table 5 (Continuation 1 of Table 4), Table 6 (Continuation 2 of Table 4), Table 7 (Continuation 3 of Table 4), Table 8 (Continuation 4 of Table 4). It is shown in Table 9 (continuation 5 of Table 4).

The zinc-based plated steel material for laser welding that satisfies the requirements of the present invention is a zinc-based plated material with a rust-preventive oil attached, even when a film is formed on the zinc-based plated steel material from which the antirust oil has been removed and the surface has been cleaned. Even when an aqueous treatment solution containing a cleaning agent as a binder component is directly applied to steel and then a film is formed by moisture drying, when these films are stacked and laser welded, there is no film at the overlapped portion. Compared to the case (No. 31 to 34 ), a weld bead having a low appearance and a small appearance and having few welding defects such as pits and blow holes can be obtained. At that time, it is not necessary to introduce new welding incidental facilities, and expensive organic insert materials and PRTR-designated chemical substances that give a load to the environment are not used for the film formation.

On the other hand, when a metal oxide that does not satisfy the requirements of the present invention is used as the main component of the film (No. 49 to 58 ), the laser weldability is poor at any film thickness and any welding speed used in the test. Further, even if a metal oxide that satisfies the requirements of the present invention is used, if the content in the film is lower than the more preferable range in the present invention (No. 23 , 24 ), mass loss, pit, blowhole generation rate Since either of these was slightly higher, the score was not so high, and the weldability tended to be somewhat poor.

Claims (10)

At least a part of the surface of the steel material coated with zinc or zinc-based alloy plating with a zinc adhesion amount of 20 g / m ² or more per side, a film thickness of 2 to 50% by volume and a metal oxide containing 0.5 to 50 μm A zinc-based plated steel material having a coating of
The binder is one or more selected from organic-inorganic composites, inorganic sols, surfactants,
Wherein the metal oxide is a metal oxide having a SnO _2, Bi ₂ O ₃ or al one or two 1500 ° C. below the melting point and 1700 ° C. or higher boiling point or decomposition temperature at normal pressure is selected, SnO, BiO, When heated under normal pressure of one or more selected from Bi ₂ O ₄ and Bi ₂ O ₅ , it is oxidized or reduced to a metal oxide having a melting point of 1500 ° C. or lower and a boiling point or decomposition temperature of 1700 ° C. or higher. A zinc-based plated steel material for laser welding, which is a changeable metal oxide, or a mixture or composite oxide of a plurality of the metal oxides.   2. The galvanized steel material for laser welding according to claim 1, wherein the metal oxide content in the film is 10% by volume or more.   2. The zinc-based plated steel material for laser welding according to claim 1, wherein 90% by volume or more of the metal oxide is fine particles having a particle size of 10 μm or less. The surfactant is a branched alkylbenzene sulfonate (structure formula C _a H _{2a + 1} -C ₆ H ₄ -SO ₃ M, M ⁺ is a branched alkylbenzene sulfonate ion C _a H _{2a + 1} -C ₆ H ₄ -SO ₃ ^- in the counter _{ion, M = Na, NH 4,} NH (C 2 H 4 OH) 3, or a _{NH 2 (C 2 H 4 OH} ) 2, the number of carbon atoms a branched alkyl group is a 10 to 16), saturated alcohol - in counterion ^- Le sulfates (structure _{C b H 2b + 1 -OSO 3} M, M + is a saturated alcohol sulfate ion C _b H _{2b + 1} -OSO ₃ M = Na, NH ₄ , NH (C ₂ H ₄ OH) ₃ , or NH ₂ (C ₂ H ₄ OH) ₂ , and the alkyl group has a carbon number b of 12 to 16), an unsaturated alcohol Sulfate ester salt (Structural formula C _c H _2c-1 -OSO ₃ M, C _c H _2c-3 -OSO ₃ M or C _c H _2c-5 -OSO ₃ M, M ⁺ is unsaturated alcohol sulfate ion C ^{_{c H 2c-1 -OSO 3 -}} , C c H 2c-3 - OSO 3 - or _{C c H 2c-5 -OSO 3} - in the counter _{ion, M = Na, NH 4,} NH (C 2 H 4 OH ) ₃ or NH ₂ (C ₂ H ₄ OH) ₂ and alkenyl Group having a carbon number c of 16 to 18), polyoxyethylene alkyl ether sulfate ester salt (structural formula C _d H _{2d + 1} O- (CH ₂ CH ₂ O) _m -SO ₃ M, M ⁺ is polyoxy polyoxyethylene alkyl ether sulfate ion _{C d H 2d + 1 O- (} CH 2 CH 2 O) m -SO 3 - in the counter _{ion, M = Na, NH 4,} NH (C 2 H 4 OH) 3, or NH ₂ (C ₂ H ₄ OH) ₂ , wherein the alkyl group has a carbon number d of 12 to 18, the ethylene oxide unit repeat number m is 2 to 4, and an α-olefin sulfonate (structural formula C _e H _{2e + 1} -CH = CH- (CH ₂ ) _x -SO ₃ M and C _e H _{2e + 1} -CH (OH)-(CH ₂ ) _y -SO ₃ M, M ⁺ is alkene sulfonate ion C _{e H 2e + 1 -CH = CH-} (CH 2) x -SO 3 - and hydroxy alkane sulfonic acid ion _{C e H 2e + 1 -CH (} OH) - with counter-ion ^- (CH _{2) y} -SO ₃ , M = Na, NH ₄ , NH (C ₂ H ₄ OH) ₃ , or NH ₂ (C ₂ H ₄ OH) ₂ , the carbon number e of the alkyl group is 13 to 16, the repeat number x of the methylene group x, y is 1 to 4), soap (structure formula C _f H _{2f +1} -COOMe or C ₁₇ H ₃₃ -COOMe, Me ⁺ is a saturated fatty acid ion C _f H _{2f + 1} -COO ^- or oleic acid ion C ₁₇ H ₃₃ -COO ^- at the counter ion, Me = Na, K, NH ₄ , NH (C ₂ H ₄ OH) ₃ , or NH ₂ (C ₂ H ₄ OH) ₂ , and the alkyl group has a carbon number f of 11 to 17), polyoxyethylene alkyl ether (structure C _g H _{2g + 1} O— (CH ₂ CH ₂ O) _n —H, wherein the alkyl group has a carbon number g of 12 to 18, and the ethylene oxide unit repeat number n is 4 to 10). or in a claim 1 laser welding galvanized steel according. The surfactant is sodium branched alkylbenzene sulfonate (structural formula C _a H _{2a + 1} -C ₆ H ₄ -SO ₃ Na, the branched alkyl group has a carbon number a of 10 to 16), saturated alcohol sulfate sodium (Structural formula C _b H _{2b + 1} -OSO ₃ Na, alkyl group carbon number b is 12 to 16), unsaturated alcohol sodium sulfate ester (structural formula C _c H _2c-1 -OSO ₃ Na, C _c H _{2c -3} -OSO ₃ Na or C _c H _2c-5 -OSO ₃ Na, the carbon number c of the alkenyl group is 16 to 18), polyoxyethylene alkyl ether sulfate sodium (structure formula C _d H _{2d + 1} O- ( CH ₂ CH ₂ O) _m -SO ₃ Na, alkyl group carbon number d is 12-18, ethylene oxide unit repeat number m is 2-4), α-olefin sulfonate sodium (structural formula C _e H _{2e + 1 -CH = CH- (CH 2)} x -SO 3 Na, C e H 2e + 1 -CH (OH) - (CH 2) a mixture of _y -SO ₃ Na, the number of carbon atoms e alkyl group 13-16 , Repeat number of methylene group x, y is 1 to 4), sodium soap (structural formula C _f H _{2 f + 1} -COONa or C ₁₇ H ₃₃ -COONa, carbon number f of the alkyl group is 11 to 17), polyoxyethylene alkyl ether (structural formula C _g H _{2g + 1} O- (CH ₂ CH ₂ O) _n- 5. The galvanized steel material for laser welding according to claim 4 , wherein the carbon number g of H and the alkyl group is 12 to 18 and the repeating number n of ethylene oxide units is one or more selected from 4 to 10). At least, a metal oxide having a SnO _2, Bi ₂ O ₃ or al least one of 1500 ° C. below the melting point and 1700 ° C. or higher boiling point or decomposition temperature at normal pressure is selected, SnO, BiO, Bi ₂ When heated under normal pressure of one or more selected from O ₄ and Bi ₂ O ₅ , it can be oxidized or reduced to change to a metal oxide having a melting point of 1500 ° C. or lower and a boiling point or decomposition temperature of 1700 ° C. or higher. Zinc or zinc-based treatment liquid in which one or both of metal oxides and one or more binder components selected from organic-inorganic composites, inorganic sols, and surfactants are dispersed in a solvent the alloy plating was applied and dried on at least a portion of one surface per 20 g / m ² or more zinc coating weight coated to become the steel surface, for laser welding, which comprises forming a film containing metal oxide A method for producing galvanized steel. 7. The method for producing a zinc-based plated steel material for laser welding according to claim 6, wherein the coating is formed only on a laser welded portion of the steel material. The surfactant is a branched alkylbenzene sulfonate (structure formula C _a H _{2a + 1} -C ₆ H ₄ -SO ₃ M, M ⁺ is a branched alkylbenzene sulfonate ion C _a H _{2a + 1} -C ₆ H ₄ -SO ₃ ^- in the counter ion, M = Na, an _{NH 4, NH (C 2 H} 4 OH) 3 or _{NH 2 (C 2 H 4 OH} ) 2,, the number of carbon atoms a branched alkyl group is a 10 to 16), saturated alcohol sulfate (structural formula _{C b H 2b + 1 -OSO 3} M, M + is a saturated alcohol sulfate ion _{C b H 2b + 1 -OSO 3} - in the counter ion, M = Na, NH ₄ , NH (C ₂ H ₄ OH) ₃ or NH ₂ (C ₂ H ₄ OH) ₂ , the alkyl group has a carbon number b of 12 to 16), an unsaturated alcohol sulfate ester salt ( Structural formula C _c H _2c-1 -OSO ₃ M, C _c H _2c-3 -OSO ₃ M or C _c H _2c-5 -OSO ₃ M, M ⁺ is unsaturated alcohol sulfate ion C _c H _{2c-1 ^{-OSO 3 -, C c H 2c}} -3 - OSO 3 - or _{C c H 2c-5 -OSO 3} - in the counter _{ion, M = Na, NH 4,} NH (C 2 H 4 OH) 3, or NH ₂ is a _{(C 2 H 4 OH) 2} , alkenyl Carbon atoms and c is 16 to 18), polyoxyethylene alkyl ether sulfate (structural formula _{C d H 2d + 1 O- (} CH 2 CH 2 O) m -SO 3 M, M + polyoxyethylene alkyl ether sulfate ion _{C d H 2d + 1 O- (} CH 2 CH 2 O) m -SO 3 - in the counter _{ion, M = Na, NH 4,} NH (C 2 H 4 OH) 3, or NH ₂ (C ₂ H ₄ OH) ₂ in which the alkyl group has a carbon number d of 12 to 18, the ethylene oxide unit repeat number m is 2 to 4, and an α-olefin sulfonate (structure formula C _e H _{2e +1 -CH = CH- (CH 2)} x -SO 3 M and _{C e H 2e + 1 -CH (} OH) - (CH 2) a mixture of _y -SO ₃ M, M ⁺ alkene sulfonate ion C _{e H 2e + 1 -CH = CH- (} CH 2) x -SO 3 - and hydroxy alkane sulfonic acid ion _{C e H 2e + 1 -CH (} OH) - with ^{_{counter-ion, - (CH 2) y -SO}} 3 M = Na, NH ₄ , NH (C ₂ H ₄ OH) ₃ , or NH ₂ (C ₂ H ₄ OH) ₂ . The carbon number e of the alkyl group is 13 to 16, the repeating number of the methylene group x, y is 1 to 4), soap (structural formula C _f H _{2f + 1} -COOMe or C ₁₇ H ₃₃ -COOMe, Me ⁺ is saturated fatty acid ion C _f H _{2f + 1} -COO ^- or oleic acid ion C ₁₇ H ₃₃ -COO ^- at the counter ion, Me = Na, K, NH 4, NH (C 2 H 4 OH) 3, or NH ₂ (C ₂ H ₄ OH) ₂ and the carbon number f of the alkyl group is 11 to 17), polyoxyethylene alkyl ether (structural formula C _g H _{2g + 1} O- (CH ₂ CH ₂ O) _n- 7. The galvanized steel material for laser welding according to claim 6 , wherein the number of carbon atoms g of the alkyl group is 12 to 18, and the number of repetitions of ethylene oxide units n is 4 to 10. Manufacturing method. The surfactant is sodium branched alkylbenzene sulfonate (structural formula C _a H _{2a + 1} -C ₆ H ₄ -SO ₃ Na, the branched alkyl group has a carbon number a of 10 to 16), saturated alcohol sulfate sodium (Structural formula C _b H _{2b + 1} -OSO ₃ Na, alkyl group carbon number b is 12 to 16), unsaturated alcohol sodium sulfate ester (structural formula C _c H _2c-1 -OSO ₃ Na, C _c H _{2c -3} -OSO ₃ Na or C _c H _2c-5 -OSO ₃ Na, the carbon number c of the alkenyl group is 16 to 18), polyoxyethylene alkyl ether sulfate sodium (structure formula C _d H _{2d + 1} O- ( CH ₂ CH ₂ O) _m -SO ₃ Na, alkyl group carbon number d is 12-18, ethylene oxide unit repeat number m is 2-4), α-olefin sulfonate sodium (structural formula C _e H _{2e + 1 -CH = CH- (CH 2)} x -SO 3 Na, C e H 2e + 1 -CH (OH) - (CH 2) a mixture of _y -SO ₃ Na, the number of carbon atoms e alkyl group 13-16 , Repeat number of methylene group x, y is 1 to 4), sodium soap (structural formula C _f H _{2 f + 1} -COONa or C ₁₇ H ₃₃ -COONa, carbon number f of the alkyl group is 11 to 17), polyoxyethylene alkyl ether (structural formula C _g H _{2g + 1} O- (CH ₂ CH ₂ O) _n- 9. The production of a zinc-based plated steel material for laser welding according to claim 8 , wherein the carbon number g of the alkyl group is 12 to 18, and the ethylene oxide unit repeating number n is one or more selected from 4 to 10). Method. In the laser welding method of welding the overlapped portion of two metal materials using a laser beam, the zinc-based plated steel material for laser welding according to any one of claims 1 to 3 is used for at least one metal material, A laser welding method, wherein a coating containing a metal oxide of a plated steel material is disposed so as to be sandwiched between the overlapping portions.