JPH0711070B2 - Galvanized steel sheet with excellent weldability, pressability and chemical conversion treatment - Google Patents

Description

TECHNICAL FIELD The present invention relates to a zinc-based plated steel sheet having excellent weldability, pressability and chemical conversion treatability.

(Prior Art) As a method for improving the weldability of a zinc-based plated steel sheet,
For example, as shown in Japanese Patent Laid-Open No. 55-110783, an oxide film such as Al ₂ O _{3 is} formed on the surface of a plated steel sheet, and the high melting point and high electric resistance of the oxide are used to improve the weldability. At the same time, it has been proposed that the contact between the electrode tip and the plated metal is prevented to prevent melting damage of the tip to extend the life.

Further, as disclosed in JP-A-59-104463, it is proposed to heat-treat the surface of a plated steel sheet to form an oxide film having a ZnO / Zn ratio of 0.1 to 0.70 and similarly improve weldability. Has been done.

However, even with such a method, it is still difficult to obtain satisfactory results on an industrial scale, and there is a strong demand for improvement in weldability of plated steel sheets.

As a method for improving the pressability of the galvanized steel sheet, for example, as described in JP-A-62-185883,
A method of forming an oxide film of Cr ₂ O ₃ by subjecting the plated steel plate surface to electrolytic chromate treatment and forming a hard film on a zinc-based plated steel plate as described in JP-A-62-192597, and pressing There is disclosed a method of improving the lubricity of a press by preventing galling and die galling at the time.

Further, as described in JP-A 1-136952, it is disclosed that the surface of a plated steel sheet is coated or coated with an organic material such as an organic lubricating film or a lubricating oil to improve pressability.

(Problems to be Solved by the Invention) However, such products have the following inadequate points when used by automobile users and the like.

The outline of the process used by automobile users consists of the process of washing the steel plate with oil, the pressing process, the degreasing process, the chemical conversion treatment process, and the painting process.In the case of electrolytic chromate treated steel plates, the chemical conversion treatment is performed in the chemical conversion treatment process. In the case of a steel sheet on which no coating film is formed and a lubricating oil or a lubricating coating is applied to the steel sheet, the oil falls off in the cleaning process, so that sufficient lubricating performance is not exhibited.
Furthermore, the degreasing process before the chemical conversion treatment imposes a load, resulting in an increase in cost. On the other hand, zinc-plated steel sheets that have been subjected to iron-zinc alloy flash plating have problems such as higher steel sheet costs compared to electrolytic chromate treatment, low cost, chemical conversion treatment, degreasing, etc. It is desired to develop a zinc-based plated steel sheet that is excellent in pressability without imposing a load on the above process.

Further, as described above, there is a strong demand for a zinc-based plated steel sheet which is excellent in chemical conversion treatment in combination with weldability and pressability.

(Means for Solving the Problems) The gist of the present invention is as follows.

(1) ZnO content on the surface of zinc-plated steel sheet is 30 to 3000 mg / m ²
Oxide, Mn oxide, P oxide, Mo oxide,
Co oxide, Ni oxide, Ca oxide, W oxide, V oxide, or one or more of boric acid is coated at 1 to 500 mg / m ² (as the amount of metal in the oxide). A zinc-based plated steel sheet having excellent weldability, pressability, and chemical conversion treatment characteristics.

(2) The weldability, pressability, and chemical conversion treatability according to the above 1, wherein the upper oxide layer contains 1 to 500 mg / m ² of one or more of SiO ₂ , TiO ₂ , and Al ₂ O ₃ . Excellent zinc-based plated steel sheet.

The zinc-based plated steel sheet of the present invention is a hot-dip galvanizing method, an electroplating method, a vapor deposition plating method, a thermal spraying method, and various other manufacturing methods.The plating composition is pure Zn, Zn and Fe, and Zn. And Ni, Zn and Al, Zn and Mn, Zn and Cr, Zn and P, etc. Z
Containing n as a main component and one or more alloy elements and impurity elements for improving various functions such as corrosion resistance.

There are also ceramic fine particles such as SiO ₂ and Al ₂ O ₃ , oxides such as TiO ₂ and organic polymers dispersed in the plating layer. Alternatively, there is a layered composition. Further, a steel sheet coated with an organic film in which particles containing Zn as a main component are dispersed is also covered. For example, an alloyed hot-dip galvanized steel sheet obtained by heating a galvanized steel sheet and a base iron to form an alloy, zinc and its alloys (for example, iron, nickel, chrome, etc. by electroplating or vapor deposition plating). Alloy) and a steel plate
Steel sheet alloyed with base iron by heating to ~ 550 ° C, not only single alloy layer but also multi-layer alloy plating by electroplating method, SiO ₂ , Al ₂ O ₃ etc. in the plating layer Dispersed ceramic particles, on these plated layers,
Alternatively, there is a steel sheet directly coated with an organic coating containing zinc particles. As the form of the rustproof steel plate, there are a double-sided plating, a single-sided plating, and a dissimilar plated steel plate having different platings on the upper and lower surfaces.

The present inventors, regardless of the type of galvanized steel sheet,
As long as the plating is mainly composed of Zn, the surface of the plated steel is Zn
It was found that by forming O, electrode protection metal containing Fe and Zn as the main components is generated at the tip of the electrode tip in spot welding, and the life of the electrode tip is greatly improved.

In the above-mentioned conventional plated steel sheet, it was unstable to form an oxide film mainly composed of ZnO in an amount of ZnO of 30 to 3000 mg / m ² (per surface) which is considered to have good weldability. here,
The oxide film mainly composed of ZnO may be, for example, a film containing not only ZnO in the oxide but also a component element contained in the plating layer or a compound such as an oxide thereof. In addition, in an electrochemical treatment such as anodization, a component or compound contained in the treatment liquid may be contained.

In order to form an oxide film mainly composed of ZnO on the surface of the galvanized layer, the present inventors contact the steel sheet with an acid-containing oxidant aqueous solution as a first method to form an oxide film mainly composed of ZnO. It has been found that it becomes easy to generate 30 to 3000 mg / m ² (per one side) with a ZnO amount, and a zinc-based plated steel sheet having excellent weldability can be provided. The function of the acid is to dissolve some of the plating layer surface to supply ions such as Zn from the plating layer, and to increase the pH of the solution in contact with the plating layer, and the oxidizer at the plating layer surface. It functions to oxidize Zn etc. in the bath to form an oxide film mainly composed of ZnO on the surface of the plating layer.

By containing, for example, 10 to 100 g / l of HNO ₃ as an oxidizing agent, Zn or the like can be oxidized to form an oxide film mainly containing ZnO on the surface of the plating layer. The lower limit of HNO ₃ is set to 10 g / l because if it is less than that, it becomes difficult to oxidize and an oxide film cannot be formed. Further, the upper limit of HNO ₃ is set to 100 g / l, the effect as an oxidant is saturated even if it is contained in excess of that, dissolves Zn and Fe on the surface of the alloy layer,
This is because the dissolution of Fe increases the amount of Fe oxide produced and reduces the effect of improving the life of the spot welding tip.

Furthermore, as an oxidizing agent, KMnO ₄ , Ca (ClO) ₂ , K ₂ Cr ₂ O ₇ , NaClO ₃ ,
By adding ClO ₂ , KNO ₃ , NaNO _3, etc., the formation of the surface film is promoted.

As a method for bringing the aqueous solution of Zn (NO ₃ ) ₂ and HNO ₃ into contact with the steel sheet, any method such as dipping or spraying may be used.
Also, after spraying by dipping or spraying, for example, if a dry heating gas is blown to the surface or the steel sheet is heated to about 100 ° C or less, even a thinner solution becomes a concentrated solution due to evaporation of water and reacts at high temperature, which is effective. Can be processed.

Thus, the composition of the oxide film and the like generated by performing the oxide film generation treatment is ZnO as a main component of Fe oxide, Zn and Fe hydroxide, which may be a single substance or a mixture of impurities such as Al. May be included. However, an oxide film containing a large amount of ZnO component, which uniformly covers the surface and has a low film resistance, is desirable from the characteristics of the surface film.

In order to form an oxide film mainly composed of ZnO, by using Zn (NO ₃ ) ₂ 100 to 600 g / l as a supplementary agent for Zn ions,
When the pH of the oxidant aqueous solution is 4 or less, it contributes to activation of the surface of the plating layer, and Zn ions can be supplied to generate ZnO.

The lower limit of Zn (NO ₃ ) ₂ is set to 100 g / l because if it is less than that, Zn oxide on the surface of the alloy layer is insufficient and an oxide film cannot be generated. In addition, the upper limit of 600 g / l is that if it exceeds that, too much film will be generated, resistance will become large, and due to resistance heat generation with the electrode tip during welding,
This is because the increase in electrode tip diameter causes deterioration of weldability.

The treatment bath contains Fe and Zn in the plating, Mn, Al, P as impurities,
Si etc. may melt out. Of these, if Zn ions are added to the bath beforehand, it is not necessary to dissolve and supply Zn ions from the plating layer, and ZnO can be used in a shorter time.
Is preferable because it causes precipitation of. In addition, it is desirable to suppress elution of other impurities to be as small as possible. Especially Fe
When it contains more than 1 g / l, Fe oxides and hydroxides are generated on the surface and the surface turns yellow, deteriorating the product quality of the steel sheet surface, and Fe oxides and hydroxides are resistance films. Therefore, the life of the spot welding tip is shortened. Therefore, the Fe ion concentration is not specified in the present invention, but it is desirable to make it as low as possible.

In order to form an oxide film mainly composed of ZnO, the steel plate is Z
N (NO ₃ ) ₂ 100-600 g / l and HNO ₃ 10-100 g / l are added to the oxidant aqueous solution at a bath temperature of 30-80 ° C for 0.2-10 seconds to form an oxide film. be able to.

The treatment bath temperature was set to 30 to 80 ° C and the lower limit was set to 30 ° C to facilitate the oxidation of Zn ions on the plating surface, and below that, the reaction rate was slow and it was difficult to obtain a surface film. . Further, the upper limit is set to 80 ° C. because the reaction proceeds too much and an oxide film is excessively generated to deteriorate the weldability. Of course, the contact time may be shortened even if the temperature exceeds 80 ° C, but it is difficult to control the temperature at a high temperature when the time is shortened, so the temperature is preferably 80 ° C or lower.

Therefore, depending on the balance with the line speed, the contact treatment time such as dipping or spraying was set to 0.2 to 10 seconds because the oxide film generation treatment is insufficient if it is less than 0.2 seconds and the weldability does not improve. The reason is that even if the treatment is performed for more than 10 seconds, the oxide film is excessively generated and the weldability is deteriorated.

As the second method, for example, Zn (NO ₃ ) ₂ .6H ₂ O: 40
In an aqueous solution of 0 g / l, HNO ₃ : 1 g / l, using zinc-based plated steel sheet as a cathode, current density of 1 to 20 A / dm ² and treatment time of 0.5 to 10 seconds to generate an oxide with excellent weldability. You can

Furthermore, as a third method, an oxide film mainly composed of ZnO can be reliably produced by performing an alloying treatment and an oxide film producing treatment after hot dipping, electroplating or vapor deposition plating. As a specific method, for example, an alloying furnace for producing an alloyed hot-dip galvanized steel sheet, the plate temperature is 400 ~ 800
By adjusting the temperature to reach 0 ° C., passing through the furnace to the surface at a speed at which alloying is completed, and then performing steam treatment by spraying water and air with a steam nozzle to secure the dew point of the atmosphere. It is also possible to effectively carry out the oxide film formation reaction. Furthermore, after hot-dip plating, electroplating or vapor deposition plating outside the line, alloying treatment and oxide film generation treatment are performed.
An oxide film mainly composed of ZnO can be reliably generated. As for the method, if a method similar to the above method is adopted, Zn
Oxide-based oxide film formation reaction can be reliably and effectively performed.

In addition to the above steam-water treatment, the oxide film generation treatment may be performed by injecting steam onto the plating surface to generate an oxide film mainly composed of ZnO, or outside the line in a heating furnace whose dew point is adjusted to an oxidizing atmosphere. Any method such as heat treatment to form an oxide film mainly composed of ZnO may be adopted.

In this way, ZnO-based oxides of 30 to 3000 mg / m ^{2 were} produced as oxides with excellent weldability on the surface of the zinc-based plated steel sheet, and oxides excellent in pressability and chemical conversion treatment were formed on the upper layer as follows. Can be generated.

In order to impart the lubricity of the press, it is effective to form a hard film on the surface. In this respect, electrolytic chromate treatment and iron-zinc alloy plating are effective, but the former cannot form a chemical conversion treatment film, and the latter requires a large amount of treatment, resulting in high cost.

The hard coating on the surface of the plated steel sheet that can solve these problems is an oxide coating and can be dissolved in a chemical conversion treatment liquid to form a chemical conversion coating, and even if the coating components are dissolved in the chemical conversion treatment liquid. It is necessary not to adversely affect the chemical conversion treatment.

The inventors of the present invention, from such a viewpoint, Mn, P, Mo, C on the surface.
It has been found that it is sufficient to form an oxide film composed of one or more of o, Ni, Ca, W, V and B. This oxide film becomes a glass-like film like the chromate film, and suppresses galling of the plating die during pressing and improves slidability. Furthermore, since it dissolves in the chemical conversion treatment liquid, unlike the chromate film, a chemical conversion treatment film can be formed, and since it is also a component of the chemical conversion treatment film, there is no adverse effect even if it dissolves into the chemical conversion treatment liquid.

Although the structure of the oxide film is not clear, a network consisting of Mn-O bond, other metal-O bond, P-O bond, B-O bond, Si-O bond, Ti-O bond, Al-O bond is formed. It is presumed that the main component is an amorphous macromolecular structure in which —OH, CO ₃ groups, etc. are partially replaced by the metal supplied from the plating.

In addition, since this film is an oxide film, it does not dissolve even in the oil cleaning process and the oil removal process, so the lubrication performance is reduced,
Does not impose a load on other processes.

Phosphoric acid or boric acid and colloidal SiO ₂ , colloidal TiO ₂ , or colloidal Al ₂ O ₃ in order to improve the adhesion and film-forming property of the oxide film. One or more of them and 500 mg / m ² or less (P, SiO ² ₂ , Ti
O ₂ and Al ₂ O ₃ ) are mixed. Thus, the oxide film structure can be made uniform, the film forming property can be improved, the press moldability can be improved, and the chemical conversion treatment property can also be improved.

Such an oxide film can be reliably produced by immersing a zinc-based plated steel sheet in an aqueous solution, spraying the aqueous solution, or subjecting the zinc-based plated steel sheet to a cathodic electrolysis treatment in the aqueous solution. At this time, in the case of zinc or zinc alloy plating of the plating metal as described above, zinc, alloy elements (metals), impurities in the aqueous solution and the like are mixed as other oxides.

Next, the coating amount range of the coating of the present invention will be described.

The amount of oxide film should be 1 mg / m ² or more as a metal in order to improve pressability, but if the amount of film exceeds 500 mg / m ² , formation of the chemical conversion treatment film becomes insufficient. Therefore, the proper coating weight of oxides, 1-500 mg / m ² as metal, and preferably 1 to 200 mg / m ^2.

Next, colloidal SiO ₂ , colloidal TiO ₂ , colloidal Al ₂ O
The total amount of one or more of ₃ is 500 mg / m ² or less (S
iO ₂ , TiO ₂ , and Al ₂ O ₃ ), preferably 200 mg / m ² or less, and if it exceeds 500 mg / m ² , chemical conversion treatability may deteriorate. A lower limit of 1 mg / m ² is sufficient.

Next, as a method for forming the oxide film as described above, for example, as the Mn-based oxide, potassium permanganate, phosphoric acid, boric acid, sodium borate, ammonium molybdate, phosphomolybdic acid, ammonium tungstate, phosphorus, etc. Tungstic acid, silicotungstic acid, ammonium vanadate, chlorides such as cobalt, nickel, and calcium, sulfates, or phosphates from 1 g / l to the solubility limit, phosphoric acid, sulfuric acid, nitric acid, hydrochloric acid, etc. to accelerate the reaction. Use the added bath.

As SiO ₂ , TiO ₂ , and Al ₂ O ₃ , 1 to 60 g / l of an aqueous colloidal fine particle solution, potassium silicofluoride, potassium titanium fluoride or the like can be added as a solid.

The zinc-based plated steel sheet as described above may be dipped in such an aqueous solution, the aqueous solution may be sprayed, or an electrolytic treatment may be performed in the aqueous solution to form a film reliably.

When the oxide film is formed in this manner, part of the plating layer and the alloy metal in the plating layer is mixed into the oxide film as other oxide.

(Examples) Next, examples of the present invention are shown in the following table together with comparative examples.

Note 1) Type of galvanized steel sheet: AS: hot-dip galvanized steel sheet (Fe10%, Al10.25%, residual Zn), EG: galvanized steel sheet, GI: hot-dip galvanized steel sheet (Al0.3%, Fe0. 8%, Pb0.1
%, Residual Zn), HA: Semi-alloyed galvanized steel sheet (Fe5%, Al
0.3%, residual Zn), normal steel with a steel plate thickness of 0.8 mm, Zn / Zn
-Cr: 1% electrogalvanized on top of electroalloy plating containing 12% Cr
/ m ² Steel plate Note 2) ZnO coating treatment conditions ・ Immersion: Zn (NO ₃ ) ₂・ 6H ₂ O: 400g / l, HNO ₃ : 70g / l 50 ° C aqueous solution for 1 to 10 seconds It was dipped to form a ZnO film.

・ Electrolysis: Zn (NO ₃ ) ₂・ 6H ₂ O: 400 g / l, HNO ₃ : 1 g / l Current density 7 A / dm ² , 1 ~ 1 g / l aqueous solution with zinc-based plated steel plate as cathode
A ZnO film was formed by electrolysis for 7 seconds.

・ Air / water spray: Zinc-based plated steel sheet after alloying (500
The surface was sprayed with 80-125 l / min of atomized water to form a ZnO film.

Note 3) Conditions for forming the upper oxide film ・ Mn oxide is produced by using a solution of potassium permanganate (50 g / l), phosphoric acid (10 g / l), sulfuric acid (3 g / l) and zinc carbonate (5 g / l) at 30 ° C. Or was electrolyzed at 7 A / dm ² for 1.5 seconds using the steel plate as a cathode and the Pt electrode as an anode, followed by washing with water and drying.

・ P oxide production is potassium phosphate 50g / l, phosphoric acid 10g
The zinc-plated steel sheet is immersed in an aqueous solution of 1 / l or the steel sheet is used as a cathode or an anode to perform electrolytic treatment (5 to 10 A / d
m ² , 1-1.5 seconds).

・ Mo oxide formation is ammonium molybdate: 50 g / l,
Phosphoric acid: Immerse the steel sheet to be treated in a solution of 10 g / l (30 ° C), or use the steel sheet as a cathode and the Pt electrode as an anode at 7 A / dm ² and 1.5
After second electrolysis, it was washed with water and dried. It was prepared by adding ammonium molybdate and phosphoric acid concentrations, and partly by adding sulfuric acid and zinc carbonate, and adjusting the temperature of the solution, the immersion time, and the amount of electrolysis.

・ Co oxide production is cobalt nitrate: 200 g / l, zinc nitrate: 15
A solution of 0 g / l and concentrated nitric acid: 1 cc / l At 30 ° C., the steel sheet to be treated was used as a cathode, a Pt electrode and an anode were electrolyzed at 7 A / dm ² for 1.5 seconds, then washed with water and dried. It was prepared by adjusting the concentrations of cobalt nitrate, zinc nitrate and nitric acid, and further adding phosphoric acid, sulfuric acid and zinc carbonate to a part of them to adjust the temperature of the solution and the amount of electrolysis.

・ Ni oxide formation is nickel nitrate: 250 g / l, zinc nitrate: 15
A solution of 0 g / l and 1 cc / l of concentrated nitric acid was used as a cathode for the steel sheet to be treated and a Pt electrode as an anode at 30 ° C., and electrolysis was performed at 7 A / dm ² for 1.5 seconds, followed by washing with water and drying. It was prepared by adjusting the concentrations of nickel nitrate, zinc nitrate and nitric acid, and further adding phosphoric acid, sulfuric acid and zinc carbonate to a part thereof to adjust the temperature of the solution and the amount of electrolysis.

・ Ca oxide production is calcium nitrate: 250 g / l, concentrated nitric acid: 1 c
The c / l solution was used as a cathode with the treated steel plate as a cathode and a Pt electrode as an anode at 30 ° C., and electrolysis was performed at 7 A / dm ² for 1.5 seconds, followed by washing with water and drying. It was prepared by adjusting the concentrations of calcium nitrate and nitric acid, and further adding phosphoric acid, sulfuric acid, and zinc carbonate to some of them to adjust the temperature of the solution and the amount of electrolysis.

・ W oxide production is ammonium tungstate: 20g /
l, phosphoric acid: dip the steel sheet to be treated in a solution of 10 g / l (30 ° C.) or use the steel sheet as a cathode and the Pt electrode as an anode,
After electrolysis at / dm ² for 1.5 seconds, it was washed with water and dried. Adjust the concentrations of ammonium tungstate and phosphoric acid, and add sulfuric acid and zinc carbonate to some of them to adjust the temperature of the solution,
It was prepared by adjusting the immersion time and the amount of electrolysis.

・ V oxide is generated by ammonium vanadate: 30 g / l, phosphoric acid: 10 g / l in an aqueous solution (30 ° C), using the steel sheet to be treated as the cathode, the Pt electrode as the anode, and electrolysis at 7 A / dm ² for 1.5 seconds. After that, it was washed with water and dried. The concentration of ammonium vanadate and phosphoric acid, and further sulfuric acid and zinc carbonate were partially added to adjust the temperature of the solution, the electrolysis time, and the electrolysis amount.

Boron oxide was produced by electrolysis in an aqueous solution of boric acid: 50 g / l under the electrolytic condition of 7 A / dm ² for 1.5 to 7 seconds, using a zinc-based plated steel sheet as a cathode. The formation of the mixed oxide film was performed by preparing a bath in which the above metal salts or acids were added and mixed.

All coating amounts are measured element amounts Note 4) Chemical conversion treatment test conditions SD5000 is used for the chemical conversion treatment liquid (zinc-phosphoric acid-fluorine treatment bath).
(Manufactured by Nippon Paint Co., Ltd.), degreasing and surface preparation were performed as prescribed, and post-chemical conversion treatment was performed. The chemical conversion coating is judged by SEM (secondary electron beam image): ○ if the coating is uniformly formed, △ if it is partially coated, × if it is not coated. It was determined.

Note 5) Pressability test conditions and evaluation method: Sample size: 17 mm × 300 mm, pulling speed: 500 mm / min, square beat shoulder R: 1.0 / 3.0 mm, sliding length: 200 mm, oil: Knoxlast 530F (Parker Kosan) Co., Ltd.) under the condition of 40.1 mg / m ² , the surface pressure was tested at several points between 100 and 600 kgf, the pulling load was measured, and the friction coefficient was determined from the slope of the surface pressure and the pulling load.

Note 6: Weldability Welding conditions are as follows.

1) Pressurizing force: 250kgf 2) Initial pressurizing time: 49Hr 3) Energizing time: 12Hr 4) Holding time: 5Hr 5) Welding current: 11KA 6) Tip tip diameter: 5.0φ (Frustum-cone type) 7) Electrode life end Judgment: Number of dots that can secure a nugget diameter of 3.6 mm at 85% of welding current 8) Electrode material: Cu-Cr (generally used) Welding is performed with one side of the plated steel sheet facing up and the other side facing down. Two sheets were piled up and the number of consecutive points was taken.

Note 7): ZnO film measurement 5% iodine methyl alcohol solution was used to dissolve only the plating layer, and the extraction residue was melted with a mixed flux (boric acid 1, sodium carbonate 3), then dissolved in hydrochloric acid and analyzed by ICP. Zinc amount to Z
Converted to nO amount.

(Advantages of the Invention) By doing so, in spot welding, the number of continuous spots can be increased, and welding can be performed for a long time without changing the tip, and the durability of the tip can be improved. In addition, productivity can be improved by welding,
Moreover, the suitable welding current range is the same level as the conventional material, and the weldability is also good.

Furthermore, in the press, the slidability is improved more than cold rolled steel sheet,
Moreover, a chemical conversion coating can be formed. As a result, it is possible to obtain excellent effects such as a lower cost than before, a load on a user's process can be reduced, and productivity by pressing can be improved.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junichi Morita 5-3 Tokai-cho, Tokai City, Aichi Prefecture Nippon Steel Co., Ltd. Inside the Nippon Steel Works (56) Reference JP-A-4-21751 (JP, A)

Claims (2)

[Claims] 1. The amount of ZnO on the surface of a galvanized steel sheet is 30 to 3000 m.
g / m ² oxide, one or ^two of Mn oxide, P oxide, Mo oxide, Co oxide, Ni oxide, Ca oxide, W oxide, V oxide or boric acid as the upper layer 1 to 500 mg / m ² for seeds or more
A zinc-based plated steel sheet having excellent weldability, pressability, and chemical conversion treatability, characterized by being coated (as the amount of metal in the oxide). 2. The weldability, pressability, and pressability according to claim 1, wherein the upper oxide layer contains 1 to 500 mg / m ² of one or more of SiO ₂ , TiO ₂ , and Al ₂ O ₃ . A zinc-based plated steel sheet with excellent chemical conversion treatability.