JP5226564B2 - Dissimilar material joining method - Google Patents

Description

  The present invention relates to a dissimilar material joining method by welding dissimilar metal members of a steel material and an aluminum material in a transport field such as an automobile and a railway vehicle, a member, a part, and a structure such as a machine and a building.

  If the joining strength in dissimilar metal members (dissimilar material joints) such as steel and aluminum can be secured, it can be applied to the above-mentioned members, parts, and structures. Can contribute. Here, the aluminum material is a general term for a pure aluminum material and an aluminum alloy material.

  However, when steel material and aluminum material are joined by welding, brittle intermetallic compounds are likely to be formed in the joint, and it is very difficult to obtain a reliable joint having high strength (joint strength). It was. Therefore, in the past, these dissimilar joined bodies (dissimilar metal members) are mainly mechanically joined by bolts, rivets, etc., but even when welding joints are used together, the reliability and airtightness of the joints There are problems such as safety and cost. On the other hand, the strength of steel and aluminum alloy materials has been increased in order to reduce the weight of parts such as automobile bodies, and steel materials are made of high-tensile steel (high-tensile steel), and aluminum alloy materials have less alloying elements and are therefore recyclable. In addition, there is a tendency that an excellent A6000 series aluminum alloy material is used.

  For this reason, even in the welding joining between different materials, the conventional low-strength different materials such as mild steel and pure aluminum alloy or A5000-based aluminum alloy are joined together with high-tensile steel materials and 6000-based aluminum alloy materials. The joining object has been changed to welding joining of different strength materials. In these high-strength dissimilar materials, the conditions for the formation of brittle Fe-Al intermetallic compounds at the joint are different, and in order to obtain reliable high joint strength, conventional low-strength dissimilar materials are welded together. For joining, it is necessary to devise new joining conditions.

  When joining dissimilar materials of steel and aluminum alloy materials, the steel material has a higher melting point, higher electrical resistance and lower thermal conductivity than the aluminum alloy material. Aluminum melts. Next, the surface of the steel material melts, and as a result, a Fe—Al-based brittle intermetallic compound layer is formed at the interface, so that high bonding strength cannot be obtained.

  In view of this, many studies have been made on methods for welding these dissimilar joints. For example, a method of brazing at a low temperature has been proposed so that a brittle Fe—Al intermetallic compound is not generated at the joint (see Patent Documents 1 and 2).

  In contrast, in fusion welding of dissimilar joints that are joined at higher temperatures, a solid wire made of an aluminum alloy to which at least 3 to 15 wt% of silicon is added is used as the welding wire, and an aluminum alloy material and galvanizing are applied to the surface. There has been proposed a method of joining the steel material thus obtained by pulse MIG welding (see Patent Document 3). In this method, along with the melting of the welding wire, silicon is also transferred to the base material, penetrates into the molten pool interface, becomes hot due to the heat of the arc, improves the wettability of the molten metal, and improves the adhesion. .

  Furthermore, a method for improving the strength of the welded joint by improving the composition of the flux used for fusion welding of the dissimilar joints has also been proposed. As an example of this, iron (steel) is made of a flux-cored wire formed by covering a flux containing fluoride (cesium fluoride, aluminum fluoride, potassium fluoride and aluminum oxide) with aluminum or an aluminum alloy. There has been proposed a method of arc welding an aluminum material (see Patent Document 4).

  In addition, steel and aluminum are applied by various welding methods using and applying a fluoride-based mixed flux containing at least one of cesium fluoride, aluminum fluoride, potassium fluoride, and zinc fluoride, such as potassium fluoride and aluminum fluoride. A welding method for joining different materials to each other has been proposed (see Patent Document 5). These methods promote the cleaning action of the steel surface by the chemical reaction of the flux, improve the wettability and adhesion of the molten metal made of aluminum, and prevent the formation of a fragile thick intermetallic compound layer.

  Further, a fluoride-based flux having an effect of reducing, dissolving and removing the oxide film from the surface of the aluminum alloy material on which a strong oxide film is formed is applied to the surface of the aluminum alloy material, so that mild steel and 6000 series aluminum alloy material are applied. A method of spot welding the two has also been proposed (see Patent Document 6). Further, these fluoride fluxes are also used for fusion welding joining between aluminum alloy materials (see Patent Documents 7 and 8).

  However, in the welding method using these fluxes, there is a problem that high joint strength cannot be obtained by wire welding between different high strength materials such as the high-strength steel material and 6000 series aluminum alloy material. For this reason, the MIG welding method and laser brazing utilizing a flux called a nocolok flux, such as a fluoride composition containing aluminum fluoride or a flux containing a fluoride composition not containing chloride, etc. A method has also been developed (Patent Documents 9 to 12, etc.). In these welding methods, a flux cored wire (hereinafter also referred to as FCW or a flux-cored wire) formed by filling the aluminum material outer shell with a flux is used as a flux supply, thereby improving workability. ing.

JP 7-148571 A JP 10-314933 A JP 2004-223548 A JP2003-2111270A JP 2003-48077 A JP 2004-351507 A JP 2004-210013 A JP 2004-210023 A JP 2007-136524 A JP 2007-136525 A JP 2007-301634 A JP 2008-68290 A

  Certainly, the MIG welding method and the laser brazing method (hereinafter also referred to as the FCW welding method) utilizing the flux-cored wire are very efficient welding methods. In addition, according to this FCW welding method, when the steel material is the lower side and the aluminum material is the upper side with respect to the welding execution direction, such as lap fillet welding, the steel material and the aluminum material are welded to each other. And a bead of aluminum welding material over both welding surfaces. For this reason, the dissimilar material joined body (joint) of high joint strength is obtained.

  However, in the FCW welding method, the positional relationship between the steel material and the aluminum material is reversed, and the steel material is the upper side and the aluminum material is the lower side with respect to the welding direction, and the aluminum material is the lower side. In such a case, a high bonding strength cannot be obtained. That is, in the case of such a positional relationship, as described later, there is a problem that it is difficult to form a bead made of an aluminum welding material particularly on the welding surface on the steel material side. As described above, in order to obtain a high joint strength, it is necessary to form a bead made of an aluminum welding material over both the steel and aluminum welding surfaces.

  Thus, with respect to the welding direction, the steel material is the upper side and the aluminum material is the lower side. This is the case of partial reinforcement from the back side (inside). Therefore, if high joint strength is not obtained in such a case, even if high joint strength is obtained when welding with the steel material as the lower side and the aluminum material as the upper side as described above, the steel material and the aluminum material In the automobile manufacturing process (car body assembling process) in which cases of different positional relationships are mixed, it is difficult to adopt.

  In view of such a problem, the present invention is an improvement of the FCW welding method, particularly as a dissimilar material joining method. That is, it is an object of the present invention to provide a dissimilar material joining method capable of ensuring high joint strength even when the above-mentioned FCW welding is performed by superimposing steel materials on the upper side and aluminum materials on the lower side with respect to the welding direction. .

In order to achieve the above object, the gist of the dissimilar material joining method of the present invention is that the dissimilar material joining method welds the steel material on the upper side and the aluminum material on the lower side with respect to the direction of the tip of the welding torch. And the position of the welding surface along the welding line with the steel material at least among the surfaces facing the direction in which the tip of the welding torch of the aluminum material faces is welded along the welding line of the steel material. Aluminum welding material that is welded along the welding line in a state of projecting upward with respect to the direction in which the tip of the welding torch is directed from the position of the surface, and that extends over both the steel and aluminum materials. Is to form a bead.

  Here, among the FCW welding methods using the flux cored wire in which the flux is filled in the aluminum material outer shell, MIG welding or laser welding is preferable in terms of increasing welding efficiency and bonding strength. .

The present inventors investigated the reason why the FCW welding method cannot obtain high joint strength due to the positional relationship between the steel material and the aluminum material. As a result, it has been found that when the aluminum material is on the lower side with respect to the welding execution direction, it is difficult for the molten aluminum to spread on the weld surface of the steel material on the upper side. Moreover, in this case, since the supply of the flux to the steel material surface becomes insufficient at the same time, the effect of improving the wettability between the molten aluminum and the steel was small, and as a result, it was also found that good bonding was not possible. The term “welding direction” as used in the present invention refers not to the direction along the welding line but to the direction in which the tip of the welding torch heads, as will be described below.

  On the other hand, if welding is performed in a state where the position of the welding surface of the aluminum material is protruded upward with respect to the welding construction direction from the position of the welding surface of the steel material, the problems can be solved, It has also been found that a bead can be formed from an aluminum weld material over both the steel and aluminum weld surfaces.

  As a result, in the present invention, a high joint strength can be stably secured even when welding with the FCW welding method or the like, with the steel material being the upper side and the aluminum material being the lower side, with the welding direction being overlapped. can do. In the above-described conventional FCW welding method, on the contrary, when the steel material is the lower side and the aluminum material is the upper side with respect to the welding direction, high bonding strength is stable as described above. Can be secured. Therefore, even in the case of an automobile manufacturing process in which the positional relationship between the steel material and the aluminum material changes, efficient welding is performed by using the present invention and the above-described conventional FCW welding method together or separately. be able to.

1 is a cross-sectional view illustrating one embodiment of the present invention. It is sectional drawing which shows the welding result (dissimilar material joint) of FIG. It is sectional drawing which shows the one aspect | mode of this invention including a welding apparatus. It is sectional drawing which shows the aspect of the conventional dissimilar material joining.

  The embodiment of the present invention and the significance of each requirement of the present invention will be specifically described below with reference to the drawings.

Positional relationship between steel and aluminum:
First, the problem and cause of welding due to the positional relationship between the steel material and the aluminum material will be described in more detail with reference to FIG. FIG. 4 schematically shows the situation of the MIG weld bead according to the positional relationship between the steel material and the aluminum material in FIGS. 4 (a) and 4 (b), respectively.

  FIG. 4A shows a case where welding is performed by superposing each other with the steel material as the lower side and the aluminum material as the upper side with respect to the welding execution direction. FIG.4 (b) is a case where it overlaps and welds each other by making steel materials into an upper side and aluminum materials as a lower side with respect to the welding construction direction like this invention.

  In general, in the dissimilar welding joint between a steel material and an aluminum material, when the steel material side is melted, it is very brittle, and a large amount of steel-aluminum intermetallic compound is generated. For this reason, it is calculated | required that a thin intermetallic compound is produced | generated and joined in the contact part of the steel material surface and the molten aluminum previously melted.

  As shown in FIG. 4A, when the steel material 2 is on the lower side with respect to the welding execution direction indicated by the arrow 4, the molten aluminum 6 (becomes a bead) from the upper aluminum material 3 is on the lower side. It tends to spread on the surface (welded surface 2a) of the steel material 2. This is also true for the flux supplied to the weld surface. Therefore, even when a flux described later is used (in the case of the FCW welding method), the flux tends to spread on the surface of the lower steel material 2 (welded surface 2a). For this reason, the wettability of the welded surface 2a of the steel material 2 and the molten aluminum 6 can be improved, and the removal of the oxide film on the surface of the steel material 2 (welded surface 2a) can be promoted. As a result, the bead 6 made of the aluminum welding material over both the welding surfaces of the steel material welding surface 2a and the aluminum material welding surface 3a can be formed, and better bonding can be realized. When the FCW welding method such as Patent Documents 9 to 12 is overlapped fillet welding or the like, the steel material is the lower side and the aluminum material is the upper side with respect to the welding execution direction, and when the aluminum materials are overlapped and welded to each other, high bonding This is why strength is obtained.

  On the other hand, as shown in FIG. 4B of the present invention, when the aluminum material 3 is on the lower side with respect to the welding direction indicated by the arrow 4, the lower aluminum is provided on the upper steel material 2 side. The molten aluminum 6 from the material 3 becomes difficult to spread. This is also true for the flux supplied to the weld surface. Therefore, even when the flux is utilized (in the case of the FCW welding method), the flux is difficult to spread on the surface of the lower steel material 2 (welded surface 2a). As a result, since the supply of flux to the surface of the steel material 2 (welded surface 2a) becomes insufficient, the wettability of the welded surface 2a of the steel material 2 and the molten aluminum 6 cannot be improved even by the FCW welding method (improvement of wettability). Small effect). Moreover, since removal of the oxide film on the surface (welded surface 2a) of the steel material 2 cannot be promoted, the bead 6 on the steel material welded surface 2a side is particularly difficult to form. As a result, the bead 6 made of the aluminum welding material over both the welding surfaces of the steel material welding surface 2a and the aluminum material welding surface 3a cannot be formed, and good bonding cannot be performed.

Features of the present invention:
The features of the present invention for solving this problem will be described in detail below with reference to FIGS. FIG. 1 shows an example of the present invention in which fillet welding is performed by superposing each other with the steel material 2 as the upper side and the aluminum material 3 as the lower side in the welding direction indicated by the arrow 4 in the same manner as in FIG. 4 (b). Indicates. FIG. 2 shows a state after the fillet welding of FIG. 1 and 2 show an example in which a steel plate automobile panel 2 such as a door is partially reinforced from the back side (inside) of the panel 2 with an aluminum alloy extruded shape member 3 or the like. .

  In FIG. 1, a concave portion 3 b that accommodates a welding surface 2 a of the steel material 2 is provided at an end portion of the aluminum material 3 that is on the lower side on the steel material 2 side. Since this recessed part 3b has a depth more than the thickness of the steel material 2, if it overlaps with this recessed part 3b in the form which accommodates the welding surface 2a of the steel material 2, the welding surface 2a of the steel material 2 will become this recessed part 3b. Therefore, the welding process direction 4 is retreated by the difference Xmm between the depth of the steel and the thickness of the steel material 2. At the same time, conversely, the weld surface 3a of the aluminum material (the weld surface along the weld line 5 with the steel material 2) is in contact with the weld surface 2a along the weld line 5 with the steel material 2 with respect to the welding direction 4. It is in a state of projecting by X mm above the position.

  As shown in FIG. 1, when at least the welding surface 3 a of the aluminum material is protruded above the position of the welding surface 2 a of the steel material 2 with respect to the welding construction direction 4, The positional relationship between the welding surface 2a and the welding surface 3a of the aluminum material 3 is reversed. That is, just as shown in FIG. 4A, at least the welding surface 3 a of the aluminum material is above the welding surface 2 a of the steel material 2 with respect to the welding direction 4.

  Therefore, as shown in FIG. 2, as in the case of FIG. 4A, the molten aluminum 6 (becomes a bead) from the weld surface 3 a of the upper aluminum material 3 is the surface of the lower steel material 2. It tends to spread over (welded surface 2a). This is also true for the flux supplied to the weld surface. Therefore, even when the flux is utilized (in the case of the FCW welding method), the flux tends to spread on the surface of the lower steel material 2 (welded surface 2a). For this reason, the wettability of the welded surface 2a of the steel material 2 and the molten aluminum 6 can be improved, and the removal of the oxide film on the surface of the steel material 2 (welded surface 2a) can be promoted. As a result, the bead 6 made of the aluminum welding material over both the steel material welding surface 2a and the aluminum material welding surface 3a can be formed, and better bonding as the dissimilar material joined body 1 can be realized.

  In FIG. 1, S and G are the surface of the concave portion 3b of the aluminum material 3 and the lower surface and the end of the steel material 2 that are prepared for wrapping around the steel material 2 around the steel material 2. It is the clearance (interval) with the surface. Here, in joining the molten aluminum (molten aluminum) and the aluminum material 3, the aluminum material 3 (welded surface 3a) is melted and integrated with the molten aluminum 6 in the same manner as in a normal welded portion, and after solidification, the beads 6 to form a strong joint.

  On the other hand, as described above, the molten aluminum 6 is widely covered and adhered to the steel material welding surface 2a by the cleaning action, the wettability and the adhesion improving action by the flux. Therefore, heat is not directly input to the steel material 2 from an arc described later (an arc 15 in FIG. 3 described later), but is indirectly input through the aluminum melt covered. For this reason, the steel material 2 is not heated and melted excessively by the arc, and a thin intermetallic compound layer of about several μm is formed at the bonding interface with the molten aluminum 6 in close contact. When this intermetallic compound layer becomes thicker than about several tens of μm, it becomes brittle and weld cracks occur and the strength deteriorates. However, a thin intermetallic compound layer of about several μm is not brittle and has a strong bonding state. It becomes.

  Thus, in order to form a thin intermetallic compound layer of about several μm at the joining interface between the molten aluminum 6 and the steel material welding surface 2a, the cleaning action, the wettability, and the adhesion improving action by the flux are very good. It becomes important. That is, when the cleaning action, the wettability, and the adhesion improving action are lowered, the molten aluminum 6 cannot sufficiently cover the steel material welding surface 2a, and as a result, the arc directly touches the steel material welding surface 2a. Therefore, the steel material welding surface 2a is excessively heated and melted to form a thick intermetallic compound layer. Conversely, even if the steel weld surface 2a is not heated, if the adhesion between the molten aluminum 6 and the steel weld surface 2a is low, a uniform intermetallic compound layer is not formed, and the molten aluminum 6 and the steel material are not formed. There may be a case where the welded surface 2a is not joined and easily peels off.

Aluminum material welding surface protrusion method:
The method of projecting the aluminum material welding surface 3a upward from the welding surface 4a than the welding surface 2a of the steel material 2 can be performed by shape design or processing of the aluminum material. For example, in the case of an aluminum material as shown in FIG. 1, the aluminum material welded surface 3 a is partially thickened in advance, and another aluminum material is joined to the aluminum material welded surface 3 a and partially thickened. There are ways to do it.

  However, depending on the design condition of the dissimilar material joined body, a method of partially thinning a portion such as an end portion overlapped with the steel material 2 on the aluminum material 3 side, such as the concave portion 3b in FIG. As shown in FIG. 3 to be described later, the method based on the shape design such as the position of the support flange (arm portion) of the steel material 2 provided on the original aluminum material is the simplest. For example, if the aluminum material 3 is an extruded shape, the thin shape portion (concave portion) and the position of the joining flange (arm portion) are included in the original shape shape and extruded, and this is later performed by cutting or the like. There is no need to form a thin portion (concave portion). Moreover, even if the aluminum material 3 is a plate material, the thin portion (concave portion) can be formed by simple cutting in the middle or before and after the forming process.

  Further, the protrusion amount Xmm of the aluminum material welding surface 3a is appropriately selected according to the design conditions, welding method, and welding conditions of the dissimilar material joined body. That is, the ease of spreading to the lower steel material welding surface 2a of the molten aluminum 6 and the ease of spreading to the lower steel welding surface 2a of the flux (improvement of wettability, promotion of removal of oxide film on the steel welding surface 2a). It is appropriately selected depending on the degree.

  When this protrusion amount is small, the molten aluminum 6 does not spread sufficiently on the steel material side plate welding surface 2a. On the other hand, if the protruding amount is too large, it is difficult to ensure the penetration into the aluminum material 3. Moreover, if welding heat input is raised too much in order to ensure penetration, the intermetallic compound at the joint interface grows thick, and in an extreme case, the steel material 3 is melted, so it is difficult to ensure the joint strength. The optimum range of this protrusion amount: Xmm varies depending on the above-mentioned conditions, but in the field of dissimilar material joining such as the automobile body described above, it is generally in the range of 0.5 mm to 4 mm.

  It should be noted that the protrusion amount: Xmm is of course appropriately designed in consideration of the above-described clearances S and G between the aluminum material 3 and the steel material 2 (in consideration of S and G depending on S and G). Also, the clearances S and G between the aluminum material 3 and the steel material 2 are appropriately designed in relation to the protrusion amount: Xmm.

Welding aspect of the present invention:
Next, an embodiment for carrying out (implementing) the present invention by the FCW welding method will be described with reference to FIG. In FIG. 3, first, the positional relationship between the steel material and the aluminum material is the same as that in FIG. 1, and the steel material 2 is placed on the upper side with respect to the welding direction in the direction from the top to the bottom illustrated in FIG. In this case, fillet welding is performed with the aluminum material 3 on the lower side and overlapping each other.

  In this FIG. 3, the example in the case of supporting the edge part of the steel plate panel 2 with the aluminum alloy extrusion shape material 3 from the back side (inner side) of this panel 2 is shown, for example, FIG. In particular, the shape of the aluminum material 3 is different. That is, the aluminum material 3 has an inverted L-shaped shape, and extends in the horizontal direction to support the end of the steel plate panel 2. The vertical wall 3d joined to the structural member. And the position which provides this flange 3c with respect to the vertical wall 3d is made lower than the welding surface 3a which is the upper end part of the vertical wall 3d (the welding surface 3a which is the upper end part of the vertical wall 3d is made to protrude upwards). ing). Thereby, the welding surface 3a (welding surface along the welding line 5 with the steel material 2) of the aluminum material is protruded above the position of the welding surface 2a of the steel material 2 with respect to the welding construction direction 4. .

  Further, on the upper surface of the flange 3c made of an aluminum material, there is provided a concave portion 3b prepared for securing a clearance (interval) for the surrounding (lower part) of the molten aluminum around the steel material 2 (lower part). The steel material side end of the recess 3b has a vertical wall shape perpendicular to the bottom surface, but the vertical wall 3d side of the aluminum material has an R (arc, curvature) like the lower surface side of the flange 3c. It is connected.

Arc welding method:
The aspect of the welding apparatus used by this invention is demonstrated using the said FIG. In the present invention, a normal welding apparatus and welding method (arc welding apparatus, method, and conditions) by the FCW welding method can be used, which is also an advantage of the present invention. In addition, in FIG. 3, although the block diagram of an arc welding apparatus (consumable electrode arc welding apparatus: MIG welding apparatus) is shown, if a laser irradiation apparatus is provided in this FIG. 3, it will become a block diagram of a laser irradiation arc welding apparatus.

  In FIG. 3, an FCW (flux-cored wire) 10 has a specific component flux described later. The FCW 10 unwound from the spool 11 is fed at a predetermined feeding speed through the welding torch 13 by the rotation of a feeding roll 12 directly connected to a wire feeding motor (not shown). At this time, the shielding gas is supplied into the welding torch 13. A welding power source (PS) 14 outputs a welding voltage and a welding current for performing arc welding, and outputs a feed control signal to the wire feed motor.

  With such a welding apparatus, an arc 15 is generated between the FCW 10 and the material to be joined, and the joining is performed. At this time, as described above, at least the welding surface 3a of the aluminum material is protruded above the position of the welding surface 2a of the steel material 2 with respect to the welding direction 4. For this reason, as shown in the said FIG. 2, the molten aluminum (not shown) from the welding surface 3a of the upper aluminum material 3 tends to spread on the lower steel material welding surface 2a. Further, the flux supplied to the welding surface by the FCW 10 is likely to spread to the lower steel material welding surface 2a. For this reason, the wettability of the steel material welding surface 2a and the molten aluminum can be improved, and the removal of the oxide film on the steel material 2 welding surface 2a can be promoted.

  As a result, even if the welded joint is formed with the steel material 2 as the upper side and the aluminum material 3 as the lower side with respect to the welding direction 4, the steel welding surface 2a and the aluminum material welding surface 3a are both welded. A bead made of an aluminum welding material can be formed, and good bonding as the dissimilar material joined body 1 can be realized.

Welding method:
FIG. 3 illustrates the case of MIG welding, but the arc welding method of the present invention includes DC MIG welding, DC pulse MIG welding, AC MIG welding, AC pulse MIG welding, and DC / AC TIG welding. Further, plasma arc welding, combined laser irradiation arc welding using arc welding and laser irradiation at the same time can be used. Laser welding (apparatus) can also be used instead of arc welding (apparatus).

Flux cored wire:
The flux cored wire (FCW) for joining dissimilar materials used in the present invention uses FCW in which a fluoride-based mixed flux is covered with an aluminum alloy skin in order to improve the efficiency of fusion welding. As this FCW, a general one in which a tubular aluminum alloy outer shell (hoop) is filled with a flux can be used.

  The FCW includes a seam type having a seam (joint: gap, opening) and a seamless type in which the seam is joined by welding or the like, and any of them may be used. The aluminum alloy used for the FCW shell is not particularly limited, but 4000 series aluminum alloys such as A4043 and A4047 and 5000 series aluminum alloys such as A5356 and A5183 can be used. In addition, aluminum alloys such as 3000 series and 6000 series may be used. Among these, A4043-WY, A4047-WY, A5356-WY, A5183-WY, and the like defined by JIS are preferably exemplified.

  As for the wire diameter of the FCW, an optimum diameter may be selected according to the welding workability including the characteristics of the wire feeder, etc., for welding work used as high-efficiency fully automatic welding or semi-automatic welding. . For example, in the case of MIG welding, general carbon dioxide shielded arc welding, etc., it may be a small diameter of about 0.8 to 1.6 mmφ which is widely used. As the wire having a smaller wire diameter is used within the range of the wire diameter, the amount of heat input during welding can be reduced and the low current condition can be achieved. As a result, scattering of the fluoride-based mixed flux itself can be prevented, welding workability can be improved, and formation of fragile intermetallic compounds can be suppressed. If the wire diameter exceeds 1.6 mm, the current to obtain a stable arc becomes excessive, the scattering of the fluoride-based mixed flux itself increases, the base material melts excessively, and the brittle intermetallic compound May lead to the generation of

  Of course, the filling rate of the flux into the FCW is relatively small, such as about 0.1% by mass or more and less than 24% by mass with respect to the total mass of the FCW, although it depends on the flux composition. A lower filling rate can prevent the flux itself from scattering and improve welding workability. If the filling rate of the flux is too small, the effect of the flux cannot be exhibited, and a sound and highly reliable welded joint cannot be obtained.

  Thus, in the present invention, it is preferable to use the FCW instead of directly applying the fluoride-based mixed flux to the weld. Considering the use in the continuous assembly process of automobile bodies, etc., the FCW is used to prevent scattering of the fluoride-based mixed flux itself, improving welding workability, and suppressing the generation of fragile intermetallic compounds. It is essential to do.

Flux composition:
In the present invention, the flux composition used (filled) in the FCW is a mixed flux having a specific composition in which fluorides such as aluminum fluoride and potassium fluoride are mixed, among the fluoride-based mixed fluxes (Nocolok). Flux) is preferable. Moreover, it is preferable to regulate the amount of chloride to 1 mol% or less or to make a fluoride composition not containing chloride. This is because, when chloride remains in the welded portion, it acts as a corrosion promoting factor for the welded portion or the dissimilar material joined body.

  In addition, when aluminum alloy powder is mixed and added to this flux, spattering during welding is reduced, and excessive wetness of the molten metal may be suppressed. When the amount of flux filling the outer skin is small, the amount of flux is not stable, and the flux filling amount (filling rate, content rate) varies depending on the part of the FCW. On the other hand, in particular, when the flux filling amount is small, mixing the flux and aluminum alloy powder into the outer shell and filling the outer shell eliminates or alleviates this problem, and at the same time, facilitates the manufacture of the FCW itself. Is also preferable.

  By using a mixed flux having such a specific composition, even a steel material coated with a relatively thick hot dip galvanizing (including alloying) can be bonded to a different material with an aluminum material. That is, the material surface with galvanized steel or aluminum can be cleaned, and the wettability of the weld metal is improved. As a result, bead formation is improved. In addition, generation of a brittle Al—Fe based intermetallic compound layer generated in the dissimilar material joint and a brittle Zn—Fe based compound layer derived from galvanization is suppressed. As a result, the bonding strength is improved. Of course, this effect is also exhibited in the dissimilar material joining between a bare steel material without galvanization and an aluminum material.

Steel:
The thickness of the steel material to be joined with different materials in the present invention is preferably in the range of 0.3 to 4.0 mm. If the plate thickness of the steel material is less than 0.3 mm, the strength and rigidity necessary for the structural member and the structural material described above cannot be secured, which is inappropriate. If the plate thickness of the steel material is too thick, it will not be possible to reduce the weight of the structural member or structural material. Further, in the present invention, the shape of the steel material to be joined with the different material is not particularly limited, and is widely used for a structural member such as an automobile body or selected from the structural member such as a steel plate, a steel shape member, a steel pipe, etc. An appropriate shape is a target for joining different materials.

  However, in order to obtain a lightweight high-strength structural member (dissimilar material joined body) such as an automobile member, the steel material is made of high-tensile steel (high tensile) having a tensile strength of 400 MPa or more, preferably 500 MPa or more. Low-strength steel and mild steel with a tensile strength of less than 400 MPa are generally low-alloy steels, and the oxide film is made of iron oxide. Therefore, diffusion of Fe and Al is facilitated, and brittle intermetallic compounds are easily formed. Further, the plate thickness for obtaining the required strength is increased, and the weight reduction is sacrificed.

Zinc plating:
The surface of the steel material to be bonded to a different material may be subjected to surface treatment except for coating with an insulating film, but if a galvanizing is provided in advance on the surface of the steel material (at least the bonding surface with the aluminum material) The wettability of the flux is improved. Moreover, since galvanization exists in the joint surface with an aluminum material, the advantage which is excellent also in the corrosion resistance of a dissimilar-material joined body is acquired. Furthermore, there is an effect of increasing the bonding strength by the following actions. Zinc plating also has the effect of delaying the time required for the formation of an interfacial reaction layer, which is an intermetallic compound of steel and aluminum, during welding.

  As these galvanizations, known steel galvanizations such as pure galvanization, alloy galvanization, and alloyed galvanization can be applied. The plating means is not particularly limited, such as electroplating, hot dipping, or alloying after hot dipping. The thickness of the galvanizing may be in the range of a normal film thickness (average film thickness) of 1 to 20 μm. When the thickness is too thin, the galvanized film is melted and discharged from the joint at the initial stage of welding during welding, and the effect of suppressing the formation of the interface reaction layer cannot be exhibited. On the other hand, when the thickness of the galvanized film is too thick, a large amount of heat input is required for melting and discharging zinc from the joint. However, when the amount of heat input increases in this way, not only the aluminum material side but also the steel material side melts, and as described above, a Fe-Al brittle intermetallic compound layer is formed thick at the interface, which is high. Bonding strength cannot be obtained.

Aluminum material:
The aluminum material to be joined with different materials in the present invention is not particularly limited to the alloy and its shape, but according to the required characteristics as each structural member described above, a widely used alloy, plate material, shape material, forging A material, a cast material, and the like are appropriately selected. However, it is desirable that the strength of the aluminum material be higher as in the case of the steel material. In this respect, Al-Mg-Si based A6000 aluminum alloy, which is widely used as a structural member of this kind, has high strength among aluminum materials, has a small amount of alloying elements, and is excellent in weldability and recyclability. It is preferable to do.

  The thickness of these aluminum materials used in the present invention is preferably in the range of 0.5 to 4.0 mm. When the thickness of the aluminum material is less than 0.5 mm, the strength as a structural material of an automobile or the energy absorption at the time of a vehicle body collision is insufficient, which is inappropriate. On the other hand, when the plate thickness of the aluminum material exceeds 4.0 mm, it is impossible to reduce the weight of the structural member or the structural material as in the case of the steel plate thickness. Note that the surface of the aluminum material to be bonded to the different material may or may not be subjected to surface treatment except for coating with an insulating film.

FCW welding conditions:
As described above, in FCW welding, in order to suppress the formation of intermetallic compounds generated at the interface between the aluminum material and the steel material, the minimum necessary base material melting is performed without melting an excessive amount of the steel material as the base material. It is preferable to select welding conditions so that a sound joining state can be obtained with a (diluted) amount.

  The welding current is 70A or more, preferably 80A or more, 120A or less, more preferably 110A or less. The larger the current, the more the intermetallic compound at the bonding interface that is generated may adversely affect the bonding strength. Therefore, it is recommended to bond under relatively low current conditions to suppress these intermetallic compounds. Is done.

  The welding voltage is 10V or more, preferably 15V or more, 30V or less, more preferably 20V or less.

  The welding speed may be appropriately determined in accordance with the welding current and the welding voltage as long as the base material Fe and Al are not excessively melted. However, considering the welding efficiency and the like, it is preferably 20 CPM or more, preferably 30 CPM or more, and 100 CPM or less, more preferably 90 CPM or less.

  As the shield gas, a general-purpose gas such as Ar can be used as appropriate, and a general-purpose flow rate can be selected as the gas flow rate, and there is no particular limitation.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and the present invention is not limited to the following examples. Of course, it is also possible to implement them, and they are all included in the technical scope of the present invention.

  As shown in FIG. 1 and FIG. 3, with respect to the welding direction 4, the steel material 2 is the upper side and the aluminum material 3 is the lower side, and the joint shape of the test pieces stacked on each other is used. A fillet welding test was conducted by FCW welding (MIG welding) shown in. At this time, the amount of protrusion (Xmm) from the steel material welding surface 2a with respect to the welding direction 4 of the aluminum material welding surface 3a was changed, and the influence of the amount of protrusion on the weldability of the dissimilar material joined body was investigated. The results are shown in Tables 1-3.

Example 1
The steel material 2 has the joint shape shown in FIG. 1, the steel material 2 is a cold-rolled steel plate (high-tensile, thickness 1.4 mm) subjected to galvannealing (GA) with a tensile strength of 980 MPa, and the aluminum material 3 is 0.2. A T6 tempered extruded material (plate thickness: 2.0 mm) of a 6000 series aluminum alloy having a% proof stress of 180 MPa was used.

  Test piece: The length of both the steel material 2 and the aluminum material 3 is 300 mm, and a flat concave portion having a length of 100 mm that accommodates the welded surface 2a of the steel material 2 at the end of the lower aluminum extruded shape 3 on the steel plate 2 side. 3b was provided. And the protrusion amount (Xmm) from the steel material welding surface 2a with respect to the welding construction direction 4 of the aluminum material welding surface 3a was changed variously by adjusting the depth of this recessed part 3b.

  At this time, the clearance S between the surface of the recess 3b of the aluminum material 3 and the lower surface of the steel 2 is defined as “plate gap S”, and the clearance G between the end of the steel 2 and the end of the recess 3b is defined as “gap G”. However, in Example 1, S and G were set to zero in common with each example.

  Welding conditions: MIG welding conditions, welding current 80 A, welding voltage 20 V, welding speed 50 cpm (cm / min). FCW has a common wire diameter of 1.0 mmφ and an aluminum alloy filler metal of A4047, fluoride flux (K3 AlF6 fluoride and aluminum alloy powder of A4047 composition) as the outer shell, 10 times the total weight of FCW. What added the mass% was used. The shielding gas was Ar.

  Joint weldability evaluation: The weldability of the joint was determined by visual observation of the bead and a peeling test using chisel. As shown in FIG. 2, the bead 6 is formed continuously and satisfactorily over both the welded surface 2a of the steel material 2 and the welded surface 3a of the aluminum material. I was in a state. And by comparison with this, it evaluated in order of (circle), (triangle | delta), and x by especially the magnitude | size of the bead by the side of the welding surface 2a of the steel materials 2. FIG. Incidentally, “x” means that the bead 6 is hardly present on the side of the welded surface 2a of the steel material 2 or is extremely small.

  In the peeling test with chisel, the tip of the bead 6 was hit near the center of the welded part (bead 6), and the head of the chisel (forging tool for cutting) was hit with a hammer once from the top with a large force. The state (destructive state) was investigated. And the thing which does not have peeling (destruction) at all over the bead 6 is evaluated as a pass (◎), and by comparison with this, depending on the size of the peeling (destruction) generated in a part of the bead 6, Evaluation was made in the order of ○, Δ, and ×. Incidentally, “x” indicates a case where the bead 6 is largely peeled off and the joint can be regarded as broken. By the way, in the peel test using this chisel, if it is ◎, it is a guide that the joint has a breaking strength of 200 N / mm or more, and if it is ×, the joint has a strength of less than about 100 N / mm. become.

  From Table 1, an example in which the welding surface 3a of the aluminum material 3 on the lower side protrudes with respect to the welding construction direction arrow 4, and the protruding amount is from 0.5 mm of number 3 to 4 mm of number 8 It can be seen that the joint weldability evaluation is good in each example in the range. On the other hand, numbers 1, 2, and 10 have poor joint weldability evaluation.

  On the other hand, in the example of number 1, the welding surface 3a of the aluminum material 3 on the lower side is the upper side of the steel material 2 with respect to the welding direction arrow 4 as shown in FIG. This is a case of being lower than the welding surface 2a. In the example of No. 2, the protrusion amount X of the welding surface 3a of the aluminum material 3 on the lower side with respect to the welding construction direction arrow 4 is too small to be zero. From these results, it is confirmed that the molten aluminum 6 does not sufficiently spread on the welding surface 2a of the steel material 2 when the projection amount X of the welding surface 3a of the aluminum material 3 with respect to the welding direction arrow 4 is small.

  On the contrary, the example of No. 10 is a case where the protrusion amount X is too large. If the protruding amount X is too large, it is proved that it is difficult to ensure the melting of the molten aluminum 6 into the aluminum material 3 as described above. On the other hand, if the heat input of welding is increased too much in order to ensure penetration, the intermetallic compound at the joint interface grows thick, and in extreme cases, the steel is melted. After all it becomes difficult.

(Example 2)
As shown in Table 2, with the projection amount X being constant, the plate gap S and the gap G were variously changed, and the welding test was performed under the same conditions of the test piece, the joint, and the welding as in Example 1 described above. The influence of these plate gaps S and gaps G was investigated.

  The plate gap S was changed from 0.5 mm to 1.5 mm, and the gap G was changed from 0 mm to 1.5 mm. As shown in Table 2, the weldability of the joint is good from the example of the number 11 of 0.5 mm to the example of the number 13 of 1.5 mm. Further, the weldability of the joint is good from the example of the number 11 of 0 mm to the example of the number 16 of 1 mm. From these results, it can be seen that if the plate gap S and the gap G are made too large, good welding cannot be performed as is conventionally known.

(Example 3)
A joint shape (groove shape) as shown in FIG. 3 is used, and as shown in Table 3, the protrusion amount X is constant, and the corner R on the “gap G” side (the upper corner R connecting the vertical wall 3d and the flange 3c). ) Was changed variously, a welding test was performed under the same welding conditions as in Example 1 described above, and the influence of the size or shape of the corner R was investigated.

  Test piece: Aluminum extruded material 3 only, the cross-sectional shape was changed as shown in FIG. 3 (the material and the proof stress were the same), the length of the flange (arm) 3c was 35 mm, the thickness was 4 mm, and the length of the vertical wall 3d was 18 mm. The thickness was 3 mm, and the thickness (width) of the upper part on the welding surface 3a side was 5 mm. And the depth of the recessed part 3b was 1 mm, and the protrusion amount from the steel material welding surface 2a with respect to the welding construction direction 4 of the aluminum material welding surface 3a was made constant with 3 mm in each example.

  From Table 3, it can be seen that even with the same plate gap S and gap G as the welding conditions in Table 2, depending on the selection of the corner R, the joint weldability is improved. That is, it is considered that the margin for the plate gap S and the gap G is improved because the molten aluminum is smoothly supplied also to the end face side of the steel material 2 due to the groove shape.

  In other words, the joint weldability is improved even when the plate gap S and the gap G are relatively large due to the design convenience and assembly error of the joint or the base structural member. This means that due to the groove shape, design errors and assembly errors can be allowed, and the plate gap S and gap G can be given a margin. Further, the groove shape having the corner R as shown in FIG. 3 does not need to be produced by machining such as cutting, and when an aluminum alloy extruded shape is used, only the design extrusion cross-sectional shape is obtained without machining. There is an advantage that such a shape can be realized.

  According to the present invention, in particular, in FCW welding, a different material that can stably ensure high joint strength even when welding with the steel material being the upper side and the aluminum material being the lower side with respect to the welding execution direction. A bonding method can be provided. Moreover, the construction method is also easy, and a joining method utilizing arc welding capable of efficiently performing wire welding can be provided. Therefore, it is useful in the field of dissimilar joints between steel and aluminum, such as the manufacture of automobile bodies.

1: Dissimilar material joint, 2: Steel material (steel plate), 2a: Steel material weld surface, 3: Aluminum material (aluminum alloy extruded profile), 3a: Aluminum material weld surface, 3b: Aluminum material recess, 4: Welding direction, 5: Welding wire, 6: Bead (molten aluminum), 10: Flux-cored welding wire, 11: Spool, 12: Feeding roll, 13: Welding torch, 14: Welding power supply, 15: Arc,

Claims (2)

To the direction in which the distal end of the welding torch is directed, steel and the upper, the aluminum material as the lower, a dissimilar materials bonded method of welding overlapped with each other, to the direction in which the tip of the welding torch of the aluminum material is directed The position of the welding surface along the welding line with at least the steel material of the surfaces facing each other is higher than the position of the welding surface along the welding line of the steel material with respect to the direction in which the tip of the welding torch faces And welding along the weld line to form a bead made of an aluminum welding material over both the steel and aluminum welding surfaces.   2. The dissimilar material joining method according to claim 1, wherein the welding is MIG welding or laser welding using a flux cored wire formed by filling a flux inside an aluminum material outer skin.

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