WO2010104088A1

WO2010104088A1 - Method for bonding dissimilar materials

Info

Publication number: WO2010104088A1
Application number: PCT/JP2010/053924
Authority: WO
Inventors: 雅男杵渕; 誠二笹部; 剛松本; 康生村井
Original assignee: 株式会社神戸製鋼所
Priority date: 2009-03-11
Filing date: 2010-03-09
Publication date: 2010-09-16
Also published as: JP5226564B2; JP2010207886A

Abstract

Provided is a method for bonding dissimilar materials that stably ensures high bonding strength, even when overlapping and welding a steel member on the top and an aluminum member on the bottom in the direction of welding. In this method, when overlapping and welding the steel member (2) on the top and the aluminum member (3) on the bottom in the direction of welding (4), the materials are welded with the position of the welded surface (3a) of the aluminum member at least along a welding line (5) protruding in the direction of welding (4) above the position of the welded surface (2a) of the steel member, and a bead (6) is formed from the aluminum welding material across the welded surfaces of the steel member (2) and the aluminum member (3).

Description

Dissimilar material joining method

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 an architecture.

In order to apply the joining (dissimilar material joined body) of different kinds of metal members such as steel and aluminum to the above-mentioned members, parts, and structures, it is necessary to ensure the joining strength. Compared to the case of only steel materials, it can significantly contribute to weight reduction and the like. 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) have been mechanically joined mainly by bolts, rivets, etc., but even when welding joints are used in combination with mechanical joints, they are joint joints. There are problems such as reliability, airtightness, 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 joint between dissimilar materials, the high strength steel material and 6000 series aluminum alloy material from the low-strength dissimilar materials such as conventional mild steel and pure aluminum alloy, A5000 series aluminum alloy, etc. The joining object is changing to welding joining of different materials. With these high-strength dissimilar materials, the formation conditions of brittle Fe-Al intermetallic compounds at the joints are different from those of conventional low-strength dissimilar materials, so reliable and high joint strength is obtained. In order to do so, 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, so the heat generation on the steel side increases, and the low melting point first Aluminum melts. Next, the surface of the steel material is melted, 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.

Therefore, many studies have been made on the welding joining method of these different types of joined bodies. For example, a method of brazing at a low temperature has been proposed so that a brittle Fe—Al intermetallic compound is not formed at the joint (see Patent Documents 1 and 2).

On the other hand, for 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 a welding wire, and an aluminum alloy material and galvanizing are used. There has been proposed a method of joining a steel material having a surface thereof with pulsed MIG welding (see Patent Document 3). In this method, as the welding wire melts, silicon moves to the base material, penetrates into the molten pool interface, becomes hot due to the heat of the arc, and improves the wettability of the molten metal, thereby improving 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 dissimilar joints has also been proposed. For example, a flux containing a fluoride (cesium fluoride, aluminum fluoride, potassium fluoride) is used as a core material, and the core material is coated with aluminum or an aluminum alloy to form steel (mild steel) with a flux-cored wire. There has been proposed a method of arc welding an aluminum material (see Patent Document 4).

In addition, steel materials using various welding methods that apply and use fluoride-based mixed flux containing one or more of cesium fluoride, aluminum fluoride, potassium fluoride, and zinc fluoride, such as potassium fluoride and aluminum fluoride There has been proposed a method of welding different materials between aluminum and aluminum (see Patent Document 5). In these methods, the chemical reaction of the flux promotes the cleaning action of the steel surface, improves the wettability and adhesion of the molten metal made of aluminum, and prevents 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, and mild steel and a 6000 series aluminum alloy material are applied. A method of spot welding is also 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 high strength different materials such as high strength steel material and 6000 series aluminum alloy material. For this reason, as a result of devising the flux composition, the MIG welding method using a flux called a nocolok flux, such as a fluoride composition containing aluminum fluoride or a flux containing no chloride, A laser brazing method has also been developed (Patent Documents 9 to 12, etc.). In these welding methods, in order to supply the flux, a flux cored wire (hereinafter also referred to as FCW or a flux-cored wire) formed by filling the aluminum material with a flux is utilized to improve workability. Is planned.

Japanese Unexamined Patent Publication No. 7-148571 Japanese Laid-Open Patent Publication No. 10-314933 Japanese Unexamined Patent Publication No. 2004-223548 Japanese Laid-Open Patent Publication No. 2003-211270 Japanese Unexamined Patent Publication No. 2003- 48077 Japanese Unexamined Patent Publication No. 2004-351507 Japanese Unexamined Patent Publication No. 2004-210013 Japanese Unexamined Patent Publication No. 2004-210023 Japanese Unexamined Patent Publication No. 2007-136524 Japanese Unexamined Patent Publication No. 2007-136525 Japanese Unexamined Patent Publication No. 2007-301634 Japanese Unexamined Patent Publication No. 2008-68290

The MIG welding method and laser brazing method (hereinafter also referred to as FCW welding method) using the above-described flux-cored wire are certainly very efficient welding methods. Further, according to this FCW welding method, in the case of overlapped fillet welding, that is, the steel material arranged on the lower side with respect to the welding direction and the aluminum material arranged on the upper side are overlapped and welded together. When doing, the bead by an aluminum welding material can be formed over the welding surface of both the said steel materials and aluminum materials. For this reason, the dissimilar material joined body (joint) of high joint strength is obtained.

However, in this FCW welding method, when the positional relationship between the steel material and the aluminum material is opposite, that is, the steel material arranged on the upper side with respect to the welding direction, and the aluminum material arranged on the lower side, In the case where welding is carried out by overlapping each other, as described later, there is a problem that it becomes difficult to form a bead 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 of aluminum weld material over both the steel and aluminum weld surfaces. It cannot be obtained.

In this way, when the steel material arranged on the upper side with respect to the welding direction and the aluminum material arranged on the lower side are overlapped with each other, for example, a steel plate automobile panel such as a door is placed on the back side of the panel. This is the case of partial reinforcement with an aluminum alloy extruded shape from the (inner side). In the automobile manufacturing process (automobile body assembly process), the positional relationship between the steel material and the aluminum material varies. Therefore, even when high bonding strength is obtained as described above when welding the steel material arranged on the lower side and the aluminum material arranged on the upper side, the high bonding strength is obtained when the positional relationship is reversed. If it is not obtained, it will be difficult to adopt it in the automobile manufacturing process.

In view of such problems, the present invention is an improvement of the FCW welding method as a dissimilar material joining method. The present invention provides a dissimilar material joining method that can ensure high joint strength even when FCW welding is performed by superimposing a steel material arranged on the upper side with respect to the welding direction and an aluminum material arranged on the lower side. The purpose is to provide.

In order to achieve the above object, the gist of the dissimilar material joining method of the present invention is that the steel material arranged on the upper side and the aluminum material arranged on the lower side are overlapped with each other along the welding line. A welding method for dissimilar materials, wherein at least the position of the welding surface of the aluminum material along the welding line is higher than the position of the welding surface of the steel material along the welding line. In this state, by welding along the weld line, a bead of aluminum welding material is formed across the welding surfaces of both the steel material and the aluminum material.
At this time, it is preferable that the welding surface of the aluminum material protrudes 0.5 to 4 mm upward with respect to the welding direction.
Further, S is an interval provided so that the molten aluminum welding material wraps around between the lower surface of the steel material with respect to the welding execution direction and the surface of the aluminum material facing the lower surface of the steel material, and the steel material G is an interval provided between the end surface of the steel material and the surface of the aluminum material facing the end surface of the steel material, the surface of the aluminum material facing the lower surface of the steel material, and the end of the steel material R, which is the radius of curvature of the curved surface to which the surface of the aluminum material facing the part surface is connected, satisfies (1) S: 1.5 mm or less, G: 1 mm or less, R: less than 3 mm, or ( 2) It is preferable to adjust so as to satisfy S: 2.5 mm or less, G: 1 mm or less, and R: 3 to 5 mm.

Here, the welding is performed by MIG welding or laser welding among the FCW welding methods using the flux cored wire filled with the flux inside the aluminum outer sheath in terms of increasing welding efficiency and joint strength. preferable.

The present inventors investigated the reason why high joint strength could not be obtained by the FCW welding method depending on the positional relationship between the steel material and the aluminum material. As a result, when the aluminum material is arranged on the lower side with respect to the welding direction, it becomes clear that the molten aluminum is difficult to spread on the welding surface of the steel material arranged on the upper side, so that good bonding cannot be performed. It was. Further, in this case, since the supply of flux to the steel material surface is insufficient, the effect of improving the wettability between the molten aluminum and the steel is small, and as a result, it has become clear that good bonding cannot be performed.

Then, the present inventors can solve the above problems by welding in a state where the position of the welding surface of the aluminum material protrudes upward from the position of the welding surface of the steel material with respect to the welding construction direction. It has also been found that a bead of aluminum welding material can be formed over both the steel and aluminum welding surfaces.

Accordingly, in the present invention, even when the steel material arranged on the upper side with respect to the welding direction and the aluminum material arranged on the lower side are overlapped with each other and welded by the FCW welding method or the like, high joint strength is achieved. Can be secured stably. In the conventional FCW welding method, when the steel material arranged on the lower side with respect to the welding direction and the aluminum material arranged on the upper side are overlapped with each other, high joint strength is stably secured as described above. can do. 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 can be achieved by using the present invention and the conventional FCW welding method in combination or using them properly. Is possible.

It is sectional drawing which shows one Embodiment of this invention. It is sectional drawing which shows the welding result (dissimilar material joint) of FIG. It is sectional drawing which shows one Embodiment of this invention with which the welding apparatus was included. (A) is sectional drawing which shows the aspect of the conventional dissimilar material joining, (b) is sectional drawing which shows the aspect of dissimilar material joining of this invention.

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

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

FIG. 4A shows a case where the steel material arranged on the lower side with respect to the welding direction and the aluminum material arranged on the upper side are overlapped and welded to each other. FIG.4 (b) is a case where the steel materials arrange | positioned above with respect to the welding construction direction and the aluminum material arrange | positioned below are mutually piled up and welded like this invention.

Generally, in the dissimilar welding joint between steel and aluminum, when the steel side is melted, a very brittle steel-aluminum intermetallic compound is produced in large quantities, so that good welding cannot be performed. 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 disposed on the lower side with respect to the welding direction indicated by the arrow 4, the molten aluminum 6 (becomes a bead) from the aluminum material 3 disposed on the upper side, It tends to spread on the surface of the lower steel material 2 (welded surface 2a). The same is 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 (welded surface 2a) of the lower steel material 2. For this reason, the wettability of the weld 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 (weld surface 2a) is promoted. As a result, the bead 6 made of the aluminum welding material can be formed over the welding surfaces of both the steel material welding surface 2a and the aluminum material welding surface 3a, and better bonding can be realized. In the case of lap fillet welding or the like, when the steel material arranged on the lower side with respect to the welding direction and the aluminum material arranged on the upper side are overlapped and welded to each other, the FCW described in Patent Documents 9 to 12, etc. This is the reason why high welding strength can be obtained by the welding method.

On the other hand, as shown in FIG. 4B of the present invention, when the aluminum material 3 is arranged on the lower side with respect to the welding construction direction indicated by the arrow 4, the steel material 2 side arranged on the upper side, The molten aluminum 6 from the aluminum material 3 is difficult to spread. The same applies when the flux is used (when the FCW welding method is used), and the flux hardly spreads 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 conventional FCW welding method cannot improve the wettability of the weld surface 2a of the steel material 2 and the molten aluminum 6 (improvement of wettability). Small effect). Moreover, since removal of the oxide film on the surface of the steel material 2 (welded surface 2a) is not promoted, the bead 6 on the steel material welded surface 2a side is particularly difficult to be formed. 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. Here, similarly to FIG. 4B, a steel material 2 arranged on the upper side with respect to the welding direction indicated by the arrow 4 and an aluminum material 3 arranged on the lower side. Are superimposed on each other and fillet welded. Moreover, FIG. 2 shows the state after the example of this invention shown in FIG. 1 is fillet welded. 1 and 2 show an example in which a steel plate automobile panel 2 such as a door is partially reinforced with an aluminum alloy extruded shape 3 or the like from the back side (inside) of the panel 2.

1, a recess 3 b is provided at the end of the aluminum material 3 disposed on the lower side on the steel material 2 side, and the recess 3 b accommodates the welding surface 2 a of the steel material 2. The recess 3b has a depth greater than or equal to the thickness of the steel material 2. Therefore, when the welding surface 2a of the steel material 2 is overlapped so as to be accommodated in the concave portion 3b, the welding surface 2a of the steel material 2 with respect to the welding direction 4 is equal to the difference X (mm) between the depth of the concave portion 3b and the thickness of the steel material 2. To retreat. At the same time, the welding surface 3a of the aluminum material (welding surface along the welding line 5 with the steel material 2) is X (mm) above the welding direction 4 from the position of the welding surface 2a along the welding line 5. ) Only protrudes.

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

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

In FIG. 1, S (plate gap) indicates the clearance (interval) between the bottom surface of the recess 3 b of the aluminum material 3 and the lower surface of the steel material 2 accommodated. That is, the plate gap S is between the surface of the steel material opposite to the welding execution direction (the lower surface located below the welding execution direction) and the surface of the aluminum material facing the steel material surface. Further, the interval is provided so that the molten aluminum welding material wraps around. G (gap) indicates the clearance between the end surface of the recess 3 b of the aluminum material 3 and the end surface of the steel material 2 accommodated. That is, the gap G is an interval provided between the end surface of the steel material and the surface of the aluminum material facing the end surface of the steel material. These plate gaps S and G are prepared for wrapping around the steel material 2 of the molten aluminum (around). Here, the joining of the molten aluminum (molten aluminum) and the aluminum material 3 is the same as a normal welded portion, the aluminum material 3 (welded surface 3a) is melted and integrated with the molten aluminum 6, and the bead 6 is solidified after solidification. Thus, a strong joint is formed.

On the other hand, as described above, the cleaning action, wettability, and adhesiveness are improved by the flux, so that the steel weld surface 2a is widely covered with the molten aluminum 6 in a close contact state. Therefore, the steel material 2 is not directly input heat from an arc described later (arc 15 in FIG. 3 described later), but is indirectly input heat through the covered aluminum molten metal. It does not melt when heated excessively. A thin intermetallic compound layer of about several μm is formed at the joining interface between the steel material 2 and the aluminum melt 6 that is in close contact. This intermetallic compound layer is brittle when it is as thick as several tens of μm or more, and weld cracking occurs and the strength deteriorates. However, a thin intermetallic compound layer of about several μm is not brittle and is strong. It becomes a state.

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 by the flux, the wettability, and the adhesion improving action are very good is important. When the cleaning action, wettability, and adhesion improving action are lowered, the molten aluminum 6 cannot sufficiently cover the steel weld surface 2a. As a result, since the arc directly touches the steel material welding surface 2a, the steel material welding surface 2a is excessively heated and melted to form a thick intermetallic compound layer. On the other hand, even if the steel material welding surface 2a is not heated, if the adhesion between the molten aluminum 6 and the steel material welding surface 2a is low, a uniform intermetallic compound layer is not formed, so the molten aluminum 6 and the steel material welding are not formed. In some cases, the surface 2a is not bonded and peeling easily occurs.

Aluminum material welding surface protrusion method:
It is possible to project the aluminum material welding surface 3 a upward from the welding surface 4 a of the steel material 2 by the shape design and processing of the aluminum material. For example, in the case of an aluminum material as shown in FIG. 1, the aluminum material welding surface 3 a is partially thickened in advance, or by joining another aluminum material to the aluminum material welding surface 3 a, the thickness is partially increased. Or just meat.

However, depending on the design condition of the dissimilar material joined body, a method of partially thinning the end portion to be overlapped with the steel material 2 on the aluminum material 3 side, such as the recess 3b in FIG. As described above, the simplest method is to design the shape so that the original aluminum material is provided with the support flange (arm portion) of the steel material 2 and the like. For example, if the aluminum material 3 is an extruded shape, if the thin portion (concave portion) and the joint flange (arm portion) are included in the original shape and extruded, the thin portion ( The trouble of forming the (concave portion) is unnecessary. Moreover, even if the aluminum material 3 is a plate material, a thin portion (concave portion) can be formed by simply cutting in the middle or before and after the forming process.

Also, the protrusion amount X (mm) 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 protrusion amount: X (mm) is easy to spread to the lower steel material welding surface 2a of the molten aluminum 6, and easy to spread to the lower steel material welding surface 2a of the flux (improvement of wettability, steel material welding surface). It is appropriately selected based on the degree of the promotion of removal of oxide film 2a).

When this protrusion amount: X (mm) is small, the molten aluminum 6 does not sufficiently spread on the steel material welding surface 2a. On the other hand, if this protrusion amount: X (mm) is too large, it is difficult to ensure the penetration into the aluminum material 3. If the welding heat input is increased too much to ensure penetration, the intermetallic compound at the bonding interface grows thick, and in the extreme case, the steel material 3 is melted, so it is difficult to ensure the bonding strength. The optimum range of the protrusion amount: X (mm) varies depending on each condition, 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.

The protrusion amount: X (mm) is appropriately determined according to the plate gap S or gap G, which is the clearance between the aluminum material 3 and the steel material 2 described above, or in consideration of the plate gap S or gap G. Designed. Further, the plate gap S and the gap G, which are the clearances between the aluminum material 3 and the steel material 2, are also appropriately designed according to the relationship with the protrusion amount: X (mm).

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, the positional relationship between the steel material and the aluminum material is the same as in FIG. 1, and the steel material 2 disposed on the upper side with respect to the welding execution direction from the top to the bottom illustrated in FIG. The case is shown in which fillet welded with the aluminum material 3 arranged on the lower side being overlapped with each other.

FIG. 3 shows an example in which, for example, the end portion of the panel manufactured from the steel plate 2 is supported from the back side (inside) of the panel by the aluminum alloy extruded shape member 3. FIG. 3 differs from FIGS. 1 and 2 particularly in the shape of the aluminum material 3. That is, in FIG. 3, the aluminum material 3 has an inverted L shape, and extends in the horizontal direction to support the end portion of the steel plate panel 2, and to extend in the vertical direction. A vertical wall 3d joined to another structural member. And the flange 3c is provided below the welding surface 3a which is the upper end part of the vertical wall 3d. That is, the welding surface 3a which is the upper end part of the vertical wall 3d protrudes upward. Thereby, the welding surface 3a of the aluminum material 3 (welding surface along the welding line 5 with the steel material 2) is protruded above the welding direction 4 from the position of the welding surface 2a of the steel material 2. .

Further, a concave portion 3b is provided on the upper surface of the aluminum flange 3c in order to secure a clearance (interval) for the molten aluminum to wrap around the steel material 2 (lower part). The end of the recess 3b far from the aluminum material 3 has a vertical wall shape perpendicular to the bottom surface, but the side of the recess 3b in contact with the vertical wall 3d is the same as the lower surface of the flange 3c. It is connected to the vertical wall 3d so as to have a curved surface with a radius of curvature R. For example, as shown also in the examples described later, the curvature radius R is less than 3 mm according to the curvature radius R of the curved surface connecting the surface of the aluminum material facing the end surface of the steel material and the bottom surface of the recess 3b. In the case (including R = 0, that is, including the case where the corners are provided at right angles), it is recommended to adjust the plate gap S to be 1.5 mm or less and the gap G to be 1 mm or less. . When the radius of curvature R is 3 to 5 mm, it is recommended that the plate gap S be adjusted to 2.5 mm or less and the gap G to be adjusted to 1 mm or less.

Arc welding method:
The aspect of the welding apparatus used by this invention is demonstrated using FIG. In the present invention, it is possible to use a welding apparatus and welding method (arc welding apparatus, method and conditions) by the usual FCW welding method, and this 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, the block diagram of a laser irradiation arc welding apparatus It becomes.

3, 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 16 is supplied into the welding torch 13. A welding power source device (PS) indicated by reference numeral 14 outputs a welding voltage and a welding current for performing arc welding, and outputs a feeding control signal to the wire feeding motor.

With such a welding apparatus, the 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 aluminum material welding surface 3a is protruded upward with respect to the welding direction 4 from the position of the steel material welding surface 2a. Thereby, as shown in the said FIG. 2, the molten aluminum (not shown) from the welding surface 3a of the aluminum material 3 protruded to the upper side is easy 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 between the steel material welding surface 2a and the molten aluminum is improved, and the removal of the oxide film on the steel material 2 welding surface 2a is promoted.

As a result, even when a welded joint is formed by the steel material 2 arranged on the upper side with respect to the welding construction direction 4 and the aluminum material 3 arranged on the lower side, the steel material welding surface 2a and the aluminum material welding surface 3a A bead of aluminum welding material can be formed over both welding surfaces. Therefore, good bonding as the dissimilar material bonded 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 having no seam in which the seam is joined by welding or the like. 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., a narrow diameter of about 0.8 to 1.6 mmφ which is generally used may be used. As the wire having a smaller wire diameter is used in the range of the wire diameter, the heat input during welding can be reduced and the welding current can be lowered. 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 1.6φmm, the current for obtaining a stable arc becomes excessive, the scattering of the fluoride-based mixed flux itself increases, the melting of the base material becomes excessive, and the fragile metal It may lead to the formation of compounds.

The filling rate of the flux into the FCW is, of course, dependent on the flux composition, but is preferably relatively small, such as about 0.1 mass% and less than 24 mass% with respect to the total mass of the FCW. A lower filling rate is preferable because it prevents scattering of the flux itself and improves 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 FCW instead of directly applying the fluoride-based mixed flux to the weld. Considering use in the continuous assembly process of automobile bodies, etc., the use of the FCW improves the welding workability by preventing the dispersion of the fluoride-based mixed flux itself, and also suppresses 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 (Noroclock) having a specific composition in which fluorides such as aluminum fluoride and potassium fluoride are mixed among fluoride-based mixed fluxes. Flux) is preferable. In addition, if chloride remains in the welded portion, the chloride acts as a corrosion promoting factor for the welded portion, and consequently, the dissimilar material joint, so the flux does not contain chloride or the amount of chloride is 1 mol% or less. A regulated fluoride composition is preferred.

When the flux filling amount in the outer skin is small, the flux amount is not stable, and the flux filling amount (filling rate, content rate) varies depending on the part of the FCW. On the other hand, when the flux filling amount is small, mixing the flux and the aluminum alloy powder and filling the outer skin eliminates or alleviates this problem and facilitates the manufacture of the FCW itself. Therefore, it is preferable. In addition, when aluminum alloy powder is mixed and added to this flux, there are cases where spatter during welding is reduced and effects such as suppression of excessive wetting of the molten metal may be obtained.

If a mixed flux having such a specific composition is used, even a steel material coated by relatively thick hot dip galvanizing (including alloying) can be joined to an aluminum material. That is, if such a mixed flux is used, the surface of the material with the galvanized steel material or the aluminum material can be cleaned, and the wettability of the weld metal is improved. As a result, the bead formation is improved. Moreover, as a result of suppressing generation of a brittle Al—Fe-based intermetallic compound layer generated in the dissimilar material joint portion and a brittle Zn—Fe-based compound layer derived from galvanization, the bonding strength is improved. Of course, this effect is also exhibited in the dissimilar material joining of a bare steel material that is not galvanized and an aluminum material.

Steel:
The thickness of the steel materials to be joined with different materials in the present invention is preferably in the range of 0.3 to 4.0 mm. If the 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 members and structural materials described above. Further, in the present invention, the shape of the steel material to be joined with the different material is not particularly limited, and a shape generally used for a structural member such as an automobile body or a steel plate, a steel shape member, and a steel pipe selected by the structural member. The shape may be appropriate.

However, in order to obtain a lightweight high-strength structural member (dissimilar material joined body) such as an automobile member, high-tensile steel (high tensile) having a tensile strength of 400 MPa or more, desirably 500 MPa or more is used. Low-strength steel and mild steel having 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. Moreover, when low strength steel or mild steel is used, the plate thickness is increased to obtain the required strength, and the weight reduction is sacrificed.

Zinc plating:
The surface of the steel material to be joined with the different material may or may not be subjected to surface treatment except for coating with an insulating film. When galvanization is previously provided on the steel material surface (at least the joint 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 that the corrosion resistance of a dissimilar material joining body is excellent is acquired. Furthermore, since galvanization has the effect of delaying the time for the interfacial reaction layer, which is an intermetallic compound of steel and aluminum, to be formed during welding, it also has the effect of increasing joint strength.

As these zinc plating, known zinc plating of steel materials such as pure zinc plating, alloy zinc plating, and alloyed zinc plating can be applied. The plating means is not particularly limited, and an alloying treatment may be performed after electroplating, hot dipping, or hot dipping. The thickness of the galvanizing may be in the normal film thickness (average film thickness) range of 1 to 20 μm. When the thickness of the galvanized film is too thin, the galvanized film is melted and discharged from the bonded part at the initial stage of joining at the time of 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 heat input becomes large in this way, not only the aluminum material side but also the steel material side is melted, 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 bonded to the different material in the present invention is not particularly limited with respect to the alloy composition and shape, and according to the required characteristics as each structural member described above, a widely used alloy composition, plate material, shape material, A forging material, a casting material, or the like is appropriately selected. However, it is desirable that the strength of the aluminum material be higher as in the case of the steel material. Therefore, Al-Mg-Si based A6000 aluminum alloy, which has high strength among aluminum materials, has a small amount of alloy elements, is excellent in weldability and recyclability, and is widely used as a structural member of this kind, is used. It is preferable to do.

The plate 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, it is inappropriate because the strength as a structural material of an automobile or the like and the energy absorption at the time of a vehicle body collision are insufficient. On the other hand, when the thickness of the aluminum material exceeds 4.0 mm, it is impossible to reduce the weight of the structural member and the structural material as in the case of the steel material. Note that the surface of the aluminum material to be joined with 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 generation of an intermetallic compound generated at the interface between an aluminum material and a steel material, it is necessary to prevent the steel material as a base material from being excessively melted. Therefore, it is preferable to select a welding condition that allows a sound joining state to be obtained with the minimum necessary base material melting (dilution) amount.

The welding current is 70 A or more, preferably 80 A or more and 120 A or less, more preferably 80 A or more and 110 A or less. The higher the current, the more the intermetallic compound at the bonding interface that is generated can adversely affect the bonding strength. Therefore, in order to suppress such an intermetallic compound, it is recommended to join at a relatively low current condition.

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

The welding speed may be appropriately determined within a range in which the base material Fe and Al are not excessively melted according to the welding current and the welding voltage. Considering the welding efficiency and the like, the welding speed is preferably 20 CPM or more, more preferably 30 CPM or more and 100 CPM or less, and further preferably 30 CPM or more and 90 CPM or less.

As the shield gas 16, a general-purpose gas such as Ar can be used as appropriate. The gas flow rate is not particularly limited, and a general flow rate can be selected.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples. Of course, the present invention can be implemented with appropriate modifications within a range that can meet the gist of the following description, and these are all included in the technical scope of the present invention.

As shown in FIG. 1 and FIG. 3, the joint shape of the test piece in which the steel material 2 arranged on the upper side with respect to the welding direction 4 and the aluminum material 3 arranged on the lower side are overlapped with each other. The fillet welding test by FCW welding (MIG welding) shown in FIG. 3 was used. 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, the plate gap S, and the gap G are changed in each example, and the weldability of the dissimilar material jointed body The effect of was investigated. The results are shown in Tables 1 to 3.

Example 1
In the joint shape shown in FIG. 1, a cold-rolled steel sheet (high-tensile, thickness 1.4 mm) subjected to alloying hot-dip galvanizing (GA) having a tensile strength of 980 MPa was used as the steel material 2. Further, as the aluminum material 3, a T6 tempered extruded material (plate thickness of 2.0 mm) of a 6000 series aluminum alloy having a 0.2% proof stress of 180 MPa class was used.

Test pieces:
The length of the test piece is 300 mm for both the steel material 2 and the aluminum material 3. A flat concave portion 3b having a length of 100 mm is provided at the end of the extruded aluminum member 3 on the steel plate 2 side. The recess 3b accommodates the welding surface 2a of the steel material 2. And the protrusion amount X (mm) from the steel material welding surface 2a of the aluminum material welding surface 3a was variously changed by adjusting the depth of this recessed part 3b.

Here, the clearance between the bottom surface of the concave portion 3b of the aluminum material 3 and the lower surface of the steel material 2 is “plate gap S”, and the clearance between the end portion of the steel material 2 and the end portion of the concave portion 3b is “gap G”. The plate gap S and gap G are shown in Table 1. In Example 1, S and G are zero in common with each example.

Welding conditions:
The conditions were MIG welding conditions, welding current 80 A, welding voltage 20 V, and welding speed 50 cpm (cm / min). FCW is an aluminum alloy filler with a wire diameter of 1.0 mmφ and an outer skin of A4047, and fluoride flux (K3 AlF6 fluoride and aluminum alloy powder of A4047 composition) is used in all FCWs. What added 10 mass% with respect to the weight was used. The shield gas 16 is Ar.

Joint weldability evaluation:
The weldability of the joint can be evaluated by visual observation of the bead and a peeling test using chisel. In the visual observation of the bead, “◎” is a state in which the bead 6 is continuously and satisfactorily formed over both the weld surface 2a of the steel material 2 and the weld surface 3a of the aluminum material as shown in FIG. . And by comparison with this, especially the magnitude | size of the bead by the side of the welding surface 2a of the steel material 2 was evaluated by (circle), (triangle | delta), and x in order with the favorable thing. Incidentally, “x” indicates the case where the bead 6 is hardly formed on the welded surface 2a side of the steel material 2 or the case where the bead is extremely small.

In the peeling test with chisel, with the tip of the chisel (cutting forging tool) attached to the vicinity of the center of the weld (bead 6), tap the chisel head with a hammer once with a large force. Thus, the peeled state (destructive state) of the bead 6 was investigated. And what was not exfoliated (destructed) at all over the bead 6 was evaluated as “◎”. And by comparison with this, according to the magnitude | size of peeling (destruction) which generate | occur | produced in a part of bead 6, it evaluated by (circle), (triangle | delta), and x in order of small peeling. Incidentally, “x” is a case where the bead 6 is largely peeled off and the joint can be regarded as broken. By the way, if the evaluation of the peel test with chisel is ◎, it is a guideline that the joint has a break strength of 200 N / mm or more, and if it is ×, the joint has a break strength of less than about 100 N / mm. become.

From Table 1, the welding surface 3a of the lower aluminum material 3 protrudes with respect to the welding direction arrow 4, and each of the protrusion amounts X ranges from 0.5 mm to 4 mm (number 3 to number 8). It can be seen that the joint weldability evaluation is good. On the other hand, in each example of

numbers

1, 2, and 10, the joint weldability evaluation is inferior.

In the example of No. 1, as shown in FIG. 4B, the welding surface 3 a of the aluminum material 3 is below the welding surface 2 a of the steel material 2 with respect to the welding direction 4. is there. In the example of No. 2, the protrusion amount X of the welding surface 3a of the lower aluminum material 3 with respect to the welding execution direction 4 is too small and is 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 4 is small.

Contrary to this, in the example of No. 10, the protrusion amount X is too large. From this result, when the protrusion 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. On the other hand, if the heat input of welding is increased too much to ensure penetration, the intermetallic compound at the bonding interface grows thick, and in extreme cases, the steel is melted, so it is still difficult to ensure the bonding strength. Become.

(Example 2)
In the same joint shape as in Example 1, the protrusion amount X is constant as shown in Table 2. In this example, the plate gap S and the gap G were variously changed, and the same test piece as in Example 1 and a welding test were performed under welding conditions, and the effects of the plate gap S and the gap G were 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 in each example (number 11 to number 13) in which the plate gap S is 0.5 mm to 1.5 mm. Further, in each example (number 11 to number 16) in which the gap G is 0 mm to 1 mm, the weldability of the joint is good. 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)
In the joint shape (groove shape) shown in FIG. 3, the protrusion amount X is constant as shown in Table 3. In this embodiment, the curvature radius R of the upper curved surface connecting the vertical wall 3d and the flange 3c is variously changed, and a welding test is performed under the same welding conditions as in the first embodiment. The effect of corner shape was investigated.

Test pieces:
The steel material 2 is the same as that of each above-mentioned Example. In the present embodiment, the material and strength of the aluminum extruded material 3 are the same, but only the cross-sectional shape of the aluminum extruded material 3 is changed as shown in FIG. The aluminum extruded material 3 has a flange (arm portion) 3c having a length of 35 mm and a thickness of 4 mm, a vertical wall 3d having a length of 18 mm and a thickness of 3 mm. 5 mm. And the depth of the recessed part 3b is 1 mm, and the protrusion amount X from the steel material welding surface 2a with respect to the welding construction direction 4 of the aluminum material welding surface 3a is 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 curvature radius R, 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 by such a groove shape.

In other words, such a groove shape allows joint weldability even when the plate gap S and gap G are relatively large due to design convenience and assembly errors of the joint or the underlying structural member. Has improved. Therefore, it can be seen that such a groove shape allows a design convenience and assembly error, and allows the board gap S and the gap G to have a margin. Further, the groove shape having the curvature radius R as shown in FIG. 3 does not need to be produced by machining such as cutting. The use of an aluminum alloy extruded shape has an advantage that such a shape can be realized without machining by only an extrusion designed to have a desired cross-sectional shape.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made as long as they are described in the claims. This application is based on a Japanese patent application filed on March 11, 2009 (Japanese Patent Application No. 2009-058174), the contents of which are incorporated herein by reference.

According to the present invention, especially in FCW welding, even when a steel material arranged on the upper side and an aluminum material arranged on the lower side are overlapped and welded to each other, the dissimilar material joint that can stably secure a high joint strength. Can provide a method. Moreover, according to this invention, the construction method is also easy and can provide the joining method using the arc welding which can perform efficient wire welding. 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, 16: Shielding gas

Claims

It is a dissimilar material joining method in which the steel material arranged on the upper side with respect to the welding construction direction and the aluminum material arranged on the lower side are overlapped with each other and welded along the welding line,
In a state where at least the position of the weld surface of the aluminum material along the weld line protrudes upward with respect to the welding direction from the position of the weld surface of the steel material along the weld line, the weld line A bead made of an aluminum welding material is formed over the welding surfaces of both the steel material and the aluminum material by welding along a steel material.
The dissimilar material joining method according to claim 1, wherein a weld surface of the aluminum material protrudes 0.5 to 4 mm upward with respect to the welding direction.
S, which is an interval provided between the lower surface of the steel material with respect to the welding direction and the surface of the aluminum material facing the lower surface of the steel material so that the molten aluminum welding material wraps around, and the end of the steel material G, which is an interval provided between the surface of the aluminum material facing the end surface of the steel material and the end surface of the steel material, the surface of the aluminum material facing the lower surface of the steel material, and the end surface of the steel material And R, which is the radius of curvature of the curved surface to which the surface of the aluminum material facing the surface is connected, is adjusted to satisfy S: 1.5 mm or less, G: 1 mm or less, and R: less than 3 mm. The dissimilar material joining method described.
S, which is an interval provided between the lower surface of the steel material with respect to the welding direction and the surface of the aluminum material facing the lower surface of the steel material so that the molten aluminum welding material wraps around, and the end of the steel material G, which is an interval provided between the surface of the aluminum material facing the end surface of the steel material and the end surface of the steel material, the surface of the aluminum material facing the lower surface of the steel material, and the end surface of the steel material 3. The curvature radius of the curved surface to which the surface of the aluminum material facing the surface R is adjusted so as to satisfy S: 2.5 mm or less, G: 1 mm or less, and R: 3 to 5 mm. The dissimilar material joining method described in 1.
5. The dissimilar material joining method according to any one of claims 1 to 4, wherein the welding is performed by MIG welding or laser welding using a flux cored wire in which a flux is filled in an aluminum outer shell.