JP5600653B2 - Dissimilar metal joining method - Google Patents

Description

  The present invention relates to a dissimilar metal joining method in which fillet welding of an aluminum alloy material and a steel material is performed by direct current TIG welding using a tungsten electrode. The aluminum alloy material referred to in the present invention is a general term for various members and parts such as a rolled plate material (cold rolled plate or the like) made of aluminum alloy, an extruded shape, or a car body formed by processing these, and steel materials and Is a general term for various members and parts such as cold-rolled steel, die steel, or a car body obtained by molding these.

  In recent years, problems with the global environment such as global warming caused by exhaust gas discharged from transportation vehicles such as automobiles have been raised, and as one of the countermeasures, fuel consumption is reduced by reducing the weight of automobiles and other vehicles. Improvement is being considered. On the other hand, there is a concern that if a vehicle is made lighter, there is a possibility that it will become a serious accident when a car or other vehicle has a collision accident. ing. For these reasons, it has been studied to apply an aluminum alloy that is lightweight and excellent in energy absorption to a part of a vehicle body of a transportation vehicle including an automobile, and has recently been put into practical use. Yes.

  However, in order to apply aluminum alloys to automobiles such as automobiles, it is necessary to design a structure that takes advantage of the characteristics of the aluminum alloy. Except for all-aluminum alloy special vehicles, the body structure is a combination of aluminum alloy materials with the steel materials that make up the body structure. Therefore, dissimilar metal joining technology between steel and aluminum alloy materials is essential. It becomes.

  However, if the dissimilar metal joining of steel and aluminum alloy material is simply performed by welding, the intermetallic compound layer (or reaction) of Fe and Al, which is highly brittle and very brittle, is formed at the joint interface between the steel material and the aluminum alloy material. Layer) is generated. That is, even though the steel material and the aluminum alloy material are apparently bonded to each other, the joint is caused by a very brittle intermetallic compound layer (or reaction layer) of Fe and Al generated at the bonding interface. There arises a problem that sufficient bonding strength cannot be obtained.

  When welding is adopted as the joining technology for steel and aluminum alloy materials, the above-mentioned problems occur. Therefore, mechanical joining technology that uses fasteners such as self-piercing rivets and bolts to join steel and aluminum alloy materials. In addition, a joining technique using an adhesive is also employed. However, these joining techniques have problems such as complicated joining work and increased joining costs, and are not widely applied.

  Currently, wire bonding such as TIG welding and spot welding are widely used for joining steel materials and the like that constitute vehicles for transportation such as automobiles. If these welding technologies can be applied to dissimilar metal joining technology between steel and aluminum alloy material, vehicles using aluminum alloy material can be manufactured in the same line and process as steel material in the factory, and joining work Can be further improved.

  Among these welding techniques, TIG welding is the most widely adopted technique for joining steel materials, etc. As described above, for dissimilar metal joining of steel materials and aluminum alloy materials, the inter-metal between Fe and Al is used. Since there is concern about the problem of generation of the compound layer, the actual situation is that not only practical use but also proposals have been made.

Under such circumstances, Patent Document 1 proposes a technique related to dissimilar metal joining between a steel material and an aluminum alloy material by TIG welding. However, this proposal only mentions TIG welding as an example of butt welding and lap welding. That is, this proposal is performed by a welding means selected from the group of laser, electron beam, plasma arc, TIG, MIG, and CO ₂ arc, and TIG welding may be TIG welding in this proposal. It is only a positioning.

  In Patent Document 2, in the dissimilar metal joining method in which the steel material is on the upper side and the aluminum alloy material is on the lower side with respect to the welding direction, and the welding surface of the aluminum alloy material is welded to each other, It has been proposed that welding is performed along the weld line in a state of protruding upward with respect to the welding construction direction. According to this method, the wettability of the molten aluminum on the weld surface of the steel material can be improved, the removal of the oxide film on the surface of the steel material (weld surface) can be promoted, and good bonding can be realized.

  Moreover, in this patent document 2, the TIG welding of the aspect using the flux cored wire (FCW) formed by filling a flux inside the aluminum material outer skin is also intended. Incidentally, many compositions of FCW used for such dissimilar metal joining have been proposed in Patent Document 3 and the like. However, these Patent Documents 2 and 3 do not disclose a specific dissimilar metal joining method between an aluminum alloy material and a steel material using TIG welding.

  For this reason, the present inventors have actually carried out a different material joining test in which an aluminum alloy material and a steel material are joined by TIG welding, and have confirmed the problems that occur at that time. Specifically, as shown in FIG. 3, the aluminum alloy material 1 is placed on the upper side, one end of the aluminum alloy material 1 is overlapped on the steel material 2, and the aluminum alloy material 1 is formed with the edge of the aluminum alloy material 1 and the surface of the steel material 2. While supplying the flux cored wire (FCW) 4 to the stepped portion 3, a dissimilar metal joining test was performed in which the aluminum alloy material 1 and the steel material 2 were fillet welded using the tungsten electrode 5. The TIG welding was performed by AC TIG welding generally used for welding the aluminum alloy materials 1 and 1 to each other.

  As a result of this dissimilar metal joining test, spattering during welding was hardly generated and good, but the molten aluminum alloy material 1 and the similarly melted FCW4 were separated into beads 6a and 6b as steel materials. It became what was called a hot-watered joining (bead) state which exists on the surface of No.2.

  In such a joined state where the beads 6a and 6b are separated from the hot water (bead), adjustments are made to greatly change the welding conditions of TIG welding, such as increasing the power (heat input) or decreasing the welding speed. Also occurred and could not be completely prevented. In such a welded (beaded) state, the joint strength of the joint (dissimilar metal joint) cannot be increased.

  In addition, this hot water separation is likely to occur in TIG welding between steel materials, particularly under high pressure of arc and welding at high speed, the shape of the molten pool becomes unstable, and the molten pool vibrates and is severe in the bead. This is known as a humping phenomenon that can cause unevenness.

  As a means for preventing the occurrence of this hot water separation, although it is a technique related to TIG welding of steel materials to the last, a method using a magnetic field and a technique in which the shape of the tip portion of the tungsten electrode is devised have been proposed. As a method of using a magnetic field, for example, a constant magnetic field is applied around the welding arc, and an electromagnetic force generated by an electromagnetic interaction between the magnetic field and an arc current flowing through the welding arc is applied to the welding arc, so that the welding arc Patent Document 4 proposes a technique in which two to-be-joined parts are joined in a continuous manner by deflecting the radial shape in the weld line direction of the to-be-joined part.

  Although the method using a magnetic field as disclosed in Patent Document 4 is certainly an effective technique for preventing the occurrence of hot water separation, a magnet device is required separately, and the electromagnetic force generated by the magnet device generates a welding arc. Therefore, the existing welding equipment cannot easily cope with it, and the cost is increased.

  On the other hand, Patent Document 5 and Patent Document 6 propose a technique in which the shape of the tip portion of the tungsten electrode is devised. The shape of the tip of a general tungsten electrode is a conical shape like the tip of a pencil. However, in Patent Document 5, the tip of the surface of the electrode rod for TIG welding having a ridge line at the tip is the most advanced shape. And the electrode which made the angle between the surfaces which form a ridgeline 40-100 degrees is proposed. In this technique, an arc point is generated along the ridge line by this technique, and the arc is prevented from creeping up to the surface near the electrode tip, thereby preventing the arc from spreading in the width direction of the bead. Thus, the arc is concentrated to enable high-speed TIG welding with a large current.

  In Patent Document 6, in a TIG welding apparatus that performs welding between steel members having narrow grooves, the tungsten electrode is directed from the upper side of the aluminum alloy material to the welding line, and the tip of the tungsten electrode is set at an angle of 30 ° to 40 °. It has been proposed that the wire is melted while the tungsten electrode is rotated within a narrow groove.

  Even if the electrode improvement technique in TIG welding between steel materials described in Patent Document 5 is applied to TIG welding of dissimilar metals between an aluminum alloy material and a steel material using FCW, it is impossible to prevent the occurrence of the above-mentioned hot water separation. . The reason for this is that TIG welding of dissimilar metals between an aluminum alloy material and a steel material using FCW is a welding between different materials. Therefore, the welding mechanism and the occurrence mechanism of hot water are different from the TIG welding between steel materials. This is probably because of this.

  The technique described in Patent Document 6 is a technique related to butt welding of thick plates and cannot be applied as it is to overlapped fillet welding of thin plates. In addition, both the technique described in Patent Document 5 and the technique described in Patent Document 6 have a problem that the electrode needs to be processed into a shape different from a normal shape, and that it is difficult to perform maintenance when the electrode is consumed.

JP 2001-47244 A JP 2010-207886 A JP 2008-68290 A JP 2008-105056 A JP-A-6-328287 JP 2004-237326 A

  The present invention has been made as a solution to the above-described conventional problems, and can perform dissimilar metal joining between an aluminum alloy material and a steel material by TIG welding that is most widely adopted for joining steel materials, and the like. An object of the present invention is to provide a dissimilar metal joining method capable of obtaining a good bead appearance and necessary joint strength.

  According to the first aspect of the present invention, at least a part of the aluminum alloy material and the steel material are overlapped, and the aluminum alloy material side is used as a positive electrode, and the flux is applied to the stepped portion formed on the edge of the aluminum alloy material and the surface of the steel material. A dissimilar metal joining method for fillet welding the aluminum alloy material and the steel material by direct current TIG welding using a rod-shaped tungsten electrode while supplying a cored wire, wherein the tungsten electrode is connected in a direction perpendicular to the steel material. The steel material is inclined at 35 ° or more and less than 60 ° (θ = 35 ° or more and less than 60 °), and the tip of the tungsten electrode is 2.0 mm or more and 4.5 mm from the surface of the aluminum alloy material. Placed at a position vertically separated (z = 2.0 mm or more and less than 4.5 mm), and the extension line of the central axis of the tungsten electrode is The position where the surface of the aluminum alloy material intersects with the aluminum alloy material is within the range of 1.0 mm or more and less than 3.0 mm from the edge of the aluminum alloy material (x = 1.0 mm or more and less than 3.0 mm), and the tungsten electrode The dissimilar metal joining method is characterized in that arc welding is performed to fillet weld the aluminum alloy material and the steel material.

  The invention according to claim 2 is the dissimilar metal joining method according to claim 1, wherein the flux cored wire is supplied from the welding progress direction.

  According to the dissimilar metal joining method of the present invention, a dissimilar metal joint between an aluminum alloy material and a steel material is prepared by a TIG welding that is most widely used for joining steel materials, and a special shape tungsten electrode is prepared. This can be done with simple equipment improvement without replacing the parts used in the equipment. In addition, regardless of the dissimilar metal bonding, the occurrence of hot water separation can be prevented, and a good bead appearance and necessary joint strength can be obtained.

It is a longitudinal cross-sectional view which shows one Embodiment of the dissimilar metal joining method of this invention. It is a perspective view which shows the state which is TIG-welding an aluminum alloy material and steel materials using a tungsten electrode. It is a longitudinal cross-sectional view which shows the state in which the dissimilar metal joining method using the conventional TIG welding is shown, and the bead is separated. It is a longitudinal cross-sectional view which shows the state which piles up and fillet-welds the same kind of metal plates.

  The present inventors previously made a proposal for performing dissimilar metal bonding between an aluminum alloy material and a steel material by TIG welding that is most widely adopted for bonding between steel materials without causing hot water separation. However, this proposal is a proposal that prevents occurrence of hot water separation by improving the shape of the tip of the tungsten electrode. However, this proposal requires processing the tip part of the tungsten electrode into a shape different from the normal shape and replacing the parts used in the current equipment. In order to find an appropriate condition for using TIG welding without dissimilar metal joining, it was further earnestly researched.

  As a result, TIG welding is performed by direct current TIG welding, and the inclination of the tungsten electrode is set to an appropriate inclination with respect to the aluminum alloy material and steel material to be welded, and the tip of the tungsten electrode is arranged at an appropriate position. Then, by irradiating the arc to an appropriate position, it was found that the dissimilar metal joining between the aluminum alloy material and the steel material can be performed by TIG welding without causing hot water separation, and the present invention has been completed. .

  First, the present inventors supplied a rod-shaped tungsten electrode while supplying a flux cored wire (FCW) by the method shown in FIG. 2 by AC TIG welding, which is most widely used for welding aluminum alloy materials. When fillet welding of the aluminum alloy material 1 and the steel material 2 was carried out using No. 5, the result was obtained that there was almost no spatter and welding was possible. However, in this general method, as shown in FIG. 3, the molten aluminum alloy material 1 and the FCW 4 are separated from each other like beads 6a and 6b and exist on the surface of the steel material 2, so-called separated hot water (beads). ) State.

  When the present inventors observed the welding situation in this case in detail, as shown in FIG. 3, the cause of the occurrence of hot water separation in the TIG welding of the aluminum alloy material 1 and the steel material 2 is from the tungsten electrode 5 during the TIG welding. It has been found that the cause is that the generated arc 7 is largely biased to the aluminum alloy material 1 side (left side in FIG. 3).

  When the arc 7 generated from the tungsten electrode 5 is biased toward the aluminum alloy material 1, the aluminum alloy material 1 starts to melt first, and the start of melting of the FCW 4 is necessarily delayed. As a result, the flux does not sufficiently spread on the surface of the steel material 2, and it becomes difficult to ensure the wettability of the molten aluminum alloy to the steel material 2 side as much as possible in the bead 6 on the steel material 2 side in the aluminum alloy material 1. Moreover, since the temperature rise of the steel material 2 also becomes relatively slow due to the bias of the arc 7 toward the aluminum alloy material 1, it is considered that the spread of the flux to the surface of the steel material 2 is inhibited.

  From these phenomena, the molten metal formed by melting the aluminum alloy material 1 becomes difficult to spread to the steel material 2 side. Furthermore, the molten metal formed by melting the aluminum alloy material 1 is pushed to the aluminum alloy material 1 side (left side in FIG. 3) by the arc 7 biased toward the aluminum alloy material 1 side. The bead 6a is solidified in the state of moving to the material 1 side. As the melting range of the aluminum alloy material 1 becomes wider, the molten metal formed by melting the aluminum alloy material 1 moves more to the aluminum alloy material 1 side.

  On the other hand, the molten metal formed by melting FCW4 spreads on the surface of the steel material 2 due to the effect of the flux. However, the arc 7 generated from the tungsten electrode 5 is pushed in the direction opposite to the aluminum alloy material 1 side (right side in FIG. 3). As a result, the molten metal formed by melting FCW4 does not mix with the molten metal formed by melting aluminum alloy material 1, and solidifies as another bead 6b in a state separated from the aforementioned bead 6a. End up. As a result, hot water separation occurs.

  In order to suppress as much as possible the occurrence of hot water separation by such a principle, it is considered important to take the following measures. (1) Melt FCW4 as soon as possible to ensure wettability. (2) The melting range of the aluminum alloy material 1 is suppressed, and the movement of the molten metal formed by melting the aluminum alloy material 1 toward the aluminum alloy material 1 is reduced. However, it is necessary to ensure melting of the aluminum alloy material 1 over the entire plate thickness direction.

  The present inventors actually performed these measures by performing a welding test, and confirmed whether or not the occurrence of hot water separation could be suppressed. Here, the following two types of improvement tests were carried out, but neither of these measures could reliably suppress the occurrence of hot water separation.

  (1) The position of the tungsten electrode 5 was moved 0.5 mm from the position shown in FIG. 3 to the steel material 1 side (right side in FIG. 3) to reduce the heat input to the aluminum alloy material 1. However, a strong arc 7 is generated between the tip of the tungsten electrode 5 and the surface of the aluminum alloy material 1, and it has not been possible to prevent the occurrence of hot water separation. Moreover, when the position of the tungsten electrode 5 was moved 1 mm to the steel material 1 side, the steel material 2 began to melt, and it became a result that the joining itself by welding could not be performed.

  (2) The power source was changed from an AC power source to a DC power source. As a result, the spread of the arc 7 could be suppressed and the melting range of the aluminum alloy material 1 could be reduced, but it was not possible to prevent the occurrence of hot water separation.

  From these test results, it was confirmed that simply changing the welding conditions based on the general measures described above does not lead to the problem of hot water separation. Therefore, the present inventors examined a new countermeasure plan that replaces the general measures (1) and (2). As a result, the direction and the target position of the arc 7 are changed from the conventional one, the distribution of heat input of the aluminum alloy material 1 / FCW4 / steel material 2 is changed, and the aluminum alloy material 1 side of the molten aluminum alloy material 1 (see FIG. It was found that suppressing the movement to the left side in Fig. 1 is effective in preventing the occurrence of hot water separation.

  Hereinafter, the present invention will be described in more detail based on embodiments shown in the accompanying drawings.

  In the present invention, for example, as shown in FIGS. 1 and 2, TIG welding of the aluminum alloy material 1 and the steel material 2 is performed by superposing at least a part of the aluminum alloy material 1 and the steel material 2 and the aluminum alloy material 1 side is a positive electrode. As described above, an arc 7 is generated by using a rod-like tungsten electrode 5 while supplying a flux cored wire (FCW) 4 to a stepped portion 3 formed by the edge of the aluminum alloy material 1 and the surface of the steel material 2. To do.

  As shown in FIG. 4, the two metal plates 11 and 12 are overlapped, and the torch (electrode) is aimed at the stepped portion 13 formed by the edge of the upper metal plate 11 and the surface of the lower metal plate 12. The fillet welding in which 15) is inclined and welded is a method generally used for welding the same kind of metal plates 11 and 12 such as steel materials or aluminum alloy materials. The inclination angle θ of the torch (electrode 15) at this time is appropriately selected within a range in which the penetration into the upper metal plate 11 and the lower metal plate 12 is appropriate. For example, one-pass fillet welding is performed in the joining of the metal plates 11 and 12 constituting a transportation vehicle including an automobile, but if the inclination angle θ of the torch (electrode 15) becomes too large, the lower side The penetration into the metal plate 12 is reduced. For example, in the case of lap fillet welding of aluminum alloy materials, the inclination angle θ of the torch (electrode) is set to 5 ° to 15 °.

  On the other hand, in the dissimilar metal joining in which the aluminum alloy material 1 and the steel material 2 are fillet welded by TIG welding using the tungsten electrode 5, the surface of the steel material 2 is also secured while ensuring the melting of the aluminum alloy material 1 and the welding material FCW4. Welding conditions for heating appropriately are necessary, and the conditions are inevitably different from welding of the same kind of metal plates such as steel materials and aluminum alloy materials. In this way, in the dissimilar metal joining in which the aluminum alloy material 1 and the steel material 2 are overlapped and welded together, the welding of the same kind of metal plates is the inclination angle of the tungsten electrode 5 for performing appropriate overlapped fillet welding, Further, it is considered that the target position when the arc 7 is irradiated from the tungsten electrode 5 (the position where the extended line of the central axis of the tungsten electrode 5 intersects the surface of one aluminum alloy material) is different.

  Therefore, the inventors conducted a welding test in which the inclination angle of the tungsten electrode 5 in TIG welding and the target position when irradiating the arc 7 from the tungsten electrode 5 were variously changed, and as a result of intensive research, Appropriate welding conditions that can form good beads 6 were found.

(Inclination of tungsten electrode)
When the tungsten electrode 5 is inclined from the direction perpendicular to the steel material 2 toward the steel material 2 side, the arc 7 irradiated from the tungsten electrode 5 is relatively directed toward the aluminum alloy material 1 side, and the molten FCW 4 is used. An action of pushing to the aluminum alloy material 1 side occurs. As a result, the melt of the aluminum alloy material 1 and the melt of FCW4 are integrated, and the effect of preventing hot water separation can be obtained. The effect begins to gradually appear when the inclination of the tungsten electrode 5 reaches 30 ° or more. In addition, since FCW4 melts early, the effect of improving the wettability of the flux is also easily exhibited. This effect appears when the inclination of the tungsten electrode 5 is 35 ° or more, and it is considered that the tensile shear strength is easily obtained.

  The hot water separation preventing effect and the wettability improving effect described above are manifested by directing the arc 7 irradiated from the tungsten electrode 5 to the aluminum alloy material 1 side as much as possible, and the inclination angle of the tungsten electrode 5 is made as large as possible. If it takes, it will express more remarkably. However, if the inclination angle of the tungsten electrode 5 is too large, the tungsten electrode 5 comes into contact with the surface of the steel plate 2, so there is a limit even if the inclination angle is increased. Considering this, the tungsten electrode 5 is in a state of being inclined at 35 ° or more and less than 60 ° from the direction perpendicular to the steel material 2 toward the steel material 2 side (θ = 35 ° or more and less than 60 °).

(Aim position of arc from tungsten electrode)
The target position when the arc 7 is irradiated from the tungsten electrode 5 (the position where the extension of the central axis of the tungsten electrode 5 intersects the surface of the aluminum alloy material) is generally performed by welding the same type of metal plates. As described above, if the stepped portion 3 is formed by the edge of the aluminum alloy material 1 and the surface of the steel material 2, the heat input to the steel material 2 becomes too large and the steel material 2 is melted, or Even if the steel material 2 is not melted, a thick intermetallic compound is generated. Therefore, even if the continuous bead 6 can be formed, cracking may occur or sufficient joint strength may not be obtained.

  As a result of studying the improvement of these problems, the present inventors set the target position when irradiating the arc 7 from the tungsten electrode 5 to the stepped portion 3 which is generally performed by welding the same kind of metal plates. It was found that it is more effective to use the aluminum alloy material 1 side, that is, the surface of the aluminum alloy material 1 instead. Specifically, the target position when the arc 7 is irradiated from the tungsten electrode 5 (the position where the extension line of the central axis of the tungsten electrode 5 intersects the surface of the aluminum alloy material 1) is set to 1 from the edge of the aluminum alloy material 1. 0.0 mm or more and less than 3.0 mm The range on the aluminum alloy material 1 side (x = 1.0 mm or more and less than 3.0 mm). Note that the aluminum alloy material 1 side means a position closer to the center of the aluminum alloy material 1 starting from the edge of the aluminum alloy material 1.

(Disposition of the tip of the tungsten electrode)
The tip of the tungsten electrode 5 needs to be arranged at a position perpendicular to the surface position of the aluminum alloy material 1 (on a perpendicular perpendicular to the surface of the aluminum alloy material 1), but at least 2.0 mm or more and 4.5 mm It is necessary to arrange at a position vertically separated (z = 2.0 mm or more and less than 4.5 mm). This position is also affected by the thickness of the aluminum alloy material 1, the inclination angle of the tungsten electrode 5, the target position of the arc 7 from the tungsten electrode 5, and the welding conditions (current voltage, welding speed, FCW supply speed). .

(Power supply)
The power source 8 (shown in FIG. 2) is generally changed from an AC power source used for welding the aluminum alloy material 1 to a DC power source, and TIG welding is performed by DC TIG welding. By using direct current TIG welding, the melting range of the aluminum alloy material 1 can be reduced.

(Other conditions)
Although the conditions described above are essential conditions, the FCW 4 is preferably supplied from the welding progress direction, and the tungsten electrode 5 may be provided with an advance angle α of about 15 ° or less. When the FCW 4 is supplied from the welding progress direction, the FCW 4 starts to melt on the front side of the molten pool of the aluminum alloy material 1, so that melt mixing of both is easy and a good bead 6 can be formed. When FCW 4 is supplied from the opposite direction of the traveling direction, FCW 4 melts behind the molten pool of aluminum alloy material 1, so that it becomes difficult to melt and mix them, and it is difficult to form a good bead 6.

  In the dissimilar metal bonding method of the present invention, the aluminum alloy material 1, the steel material 2, and the flux cored wire (FCW) 4 are not particularly limited in material, but it is recommended to use the materials described below.

(Aluminum alloy material)
As the aluminum alloy material 1 to be welded, the 3000 series, 5000 series, 6000 series, and 7000 series defined by JIS or AA standards according to the required characteristics of the vehicle body structure to be applied, such as strength, molding, or corrosion resistance. An aluminum alloy such as can be used. However, from the viewpoint of reducing the thickness of the aluminum alloy material 1 to meet the demand for reducing the weight of the vehicle body such as an automobile, among these aluminum alloys, it is preferable to use an aluminum alloy having particularly high strength and excellent formability.

  In addition, the Si-to-Mg mass ratio (Si / Mg) in the component composition is 1 or more, and Si is excessively contained relative to the Mg content. Si-rich 6000 series such as 6N01, 6016, 6111, and 6022 It is particularly preferable to use an aluminum alloy. The joint after welding using the aluminum alloy material 1 made of these 6000 series aluminum alloys is subjected to an artificial aging treatment at an extremely low temperature of 160 to 180 ° C. and for an extremely short time of about 10 to 50 minutes. It also has the feature that it can recover the strength and elongation once lowered by the influence.

  These aluminum alloy materials 1 are subjected to solution treatment and quenching treatment (quality symbol T4), subsequent aging treatment (quality symbol T6), and overaging treatment (quality symbol T7) after cold rolling or hot extrusion. Is used as a welding base material. Incidentally, the aluminum alloy material 1 does not necessarily have to be a plate-shaped cold-rolled plate as a whole, and it is sufficient that at least the overlapping portion with the steel material 2 is a plate shape. In addition, extruded shapes having various shapes can be used, and further, vehicle body members and parts molded into a predetermined shape may be used. The thickness of the plate-like portion of the aluminum alloy material 1 is preferably 1 to 3 mm. If the aluminum alloy material 1 is too thin, it will not be possible to ensure the required strength and rigidity as an automobile member, while if it is too thick, it will be difficult to perform welding.

(Steel)
As the steel material 2 that is a material to be welded, various steel plates or shaped steels such as mild steel, high-tensile steel (high-tensile steel), and stainless steel cold-rolled steel plate can be used. Further, the steel material 2 may be a member or a part for a vehicle body obtained by molding these materials into a predetermined shape. From the viewpoint of reducing the thickness of the steel material 2 in response to the demand for weight reduction of the vehicle body such as an automobile, a high-strength steel material such as a high-tensile steel plate (high-tensile steel) having a known component composition including Si, Mn and the like and a tensile strength of 450 MPa or more. Is preferably used.

  In addition, assuming that the steel material 2 is used as an automobile member, the thickness of the steel material 2 (at a portion to be welded) such as a cold-rolled steel plate is preferably 0.3 to 3.0 mm. As in the case of the aluminum alloy material 1, if the thickness of the steel material 2 is too thin, the required strength and rigidity as an automobile member cannot be ensured. On the other hand, if it is too thick, it becomes difficult to perform welding.

  The steel material 2 preferably has a zinc-based or aluminum-based coating layer formed on the surface thereof for the purpose of welding efficiency and good bead formation, but the steel material 2 remains (bare). It doesn't matter. When forming the coating layer, it can be formed by means such as hot dipping or thermal spraying.

(Flux cored wire)
As the flux cored wire (FCW) 4, FCW4 that has been commercially available for joining different materials between the aluminum alloy material 1 and the steel material 2 can be used. Such FCW4 is a well-known FCW4 developed for improving the efficiency of fusion welding, and the flux is, for example, a tubular outer shell (also called a hoop) made of a standard aluminum alloy such as A4047 or A4043 containing Si. It is filled as a core material.

  The wire diameter of FCW4 is preferably a small diameter of about 0.8 to 1.6 mmφ, which is widely used for highly efficient full-automatic welding or semi-automatic welding. Moreover, as a flux, it is preferable to use the flux which consists of a fluorine compound type composition called common name "Nocolok" for joining the dissimilar materials of the aluminum alloy material 1 and steel materials. This flux is a well-known flux in which an oxide (such as aluminum oxide) or an aluminum alloy powder is appropriately mixed in addition to the fluorine compound.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

  As shown in FIG. 2, one end portion of the aluminum alloy material 1 is overlapped on one end portion of the steel material 2, and the aluminum alloy material 1 side is used as a positive electrode, and the edge of the aluminum alloy material 1 and the surface of the steel material 2 are formed. While supplying the flux cored wire (FCW) 4 to the stepped portion 3, a welding test for performing TIG welding using the rod-shaped tungsten electrode 5 was performed.

  The aluminum alloy material 1 uses a 6000 series (6022) aluminum alloy cold-rolled plate having a thickness of 1.2 mm or 2.0 mm, and the steel material 2 is a 980 MPa-class cold-rolled plate having a thickness of 1.4 mm. A 1.4 mm 1470 MPa class cold rolled sheet or a 1.4 mm thick 980 MPa class GA steel sheet was used.

  Further, the flux cored wire (FCW) 4 contains 10% by mass of a Cs-based flux, the skin material is an aluminum alloy to which 1.25% by mass of Si is added, and the wire diameter is 1.2 mm.

  The welding conditions were direct current TIG welding, current of 80 to 120 A, welding speed of 30 cm / min, filler supply speed of 6 to 10 m / min, and shielding gas of 20 L / min using Ar gas. Further, welding was performed such that the advance angle α of the tungsten electrode 5 was 5 ° to 15 °, and the length of the bead 6 was 200 mm.

  The test results were evaluated by the appearance and tensile shear strength (joint efficiency) of the formed beads 6.

  As shown in FIG. 5, the appearance of the bead 6 is such that the bead 6 is continuously and satisfactorily formed over both the weld surface of the aluminum alloy material 1 and the weld surface of the steel material 2, and it can be determined that the wettability is good. Is indicated by “◯”, and the bead 6 is continuously formed, but “△” indicates that the wettability can be judged to be poor, and the hot water separation as shown in FIG. Each thing was marked with an “x” and rejected.

  In addition, the tensile shear strength (joint efficiency) was determined by measuring a tensile test by cutting out two strip-shaped test pieces each having a plate width of 20 mm including the welded portion from the dissimilar joint after TIG welding. After obtaining the average value of the two tensile rupture strengths obtained as a result, the joint efficiency, which is the ratio to the tensile rupture strength of the base material 6000 series (6022) aluminum alloy cold-rolled sheet, was determined. It evaluated by comparing with the joint efficiency of the overlap fillet welded joint of the 6000 type | system | group (6022) aluminum alloy cold-rolled plates manufactured by TIG welding using the welding wire for alloys.

  Since the joint efficiency per unit weld line of the 6000 series (6022) aluminum alloy cold-rolled lap fillet welded joints is 60% or more, the joint efficiency of the TIG-welded dissimilar lap fillet welded joint is at least the same level. Those with 60% or more passed as “◯”, those with a joint efficiency of 40% to less than 60% as “Δ”, and those with less than 40% as “x”, respectively. The test results are shown in Table 1.

  The inclination angle (electrode angle) θ toward the steel material side of the tungsten electrode is set to 35 ° or more and less than 60 ° (θ = 35 ° or more and less than 60 °). The target position of the arc from the tungsten electrode is arranged in the range closer to the inner side of 1.0 mm or more and less than 3.0 mm from the edge of the aluminum alloy material (x = 1.0 mm or more and less than 3.0 mm) (target position). The tip part of the tungsten electrode is disposed (height) at a position (z = 2.0 mm or more and less than 4.5 mm) separated from the surface position of the aluminum alloy material by 2.0 mm or more and less than 4.5 mm. In Invention Examples 1 to 10 that satisfy all the requirements, both the appearance and tensile shear strength of the beads were “◯”, and excellent appearance and bonding strength could be obtained. In other words, in TIG welding, both the prevention of the occurrence of bead segregation, which is difficult to be compatible with each other, the suppression of the formation of an intermetallic compound layer (or reaction layer) at the interface, and the ensuring of the penetration of the aluminum alloy are compatible. Is done.

  On the other hand, Comparative Examples 1-5 and 6-10 have the requirement that the inclination angle (electrode angle) θ toward the steel material side of the tungsten electrode is 35 ° or more and less than 60 ° (θ = 35 ° or more and less than 60 °). In Comparative Examples 1, 3, 7, 9, and 10, the target position of the arc from the tungsten electrode is within the range of 1.0 mm to less than 3.0 mm from the edge of the aluminum alloy material (x = 1.0 mm or more and less than 3.0 mm), and Comparative Examples 3, 67, and 10 have a tungsten electrode tip portion of 2.0 mm or more and less than 4.5 mm from the surface position of the aluminum alloy material. It does not satisfy the requirement of disposing at an upwardly separated position (z = 2.0 mm or more and less than 4.5 mm). As a result, at least one of the appearance and the tensile shear strength of the bead was “Δ” or “×”, and the result was a failure.

DESCRIPTION OF SYMBOLS 1 ... Aluminum alloy material 2 ... Steel material 3 ... Step part 4 ... Flux cored wire (FCW)
5 ... Tungsten electrodes 6, 6a, 6b ... Bead 7 ... Arc 8 ... Power supply

Claims (2)

While superposing at least a part of the aluminum alloy material and the steel material, with the aluminum alloy material side as the positive electrode, while supplying the flux cored wire to the stepped portion formed on the edge of the aluminum alloy material and the surface of the steel material, A dissimilar metal joining method for fillet welding the aluminum alloy material and the steel material by direct current TIG welding using a rod-shaped tungsten electrode,
The tungsten electrode is in a state inclined from the direction perpendicular to the steel material to the steel material side by 35 ° or more and less than 60 ° (θ = 35 ° or more and less than 60 °),
The tip portion of the tungsten electrode is arranged at a position (z = 2.0 mm or more and less than 4.5 mm) vertically separated from the surface of the aluminum alloy material by 2.0 mm or more and less than 4.5 mm,
The position at which the extension line of the central axis of the tungsten electrode intersects the surface of the aluminum alloy material is within the range of 1.0 mm or more and less than 3.0 mm from the edge of the aluminum alloy material (x = 1.0 mm) And less than 3.0 mm)
Dissimilar metal joining method characterized by fillet welding the aluminum alloy material and steel material by irradiating an arc from the tungsten electrode. The dissimilar metal joining method according to claim 1, wherein the flux cored wire is supplied from a welding progress direction.

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