Method for joining dissimilar materials

Abstract

To provide a method for joining dissimilar materials of a plate-shaped member to be joined having a dissimilar electric resistivity and capable of suppressing decrease of a plate thickness of the member to be joined while securing satisfactory a joint strength.SOLUTION: In such a case that a steel plate 1 having a large electric resistivity and an aluminum plate member 2 having a small electric resistivity are joined, an electric resistivity of a contact interface of the steel plate 1 and the aluminum plate member 2 is further larger than the electric resistivity of the steel plate 1, therefore, when an applied current is conducted with a large current increasing rate for an extremely short time between electrodes 3 with interposed both joint members, temperature of only the contact interface and a neighborhood region thereof is largely elevated, by virtue of heat generation of the contacting interface and the neighboring region thereof, the contacting interface region with the steel plate 1 of the aluminum plate member 2 having a low melting point is melted and, by solidification of melting material thereof, the steel plate 1 and the aluminum plate member 2 are welded.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for joining dissimilar materials, and more particularly to a method for joining a first plate-shaped member to be joined and a second plate-shaped member to be joined having a lower electrical resistivity than the first member to be joined. [Background technology]

[0002] Resistance welding, which is one of the joining methods, has advantages such as less distortion, good appearance, and short welding time, and is widely adopted in the automobile industry, especially in the manufacture of car bodies. As is well known, resistance welding, also known as spot welding, is performed by melting the joined members themselves with Joule heat caused by the contact resistance between the members to be joined. The most common joined members for car bodies in such resistance welding are steel plates, so-called steel plates. On the other hand, for example, aluminum (alloy) plates are being used to reduce the weight of car bodies. Although resistance welding technology between aluminum joined members is being established, dissimilar material resistance welding, especially mass-produced resistance welding, between aluminum joined members and iron-based material joined members, for example steel plates, is difficult to obtain sufficient joining strength (also called joint strength) because the electrical resistivities and melting points of the two materials are significantly different, and as a result, it is still under development.

[0003] A method for joining dissimilar materials having different electrical resistivities and melting points by resistance welding is described, for example, in Patent Document 1. This dissimilar material joining method is said to be capable of joining dissimilar materials, such as an aluminum member to be joined and a steel member to be joined, with excellent joining strength, by precisely specifying, for example, the electrode tip shape, welding current value, current flow time, and pressure. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2014-94408 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the method for joining dissimilar materials, an aluminum member and a steel member, by resistance welding, as described in the above Patent Document 1, a Fe 2 Al 3 or FeAl 3 The problem is that aluminum-iron alloys such as these are generated as brittle intermetallic compounds (hereinafter referred to as IMCs (Inter Metallic Compounds)), and the presence of these IMCs significantly reduces the joint strength of both joined members. In the dissimilar material joining method according to Patent Document 1, the plate thickness of the aluminum workpieces to be joined is significantly reduced, so that the IMCs can be expelled to the outside of the joint region, thereby ensuring the joint strength. However, such a significant reduction in the plate thickness of the aluminum workpieces to be joined leads to a reduction in the strength of the aluminum workpieces themselves and a reduction in their marketability, such as their appearance, particularly in robot-mounted resistance welding of plate members for vehicle bodies.

[0006] The present invention has been made in consideration of the above-mentioned problems, and its object is to provide a method for joining dissimilar materials, plate-shaped workpieces having different electrical resistivities, which can suppress a reduction in the plate thickness of the workpieces while ensuring sufficient joining strength. [Means for solving the problem]

[0007] A dissimilar material joining method for achieving the above object includes the steps of: A plate-shaped first member to be joined and a plate-shaped member having a lower electrical resistivity than the first member to be joined. a first member to be joined and a second member to be joined by sandwiching the first member and the second member between opposing electrodes and applying pressure and current thereto, The electrode is heated so that the melting point of the first member to be joined does not exceed the melting point of the first member to be joined except at the interface between the first member to be joined and the second member to be joined. The frequency is 5 kHz or higher The method is characterized in that an applied current is applied at a predetermined current increase rate for a predetermined period of time, and the heat generated at the contact interface melts the area near the contact interface between the second joined member and the first joined member, thereby welding both joining members.

[0008] According to this configuration, for example, when joining a plate-like first joined member having a high electrical resistivity such as a steel plate and a plate-like second joined member having a low electrical resistivity such as an aluminum plate member, the electrical resistivity of the interface between the first joined member and the second joined member is even higher than that of the first joined member, so that when an applied current is applied for a very short time between the electrodes sandwiching the two joined members, the interface between the two joined members is heated, and only the interface and its neighboring regions are significantly heated. This large temperature rise only at the interface between the two joined members and its neighboring regions is achieved by applying an applied current between the electrodes for a very short time with a large current increase rate. As a result, for example, in the case of a steel plate and an aluminum plate member, since the melting point of the aluminum plate member is lower than that of the steel plate, the temperature rise of the interface between the two joining members and the area nearby melts the area near the interface between the aluminum plate member and the steel plate, and the molten material solidifies to weld the first joined member, for example, the steel plate, and the second joined member, for example, the aluminum plate member. At this time, the second joined member, for example, the aluminum plate member, melts and solidifies only in the area near the interface between the first joined member, for example, the steel plate, so that the reduction in the plate thickness of the second joined member can be suppressed. In addition, the first joined member, which has a high melting point, for example, a steel plate, does not melt or hardly melts, so that IMC (intermetallic compound) such as an aluminum-iron alloy does not form or hardly forms, and the joining strength of both joined members can be ensured. In addition, an alternating current is usually applied between the electrodes sandwiching the multiple plate-shaped workpieces, but in order to achieve a large current increase rate, it is necessary to increase the frequency of the applied current. For example, in order to achieve a current value of 15 to 25 kA with a current rise time of 20 msec or less, the frequency of the applied current needs to be 5 kHz or more. The applied current frequency of a typical spot welding is at most about 3 to 4 kHz, and with this power supply frequency, the current increase rate immediately after the start of current flow is limited. As a result, the current value of 15 to 25 kA cannot be reached in a short time of 20 msec or less, and the temperature rise behavior of the workpieces as described above cannot be obtained. In contrast, by setting the frequency of the applied current to 5 kHz or more, the current value of the current can be raised at a large current increase rate immediately after the start of current flow, and thus the current value of 15 to 25 kA can be obtained with a current rise time of 20 msec or less, and the temperature rise behavior of the workpieces as described above can be obtained, and both workpieces can be well welded.

[0009] In another aspect of the present invention, the second member to be joined has a melting point lower than the melting point of the first member to be joined.

[0010] According to this configuration, when the second joined member is an aluminum plate member and the first joined member is a steel plate, the melting point of the aluminum plate member is lower than that of the steel plate, so that the temperature rise of the interface between the two joining members and the area nearby melts the area near the interface between the aluminum plate member and the steel plate, and the molten material solidifies to reliably weld the two joining members and also suppress a decrease in the plate thickness of the aluminum plate member. At that time, the steel plate with a high melting point does not melt or melts very little, so no or very little IMC occurs at the joint between the two joining members, and the joining strength of the two joining members can be ensured.

[0011] A further configuration of the present invention is characterized in that the current rise time of the energization is 20 msec or less, and the specified current increase rate is a value that satisfies the condition that the current value reaches 15 to 25 kA within the specified time of the energization.

[0012] According to this configuration, the electrical resistivity of the interface between the two joining members is higher than that of the first joining member only for a short time until the temperature of the first joining member itself is raised by current flow, and by passing current between the electrodes only for this very short time, the interface between the two joining members is heated, and the interface between the second joining member and the first joining member and the surrounding area can be heated. Since the current rise time of general spot welding is at least 30 msec., it can be said that the current rise time of 20 msec. or less of the present invention is far shorter than the current rise time of general spot welding. Furthermore, in order to melt the area near the interface between the second joining member and the first joining member in this short time, it is necessary to apply a current at a current increase rate such that the current value reaches 15 to 25 kA during the current flow time, and by satisfying this condition, the area near the interface between the second joining member and the first joining member is melted, and the molten material is solidified, thereby reliably welding the two joining members. As is well known, the current value achieved in typical spot welding is also about 15 to 25 kA (however, this depends on the plate thickness), but since the current flow time is short, at 20 msec or less, it can be said that the current flow increase rate of the present invention is far greater than the normal current flow increase rate.

[0013] In order to achieve the above object, a resistance welding device is provided, A resistance welding apparatus having opposing electrodes sandwiching a plate-shaped first joined member and a plate-shaped second joined member having an electrical resistivity lower than that of the first joined member, and a current control device which applies an applied current to the electrodes, the resistance welding apparatus resistance-welding the first joined member and the second joined member by applying a predetermined applied current from the current control device to the electrodes, The current control device is configured to apply current to the electrodes having a frequency of 5 kHz or more at a predetermined current increase rate and for a predetermined period of time so that the melting point of the first joined member is not exceeded except at the abutment interface between the first and second joined members, and the current application generates heat at the abutment interface, melting the area of ​​the second joined member near the abutment interface with the first joined member, thereby welding the two joined members. With this configuration, the same effect as that described in claim 1 of the method invention can also be obtained in claim 4 of the apparatus invention.

[0014] A further configuration of the resistance welding device of the present invention is characterized in that the current rise time of the energization is 20 msec or less, and the specified current increase rate is a value that satisfies the condition that the current value reaches 15 to 25 kA within the specified time of the energization. With this configuration, the same advantageous effects as those described in claim 3 of the method invention can also be obtained in claim 5 of the apparatus invention. Effect of the Invention

[0015] As described above, according to the present invention, the region of the second joined member near the interface with the first joined member is melted, and the molten material solidifies to weld both joining members, thereby making it possible to suppress a reduction in the plate thickness of the second joined member.In addition, since the first joined member does not melt or only barely melts, IMC such as aluminum-iron alloy does not occur or only barely occurs, and the joining strength of both joining members can be ensured. [Brief description of the drawings]

[0016] [Figure 1] 1 is a schematic configuration diagram of a resistance welding apparatus to which a dissimilar material joining method according to the present invention is applied; [Diagram 2] 3 is an explanatory diagram of a current flow and an associated temperature change in a resistance welding method showing one embodiment of a dissimilar material joining method carried out by the resistance welding apparatus of FIG. 1. FIG. [Diagram 3] 3 is an explanatory diagram of energizing current and associated temperature change in a resistance welding method showing a comparative example of a dissimilar material joining method carried out by the resistance welding apparatus of FIG. 1. FIG. [Figure 4] FIG. 4 is an explanatory diagram of the electrical resistivity of two members to be joined and their abutting interface used in the resistance welding methods of FIGS. 2 and 3. [Diagram 5] 3 is a cross-sectional view of a joint after joining by the resistance welding method of FIG. 2. [Figure 6] 4 is a cross-sectional view of a joint after joining by the resistance welding method of FIG. 3. FIG. [Figure 7] FIG. 4 is an explanatory diagram of an IMC thickness of a joint formed by the resistance welding method of FIGS. 2 and 3. [Figure 8]FIG. 2 is an explanatory diagram of the thickness and bonding strength of an IMC made of an aluminum-iron alloy. [Figure 9] FIG. 4 is a diagram illustrating the relationship between current value and temperature depending on the applied current frequency. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the dissimilar material joining method of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of a resistance welding device to which the dissimilar material joining method of the present invention is applied. This resistance welding device is for performing so-called spot welding (spot resistance welding), and for example, a plate-shaped first joined member is a steel plate 1, and a plate-shaped second joined member is an aluminum plate member 2, and these different types of metal plates are welded together. In this resistance welding device, for example, the overlapped first joined member and the second joined member are sandwiched by opposing electrodes 3 with a predetermined pressure force, and in this state, a predetermined applied current is applied between the electrodes 3 by an energization control device 4 to perform resistance welding. The electrodes 3 are equipped with a pressure device (not shown) composed of, for example, a servo motor, an oil / pneumatic cylinder, a spring, etc. The resistance welding device shown in the figure is schematic, and the actual electrodes 3 and pressure device are attached, for example, to a manipulator of an industrial robot in a mass-produced vehicle body manufacturing line. Therefore, the energization control device 4 is configured to be linked to, for example, an operation control device of the industrial robot, or is configured to be integrated therewith. The configuration of the electrode 3, for example the R shape of the tip, is set appropriately. This resistance welding device can be used by partially improving an existing device as necessary. Also, a new device may be created.

[0018] FIG. 2 shows the current flow and the associated temperature change over time in an embodiment of the resistance welding method performed by the resistance welding apparatus of FIG. 1. FIG. 3 shows, as a comparative example, the current flow and the associated temperature change over time in an example of a conventional resistance welding method. As is well known, the electrical resistivity of aluminum is lower than that of iron. Also, the melting point of aluminum is lower than that of iron. In general resistance spot welding between steel sheets, the current rise time is at least 20 msec, and the current is passed for a total of 100 msec or more to melt the base material near the interface by the Joule heat at the interface between the two steel sheets, and the molten material solidifies to form a nugget, which welds both joining members. In resistance spot welding between aluminum plate members, it is necessary to remove the oxide film on the surface of the plate members, and because the electrical resistivity is small as mentioned above, the current value of the applied current must be increased in order to obtain the necessary Joule heat, and therefore the current flow time must be shortened. However, just like resistance spot welding between steel plates, the plate members are welded together by melting the base material near the contact interface between the plate members and solidifying the molten material to form a nugget.

[0019] In contrast, in dissimilar material resistance spot welding of a steel plate 1 and an aluminum plate member 2, as described in detail later, there are problems with the presence of IMC made of aluminum-iron alloy and the reduction in plate thickness (also called base metal thinning) of the aluminum plate member 2, which has a low melting point. As is clear from a comparison of Figs. 2 and 3, the resistance welding method of this embodiment has a very short current flow time compared to the comparative example of the conventional style. In the resistance welding method of Fig. 3, the current rise time is 20 msec. and the current flow time is 100 msec. or more, but in the resistance welding method of Fig. 2, the current rise time is 20 msec. or less, preferably 5 to 10 msec., and current is passed for a predetermined current flow time depending on the material and plate thickness. For comparison, the current reach values ​​of the two resistance welding methods are set to be equal at 15 to 25 kA, but due to the difference in current flow time, the current increase rate in the resistance welding method of Fig. 2 is much greater than that in Fig. 3.

[0020] FIG. 4 shows the change in electrical resistivity over time with respect to the time of current flow (the time axis scale is larger than that of FIG. 2 and FIG. 3). The time of current flow means the temperature rise of the material through which current is passed. As is clear from the figure, the electrical resistivity of the aluminum plate member 2 (aluminum plate in the figure) is smaller than that of the steel plate 1. The electrical resistivity of the contact interface between the aluminum plate member 2 and the steel plate 1 (Al-Fe in the figure) is even greater than the electrical resistivity of the steel plate 1. Furthermore, the electrical resistivity of both increases with increasing temperature. As a result, when the temperature inside the steel plate rises to the same temperature as the temperature of the contact interface with the aluminum plate member 2, the electrical resistivities of both also become the same. The time during which the electrical resistivity of this contact interface is higher than the electrical resistivity inside the steel plate is a short time after the start of current flow. If a sufficient current value can be applied within an even shorter period of time, the heat generated at the interface between the aluminum plate member 2 and the steel plate 1 can raise the temperature of only the interface and its surrounding area, and the heat transfer melts the area near the interface between the aluminum plate member 2 and the steel plate 1, which has a low melting point, and the molten material solidifies (coagulates) to weld the two joining members. This welding form is close to what is called interfacial bonding. Furthermore, with this welding method, the steel plate 1 (iron) does not melt or barely melts, so that IMC made of aluminum-iron alloy is not formed or barely formed, and the joining strength can be ensured.

[0021] The current control in FIG. 2 is based on the above findings, and therefore the current rise time is set to a very short time of 20 msec or less, preferably 5 to 10 msec. Furthermore, by achieving a sufficient current value of 15 to 25 kA in this very short current flow time, it is possible to raise the temperature only at the contact interface between the aluminum plate member 2 and the steel plate 1 and its neighboring region, as described above, as evidenced by the fact that the internal temperatures of the steel plate 1 and the aluminum plate member 2 are only raised to a relatively low temperature. In the figure, the internal temperature of the aluminum plate member 2 does not reach the melting point of aluminum, but exceeds the melting point in the neighboring region of the contact interface with the steel plate 1, and as a result, the neighboring region of the contact interface between the aluminum plate member 2 and the steel plate 1 is melted. The two joining members are welded by the melting and solidification (coagulation) of this aluminum base material. Furthermore, the fact that the internal temperature of the aluminum plate member 2 does not reach the melting point means that the melting of the aluminum plate member 2 does not progress in the plate thickness direction, and therefore the reduction in the plate thickness of the aluminum plate member 2 can be suppressed.

[0022] In contrast, the current rise time in Fig. 3 is 30 msec or more, and then the current is cut off. However, during this current flow, not only the temperature of the contact interface between the aluminum plate member 2 and the steel plate 1 rises, but also the internal temperature of the steel plate 1, and the internal temperature of the aluminum plate member 2 reaches the melting point of aluminum due to the heat transfer and heat conduction of this heat. This means that the melting of the aluminum plate member 2 progresses in the plate thickness direction, and therefore the plate thickness of the aluminum plate member 2 is greatly reduced. In addition, since the internal temperature of the steel plate 1 also reaches the melting point, an IMC made of an aluminum-iron alloy is generated, which is expected to reduce the joint strength.

[0023] FIG. 5 is a cross-sectional view of a joint between an aluminum plate member 2 and a steel plate 1 by the resistance welding method of FIG. 2. The upper side of the figure is the aluminum plate member 2, and the lower side is the steel plate 1. As is clear from the figure, this resistance welding method effectively suppresses the reduction in plate thickness, particularly of the aluminum plate member 2, and also suppresses the deformation of the base material of both joint members. FIG. 6 is a cross-sectional view of a joint between an aluminum plate member 2 and a steel plate 1 by the resistance welding method of FIG. 3. As in FIG. 5, the upper side of the figure is the aluminum plate member 2, and the lower side is the steel plate 1. As is clear from the figure, this resistance welding method significantly reduces the plate thickness of the aluminum plate member 2 at the joint. In addition, the base material deformation of both joint members is significant along with the reduction in plate thickness of the aluminum plate member 2. This is thought to be due to the fact that not only the aluminum plate member 2 but also the inside of the steel plate 1 reaches the melting point, as described above.

[0024] FIG. 7 is an explanatory diagram of the IMC thickness by the resistance welding method of FIG. 2 and FIG. 3 (current control in the figure), and FIG. 8 is a correlation diagram between the IMC thickness and the joint strength. As described above, this IMC is made of an aluminum-iron alloy. First, as is clear from FIG. 8, as the thickness of the IMC increases, the joint strength between the aluminum plate member 2 and the steel plate 1 decreases significantly, and eventually decreases until they cannot be joined. The actual thickness of this IMC is on the order of microns, and does not appear in the cross section at the plate thickness level of, for example, FIG. 5 or FIG. 6. As shown in FIG. 7, in the resistance welding method of FIG. 2, the thickness of the IMC is relatively small, and does not exist or is almost absent, especially in the part far from the center of the joint. It has been confirmed that the aluminum plate member 2 and the steel plate 1 are welded by the molten aluminum solidification layer even in the region where the IMC does not exist. On the other hand, in the resistance welding method of FIG. 3, the thickness of the IMC is large, especially at the peripheral part of the joint, so that a decrease in the joint strength of both joint members is inferred.

[0025] The joining strength of the joint between these aluminum plate members 2 and steel plate 1 was measured. In the test, the aluminum plate members 2 and steel plate 1, both of which had a plate thickness of 1.2 mm, were used, and welding was performed with the pressure applied by the electrode 3 set to 3 kN or less, a current value of 15 to 25 kA, and a current flow time of 100 to 500 msec. As a result, the shear strength of the joint between the aluminum plate member 2 and the steel plate 1 by the resistance welding method of FIG. 2 was greater than the shear strength of the joint made by resistance welding between aluminum plate members, and was also greater than the shear strength of the joint made by the resistance welding method of FIG. 3. In addition, the peel strength of the joint between the aluminum plate member 2 and the steel plate 1 by the resistance welding method of FIG. 2 was brought close to the peel strength of the joint made by resistance welding between aluminum plate members, whereas the peel strength of the joint made by the resistance welding method of FIG. 3 was correspondingly smaller than the peel strength of the joint made by resistance welding between aluminum plate members.

[0026] As described above, in order to reach the ultimate current value of 15 to 25 kA in a short current rise time of 20 msec or less, preferably 5 to 10 msec, the frequency of the current applied to the electrode 3 must be increased to 5 kHz or more, and in some cases up to about 10 kHz. FIG. 9(a) shows the aluminum plate member surface temperature (solid line), aluminum plate member internal temperature (dash line), and steel plate surface temperature (dashed line) when the frequency of the energized alternating current rectified to DC is 5 kHz. Similarly, FIG. 9(b) shows the aluminum plate member surface temperature (solid line), aluminum plate member internal temperature (dash line), and steel plate surface temperature (dashed line) when the energized alternating current frequency is less than 5 kHz, specifically 3 kHz. When the frequency of the applied current is low (3 kHz), the rate of increase of the energized current value is limited, and as a result, it takes a long time (about 30 msec) for the ultimate current value to reach 25 kA. As a result, even if the current value reaches a peak, the difference between the surface temperature of the steel sheet and the surface temperature of the aluminum sheet member does not become large, and as described above, the temperature rises to the inside of the steel sheet 1 over a long current application time, and the aluminum sheet member 2 heats up to the inside due to the heat, melting throughout the entire sheet thickness. In contrast, by setting the frequency of the applied current to 5 kHz or more, the current value rises at a large current increase rate immediately after the start of current application, and the current value reaches 25 kA in an extremely short time (5 msec or less). As a result, since the difference between the surface temperature of the steel sheet and the surface temperature of the aluminum sheet member 2 becomes large after the current application ends, the surface of the steel sheet 1, i.e., the contact interface, is greatly heated by this short current application, and the contact interface of the aluminum sheet member 2 with the steel sheet 1 and its neighboring area are melted by the heat, and the two joining members can be welded by the solidification of the molten material. At that time, the inside of the aluminum sheet member 2 does not heat up significantly as shown in the figure, and melting does not progress in the thickness direction.

[0027] In this manner, in the dissimilar material joining method of this embodiment, when joining a steel plate 1 (plate-shaped first joined member) having a high electrical resistivity and an aluminum plate member 2 (plate-shaped second joined member) having a low electrical resistivity, the electrical resistivity of the interface between the steel plate 1 and the aluminum plate member 2 is greater than that of the steel plate 1. Therefore, when an applied current is applied at a large current increase rate for a very short time between the electrodes 3 sandwiching both joining members, the interface between the two joining members is heated, and only the interface and its neighboring region is significantly heated. As a result, the interface between the two joining members and its neighboring region is heated, and the aluminum plate member 2, which has a low melting point, melts in the neighboring region between the steel plate 1 and the aluminum plate member 2, and the molten material is solidified, thereby welding the steel plate 1 and the aluminum plate member 2. At this time, the aluminum plate member 2 melts and solidifies only in the neighboring region between the interface with the steel plate 1, for example, so that a reduction in the plate thickness of the aluminum plate member 2 can be suppressed. Furthermore, since the steel plate 1 having a high melting point does not melt or melts very little, IMC such as aluminum-iron alloy does not occur or hardly occurs, and the joining strength of both joining members can be ensured.

[0028] Furthermore, by setting the specified current flow time to 20 msec or less and setting the current increase rate to satisfy the condition that the current value reaches 15 to 25 kA within this specified current flow time, the area near the contact interface between the aluminum plate member 2 and the steel plate 1 melts, and the molten material solidifies, thereby reliably welding the two joining members.

[0029] Furthermore, by setting the frequency of the current applied to the electrode 3 to 5 kHz or more, the current value can be increased at a large current increase rate immediately after the start of current flow, and as a result, a current value of 15 to 25 kA can be achieved in a current rise time of 20 msec or less, and the temperature rise behavior of the joined members can be obtained, making it possible to satisfactorily weld both joining members.

[0030] Although the dissimilar material joining method according to the embodiment has been described above, the present invention is not limited to the configuration described in the above embodiment, and various modifications are possible within the scope of the gist of the present invention. For example, in the above embodiment, a steel plate 1 and an aluminum plate member 2 are used as the first and second joined members having different electrical resistivities, but these joined members are not limited to the steel plate 1 and the aluminum plate member 2. The gist of the present invention is that the contact interface between the second joined member having a low electrical resistivity and the first joined member and the area nearby are melted, and the molten material is solidified to weld both joined members. The present invention can be applied to any joined member as long as the plate-shaped joined member conforms to this technical feature. One example of such a case is a steel plate having a carbon content that differs by a predetermined value or more. [Explanation of symbols]

[0031] 1 Steel plate (first member to be joined) 2. Aluminum plate member (second joined member) 3 electrodes

Claims

1. A plate-shaped first member to be joined and a plate-shaped member having a lower electrical resistivity than the first member to be joined. a first member to be joined and a second member to be joined by sandwiching the first member and the second member between opposing electrodes and applying pressure and current thereto, a current having a frequency of 5 kHz or more is applied to the electrodes at a predetermined current increase rate and for a predetermined period of time so that the melting point of the first member is not exceeded except at the interface between the first and second members, and the heat generated at the interface melts a region of the second member near the interface with the first member, thereby welding the two members to be joined.

2. 2. The method for joining dissimilar materials according to claim 1, wherein the melting point of the second member is lower than the melting point of the first member.

3. The method for joining dissimilar materials according to claim 1 or 2, characterized in that a current rise time of the current flow is 20 msec or less, and the predetermined current increase rate is a value that satisfies a condition that a current value reaches 15 to 25 kA in the predetermined time of the current flow.

4. A resistance welding apparatus having opposing electrodes sandwiching a plate-shaped first joined member and a plate-shaped second joined member having a lower electrical resistivity than the first joined member, and a current control device which applies an applied current to the electrodes, the current control device applying a predetermined applied current to the electrodes to perform resistance welding between the first joined member and the second joined member, The energization control device includes: a current having a frequency of 5 kHz or more is applied to the electrodes at a predetermined current increase rate and for a predetermined period of time so that the melting point of the first workpieces is not exceeded except at the contact interface between the first workpieces and the second workpieces, a resistance welding apparatus for welding the first and second workpieces together by melting a region of the second workpiece adjacent to the interface between the first workpiece and the second workpiece due to heat generated at the interface by the current passing therethrough.

5. The resistance welding device according to claim 4, wherein a current rise time of the current supply is 20 msec or less, and the predetermined current increase rate is a value that satisfies a condition that a current value reaches 15 to 25 kA within the predetermined time of the current supply.

Images