JP2861819B2 - Resistance welding method for dissimilar metals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a dissimilar metal, such as aluminum and steel, or steel and titanium, in which a brittle intermetallic compound is formed at the joint interface when welding is performed, and it is difficult to obtain high joint strength. To a resistance welding method.

[0002]

In the welding of dissimilar metals such as aluminum and steel, aluminum and titanium, titanium and steel,
It is known that a brittle intermetallic compound is formed at the joint interface, and high joint strength cannot be obtained. In this specification, when simply referred to as aluminum, it means pure aluminum and an aluminum alloy, and similarly, titanium and the like mean the pure metal and the alloy.

Conventionally, such dissimilar metal joining methods include mechanical joining methods such as screws, bolts, fittings, solid-state joining methods such as explosion, hot rolling, friction rolling, and bonding. A method is being considered. However, mechanical joining and joining by adhesion have problems in reliability, airtightness, workability, and the like. Further, in the solid-phase joining method, there are problems that the shape of the joining material is greatly restricted and workability is low.

[0004] Under such circumstances, development of a method of joining dissimilar metals which is simpler and has higher workability is expected. In particular,
Since the joining of aluminum and steel is an indispensable technology for reducing the weight of automobiles, establishment of a simple and efficient joining method using resistance welding is expected.

[0005] The current situation and problems of resistance welding of dissimilar metals will be described below, taking spot welding of aluminum and steel, which is attracting attention from the viewpoint of weight reduction of a vehicle body.

[0006] In spot welding of aluminum and steel, there is a problem that physical properties such as melting point, electric resistance, and thermal conductivity are largely different from each other. For example, when a thin plate of aluminum and steel is overlapped and simply spot welded,
Since the melting point of aluminum is less than half the melting point of steel and aluminum has higher thermal conductivity, heat generated by resistance welding is conducted from the steel side to the aluminum side,
Since one-sided melting of aluminum occurs, the damage of the aluminum-side plate surface due to welding is large. In this process, an intermetallic compound is formed at the bonding interface, and a nugget is also formed unevenly. Therefore, high joint strength cannot be obtained.

As one of countermeasures, it is considered that an intermediate layer is interposed between aluminum and steel. For example, Japanese Patent Laid-Open Publication No.
A technique of interposing a foil is disclosed. In addition, Japanese Unexamined Patent Application Publication No.
JP-A-251676 and JP-A-6-39558 disclose techniques for providing a plating layer on a steel surface in contact with aluminum.

[0008]

However, these conventional techniques cannot stabilize high joint strength.
This is because, in the prior art, the intermediate layer is merely an insert material interposed between aluminum and steel, and the intermediate layer is not sufficiently designed in consideration of a large difference in physical property values between aluminum and steel.

That is, the difference in melting point between aluminum and steel is 3
Far above 00K. According to the investigation by the present inventors, in the case of such dissimilar metals having a large difference in melting point, stable joint strength cannot be obtained with one intermediate layer. Conversely, when the melting point difference is 300K or less, such as steel and titanium, 1
Stable joint strength can be obtained even with two intermediate layers.

In other words, the above-mentioned prior art is effective for joining steel and titanium, but cannot be sufficiently effective when used for joining aluminum and steel, which is the original joining object. is there.

An object of the present invention is to provide a resistance welding method for dissimilar metals capable of stably obtaining high joint strength irrespective of the type of joining material.

[0012]

An intermediate layer is considered to be indispensable for resistance welding of dissimilar metals. In the process of investigating the behavior of the middle layer, its ideal function became clear. The ideal function of the intermediate layer found by the present inventors will be described with reference to FIG.

[0013] A, B is a metal dissimilar to be joined, the melting point T _A metal A is lower than the melting point T _B of the metal B. That is, T _A <T _B. X is an intermediate layer, and metals A and B
Intervening between them. Metals A and B are resistance-welded (in this case, spot-welded) by sandwiching the intermediate layer X between the metals A and B and sandwiching the metals A and B between the electrodes and applying pressure.

At this time, by the action of the intermediate layer X, the excessive melting points of the metals A and B are suppressed, and the metals A and B are early in welding.
It prevents direct contact of B and prevents the formation of intermetallic compounds at the bonding interface. After the joining surfaces of the metals A and B are heated to a required temperature, the intermediate layer X is completely melted and discharged from the joining interface by the pressing force. As a result, the joining surfaces of the metals A and B heated to appropriate temperatures can be instantaneously overlapped and joined directly.

This is the ideal function of the intermediate layer X. That is, the intermediate layer X is not merely used as an insert material, but functions as a medium for controlling the timing of heating and melting the metals A and B. More specifically, by the action of the intermediate layer X, the timings of heating and melting of the joining surfaces of the metals A and B are adjusted, and when each joining surface is in a state most suitable for joining, the intermediate surfaces are joined from the joining surfaces. The layers are discharged and the metals A and B are directly joined.

In order to make the intermediate layer X have such an ideal function, it is necessary to reflect the difference in the physical properties of the metals A and B in the design of the intermediate layer X. As a result, it has been found that this can be achieved by giving certain conditions to the intermediate layer X based on the physical properties of the metals A and B.

Further, in the case where the melting points of the metals A and B are significantly different from each other, such as aluminum and steel, if only the intermediate layer X is used, the metals A and B react and form a brittle intermetallic compound. It turned out that joining strength was not obtained. This is because when the melting points of the metals A and B are significantly different, the intermediate layer X is heated before the metal B having a high melting point is heated to an appropriate temperature.
Is melted and discharged, and as a result, the molten metals A and B continue to be in contact with each other until the joining is completed, forming a brittle intermetallic compound. In other words, the method using only the intermediate layer X is effective only when the difference between the melting points of the metals A and B is small.

As a result of investigating various combinations of intermediate layers, if the melting points of the metals A and B are greatly different, it is necessary to use another intermediate layer Y having different physical properties as shown in FIG. Turned out to be.

The present invention has been made based on the above findings, and has the following two methods for resistance welding of dissimilar metals.

[0020] 1) dissimilar metals A melting point difference is 300K or less, B (in the resistance welding of the melting point _{T B)} of the melting point _{T A} <metal B of the metal A, melting point _(T A -300) K or _{T B} below By interposing the intermediate layer X between the metals A and B, the intermediate layer X is instantaneously melted by resistance heating at the time of resistance welding, and the molten intermediate layer X is discharged from the joining interface by the pressing force. Then, the metals A and B are directly joined.

[0021] 2) different melting points dissimilar metals A, in the resistance welding of B (melting point T _B melting point T _A <metal B of the metal A), the intermediate layer is not more than the melting point (T _A -300) K or T _A X and an intermediate layer Y having a melting point of T _A or more and T _B or less,
Intermediate layers X and Y are instantaneously melted by resistance heating during resistance welding by interposing metal layers A and B such that intermediate layer X is located on metal A side and intermediate layer Y is located on metal B side. At the same time, the molten intermediate layers X and Y are discharged from the bonding interface by the pressing force, and the metals A and B are directly bonded.

The thickness of the intermediate layer is as follows: 0 <R _X × d _X ^1/4 <R _X × 0.5 ^1/4 (1) Z _AB × 3500 <R _Y × d _Y ^1/4 <R _Y ^{× 0.5 1/4 ... (2) Z} AB = (R A / K A) × (K B / R B) × (1 / T B) 0 <d A, d B ≦ 3 d i: thickness (Mm) R _i : specific resistance (μΩ · mm) K _i : thermal conductivity (cal / cm ² / cm / s / ° C.) However, in the first method using no intermediate layer Y, the condition (2) is unnecessary.

The welding current and welding time are as follows: I _O = α × (Z _AB × T _B ) × (1 / t ^1/2 ) +9 (3) Z _AB = (R _A / K _A ) × (K _{B / R B) × (1 /} T B) 350 <α <550 0 <t O <100 I O: welding current (kA) t _O: welding time (ms) R _i: specific resistance (μΩ · mm) K _i : Thermal conductivity (cal / cm ² / cm / s / ° C.) α: desirably a constant

[0024]

The first method is effective only when the difference between the melting points of the metals A and B is 300 K or less, and is applied only in this case. Specifically, for example, metal A is steel and metal B is titanium. When the metal A is steel and the metal B is titanium, the intermediate layer X is, for example, Ni-Zn, Zn, Ti
-Mn, Al and alloys thereof, Mg and alloys thereof can be used.

In the second method, the difference between the melting points of metals A and B is 300K.
Is effective when the melting point exceeds 300 K, but it can be naturally used also when the melting point difference is 300 K or less (for example, joining of steel and titanium). As a combination of metals A and B having a melting point difference exceeding 300 K, for example, metal A may be aluminum and metal B may be steel. In this case, the intermediate layer X is made of Al
-Si, Zn, etc., and Al-Mn,
Ni-Zn, Cu, Ni, or the like can be used.

FIG. 2 shows a tensile test result of the joint when the material and the thickness of the intermediate layer X are changed in the first method (spot welding), and the melting point and the specific resistance × (thickness) ¹ using the thickness as a parameter. It is arranged according to the relationship with ^{/ 4} . Metal A is steel (1.0mm thick), Metal B is titanium (1.0m thick)
m). The welding conditions are 1ms-32kA-1960N
And Open marks indicate base material breakage, and black marks indicate interface peeling.

As can be seen from the figure, when the difference in melting point between the metals A and B is 300 K or less, the melting point of the intermediate layer X is equal to or more than the melting point T _A -300 of the metal A and the melting point T of the metal B.
_{B It} is necessary to use the following. An appropriate mid layer X is
Here, there are three types: Ni-Zn, Zn, and Ti-Mn.

[0028] When the melting point of the intermediate layer X is higher than the melting point T _B of the metal B, both bonding surfaces of the metal A is abnormally heated during the joining,
The metal A melts rather than the intermediate layer X, and the bonding interface of the intermediate layer X remains after bonding. Therefore, high joint strength cannot be obtained. Further, the melting point of the intermediate layer X is (melting point T _A −3 of metal A).
If the temperature is less than K), the intermediate layer X is melted in the initial stage of the joining and discharged from the joining surface, so that the joining surface of the metal B cannot be sufficiently heated, and the metals A and B come into contact with each other, and the joining interface Therefore, a high joint strength cannot be obtained because an intermetallic compound is formed at the same time.

The particularly desirable melting point of the intermediate layer X is from T _{A to} T _B.

FIG. 3 shows a tensile test result of the joint when the material and thickness of the intermediate layers X and Y were changed in the second method (spot welding).
(Thickness) It is arranged in relation to ^1/4 . Metal A is aluminum (thickness 1.0mm), Metal B is steel (thickness
1.0 mm). The welding conditions are 1ms-50kA-19
60N. Open marks indicate base material breakage, and black marks indicate interface peeling.

As can be seen from the figure, the intermediate layer X on the metal A side
Mp (melting point T _A -300 metal A) K above as, the following melting point T _A metal A, melting point as an intermediate layer Y of the metal B side than the melting point T _A metal A, the melting point T _B of the metal B By using the following, the difference in melting point between metals A and B is 300
Even when it exceeds K, high joint strength can be obtained.
In this case, X is two types of Zn and Al-Si, and Y is four types of Al-Mn, Cu, Ni-Zn and Ni.

In the second method, the intermediate layer X having the lowest melting point contacts the metal A on the low melting point side, and this intermediate layer X
Melting occurs. After the intermediate layer X is melted, the surface of the metal A having the next highest melting point is melted, the oxide layer on the surface is destroyed, and the active surface of the metal A appears. Subsequently, the intermediate layer Y having the next highest melting point melts, and an active surface of the metal B appears. Finally, the oxide film existing on the surfaces of the molten intermediate layers X and Y and the metal A is extruded from the joint interface by the welding pressure, and the surfaces of the active metals A and B are solidified. The metal A and B having high strength are joined by being overlapped.

As described above, the intermediate layers X and Y control the heat generation and melting phenomena in resistance welding to suppress the melting of the base material, destroy the oxide film on the aluminum surface, discharge the molten layer and the oxide film, and activate the active surface. Contributes to the formation of a bonding process, and imparts high strength to the bonding interface.

When the melting points of the intermediate layers X and Y are both higher than the melting point of the metal A, the surface of the metal A is melted in the initial stage of melting, and thereafter the thickness of the metal A is larger than that of the intermediate layers X and Y. Is large, the welding heat is mainly consumed for melting the metal A, and as a result, a nugget biased toward the metal A is formed. Moreover, since the melting points of the intermediate layers X and Y are higher than that of the metal A,
The melting of the intermediate layers X and Y becomes insufficient, and the discharge of the intermediate layers X and Y from the joint interface becomes incomplete. Therefore, high strength cannot be obtained even when joining is performed.

When the melting points of the intermediate layers X and Y are both lower than the melting point of the metal A, the intermediate layers X and Y are initially formed in the same manner as in the method disclosed in JP-A-4-251676. Is melted and discharged, and the joining is completed without sufficiently providing the effect of the intermediate layer, so that high joining strength cannot be obtained.

If the melting point of the intermediate layer Y on the side of the high melting point metal B is lower than the melting point of the metal A and the melting point of the intermediate layer X on the side of the low melting point metal is higher than the melting point of the metal A, the intermediate layer Y is initially formed. Is melted and the intermediate layer X is also discharged from the bonding interface by the melting, so that the effect of the film cannot be obtained.

That is, in the second method, the low-melting-point intermediate layer X located on the side of the low-melting-point metal A concentrates heat generation at the bonding interface, and after the intermediate layer X is melted, the metal A is melted. By activating the bonding surface of the metal A and further melting the high melting point intermediate layer Y located on the high melting point metal B side,
Efficiently discharging these molten layers, and the active metal A,
B is joined directly by overlapping the joining surfaces. Therefore, the timing of melting the metals A and B and the intermediate layers X and Y is important, and it is necessary to have the above-mentioned melting point relationship. Needless to say, such an effect cannot be obtained when the number of the intermediate layers is one.

Regarding the brittle intermetallic compound formed at the bonding interface, which is most concerned in the bonding of the metals A and B, as described above, the molten layer is completely discharged from the bonding interface and the active surface is directly overlapped. Therefore, the intermetallic compound is not formed.

In the present invention, from the viewpoint of further activating the surface of the low melting point metal A, it is effective to provide the low melting point intermediate layer Z on the bonding surface of the metal A. The intermediate layer Z needs to have a melting point lower than that of the metal A for the reason described above, and a sufficient effect can be obtained even if the intermediate layer Z has the same component as the low melting point intermediate layer X described above.

The particularly desirable melting point of the intermediate layer Y is (T _B −
100) K or less and (T _A +50) K or more. When the melting point of the intermediate layer Y approaches the melting point T _B of the metal B, the molten metal B is increased, when approaching the melting point T _A metal A, to the molten metal A increases, high joining either case There is a possibility that strength cannot be obtained.

The desired melting point of the intermediate layer X is, (T _A -5
0) K or less, and (T _A -300) K or more. Middle layer X
When the melting point of the metal A approaches the melting point T _{A of the} metal A, the melting of the metal A increases. When the melting point T _{A is} too far from the melting point T _{A of the} metal A, the intermediate layer X is melted and discharged in the early stage of welding. May not be able to obtain a sufficient effect.

Metals A and B to which the welding method of the present invention can be applied
Table 1 shows typical combinations of the intermediate layers in each combination.

[0043]

[Table 1]

In the present invention, since resistance welding is performed, specific resistance and thickness are related to melting of the metals A and B and the intermediate layer together with the melting point.

For example, even if the melting point of the intermediate layer satisfies the above condition, if the melting point is higher than the melting point T _A of the metal A, the heat generated in the intermediate layer is transmitted to the metal A, and the melting of the intermediate layer is insufficient. Becomes

More specifically, for example, the second method [FIG.
(B)], when Cu is used as the intermediate layer Y on the metal B side, since its thermal conductivity is large and its specific resistance is small,
If the layer thickness is small, heat generation at the interface is small, and the intermediate layer Y does not melt, so that the bonding surface of the metal B is insufficiently heated, and the intermediate layer Y remains at the bonding interface and the joint strength decreases. (FIG. 3).

When the specific resistance and the thickness of the intermediate layer are large,
The intermediate layer does not melt sufficiently and cannot fulfill its function.

As a result of organizing the experimental results from these viewpoints, the conditions (1) and (2) were obtained. Table 2 shows the appropriate thickness of the intermediate layer obtained from these conditions.

Note that Ni-Zn, Ti-Mn, Al-S
The melting point of alloys such as i and Al-Mn can be adjusted over a wide range by changing the component ratio.

[0050]

[Table 2]

If the specific resistance and thickness of the intermediate layer X are excessive in the first method, the melting becomes insufficient, and it becomes difficult to discharge the intermediate layer X from the bonding interface. The lower limit is not particularly limited, since the intermediate layer X only needs to function as a barrier for preventing contact between the metals A and B. Also in the second method, only the upper limit is required for the specific resistance and thickness of the intermediate layer X for the same reason. If the specific resistance and thickness of the intermediate layer Y are excessively large, melting becomes insufficient and it becomes difficult to discharge from the bonding interface. If the specific resistance and thickness are too small, the bonding surface of the metal B on the high melting point side is sufficiently reduced. High joint strength cannot be obtained because it is not heated.

For the intermediate layers X and Y, any of powder, foil, plating and the like can provide a sufficient effect, and each intermediate layer can have a different or similar multilayer structure.

When the intermediate layers X and Y are collectively formed on one of the joining surfaces of the metals A and B, the intermediate layer is not required on the joining surface of the other metal. Becomes unnecessary. For example, the intermediate layers X and Y
Is a surface-treated steel sheet formed by plating or the like.

[0054] Metal A, the thickness d _A of B, had a d _B as 0.3mm or less, in order to perform a small resistance welding of welding heat input.

As a welding method, not only spot welding but also resistance welding such as seam welding, DC butt welding and projection welding can be applied.

In the present invention, welding conditions are also important. If the welding current is too high even with the proper middle layer,
Since the intermetallic compound is formed by the reaction of the metals A and B, a high joint strength cannot be obtained. If the amount is too small, the melting of the intermediate layer becomes insufficient and the joining of the metal B on the high melting point side is performed. Since the surface is not sufficiently heated, high joint strength cannot be obtained.

FIG. 4 shows that in the first method (spot welding), metal A is steel (thickness 1.0 mm) and metal B is titanium (thickness).
1.0 mm), the appropriate intermediate layer X (Ni, thickness
0.1 mm) and the appropriate welding conditions at this time were examined.

FIG. 5 shows that when the metal A is aluminum (1 mm thick) and the metal B is steel (1 mm thick) in the second method (spot welding), an appropriate intermediate layer X (Zn,
Thickness 0.1 mm) and the intermediate layer Y (Al-Mn, 0.01 m)
m) was used to examine the proper welding conditions at this time.

As a result of organizing these experimental results, the condition (3) was obtained. Table 3 shows the appropriate welding current I _O (appropriate welding current when the welding time is 1 ms) obtained from these conditions.
Shown in

[0060]

[Table 3]

The reason why the welding time t _{O is set} to 100 ms or less is to suppress the formation of intermetallic compounds at the bonding interface by performing the bonding in a short time.

[0062]

EXAMPLES Examples of the present invention will be shown below, and the effects of the present invention will be clarified by comparison with comparative examples.

When the melting point difference between the metals A and B is 300 K or less , the thickness of the metal A (1 mm thick steel plate (SPCD)) and the metal B (1 mm thick titanium plate (TP25)) are spot-welded. 0.005 to 0.5mm Pb, Z
n, Al-Mn, Cu, Ni-Zn, Ni, Zr, Mo
Was used. Tables 4 and 5 show the breakdown of the intermediate layer.

Welding time 1 to 400 ms, welding current 5 to 8
Spot welding was performed under the conditions of 0 kA and a pressure of 1960 N, and the joint strength was evaluated from the fracture position in the cross tension test. The results are shown in Tables 6 to 9. Of these results, FIG. 2 shows the effect of the type and thickness of the intermediate layer on the joint strength, and FIG. 4 shows the effect of the welding current.

As can be seen from Tables 6 to 9, metals A and B
Is less than 300K, the first method is effective,
The second method is, of course, valid.

When the difference in melting point between metals A and B exceeds 300K
Thick aluminum plate of 1mm is expedient metal A (A505
2) When spot-welding a steel plate (SPCD) having a thickness of 1 mm, which is a metal B, a P having a thickness of 0.005 to 0.5 mm is used.
b, Zn, Al-Mn, Cu, Ni-Zn, Ni, Z
An intermediate layer composed of r and Mo (Tables 4 and 5) was used.

Welding time 1 to 400 ms, welding current 5
Spot welding was performed under the conditions of ８０80 kA and a pressure of 1960 N, and the joint strength was evaluated from the fracture position in the cross tension test. The results are shown in Tables 10 to 16. Of these results, FIG. 3 shows the effect of the type and thickness of the intermediate layer on the joint strength, and FIG. 5 shows the effect of the welding current.

As can be seen from Tables 10 to 16, when the difference in melting point between metals A and B is 300 K or less, the second method is effective, but the first method is not effective.

[0069]

[Table 4]

[0070]

[Table 5]

[0071]

[Table 6]

[0072]

[Table 7]

[0073]

[Table 8]

[0074]

[Table 9]

[0075]

[Table 10]

[0076]

[Table 11]

[0077]

[Table 12]

[0078]

[Table 13]

[0079]

[Table 14]

[0080]

[Table 15]

[0081]

[Table 16]

[0082]

As described above, the method for resistance welding of dissimilar metals of the present invention enables simple and efficient welding by resistance welding even for dissimilar metals which are difficult to join by ordinary welding. It brings great industrial advantages to the production fields where weight reduction is required for railways and railway vehicles.

[Brief description of the drawings]

FIG. 1 is a view schematically showing a welding method of the present invention.

FIG. 2 is a diagram showing the effectiveness of the first method.

FIG. 3 is a view showing proper welding conditions in a first method.

FIG. 4 is a diagram showing the effectiveness of the second method.

FIG. 5 is a view showing proper welding conditions in a second method.

[Explanation of symbols]

 A, B Metal to be joined (A is low melting point side, B is high melting point side) X, Y Intermediate layer

──────────────────────────────────────────────────続 き Continued from the front page (72) Inventor Junichi Uchida 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal Industries, Ltd. (56) References JP-A-64-48681 (JP, A) Kaihei 4-55066 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) B23K 11/20

Claims (4)

(57) [Claims] 1. A dissimilar metal A melting point difference is 300K or less, in the resistance welding of B (melting point _{T B} melting point _{T A} <metal B of the metal A), melting point _(T A -300) K or _{T B} below the intermediate layer X to Rukoto is interposed between the metal a, B is
Instantly melts the intermediate layer by resistance heating during resistance welding
At the same time, the molten intermediate layer is
A method for resistance welding of dissimilar metals, characterized in that the metals A and B are directly joined by discharging from a surface . Wherein the melting point is different from dissimilar metals A, in the resistance welding of B (melting point _{T B} melting point _{T A} <metal B of the metal A), melting point _(T A -300) intermediate layer is less than K or more _{T A} X
If, Rukoto metal A, is interposed between the B, as a melting point and an intermediate layer Y is less than T _A or T _B, the intermediate layer Y intermediate layer X is located on the metal side A is positioned on the metal B side By resistance welding
At the same time, the intermediate layer is instantaneously melted by resistance heating,
The molten intermediate layer is discharged from the joint interface by pressing force
Wherein the metals A and B are directly joined to each other. Wherein the intermediate layer X, the thickness of the ^{_{Y 0 <R x × d x}} 1/4 <R x × 0.5 1/4 ... (1) Z AB × 3500 <R Y × d Y 1 / ^{_{4 <R Y × 0.5 1/4 ...}} (2) Z AB = (R A / K A) × (K B / R B) × (1 / T B) 0 <d A, d B ≦ 3 d _i : thickness (mm) R _i : specific resistance (μΩ · mm) K _i : thermal conductivity (cal / cm ² / cm / s / ° C.) 3. Resistance welding method for dissimilar metals. 4. A welding _{current, I o = α × (Z} AB × T B) × (1 / t 1/2) +9 ... (3) Z AB = (R A / K A) × (K B / _{R B) × (1 / T} B) 350 <α <550 0 <t o <100 I o: welding current (kA) _{t o:} welding time (ms) _{R i:} specific resistance (μΩ · _{mm) K} i: The method for resistance welding of dissimilar metals according to claim 1, wherein the thermal conductivity (cal / cm ² / cm / s / ° C.) α is a constant.