JPH05111778A - Resistance welding method for different kinds of metals - Google Patents

Abstract

PURPOSE:To obtain sure and stable joint strength with a low welding current by performing resistance welding to satisfy specified conditions in resistance welding of aluminum (Al) and non-Al metal with clad material used as insert material. CONSTITUTION:The clad materials 3 with respective different kinds of metals as main components are sandwiched between the non-Al metal 2 having resistivity >= two times Al and Al so that the same kind of metals come into contact with each other and the non-Al metal and Al are subjected to resistance welding under the following conditions. The conditions of tA tM t<=2.0, 0.2<=Y/X<=7, I<=18 and I0-2<=I<=I0+2 are satisfied wherein I0 is the formula (1) and tA, tM, t, X, Y, RA, RM and I denote thickness (mm) of Al which is material to be joined, thickness (mm) of the non-Al metal to be joined to Al, total thickness (mm) of the clad material, thickness (mm) of the non-Al metal in the clad material, thickness (mm) of Al in the clad material, a resistivity value (muOMEGA.cm) of Al, a resistivity value (muOMEGA.cm) of the non-Al metal and a welding current (KA), respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance welding method for dissimilar metals such as aluminum and steel, aluminum and titanium, one metal of which is to be joined is aluminum.

[0002]

2. Description of the Related Art It is known that in welding of dissimilar metals such as aluminum and steel, and aluminum and titanium, sufficient bonding strength cannot be obtained because a metal compound is formed at the bonding interface to cause embrittlement. There is. For joining such dissimilar metals, mechanical joining methods such as bolts, screws, and fitting have been conventionally used, but there are problems in reliability and airtightness. Therefore, various solid-phase bonding methods have been tried, but there are limitations to their application. For example, the friction welding method is limited to rotating bodies having good symmetry, and the explosion welding method and the hot rolling method require special equipment and pretreatment, and are also limited in terms of shape. In the diffusion bonding method,
There were defects in terms of equipment and efficiency.

Therefore, recently, a relatively simple and reliable welding method for dissimilar metals using a clad material has been proposed. This is a method in which welding is performed through a clad material having two kinds of metal materials, which are the same as the respective dissimilar metals to be joined, on both sides. For example, "light metal" (vol.
No. 7 (1989) No. 10 railcar hybrid structure assembly structure), as shown in FIG. 4, when stainless steel and aluminum are joined, a clad material made of stainless steel and aluminum is used as an insert material. A welding method is disclosed. Then, as the welding, an arc welding method, a spot welding method, or the like is used.

[0004]

The welding method for dissimilar metals using such a clad insert material uses a clad material having two kinds of metal materials, which are the same as the dissimilar metals to be joined, on both sides. The feature is that welding of dissimilar metals is replaced with welding of similar metals. However, even in the welding of similar metals, for example, in resistance welding between aluminum, compared to steel materials, aluminum has higher electric conductivity and thermal conductivity, so even if the same current is applied, the heat generation is small and the generated heat is small. Since it is easy to escape, it is necessary to concentrate heat by applying a large current for a short time.

For example, in the case of spot-welding steel plates having the same plate thickness or aluminum plates, the aluminum plate has a welding current three times as high as that of the steel plate and a welding time of 1 /
It should be about 7 to 1/8. So now,
In spot welding between aluminum plates, welding current is 20
Values of about 50 kA and energization time of about 5 to 10 cycles are used, and it is required as a characteristic of the welding machine to supply a large current accurately and in a short time (for example, Sumi Light Metal Technique 1
991. vol. 32 No. 1p56-57). Therefore, the conventional welding machine for steel having a low power factor cannot perform sufficient welding, and it is said that new equipment is required for the welding.

From the above, even in the resistance welding of aluminum and non-aluminum metal using the clad insert material, a large current is produced in a shorter time than the resistance welding of steel due to the existence of a joint surface between aluminum. It was required to flow and weld, and the introduction of new equipment was unavoidable.
Further, even if a large current is applied in a short time, the state of the nugget at the bonding interface varies, and it is difficult to obtain stable strength.

An object of the present invention is to provide a resistance welding method for dissimilar metals capable of sufficiently and stably joining aluminum and non-aluminum metal with a welding current smaller than welding of aluminum.

[0008]

FIG. 1 shows a situation in which aluminum and steel are spot-welded by using these clad materials. 1 is aluminum as a material to be welded, 2 is steel as a non-aluminum metal to be welded to aluminum 1, 3 is insert material, 3a is aluminum in insert material 3, 3b is steel as non-aluminum metal in insert material 3, 4 is an electrode, insert material 3
Aluminum 3a in is aluminum 1, and
Steel 3b is in contact with steel 2, respectively.

According to the investigation by the present inventors, in the spot welding shown in FIG. 1, the joining surface between steels is first heated and melted by the energization during welding to form a nugget. Then
This heat propagates through the clad interface to the aluminum side having high thermal conductivity, and along the galvanic path of the welding current, melts the aluminum forming the clad,
It also transfers heat to the joint surface between aluminum and contributes to the formation of a nugget between aluminum. Then, the molten layer grown from the clad interface and the molten nugget of aluminum are combined to form a nugget that spreads from the clad interface to the aluminum bonding surface.

From the results of such investigations, the present inventors
When a clad material is used as an insert material, since the specific resistance of steel is higher than that of aluminum, the heat generated at the contact surface of steel assists the formation of a nugget on the aluminum side by the energization during welding, Therefore, it is possible to obtain sufficient strength even under resistance welding conditions for steel without requiring a large current for a short time such as the joining conditions between aluminum, and to stabilize the joint strength, aluminum Since the heat generated on the dissimilar metal side contributes to the nugget between the two, we obtained a new finding that the composition ratio of the clad material becomes the point of joining.

The present invention has been made on the basis of the above findings. The non-aluminum metal having a specific resistance of at least twice that of aluminum and the aluminum are in contact with the clad material containing the different metal as a main component. A resistance welding method for dissimilar metals is characterized in that the following conditions (1) to (4) are satisfied when resistance-welding the non-aluminum metal and aluminum by sandwiching them as described above. t _A , t _M , t ≦ 2.0 (1) 0.25 ≦ Y / X ≦ 7 (2) I ≦ 18 (3) I _O −2 ≦ I ≦ I _O +2 (4) where

[0012] t _A : Thickness of aluminum to be joined (mm) t _M : Thickness of non-aluminum metal joined to aluminum (mm) t: Total thickness of clad material (mm) X: Thickness of non-aluminum metal in clad material (mm) Y: thickness of the aluminum in the cladding material (mm) R _a: specific resistance of aluminum (μΩ · cm) R _M: specific resistance value of the non-aluminum metal (μΩ · cm) I: welding current (kA)

[0013]

FIG. 2 shows various data obtained by the present inventors in resistance welding (spot welding) of the steel plate and the aluminum plate of FIG. 1 to the optimum welding current and the plate thickness of the entire welded material including the clad material. , And a composition ratio of a clad material (ratio of aluminum thickness to steel thickness).

As can be seen from the figure, the optimum welding current I _O is represented by the above equation, and becomes smaller as the ratio of steel in the clad material increases. Remarkably lower than that of welding. Then, when resistance welding is performed by the method of the present invention, it is possible to perform stable welding using a lower current than that used for conventional aluminum welding, despite having a joining surface between aluminums. The inventors have confirmed that the same relationship holds between the optimum welding current I _O and the plate thickness when the non-aluminum metal combined with aluminum is other than steel.

In the method of the present invention, the respective thicknesses t _A and t _{M of} aluminum and non-aluminum metal to be joined and the total thickness t of the clad material are set to 2 mm or less, which means that resistance welding with a small heat input amount is performed. This is because.

Thickness X of the non-aluminum metal in the clad material
And the thickness Y of aluminum (Y / X),
If the aluminum is too thick, the calorific value of the non-aluminum metal becomes smaller than that of the aluminum, and the equation representing the optimum welding current I _O cannot be satisfied. As a result, when the welding current is about the welding condition for steel, the nugget formation at the joint surface between aluminum becomes insufficient, and the joint strength decreases. On the other hand, if the aluminum is too thin, the amount of heat generated becomes excessive at the optimum welding current I _O , increasing the amount of aluminum dissolved. As a result, scattering occurs and a sound joint cannot be obtained. Therefore, Y / X is set to 0.25 or more and 7 or less.

Regarding the welding current I, the optimum welding current I _O
Stable bonding strength can be obtained up to ± 2 kA based on (kA), but if it is less than (I _O -2) kA, nugget growth is insufficient and high strength cannot be obtained. Also, (I
_If it exceeds _O +2) kA, the nugget at the joint surface between the non-aluminum metals grows too much and comes into contact with the clad interface and destroys it. As a result, the non-aluminum metal mixes with the molten aluminum to form a brittle intermetallic compound, so that high strength cannot be obtained with good stability. Therefore, the welding current I is set to (I _o -2) kA or more and (I _o +2) kA or less.
The absolute amount of the welding current I is set to 18 kA or less is
This is because resistance welding with a small heat input amount is performed.

As the non-aluminum metal welded to aluminum, the specific resistance is about twice that of aluminum (6 μΩ · c
m) or more metal, such as Fe (9.71 μΩ)
・ Cm), stainless steel (70μΩ ・ cm), Ta (1
2.45μΩ ・ cm), Ti (42μΩ ・ cm), Zr
(40 μΩcm) and the like.

The clad material is not particularly limited in terms of manufacturing method, and may be any material that is joined with a sufficiently high strength by a known method such as rolling clad, explosive clad, diffusion clad and the like. Further, the aluminum and non-aluminum metal forming the clad material do not have to be the same as those metals to be joined, and may have a similar composition that does not hinder the same type joining.

[0020]

EXAMPLES Examples of the present invention will be described below.

1 mm thick aluminum plate and 0.8 m thick
In spot welding of m steel plate (SPCD),
A clad material made of each metal and having a total thickness of 0.5, 1, 2.5 mm was used as an insert material. Similarly, 0.8mm SUS304 steel plate, Ta plate, 1mm aluminum plate,
A Zr plate and a Ti plate were spot-welded using each clad material. After welding, the cross tension test shown in FIG. 3 was performed to evaluate the joint strength from the fractured state of each test piece. The results are shown in Tables 1 and 2.

The fracture position / form indicated as a button is a fracture form that is usually seen in a cross tension test when strong joining is performed by spot welding, and the fracture occurs from the periphery of the nugget to the base metal. The result is a buttonhole-like shape. On the other hand, in the case where sufficient joining is not performed by spot welding, a flat fracture surface with a small plastic deformation is obtained.

According to the method of the present invention, sufficient and stable strength can be secured with a welding current smaller than the conventional welding conditions for aluminum, despite having a joining surface for aluminum.

[0024]

[Table 1]

[0025]

[Table 2]

In addition, although the present invention is applied to spot welding in the above-mentioned embodiment, the present invention is not limited to this and can be applied to various resistance welding such as projection welding and seam welding.

[0027]

As is apparent from the above description, the resistance welding method for dissimilar metals according to the present invention has a joint surface between aluminums that requires a large current for a short time, but has a conventional aluminum welding method. Reliable and stable welding can be performed with less current than welding. Therefore, welding with a general-purpose welding machine for steel or the like becomes possible, and the introduction of new equipment becomes unnecessary. In addition, even if new equipment is introduced,
A small capacity can be used and the effect of reducing the cost required for equipment is great.

[Brief description of drawings]

FIG. 1 is a schematic view showing one embodiment of the method of the present invention.

FIG. 2 is a table showing the relationship between the plate thickness and the optimum welding current with the composition ratio of the clad insert material as a parameter.

FIG. 3 is an explanatory diagram of a cross tension test.

FIG. 4 is an explanatory diagram of a conventional welding method.

[Explanation of symbols]

 1 Aluminum to be bonded 2 Non-aluminum metal bonded to aluminum 3 Clad material 3a Aluminum in clad material 3b Non-aluminum metal in clad material 4 Electrode

Claims (1)

[Claims] 1. A non-aluminum metal having a specific resistance that is at least twice that of aluminum, and a non-aluminum metal sandwiching a clad material containing a different metal as a main component so that the same metal contacts. A resistance welding method for dissimilar metals, characterized in that the following conditions (1) to (4) are satisfied in resistance welding with aluminum. t _A , t _M , t ≦ 2.0 (1) 0.25 ≦ Y / X ≦ 7 (2) I ≦ 18 (3) I _O −2 ≦ I ≦ I _O +2 (4) where t _A : Thickness of aluminum to be joined (mm) t _M : Thickness of non-aluminum metal joined to aluminum (mm) t: Total thickness of clad material (mm) X: Thickness of non-aluminum metal in clad material (mm) Y: thickness of the aluminum in the cladding material (mm) R _a: specific resistance of aluminum (μΩ · cm) R _M: specific resistance value of the non-aluminum metal (μΩ · cm) I: welding current (kA)