JPH04356376A - Electrode for spot welding - Google Patents

Abstract

PURPOSE:To provide an electrode which causes less wear of the tip part of the electrode and less the deterioration of the strength of a welded part when a spot welding is continuously carried out. CONSTITUTION:The part where a copper or a alumina dispersion reinforcing copper electrode are in contact with a welded member is provided with a covering layer of tin.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to spot welding electrodes,
In particular, it relates to electrodes for spot welding aluminum and aluminum alloys.

0002

[Prior art] Highly conductive electrodes for spot welding,
High thermal conductivity and excellent high-temperature strength are required, and electrodes made of precipitation hardening copper alloys such as chromium copper, zirconium copper, and zirconium chromium copper have been widely used. Recently, electrodes made of alumina dispersion-strengthened copper, in which fine alumina particles are dispersed in a copper base, have also been put into practical use, and have shown significant improvements in heat resistance, welding resistance, etc.

Alumina dispersion-strengthened copper electrodes are also used for spot welding aluminum and aluminum alloys (hereinafter referred to as aluminum), but they have recently been applied to highly automated, continuous, and high-speed spot welding operations. In this case, problems often occur with respect to the wear resistance of the electrode tip and the strength of the spot weld.

In order to solve this problem, an electrode has been proposed in which a thin film of a metal having high hardness and high melting point, such as W, is formed on the part of the electrode that comes into contact with the workpiece to be welded (Japanese Unexamined Patent Application Publication No. 1983-1999). However, since this electrode is expensive and has insufficient workability, problems remain in practical use.

[0005] Co-based alloy or C
An electrode coated with an r-based alloy (Japanese Patent Publication No. 63-30185) or an electrode coated with Al (Japanese Patent Publication No. 60-4
No. 8275) has also been developed, but Co and Cr have problems in terms of cost, and problems remain in terms of electrode durability. In addition, in the case of Al-coated electrodes, in order to reliably extend the electrode life and obtain a high-strength weld, sufficient pretreatment is required to remove the oxide film from the aluminum surface, which is the workpiece to be welded. However, pretreatment is time-consuming because the oxide film on the aluminum surface must be completely removed by mechanical treatment with a wire brush.

[0006]

SUMMARY OF THE INVENTION The present invention was made as a result of studies on various metal coatings suitable for spot welding of aluminum in order to solve the above-mentioned conventional problems. To provide an electrode for spot welding, which causes less wear and tear on the tip of the electrode, less decrease in strength of the welded part when spot welding is performed continuously, and requires relatively little effort in pretreatment of aluminum as a workpiece to be welded. It is in.

[0007]

[Means for Solving the Problems] A spot welding electrode according to the present invention for achieving the above object is provided with a coating layer of Sn on a portion of an alumina dispersion-strengthened copper electrode for spot welding that contacts a workpiece to be welded. It is characterized by

[0008] Alumina dispersion strengthened copper has an aluminum content of 0.
．． 05 wt% or more, preferably aluminum content 0.05
Dispersing alumina particles containing ~1.7 wt%;
More than 50% of the aluminum amount is alumina, and the remainder consists of copper and unavoidable impurities.

[0009] In order to produce an electrode tip for spot welding of alumina dispersion-strengthened copper, the Cu-Al alloy powder having the above structure is internally oxidized by heating to a high temperature in an oxidizing atmosphere, and the Al component is converted into alumina (Al2O ) is a dispersion-strengthened copper powder in which alumina particles are finely dispersed in a copper matrix. Then, if necessary, excess copper oxide is reduced by heating in a reducing atmosphere, and then the powder is sealed in a copper cylindrical container, hot extruded, and cold drawn to form a bar of a predetermined diameter. This bar material is cut or forged and then cut into an electrode tip shape.

After forming into the shape of an electrode tip, the tip end of the tip is coated with Sn. As a coating method, a plating method such as electroplating, electroless plating, spot plating, hot-dip plating, or a method of soldering Sn is used. In addition, S
Small amounts of Ag, B, Bi, Co, Cr, Fe,
In, Mo, Ni, P, Sb, Te, Ti, Pb, Zr
, W is included, there is no change in performance.

[0011] The thickness of the Sn coating layer is 0.03 to 400 μm.
m is desirable. If the thickness is less than 0.03 μm, the effect of Sn coating on reducing wear on the tip of the electrode is small;
If it exceeds this value, the coating layer will be deformed during spot welding, and the shape of the tip of the electrode tip will likely become inappropriate.

[0012] After Sn coating, a suitable heat treatment is performed to diffuse Sn into the electrode, and the intermetallic compound of the Cu-Sn alloy is
By forming a phase (Cu3Sn), an electrode with even greater durability can be obtained. Preferred heat treatment conditions are a heating temperature of 200°C or more and a heating time of 10 minutes or more.

[0013]

[Function] The spot welding electrode according to the present invention has the above-described structure, and since the Sn coating layer formed at the tip of the electrode has the function of reducing wear and tear on the electrode, the electrode has a long life.

[0014]

[Examples] Examples of the present invention will be explained below in comparison with comparative examples. Example 1 Ar gas atomized powder of Cu-0.4 wt% Al alloy was heated in the atmosphere at 300 °C for 1 h to oxidize the surface.
Internal oxidation was carried out under heating conditions of 00°C x 5h. Then 50
After being heated and reduced in hydrogen gas at 0°C for 1 h, it was crushed and C
It was sealed in a U-made can. This was extruded as a billet at 900°C to a diameter of 30 mm. After extrusion, a rod with a diameter of 16 mm was formed by cold drawing, and an electrode tip with an outer diameter of 16 mm and a tip radius of 100 mm was formed from this rod, and a Sn coating layer of 0.06 μm and 3 μm was applied to the tip of the electrode tip by substitution Sn plating. Established. The Sn coating layer with a thickness of 380 μm was formed by hot-dip plating. Displacement plating method: degrease the material,
After washing with water, etching in an acid solution consisting of sulfuric acid and nitric acid, and washing with water, "Substar SN" manufactured by Okuno Pharmaceutical Co., Ltd.
- Plating was carried out at 60°C in baths P2 and L2. Hot-dip plating method: After degreasing the material, it was immersed in a molten Sn bath.

Example 2 The tip of an electrode tip prepared in the same manner as in Example 1 was soldered to have a thickness of 0.06 μm, 3 μm, and 38 μm.
A coating layer of Sn with a thickness of 0 μm was provided. The coating of Sn by soldering was carried out by a method in which Sn solder placed on the tip of the electrode tip using flux was heated with a torch to melt it and then built up.

Example 3 Similar to Example 1, the thicknesses of 0.05 μm, 2 μm and 370 μm were formed by displacement plating or hot dipping.
The Sn coating layer-coated electrode chip of m was heated in the air at 200° C. for 5 hours to diffuse a portion of Sn into the electrode. After the heat treatment, when the cross section of the tip of the chip was observed under a microscope, it was observed that an intermetallic compound ε phase of a Cu-Sn alloy was formed in a part of the structure.

Example 4 Thickness 0 formed by the same soldering method as Example 2
．． Electrode chips with Sn coating layers of 05 μm, 2 μm, and 370 μm were heated at 200° C. for 5 h in the atmosphere.
A portion of Sn was diffused into the electrode. When the cross section of the tip of the chip was observed under a microscope after heat treatment, it was found that Cu was present in a part of the structure.
It was observed that an intermetallic compound ε phase of the -Sn alloy was formed.

Comparative Example 1 The tip of an electrode tip manufactured in the same manner as in Example 1 was soldered to a thickness of 0.02 mm by the same soldering method as in Example 2.
A Sn coating layer of .mu.m and 430 .mu.m was provided.

A softened 5083 alloy material (O material) with a thickness of 1 mm was used as the material to be welded. As a pretreatment, it was immersed in a commercially available solvent to degrease it, washed with water, and then treated with an alkaline cleaner (carbonic acid containing sodium silicate as an inhibitor). Soda solution, 8
0°C) for 5 minutes, washed with water and dried.

[0020] Next, each pair of electrodes produced in Examples 1 to 4 and Comparative Example 1 was placed at symmetrical positions on the front and back sides of the pretreated aluminum plate to be welded, and a three-phase low frequency spot welding machine was used. Welding current (effective current)2.
2KA, energizing time 0.083 seconds, pre-pressure 900kg
f, 1000 continuous spot welds were performed under the welding conditions of a welding pressure of 300 kgf, and the tensile shear load of the spot weld was measured every 10 welds. Furthermore, the tensile shear load of spot welds is JIS Z
The number of consecutive spot welds that resulted in less than 171 kgf/point of 3140A class was measured, and the tensile shear load of the spot weld until that number was reached was measured every 10 welds, and the average value was determined. The results are shown in Table 1.

[0021]

[Table 1]

From the results in Table 1, it can be seen that the electrode according to the present invention shows a small decrease in the strength of the welded part in the continuous spot welding test, and exhibits good performance that can withstand continuous use.

[0023]

As described above, the spot welding electrode provided by the present invention solves the problems of short-term wear and tear of the electrode tip and reduced strength of the welded part during continuous and high-speed spot welding work. In particular, if the Sn coating is applied by soldering, worn electrodes can be easily repaired even at spot welding sites.

Claims (5)

[Claims] 1. An electrode for spot welding, comprising an alumina dispersion-strengthened copper electrode for spot welding, and a coating layer of Sn is provided on a portion of the alumina dispersion-strengthened copper electrode that contacts a member to be welded. [Claim 2] The thickness of the Sn coating layer is 0.03 to 400 mm.
The spot welding electrode according to claim 1, which has a diameter of .mu.m. 3. The spot welding electrode according to claim 1, wherein the Sn coating layer is formed by plating. 4. The spot welding electrode according to claim 1, wherein the Sn coating layer is formed by soldering. 5. A portion of the Sn coating layer is diffused into the electrode,
The spot welding electrode according to claim 1, wherein an intermetallic compound ε phase of a Cu-Sn alloy is formed.