JPS6048275B2 - Electrode for resistance spot welding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrode for resistance spot welding for aluminum or aluminum alloys.

More specifically, the present invention relates to a highly durable resistance spot welding electrode for aluminum or aluminum alloy, which is provided with a thin coating layer of aluminum or aluminum alloy at the tip of the electrode. Conventionally, aluminum or aluminum alloy (hereinafter both are collectively referred to simply as "aluminum")
Materials for electrodes for resistance spot welding of metals, including metals, are required to have high electrical conductivity and thermal conductivity, as well as excellent mechanical strength at room temperature and high temperature.

Single materials such as Cr-cuN2--Cu)Zr-Cr-Cu alloys have been used to meet these requirements. These materials usually have a conductivity of 75% or more, and are alloys with high-temperature strength due to the precipitation of added elements such as Cr and Zr into the copper fabric, making them ideal materials for electrodes. It is something. However, under harsh operating conditions due to increased productivity, the shape of the tip of the electrode must be often modified during welding in order to maintain the quality of the welded part even when using electrodes made of the above materials. Because they have poor durability, they must be replaced at an early stage, and this is one of the bottlenecks in streamlining production. In particular, it is known that electrodes used for resistance spot welding of aluminum have a shorter lifespan than electrodes used for resistance spot welding of mild steel. In other words, when an electrode is attached to a welding machine and spot welding is performed continuously on a base material made of aluminum, as the number of welds (spot welds) increases, the aluminum of the base material is picked up at the tip of the electrode, and conversely, the base material aluminum is picked up at the tip of the electrode. A phenomenon occurs in which the copper component of the electrode is picked up on the spot welding surface of the aluminum material, causing the electrode to wear out, impairing the appearance of the welded surface, and having an unfavorable effect on the strength of the welded part. Generally, the life of an electrode for resistance spot welding of aluminum is affected by the material of the electrode, its shape, the pretreatment method of the base metal, the type of welding machine, welding conditions, the cooling capacity of the electrode, etc.・In addition, in applications that require high-quality spot welding, such as resistance spot welding of vehicle and aircraft parts, the base material must be carefully pretreated and the shape of the electrode tip must be adjusted to ensure the so-called dressing interval. Conventionally, this has been done in cycles of around 20 points. This short dressing interval ultimately means that the life of the electrode is short, or in other words, the durability is low. Although various improvement methods such as Ni plating have been proposed5, satisfactory results have not yet been obtained. In view of the above-mentioned circumstances, the present inventor conducted various studies in order to obtain a highly durable electrode that can be applied to aluminum resistance spot welding. The present invention was completed based on the knowledge that an electrode shaped like this has excellent durability and that the dressing interval can be lengthened accordingly, making it possible to rationalize spot welding.

Hereinafter, the present invention will be explained in more detail. As the base material of the electrode of the present invention, pure copper, Cr-Cu type, Zr-Cu type, Zr-Cu type, Zr-Cu type, Zr-Cu type, etc.
A chip molded from a known r-Cr-Cu type copper or copper base metal is used.

In addition, methods for forming a thin coating layer of aluminum on the tip of the tip include a method of fixing the tip to a check on a lathe and pressing aluminum onto the tip while rotating, and a method of coating the tip surface with aluminum. However, the former method is easier, that is, pressing aluminum onto the chip until the copper color of the chip fabric is no longer visible, forming a covering layer of aluminum everywhere. . Resistance spot welding of aluminum as a base material using the electrode of the present invention can be carried out under the same conditions as conventional methods.

As described above, the present invention provides a resistance point formed by forming an aluminum coating layer on the tip of a tip molded product for a known electrode made of, for example, copper, Cr-Cu system, Zr-Cr-Cu system, etc. The present invention provides electrodes for welding.

That is, by having the above-mentioned structure, as shown in the examples below, there are two advantages of excellent durability and long dressing intervals, and the tensile and shear strength etc. are not lower than that of the conventional method. do not have. Example 1 Length: 61.57 Wt) Diameter: 25 Tf Un) Water cooling hole (Length: 61.57 Wt) Diameter: 25 Tf Un) obtained by molding a known Cr-Cu (chromium copper) alloy
The distance between the tip of the electrode tip (diameter 39wrm) is 1
6.5-, the tip R surface is 25 (YmL (7) Fix the R-type tip to the chuck of the lathe, and press a pure aluminum plate against the tip of the tip while rotating the tip and apply sliding pressure to cover the entire tip surface. A desired electrode was obtained by covering the chip with an aluminum film until the material of the chip was no longer visible.

Example 2 Plate thickness 2.5TwL (7) JISH4 as base material
Using OOO's A5O83P-0 alloy, as a pretreatment,
The surface was immersed in 5% caustic soda solution (60°C), taken out and washed with water, immersed in 15% nitric acid (air temperature), taken out, washed with water, dried, and many stainless steel wires with a diameter of 0.157 T$t were planted. The contact surface and mating surface of the electrode were polished using an electric brush.

An electrode obtained by the method of Example 1 and, as a comparative example, an electrode made of an uncoated chip made of the same material and the same shape were prepared, and each pair was placed at symmetrical positions on the front and back of the base material that had undergone the above pretreatment. Then I did resistance spot welding. A three-phase low-frequency welding machine was used as the welding machine. The welding conditions are: squeeze and forge pressure of 2.580k9, welding pressure of 1.180k9, squeeze time of 40 cycles, forge delay time of 8 cycles, heat current of 94500Amp (heat current of 94500Amp) and decay current of 3.
0000A) Heat time was 4 cycles, decay time was 8 cycles, cool time was 3 cycles, and hold time was 40 cycles. Then, by visual inspection,
Spot welding was performed continuously using the inventive product and the comparative product without dressing in the middle, and the number of initial welding points where the base metal adhered to the electrode and was picked up was calculated. The amount of Cu in the weld indentation (B) was determined, and the tensile shear strength (C) was measured (average value) at each of 30 weld points. The results are shown in Table 1. Note 1: The amount of Cu was measured as follows. Cu on the surface of the welded part was dissolved in nitric acid, a coloring solution was added thereto, and the solution was analyzed by spectrophotometry.

Note 2: Tensile shear strength was measured as follows.

The test was carried out in accordance with JIS Z3l36, tensile shear and fracture test method for spot welding.

Note 3: The aim was to set the nugget diameter to 5VT (T: base metal pressure 2.5 -), that is, 7.9 wun or more.

Claims (1)

[Claims] 1. A resistance spot welding electrode with a coating layer of aluminum or aluminum alloy on the tip.