JPH06306511A - Electrode for spot welding and its production - Google Patents

Abstract

PURPOSE:To produce an electrode for spot welding excellent in electric conductivity, thermal conductivity, high temp. strength, corrosion resistance and workability and having a long service life at a low cost by immersing a green compact obtd. by mixing Cu powder and Sn powder into water-soluble flux and thereafter executing two-stage sintering in the air. CONSTITUTION:Cu powder and Sn powder are mixed in such a manner that the content of Sn is preferably regulated to 5 to 35wt.%, and this mixed powder is packed into a compacting die and is compacted by a hydraulic press or the like. Next, this green compact is immersed into water-soluble flux, is thereafter subjected to primary sintering at a low temp. of about 300 to 400 deg.C in the air and is subsequently subjected to secondary sintering at a higher temp. of about 500 to 700 deg.C. Or, the same green compact may succeedingly be subjected to secondary sintering after the primary sintering in a reducing atmosphere or in vacuum. In this way, the electrode for spot welding constituted of a sintered body in which a Cu-Sn alloy layer is formed can be obtd. Preferably, this electrode is fixed to the tip of a Cu-Cr alloy material by screwing and is used for welding.

Description

Detailed Description of the Invention

[0001]

[Industrial application] Aluminum alloys are used for body sheets, frames (chassis), etc. as automobiles become lighter. The present invention relates to an aluminum alloy spot welding electrode used for joining these plate materials and a manufacturing method thereof.

[0002]

2. Description of the Related Art The conventional welding methods for metals are roughly classified into electrical, chemical, mechanical, and
There is a welding method that uses ultrasonic waves and light energy. Among them, resistance spot welding by electric energy is mainly used for welding steel sheets for automobiles. Although this resistance spot welding method can be used easily and inexpensively, troubles such as abrasion and cracking of the electrode tip and welding with the material to be welded frequently occur. Therefore, in order to improve the appearance of the electrode, it is dressed each time and used, but there is a drawback that not only the number of steps is increased but also the life of the electrode itself is shortened.

In recent years, aluminum alloys used for body sheets having high strength and high workability have been studied for the purpose of reducing the weight of automobiles, and the welding process itself has become complicated as the speed of the welding process for these members has increased. It was However, compared with the conventional steel sheet, the aluminum alloy has a problem that the electrode life during spot welding is extremely short and hinders efficient production. Note that no material has been found so far that significantly improves the performance of the conventional copper-chromium alloy electrode. Therefore, development of an aluminum alloy spot welding electrode having high welding characteristics and wear resistance has been strongly demanded.

The properties required for this aluminum alloy spot welding electrode are that it has a high electrical conductivity and a high thermal conductivity (these prevent the electrode temperature from rising), the room temperature hardness is hard, and the welding material adheres. Examples include alloying, difficulty in diffusion, difficulty in picking up, ease of processing (cutting and polishing), that is, easy dressing, low cost, and the like.

However, in the current electrodes for resistance spot welding of aluminum alloys, the material to be welded and the electrode material diffuse during welding to show an alloying reaction, welding or cracking of the tip of the welding electrode,
There are problems that deformation and the like are likely to occur and the life of the electrode is extremely shortened, and that the reaction layer is corroded and deteriorated to increase electrode consumption, and at the same time, the soft reaction layer is deformed by welding heat and electrode consumption is increased. Therefore, there are still many undeveloped parts.

[0006]

The present invention has been studied in view of this, and as a result, the electrical conductivity, thermal conductivity, and
It is a material for resistance welding electrodes that has excellent high temperature strength, corrosion resistance, and workability, is inexpensive, and has a long life.

That is, one of the electrodes of the present invention is a sintered body having a Cu--Sn alloy layer formed thereon, and the other is a sintered body having a Cu--Sn alloy layer formed thereon. It is fixed to the tip of a Cr alloy member.

Further, one of the manufacturing methods of the electrode of the present invention is:
Cu powder and Sn powder are mixed to form a green compact, and the green compact is immersed in a water-soluble flux, and then 1
The secondary sintering is performed, and then the secondary sintering is performed at a higher temperature.

In another manufacturing method, Cu powder and Sn powder are mixed to form a green compact, and the green compact is subjected to primary sintering at a low temperature in a reducing gas atmosphere or in a vacuum. After that, secondary sintering is performed at a higher temperature in a reducing gas atmosphere or in a vacuum.

As described above, in the present invention, a sintered alloy of Cu powder and Sn powder is used. This is a problem because ingots obtained by melting Cu and Sn have large segregation, but metal powder This is because the use of is advantageous in that a uniform mixed powder can be obtained and a uniform electrode material without segregation can be obtained. Also this C
The u-Sn sintered body can be used as it is as an electrode, but the sintered body is screwed to the tip of a rod-shaped Cr-Cu alloy member which is a conventional electrode, and electron beam welding, laser welding and mechanical welding are performed. You may use as an electrode. With such a configuration, there is an effect of preventing the temperature rise of the electrodes.

Next, the manufacturing method of the present invention will be described in more detail. Cu powder and Sn powder are sufficiently pulverized by a ball mill etc., and the content of Sn powder is adjusted to 5 to 35% by weight, and the two are mixed and then filled in a molding die and then subjected to normal hydraulic press or CIP (cold isostatic pressing). Molding). After that, the molded body is subjected to primary sintering at a low temperature in a reducing gas atmosphere or in a vacuum, and subsequently to secondary sintering at a higher temperature in a reducing gas atmosphere or in a vacuum. Although a sintered body can be obtained, the following method can also be used.

That is, the above-mentioned molded body is first immersed in a water-soluble flux, and then in the atmosphere at a temperature of 300 to 400 ° C. for 10 to 90 ° C.
By holding for 1 minute and performing primary sintering, Cu-
An intermetallic compound layer of Sn is formed, and subsequently the above-mentioned compound layer is formed on the whole by secondary sintering which is also held in the atmosphere at a higher temperature of 500 to 700 ° C. for 10 to 90 minutes. Increase the hardness of. Thus, the reason why the green compact is immersed in the flux prior to the sintering is to reduce the surface of the Cu powder or the Sn powder by using the reducing action of the flux to accelerate the sintering, and thereby, in the atmosphere. It became possible to sinter. As the flux, chlorides such as hydrochloric acid, ammonium chloride, zinc chloride, lithium chloride, etc. used for soldering, fluorides such as potassium fluoride, sodium fluoride, boric acid, boride such as borax, or a mixture thereof are used. Can be used.

In addition, the sintering is performed in two stages by the primary sintering at a low temperature to generate an intermetallic compound which improves the strength and the pick-up resistance, and the secondary sintering at a high temperature causes the sintering structure as a dense electrode. This is to obtain a structure.

[0014]

EXAMPLES Examples of the present invention will be described below.

Example 1 Cu powder having a particle size of 10 μm, which was a mixture of Sn powder having an oxygen content of 300 ppm and a particle size of 10 μm in a weight ratio of 15%, was ground and mixed for 6 hours in a ball mill, sieved, and then hydraulically pressed to a diameter of 20 mm × length. A molded body having a size of 20 mm was produced.
After soaking this compact in water-soluble flux for 1 to 5 minutes, put it on a quartz board and put it in an atmospheric furnace at 380 ° C for 10 minutes to perform primary sintering, and then put it in an atmospheric furnace at 600 ° C for 20 minutes. 2
As a result of forming the Cu-Sn compound layer by the subsequent sintering,
Surface oxidation hardly occurred, and a good sintered electrode material was formed. The micro Vickers hardness of the surface layer of this sintered body is 1
It was between 30 and 270.

This sintered body is processed into a shape as shown in FIGS. 1A and 1B, and a 1% Cr-Cu rod having a shape shown in FIGS. Welded to form an electrode having the shape shown in FIG. Welding current 220
A518 under conditions of 00A, pressure 300kgf, and energizing time 3 cycles
When 2P-0.1mmt aluminum alloy sheet was continuously spot-welded, the result was that there was no problem even with continuous 5500 RBI exceeding 3000 RBI.

As described above, the present invention focuses on the fact that a compound layer of Cu and Sn can be easily formed even at a low temperature. In order to rapidly grow the compound layer of Cu and Sn, pressure molding is performed using powders of Cu and Sn. Cu-S is obtained by subsequent primary sintering.
This is an early formation of a uniform compound layer of n. Furthermore, good results were obtained because a Cr-Cu alloy rod having high thermal conductivity and conductivity was used as the base material.

(Example 2) Next, using the same Cu powder and Sn powder as in Example 1, a compact having a diameter of 20 mm and a length of 30 mm was obtained and sintered under the same conditions to obtain an electrode material for spot welding. Manufactured. A welding current was changed to 26000 A using an electrode obtained by processing this electrode material, and A5 was used under the same conditions as in Example 1 except for the above.
182P-0.1mmt aluminum alloy sheet was continuously spot welded. As a result, there were no problems with 7500 RBI in a row.

COMPARATIVE EXAMPLE 1 Commercially available 1% Cr-Cu 30%
An electrode material having a Cr—Cu microstructure was obtained by performing partial melting with a beam current of mmA, quenching with the heat capacity around Cr and forcing solid solution of Cr. The surface hardness was about 100 in terms of micro Vickers hardness. Then, this Cr-Cu alloy was processed into an electrode shape, and continuous spot welding was performed on the same aluminum alloy sheet under the conditions of Example 1 while repeating the dressing of the electrode. When the number of dots was 850, the electrode tip started to crack. Therefore, the dressing was applied again, but the electrode tip was deeply cracked and unusable.

As described above, according to the present invention, Cu and Sn powders are mixed by a ball mill or the like, and the powders are mixed with a hydraulic press or C
It is molded by IP (cold isotropic pressure press), etc., the green compact is immersed in a water-soluble flux, and primary sintering and secondary sintering are performed in a heating furnace in the atmosphere to improve hardness. Then, a sintered body of Cu-Sn alloy was used as an electrode, or this sintered body was used as an electrode tip to perform electron beam welding on a Cr-Cu rod to form an electrode. That is Cu
A compound layer was formed on a sintered body obtained by sintering a green compact of Sn powder and Sn powder, and the compound layer was attached to a resistance spot welder using the electrode tip as an electrode tip and welded to an aluminum alloy sheet. Welding, cracking or diffusion of the electrode tip,
Good welding is possible without corrosion and distortion.

The present electrode is effective not only for aluminum alloy plates but also for Zn-plated copper plates. Further, the welding machine to be used is not limited to the single-phase AC welding machine, and any welding machine such as a single-phase rectification welding machine, an inverter DC welding machine, or a three-phase rectification welding machine is effective.

[0022]

As described above, according to the present invention, various troubles such as electrode cracking and welding during the aluminum alloy spot welding process are eliminated, and high-performance welding is possible in spot welding of aluminum alloy sheets, etc. That is, a remarkable effect is obtained industrially.

[Brief description of drawings]

FIG. 1 shows an example of the shape of an electrode of the present invention (a)
Is a plan view and (b) is a side view.

FIG. 2 shows an example of a Cu—Cr alloy rod for fixing the electrode of the present invention to the tip, (a) is a plan view, and (b) is a side sectional view.

FIG. 3 is an explanatory view showing an example of a spot welding electrode using the present invention.

Claims (4)

[Claims] 1. An electrode for spot welding, comprising a sintered body having a Cu—Sn alloy layer formed thereon. 2. A sintered body on which a Cu—Sn alloy layer is formed is C
An electrode for spot welding, which is fixed to the tip of a u-Cr alloy material. 3. A Cu powder and an Sn powder are mixed to form a green compact, which is immersed in a water-soluble flux and then primary-sintered at a low temperature in the atmosphere, and then at a higher temperature. A method for manufacturing an electrode for spot welding, which comprises performing secondary sintering with. 4. A Cu powder and an Sn powder are mixed to form a green compact, and the green compact is subjected to primary sintering in a reducing gas atmosphere or in a vacuum at a low temperature, and then a reducing gas. A method for manufacturing an electrode for spot welding, which comprises performing secondary sintering at a higher temperature in an atmosphere or in a vacuum.