JPH07166274A - Electrode material for resistance welding of aluminum and production thereof - Google Patents

Abstract

PURPOSE:To provide an electrode material capable of prolonging the service life of an electrode five or more times those of conventional ones at the time of spot welding of aluminum and also capable of welding an aluminum sheet similarly to a steel sheet, e.g., in an automobile assembly line. CONSTITUTION:An ingot consisting of, by mass, 0.03-0.5% Ag, 0.004-0.10% O, and the balance Cu with inevitable impurities, is hot-worked, subjected, if necessary, to cold working and process annealing, and then subjected to final cold working at a draft of 5-90%, preferably 10-75%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode material for resistance welding of aluminum and a method for producing the same, and more particularly to an electrode material suitable for spot welding of aluminum (including an aluminum alloy; the same applies hereinafter) and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, automobiles have been actively reduced in weight from the viewpoint of environmental protection, and the use of aluminum for automobile members has been increasing. Spot weldability is required as one of the important characteristics for aluminum members for automobiles, particularly for aluminum sheet materials used as vehicle body panels. However, aluminum has higher thermal conductivity and electrical conductivity than steel that has been conventionally used as a vehicle body panel, and its spot welding requires a large current and a short time of current application, which causes severe electrode wear. However, there is a problem that the life of the electrode becomes extremely shorter than that of the above welding, and there is a demand for the development of an electrode material having excellent spot weldability of aluminum.

Conventionally, welding electrode materials for steel plates such as chrome copper and zirconium chrome copper have been used as aluminum spot welding electrode materials. When aluminum spot welding is performed with these electrodes, the electrodes wear as described above, and since aluminum has a lower melting point than steel, the aluminum melted during welding adheres to the electrode tips and reduces welding efficiency. There is a drawback. Therefore, in an automobile assembly line, the electrode tip has to be dressed at every several tens to several hundreds of hit points, resulting in markedly lower productivity than spot welding of a steel sheet. The adhesion phenomenon of aluminum to the electrode tip is also found in seam welding of aluminum materials, which makes continuous welding for a long time difficult.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems in resistance welding such as spot welding and seam welding of aluminum. An object of the present invention is to provide an electrode material for resistance welding of aluminum in which the adhesion of molten aluminum is avoided and the electrode is less worn, and a method for producing the same.

[0005]

The electrode material for resistance welding of aluminum and the method for producing the same according to the present invention for achieving the above object are, in mass%, Ag: 0.03 to 0.
5%, O: 0.004 to 0.10%, and the balance of Cu and unavoidable impurities is the first characteristic of the material structure. Ag: 0.05 to 0.39%, O: 0 .00
The second and third characteristics in terms of material structure are that it contains 4 to 0.020%, the balance is Cu and unavoidable impurities, and the hardness is H _V 90 or more.

Further, the above-mentioned alloy ingot is hot-worked, cold-worked and without intermediate annealing, and finally cold-worked at a working ratio of 5 to 90%. And

Ag and oxygen (O) are added as essential components to the electrode material of the present invention. A preferable range of the Ag content and the oxygen content is% by mass, and Ag:
It is in the range of 0.03 to 0.5% and O: 0.004 to 0.10%. To obtain stable electrode performance, Ag: 0.0
5 to 0.39% and O: 0.004 to 0.020% are more preferable. Ag has the effect of increasing the softening temperature of the material and keeping the conductivity of Cu at a high value without lowering it. The content of Ag is 0.0
If it is less than 3%, the softening temperature is lowered to 250 ° C. or less, so that the electrode is severely worn during welding and the electrode life is shortened.
If it exceeds 0.5%, the electric conductivity is lowered and the weldability is deteriorated.

Oxygen in the electrode material has an effect of forming an oxide film on the tip surface of the electrode during welding, and preventing molten aluminum from adhering to the electrode tip. Generally, when the oxygen content in Cu increases, hydrogen (H), S, etc. react during casting, and H ₂ O, S
Since O ₂ is generated and becomes an ingot defect and causes breakage in the subsequent cold working, for example, the oxygen amount of tough pitch copper cast in the atmosphere is limited to 100 to 300 ppm, and the melting atmosphere is controlled to cause defects. Oxygen-free copper (oxygen content of 10 ppm or less) has been reduced, but the present invention was made based on the finding that a Cu-Ag alloy having a relatively high oxygen content has good weldability. Is. The preferable range of oxygen amount is 0.004 to
It is 0.10%. If it is less than 0.004%, the oxide film is not sufficiently formed on the tip surface of the electrode and aluminum is likely to adhere during welding, resulting in severe wear of the electrode, and if the oxygen content exceeds 0.10%, the castability of the material will be poor. descend.

The resistance welding electrode material of the present invention is manufactured by melting the alloy material having the above composition in the atmosphere, in an inert atmosphere or in a vacuum, and after casting, hot working such as hot extrusion to the ingot. Then, if necessary, cold working such as drawing and intermediate annealing are performed, and finally 5 to 90%, preferably 1
Final cold working is performed at a working degree of 0 to 75%. If the final cold workability is less than 5%, a hardness of H _V 90 or higher cannot be obtained and the tip of the electrode is easily deformed. If the processing exceeds 90%, the conductivity decreases, many processing defects such as dislocations are introduced, the driving force for recrystallization increases, and the softening temperature increases to 50%.
Since the temperature is lowered by -100 ° C, the tip of the electrode is easily deformed.

[0010]

In the present invention, due to the high thermal conductivity, electrical conductivity and heat resistance of the electrode material containing Ag and the high hardness of H _V 90 or more, heat generation and softening during welding are reduced and the electrode tip diameter Expansion is suppressed, and oxygen in the electrode material forms an oxide film on the tip surface of the electrode during welding to suppress aluminum adhesion.The interaction of these reduces wear on the electrode during resistance welding of aluminum and improves electrode life. Can be made.

[0011]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples. Example 1 Electrolytic copper and Ag ingot were melted in a high frequency melting furnace, the molten metal surface was covered with zinc chloride powder in order to prevent excessive copper oxidation and keep the molten metal warm, and the mixture was uniformly stirred and then put into a graphite mold. After casting, an ingot having a diameter of 120 mm and a length of 250 mm was obtained. The composition of the ingot is shown in Table 1. An extruding billet having a diameter of 92 mm and a length of 200 mm was cut from this ingot and extruded at a temperature of 900 ° C. into a rod having a diameter of 25 mm. Then, the extruded material was cold drawn to a diameter of 20 mm. The properties of the cold drawn material are 0.5% by mass of commercially available Cr, 0.
The results are shown in Table 1 in comparison with a zirconium-chromium-copper electrode containing 05 mass% Zr.

In Table 1, the softening temperature is the temperature at which the hardness measured at the test temperature for 1 hour in an atmospheric furnace becomes equal to or lower than the average value of the hardness before softening and the hardness after completely softening. In order to evaluate the electrode life, the tip diameter of the cold drawn material is 6 m
Molded into m (40R) electrode and used as a welding base material with 1mm plate thickness of Al
-4.5mass% Mg-0.3mass% Cu After commercially pickling the shot dull finish material of the alloy plate, commercially available general molding oil R303
Using a three-phase low frequency type spot welder with water applied to the electrode, pre-pressurizing 9kN, welding pressurizing 3.5kN, welding current 22-24kA, continuous welding speed 1 time / A spot welding test was conducted under the condition of 3 s. The number of RBI start points is 10
Insert pressure sensitive paper (prescale) between the upper and lower electrodes for each dot,
The first point was a hole with a diameter of 1 mm or more at the tip of the electrode. The number of times of forming a defective nugget was set such that the nugget formed on the base material was observed every 10 points and the nugget was separated into two for the first time. This point corresponds to the electrode life.

[0013]

[Table 1]

As shown in Table 1, Cu-A of the present invention
Compared with the zirconium-chromium-copper electrode that has been conventionally used for spot welding aluminum, the g-O electrode has a higher conductivity, the number of spots for wear start and the number of defective nuggets formed are significantly improved, and excellent spot welding for aluminum Have a lifespan.

Example 2 By applying the same casting method as in Example 1, an ingot having a composition shown in Table 2 and a diameter of 267 mm and a length of 2000 mm was produced. From this ingot, an extrusion billet having a diameter of 254 mm and a length of 600 mm was cut, extruded at a temperature of 880 ° C into a rod having a diameter of 40 mm, and then cold drawn to a diameter of 20 mm. The properties of the cold drawn material were measured, and the same spot welding test as in Example 1 was performed to evaluate the electrode life. The results are shown in Table 2. As can be seen from Table 2, all of the electrode materials according to this example exhibited excellent conductivity, heat resistance and electrode life.

[0016]

[Table 2]

Comparative Example 1 An electrode material having the composition shown in Table 3 was manufactured by the same casting and processing method as in Example 2, and the same spot welding test as in Example 1 was conducted. The results are shown in Table 3. As can be seen in Table 3, Comparative Material No. 1 has a low softening temperature, poor heat resistance, a small number of points for wear start, and a defective nugget formation count of 2000 or less because of its low Ag content. . No. 2 has a too high Ag content, and the conductivity decreases. In No. 3, the oxygen content is low, and the oxide film is not sufficiently formed on the electrode tip surface, so the electrode life is short. No. 4 had too much oxygen content and had many gas holes in the ingot, and could not be processed. Table 3
In the above, those outside the limiting conditions of the present invention are underlined.

[0018]

[Table 3]

Example 3 An extrusion billet having the same diameter as in Example 2 and having the composition shown in Table 4 was prepared in the same manner as in Example 2. The billet was extruded at a temperature of 880 ° C. into a bar material having a diameter of 80 mm, and then subjected to final drawing processing while changing the cold workability to 5%, 10%, 60% and 90%. Various properties of these drawn materials were measured and the same spot welding test as in Example 1 was performed. The results are shown in Table 4. As can be seen from Table 4, the electrode materials according to this example exhibited any excellent conductivity, heat resistance and electrode life.

[0020]

[Table 4]

Comparative Example 2 An extruded material having a composition shown in Table 5 and having a diameter of 80 mm was produced according to the same casting and processing method as in Example 3, and was subjected to final cold working at a cold working ratio of 3% and 93%. Drawing processing was performed, various characteristics were measured, and a spot welding test similar to that in Example 1 was performed. The results are shown in Table 5. As shown in Table 5, the test material No. 5 having a cold workability of 3% has a low hardness, and the cold workability is 93%.
% Of the test material No. 6, the crystal grains were elongated, the grain boundaries increased, and the amount of diffusion of aluminum increased, and thus the wear of the electrodes was large. In Table 5, those that did not meet the limiting conditions of the present invention are underlined.

[0022]

[Table 5]

Example 4 An electrode material having the composition shown in Table 6 was melted in the same atmosphere as in Example 1 and vacuum-melted, and cast into an ingot having a diameter of 120 mm and a length of 200 mm. After milling a billet with a diameter of 92 mm and a length of 150 mm, it is extruded at a temperature of 880 ° C into a rod with a diameter of 25 mm, and the diameter is 20 mm.
Cold drawn until. The hardness, heat resistance and conductivity of this cold drawn material were measured, and a spot welding test was performed using the same welding base material as in Example 1 and a single phase AC stationary spot welding machine. Welding conditions conform to WES7302,
The castle was designed so that a nugget with a diameter of 5 mm could be obtained, and the continuous welding speed was once per 2 s. The measurement and test results are shown in Table 6 in comparison with a commercially available chromium copper electrode. As can be seen from Table 6, the electrode material according to this example has good hardness, electrical conductivity, and heat resistance, and has a remarkably excellent electrode life for aluminum spot welding. The heat resistance was evaluated by the hardness after heating at a temperature of 300 ° C. for 1 hour.

[0024]

[Table 6]

[0025]

As described above, according to the present invention, the electrode life at the time of spot welding of aluminum can be extended to 5 times or more of that of the conventional product. For example, an aluminum plate is welded to a steel plate in an automobile assembly line. There is provided an electrode material that enables The electrode material of the present invention can achieve similar life improvement not only in spot welding of aluminum but also in seam welding of aluminum.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keizo Namba 5-11-3 Shimbashi, Minato-ku, Tokyo Sumitomo Engineering Co., Ltd.

Claims (4)

[Claims] 1. In mass%, Ag: 0.03 to 0.5%,
O: An electrode material for resistance welding of aluminum, which contains 0.004 to 0.10% and is composed of the balance Cu and unavoidable impurities. 2. Ag: 0.05 to 0.39 in mass%
%, O: 0.004 to 0.020%, and the balance Cu and unavoidable impurities, and an electrode material for resistance welding of aluminum. 3. The electrode material for resistance welding of aluminum according to claim 1, having a hardness of H _V 90 or more. 4. The copper alloy ingot according to claim 1 or 2 is hot-rolled, cold working and intermediate annealing are not performed, and final cold working is performed at a working ratio of 5 to 90%. A method for producing an electrode material for resistance welding of aluminum, which is characterized.