JP3378621B2 - Electrode for resistance welding and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance spot welding electrode having a long life when spot welding a plated steel sheet, aluminum and an aluminum alloy sheet used in the automobile industry and the like, and a method for producing the same.

[0002]

2. Description of the Related Art The reduction of electrode life in spot welding of Zn-plated steel sheets and aluminum alloy sheets is a serious problem in automobile production, and there is a demand for long-life spot welding electrodes. In order to improve the life of the spot welding electrode, it is considered necessary to improve the characteristics of the electrode material such as electric conductivity, thermal conductivity and heat resistance. For example, in Cu
A Cu-Cr alloy that contains about 0.8 mass % (hereinafter mass % is simply referred to as%) of Cr and is strengthened by utilizing precipitation hardening, or an oxide such as Al ₂ O ₃ or TiO ₂ in Cu. Particle-dispersed Cu in which about 1% of particles are added and dispersed
Alloys are used.

However, these electrodes have not yet fully satisfied the above requirements. In particular, in spot welding of an aluminum alloy plate, Al reacts with Cu of the electrode to form a brittle alloy layer, and the phenomenon of the alloy layer peeling occurs, which shortens the life of the electrode. It has been closed up.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been studied in view of the above, and as a result, a plated steel sheet having a long life, which is required for a welding electrode, has good thermal conductivity, good electrical conductivity, high temperature strength, and high temperature heat resistance, This is an electrode for resistance spot welding of aluminum and aluminum alloy and a method for manufacturing the same.

That is, the electrode of the present invention is an electrode for spot-welding a plate material to be welded by contacting the plate material to be welded with electricity and containing Cr: 1.5 to 20%, or further Si,
P, Mg, Co, Ag, Ni, Be, Al, Sn, Zr
1% or more of each of them is contained in an amount of 1% or less, and the balance consists of Cu and unavoidable impurities.
The shape is an ellipsoid, the aspect ratio thereof is 1.5 to 50, the longitudinal direction thereof is parallel to the plate surface of the plate material when the electrode is brought into contact with the plate material to be welded, and the Vickers hardness is 140. The above is a feature.

[0006]

[0007]

[Function] Originally, the Cr solid solution limit amount of Cu-Cr alloy is 0.8
%, And addition amounts above this level do not contribute to curing. Therefore, in the present invention, the matrix is ordinary Cr0.8.
% -Cu alloy, and by adding Cr to the solid solution limit or more, a structure in which Cr is crystallized and dispersed in the matrix is obtained. That is, it can be regarded as a composite material in which Cr crystallized substances are dispersed in the matrix of the Cu-Cr precipitation hardening type alloy. The dispersed crystallized substances have the effect of suppressing the reaction between the plate material to be welded and the electrode.

In the first electrode of the present invention, the main component of Cr is
Is a hypereutectic composition and is added to crystallize the primary crystal Cr. If it is less than 1.5%, the amount of primary crystal Cr crystallized is not sufficient, and the effect of improving the electrode life cannot be seen. On the other hand, if it exceeds 20%, the castability will be poor, and it will be difficult to obtain a sound ingot, and the decrease in conductivity will be considerably large. In addition, it has an adverse effect on cold workability and machinability.

That is, in a Cu-based alloy containing Cr: 1.5 to 20%, if Cr is crystallized and dispersed in a Cu matrix, the thermal conductivity and the electrical conductivity are not significantly lowered, and high strength and high temperature are achieved. It was found that it is possible to have heat resistance and the life of the electrode can be improved.

However, as a result of examination, this Cr crystallized substance was
The distribution turned out to be important. That is, it has been found that when the primary crystal Cr is made directional, the effect of improving the electrode life is higher than when finely dispersed even with the same amount of crystallization, as compared with the case of crystallization in a dendrite state during casting. In particular, the longer the electrode life was, the more the longitudinal direction of the Cr crystallized product was made parallel to the plate surface of the plate material when the electrode was brought into contact with the plate material to be welded. Although the mechanism is not known in detail, it is considered that this is because the dispersed Cr effectively acts to suppress the reaction with the material to be welded.

As a method for imparting directionality to such primary crystal Cr, a temperature gradient is provided during solidification, so-called unidirectional solidification, or an ingot is prepared by a usual method, and then hot extrusion is carried out to obtain a relatively high temperature. Easy to achieve. Cold working such as subsequent drawing is also effective.

The average grain size of the crystallized Cr grains in the cross section perpendicular to the longitudinal direction is 0.1 to 70 μm, and the ratio (aspect ratio) of the grains to the longitudinal direction is 1.5 to 50.
In this case, the effect of extending the life of the electrode is remarkable.

Next, the second electrode of the present invention, Cr: 1.5 to 2
0%, Si, P, Mg, Co, Ag, Ni, Be, A
1% of l, Sn, Zr or 1% or more of each, 1%
The reason for limiting the composition range of the Cu-based alloy contained below will be described below.

Cr: For the above reason.

Si: an element that contributes to the improvement of strength,
It is preferable that the content is 0.01% or more, but if it exceeds 1%, the electrical conductivity decreases and the hot workability deteriorates.

P: It has the effect of facilitating the quenching treatment, and it is preferably contained in an amount of 0.01% or more, but if it exceeds 1%, it segregates at the grain boundaries to lower the corrosion resistance and, at the same time, the electrical conductivity deteriorates.

Mg: An element which improves the hot workability by fixing S inevitably mixed in as a compound MgS with stable Mg in the mother phase. And it is preferable to contain 0.01% or more, but if it exceeds 1%, Cu + M is contained in the ingot.
When a eutectic of gCu ₂ is generated and heated to a temperature of 722 ° C. or higher, cracking occurs and hot workability deteriorates.

Co: Improvement of conductivity and prevention of coarsening of crystal grains due to temperature rise, contributing to heat resistance. And 0.
It is preferable that the content is 01% or more, but if it exceeds 1%, there is no significant change in characteristics, but it deteriorates with time.

Ag: It has an effect of preventing the generation of sparks, and it is preferably contained in an amount of 0.01% or more, but if it exceeds 1%, the conductivity and the melting point are lowered.

Ni: It has the effect of improving strength, and it is preferably contained in an amount of 0.01% or more, but if it exceeds 1%, the conductivity is lowered.

Be: There is an effect of improving the strength, and it is preferable to contain 0.01%, but if it exceeds 1%, there is no great change in the strength improvement and the conductivity is lowered, which is economically inferior.

Al: It has the effect of suppressing the oxidation of the electrode base material, and it is preferably contained in an amount of 0.01% or more, but if it exceeds 1%, the conductivity decreases and the electrode life shortens.

-Sn: Cu-Cr alloy dissolved in a matrix,
It has the effect of improving high temperature strength and extending the life of the electrode.
It is preferable that the content is 0.01% or more, but if it exceeds 1%, the above effect is not significantly changed and the conductivity is lowered.

Zr: Precipitated as fine Cu ₅ Zr in Cu and contributes to the improvement of strength and heat resistance. And it is preferable to contain 0.01% or more, but 1%
If it exceeds, there is no significant change in the strength improvement, but the conductivity decreases.

Further, in the production method of the present invention, the solution treatment, cold working and aging treatment are for increasing the strength of the matrix, and it is necessary to have a fine precipitation strengthening structure. That is, also in the present invention, since Mactrix is the same as a normal Cu-Cr alloy, it is important to precipitate and harden the matrix, and if it is insufficient, the conductivity is low or the hardness is low. The electrode life cannot be improved.

If the solution treatment temperature at this time is less than 800 ° C., solution treatment cannot be sufficiently performed, and if it exceeds 1050 ° C., there is a risk of local melting. And aging treatment is less than 400 ℃,
Aging is extremely slow, and the aging time is too long to be industrial, and when it exceeds 550 ° C, it is overaged and the strength is insufficient.

[0027]

EXAMPLES Examples of the electrode life (continuous spotting property) of the resistance spot welding electrode according to the present invention will be specifically described below.

Example 1 Using the alloys having the compositions shown in Table 1, a φ16 cap tip type DR type spot welding electrode was produced from a φ16 rod obtained by the following method.

Inventive Examples 1 to 5: Ingots of Cu-1.5 to 20% Cr alloy melted in a nitrogen atmosphere using a high frequency melting furnace were hot extruded at 900 ° C. to obtain φ20 rods. After that, a solution heat treatment at 1000 ° C. was performed, this was processed to φ16, and then an aging treatment was performed at 450 ° C. Through this extrusion step and cold working step, the Cr particles can be arranged in parallel to the extrusion direction. Then, an electrode is cut out from this extruded material in a direction perpendicular to the extruding direction so that the longitudinal direction of the Cr crystallized material as the electrode becomes parallel to the plate surface when the electrode comes into contact with the plate material to be welded. Obtained.

Inventive Example 6; A bar material of φ16 mm in which Cr is arranged in the longitudinal direction by unidirectional solidification in which a temperature gradient is provided during casting of a Cu-10% Cr alloy melted in a nitrogen atmosphere using a high frequency melting furnace. Got After that, solution treatment was performed at 1000 ° C, and then aging treatment was performed at 450 ° C. Then, the electrode was cut out in a direction perpendicular to the longitudinal direction of this rod to obtain an electrode in which the longitudinal direction of the Cr crystallized product was parallel to the electrode contacting plate surface as in the above.

The Cr particles obtained in Examples 1 to 6 of the present invention had an average particle size of 5 to 30 μm and an aspect ratio of 2 to 30.

Comparative Examples 1 and 2 were produced by the same method as in Examples 1 to 5 of the present invention, but had Cr amounts of 0.7% and 25%.

Comparative Example 3: A Cu-10% Cr alloy ingot produced by melting in a nitrogen atmosphere using a high frequency melting furnace was hot extruded into a bar of φ20, and then a solution treatment at 1000 ° C. was performed. After processing this to φ16, it was subjected to an aging treatment at 450 ° C. to obtain a material in which the longitudinal direction of the Cr crystallized substance was perpendicular to the electrode contact plate surface.

Comparative Example 4: A Cu-10% Cr alloy melted in a nitrogen atmosphere was cast directly in a φ16 mold using a high-frequency melting furnace to form a bar without hot extrusion, and then 1000 ℃
Solution treatment and then aging treatment at 450 ° C., and the Cr particles have no directionality.

Comparative Example 5: An ingot of Cu-11% Cr alloy was melted in a nitrogen atmosphere using a high frequency melting furnace at 900 ° C.
After being hot extruded into a bar material having a diameter of φ20, a solution treatment was performed at 750 ° C. This was processed to φ16, and then an aging treatment was performed at 450 ° C. Electrodes were cut out from this rod at right angles to its longitudinal direction to obtain electrodes in which the longitudinal direction of the Cr crystallized product was parallel to the electrode contact plate surface.

Comparative Example 6 A Cu-10% Cr alloy melted in a nitrogen atmosphere using a high-frequency melting furnace was unidirectionally solidified into a bar material having a diameter of φ20, which was then subjected to a solution heat treatment at 1000 ° C. After processing to φ16, it was aged at 280 ° C. An electrode was cut out from this bar in a direction perpendicular to the longitudinal direction of the rod to obtain an electrode in which the longitudinal direction of the Cr crystallized product was parallel to the electrode contacting plate surface.

Using the electrode thus produced, two aluminum alloy plates AA5182 having a thickness of 1 mm were stacked and continuous spot welding was performed to measure the electrode life at that time. Welding was performed using a single-phase rectification resistance welding machine with a pressing force of 300 kgf, energizing time of 5 cycles, and welding current of 25 kA.

On the other hand, in the electrode life test of the Zn-plated steel sheet, the electrode shape was DR type φ16, and the material to be welded was
Two 0.7 mm thick Zn-plated steel sheets were stacked and continuously spot-welded. Welding uses a single-phase AC resistance welding machine, pressure: 270kgf, energizing time: 3 cycles, welding current: 8.5kA
I went there.

The electrode life was evaluated by measuring the nugget diameter 3.
The life was defined when it became 6 mm or less. Table 1 shows the characteristics and life test results of these electrodes.

[0040]

[Table 1]

All of the examples of the present invention had an electrode life of 3,000 or more in the case of an aluminum alloy and 10,000 or more in the case of a Zn-plated steel sheet. On the other hand, the electrode lifetimes of the conventional method and the comparative example were far shorter than those of the present invention.

(Example 2) Using the alloys having the compositions shown in Table 2, as in Example 1, φ
A φ16 cap type DR type spot welding electrode was produced from 16 rods.

Inventive Examples 7 to 14: Alloys having the compositions shown in Table 2 were melt cast in a nitrogen atmosphere using a high frequency melting furnace.
This ingot was hot extruded at 900 ° C. to form a bar material having a diameter of 20 mm, then subjected to solution treatment at 1000 ° C., processed to φ16, and then subjected to aging treatment at 450 ° C. By cutting out an electrode from this bar at right angles to the extrusion direction, C
An electrode was obtained in which the longitudinal direction of the r-crystallized product was parallel to the plate surface of the plate material to be welded with which the electrode abuts.

Comparative Examples 7 to 10 were produced by the same method as in Examples 7 to 14, but the amount of subcomponents other than Cr was larger than that of the present invention.

Using the electrode thus manufactured, an aluminum alloy plate AA518 having a thickness of 1 mm was used as in Example 1.
2 and 0.7 mm thick Zn-plated steel sheets were continuously spot-welded. The welding method and conditions are the same as in Example 1. The electrode life is evaluated by measuring the nugget diameter 3.
The life was defined when it became 6 mm or less. Table 2 shows the characteristics and life test results of these electrodes.

[0046]

[Table 2]

It can be seen that all of the examples of the present invention have a longer electrode life than the comparative examples in which the amount of the subcomponent additive element is too large.

[0048]

As described above, according to the present invention, the electrode life can be remarkably improved as compared with the conventional electrode. Therefore, it greatly contributes to the improvement of resistance spot welding, which has been the biggest bottleneck for aluminum in mass production of automobiles, and the improvement of the electrode life of plated steel sheets.

The product of the present invention can also be applied to spot welding in which plated steel sheets and rolled steel sheets (steel without plating) are stacked and spot welding in which plated steel sheets and rolled steel sheets are mixed (alternate).

The welding machine used for this resistance spot welding is a conventionally used single-phase AC welding machine, single-phase rectification welding machine, three-phase low-frequency welding machine, three-phase rectification welding machine, inverter welding machine, Any of a condenser type welding machine and the like may be used.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoru Suzuki 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Tomiharu Okita 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Aluminum Co., Ltd. (72) Inventor Mikiharu Suzuki 1 Toyota-cho, Toyota-shi, Aichi Toyota Automobile Co., Ltd. (72) Inventor Koji Nomura 1 Toyota-cho, Toyota-shi, Aichi Toyota Automobile Co., Ltd. (72 ) Inventor Hideo Tachikawa 41, Nagachote, Nagakute-cho, Aichi-gun, Aichi Prefecture, 1st in Yokota Central Research Institute Co., Ltd. (72) Inventor Goro Watanabe, 1st, 41-number, Nagakute-cho, Aichi-gun, Aichi-gun, 1st, Yokota, Toyota Chuo In the laboratory (56) Reference JP 49-78623 (JP, A) JP 3-294439 (JP, A) JP -13851 (JP, A) JP-A-53-29213 (JP, A) JP-A-58-197241 (JP, A) JP-A-59-193233 (JP, A) Actual development 61-82876 (JP, U) ) (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 1/00-49/14 B22D 27/04 B23K 11/30 C22F 1/08

Claims (2)

(57) [Claims] 1. An electrode for spot-welding a plate to be welded by energizing the plate to be welded with Cr: 1.5
〜20mass% and balance Cu and unavoidable impurities,
Moreover, the crystallized Cr particles have an ellipsoidal shape with an aspect ratio of
An electrode for resistance welding, wherein the resistance welding electrode has a length of 1.5 to 50, a longitudinal direction thereof is parallel to a plate surface of the plate material when the electrode is brought into contact with the plate material to be welded, and a Vickers hardness is 140 or more. 2. An electrode for spot-welding a plate to be welded by abutting the plate to be energized and Cr: 1.5
~ 20mass%, Si, P, Mg, Co, A
One or more of g, Ni, Be, Al, Sn, and Zr are contained in an amount of 1 mass% or less, and the balance is Cu and inevitable impurities. The crystallized Cr particles have an ellipsoidal shape and an aspect ratio. Is 1.5 to 50, the longitudinal direction thereof is parallel to the plate surface of the plate material when the electrode is brought into contact with the plate material to be welded, and the Vickers hardness is 140 or more.