JP3535940B2 - Spot welding electrode 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 an electrode for spot welding, which is suitable for spot welding of Al or Al alloy, and has a significantly improved electrode life, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Resistance spot welding is the most frequently used welding method in the assembly process of automobiles. Conventionally, rolled steel sheets, especially galvanized steel sheets, have been widely used for automobile body sheets, but recently, due to energy saving, environmental problems, etc., weight reduction of automobiles has been demanded.
Alloys have come into use. The Al or Al alloy spot welding electrode has high temperature strength, high electrical conductivity, and high thermal conductivity, and has a relatively low cost Cu-
1wt% Cr alloy is used. By the way, the electrode is required to have sufficient strength to withstand the pressing force during spot welding and sufficient thermal conductivity (electrical conductivity). When the thermal conductivity is low, the tip of the electrode reacts with the material to be welded and alloys, the alloyed part is transferred to the material to be welded, the electrode is consumed, and the current density decreases accordingly, resulting in welding. The nugget (press-bonded portion) becomes small, and a predetermined welding strength (tensile shear load) cannot be obtained.

[0003]

It is said that the life of an electrode when spot-welding a galvanized steel sheet with a conventional Cu-1wt% Cr alloy electrode is 5,000 points or more (10,000 points or more in the case of rolled steel sheet). There is. On the other hand, the number of Al or Al alloys is about 1,000, and a metal plated with such as Zn has a shorter life. Note that the electrode life is the number of spots until a predetermined welding strength cannot be obtained during continuous spot welding. In the automobile industry, it is an important issue to improve the electrode life when welding Al or Al alloys and their metal-plated materials to more than 5,000 points, which is equivalent to that of current plated steel sheets. Is strongly desired. From this, the present inventors have studied the cause of the short life of Cu-1wt% Cr alloy electrode when spot welding Al or Al alloy, the cause is Cu-
Since the 1 wt% Cr alloy electrode has insufficient strength, it was found that it can be improved by adding a large amount of Cr, and further research was conducted to complete the present invention.

[0004]

The invention according to claim 1 is
In an electrode for spot welding, in which a material to be welded is pressed and electrically heated to be welded, the electrode contains 10 to 30 wt% of Cr, the balance consists of Cu and inevitable impurities, and the crystallized product of Cr is in a Cu matrix. The electrode for spot welding is characterized in that it extends in the pressing direction and is dispersed into fibers, and has a tensile strength of 800 N / mm ² or more and an electrical conductivity of 75% IACS or more.

According to a second aspect of the present invention, in an electrode for spot welding by pressing a material to be welded and heating it with electric current, Cr is 10 to 10.
1 or 2 selected from C, B and N containing 30 wt%
0.001 to 0.1 wt% in total containing at least one species, consisting of the balance Cu and unavoidable impurities, and the crystallized product of Cr in the Cu matrix of the electrode is dispersed in the fiber shape by stretching in the pressing direction,
This spot welding electrode is characterized by a tensile strength of 800 N / mm ² or more and an electrical conductivity of 75% IACS or more.

The invention according to claim 3 is spot welding in which a copper alloy containing 10 to 30 wt% of Cr and the balance of Cu and inevitable impurities is subjected to hot working, solution treatment, cold working, and aging treatment. The method for manufacturing an electrode for use, wherein the cross-sectional reduction rate in the cold working is 90% or more, and the aging treatment is 400 to 600.
A method for manufacturing an electrode for spot welding, which is performed within a temperature range of ° C.

The invention according to claim 4 contains 10 to 30 wt% of Cr, and 0.001 to 0.1 wt% in total of one or more selected from C, B and N, and the balance is Cu and unavoidable. Of a spot welding electrode to which hot working, solution treatment, cold working, and aging treatment are applied to a copper alloy consisting of static impurities,
The method for producing an electrode for spot welding is characterized in that the area reduction rate in the cold working is 90% or more and the aging treatment is performed within a temperature range of 400 to 600 ° C.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the spot welding electrode of the present invention, the crystallized substance of Cr is expanded in the pressing direction in the pressing direction and dispersed in a fiber shape by increasing the strength in the pressing direction and welding. This is to prevent the electrodes from being deformed at times. Here, the fiber shape means a rod shape, a string shape, a section shape,
The shape is an arbitrary elongated shape such as a thread shape or an indefinite shape, and the cross-sectional shape is also an arbitrary shape such as a circle, an ellipse, or a polygon. Further, when the ratio L / T of the length L and the diameter T of the fibrous extension of the Cr crystallized product exceeds 3, it is desirable that higher strength can be obtained. As the length L and the diameter T, it is preferable to use the values obtained by randomly sampling and measuring the fibrous extensions of Cr and averaging them. The number of samples at this time is preferably 20 or more. In this invention, the reason why the Cr amount is specified to be 10 to 30 wt% is 10 w
This is because if it is less than t%, sufficient strength cannot be obtained, and if it exceeds 30 wt%, cold working becomes difficult.

In the present invention, the reason why the tensile strength is specified to be 800 N / mm ² or more is that if the tensile strength is less than 800 N / mm ² , the electrode may be deformed during spot welding. Tensile strength
To obtain 800 N / mm ² or more, Cr is contained in an amount of 10 to 30 wt%, and the crystallized product of Cr is dispersed in a Cu matrix in the form of fibers extending in the pressing direction. In this invention, the reason why the conductivity is specified to be 75% IACS or more is as follows.
If it is less than 75% IACS, the thermal conductivity (heat dissipation) is poor and the temperature of the electrode tip rises, alloying occurs with the material to be welded and the melting point decreases, and the welding frequency with the material to be welded decreases. This is to increase. Most of Cr crystallizes out, but a part of it solid-dissolves, significantly reducing the conductivity. To increase the conductivity to 75% IACS or higher,
This is achieved by precipitating solid solution Cr by aging treatment.

In the invention according to claim 2, C, B, N
Each element of makes the distribution state of the fibrous extension of the Cr crystallized substance more uniform. It also has the function of increasing the strength and slightly reducing the welding frequency. The total amount of C, B and N
The reason for defining 0.001 to 0.1 wt% is that the total amount is 0.001 wt%
If it is less than 0.1%, the effect cannot be sufficiently obtained, and if it exceeds 0.1% by weight, workability is deteriorated. The reasons for defining the tensile strength and the conductivity in this invention are the same as those in the invention of claim 1.

The invention according to claim 3 is the method of manufacturing an electrode according to claim 1. Although various methods can be considered to disperse the crystallized Cr of the Cu-Cr alloy in the fiber shape with the length direction oriented in the pressing direction, as a method that can be easily realized industrially, cooling with a high reduction in area is possible. There is a method of machining. In this case, since Cr has a larger deformation resistance than Cu, the Cr crystallized product does not form a fiber due to insufficient elongation in low working, and is not sufficiently oriented in the pressing direction, and thus the resulting electrode lacks strength, Life cannot be significantly improved. In the present invention, the reason why the cross-sectional reduction rate in cold working is limited to 90% or more is that if it is less than 90%, the Cr crystallized product cannot be sufficiently expanded into a fiber shape, and the electrode has sufficient strength (800 N / m
m ² or more). The cross-section reduction rate in cold working is required to be 90% or more, preferably 99% or more. The characteristics of the electrode, especially the strength, can be adjusted by the reduction rate of the cross section. In this invention, solid solution Cr is precipitated and the conductivity is restored by the aging treatment. The reason why the aging treatment temperature is specified to be 400 to 600 ° C is that the conductivity does not recover sufficiently below 400 ° C.
This is because, when the temperature exceeds ℃, the Cr crystallized product elongated in the form of fiber is spheroidized and the strength is reduced, and in any case, the electrode life is not significantly improved. When the aging treatment is performed a plurality of times, it is sufficient that at least one of them satisfies the temperature condition.

The invention according to claim 4 is the method for producing an electrode according to claim 2, wherein the copper alloy according to claim 1 is added with a trace amount of C, B and N. It has the same structure as the above, and the same effect.

The electrode of the present invention is particularly suitable for spot welding Al or Al alloy. Al alloys to be welded are Al-Cu series, Al-Mn series, Al-Si series, Al-Mg
System, Al-Mg-Cu system, Al-Mg-Si system, Al-Zn-Mg system, Al-Zn-Mg-
It is a Cu-based Al alloy. The electrode of the present invention is naturally applicable to a rolled steel plate and a galvanized steel plate. As the spot welder that produces the effect using the electrode, a single-phase AC welder, a single-phase rectifier welder, a three-phase low-frequency welder, a three-phase rectifier welder, an inverter welder, and a condenser welder. There are machines, etc.

[0014]

EXAMPLES The present invention will be described in detail below with reference to examples. (Example 1) An alloy having the composition shown in Table 1 was melted to a diameter of 200 m.
It was cast into a cylindrical billet having a length of m and a length of 600 mm. Where C,
The addition of B and N was carried out by adding powders of Cr-C, Cr-B and Cr-N compounds into the molten metal. The obtained ingot is
The electrode was processed by any of the methods shown in. The ingot was reheated at 1000 ° C. for 1 hour, hot extruded to a diameter of 60 mm and then trimmed to a diameter of 56 mm. Next, cold drawing is performed to a diameter of 18 mm (area reduction rate 90%), and then 500 ° C.
Was subjected to aging treatment for 2 hours, then set in the shape of the electrode, and externally cut to form an electrode. The ingot is homogenized at 1000 ℃ for 5 hours and the diameter is 180m.
trimmed to m. Next, cold drawing is performed up to a diameter of 18 mm.
(Cross-section reduction rate 99%), then aging treatment was performed at 500 ° C. for 2 hours, then set up in the shape of the electrode, and this was externally cut to finish the electrode. The ingot was reheated at 1000 ° C. for 1 hour, hot extruded to a diameter of 68 mm and then trimmed to a diameter of 64 mm. Next, cold drawing is performed up to a diameter of 56 mm (23% reduction in area), and then 500 ° C.
After aging treatment for 2 hours, cold drawing is performed again to a diameter of 18 mm (cross-section reduction rate 90%), then 380 ° C.
Was subjected to temper annealing for 2 hours, then set up in the shape of the electrode, and externally cut to finish the electrode. The ingot was reheated at 1000 ° C. for 1 hour, hot extruded to a diameter of 60 mm and then trimmed to a diameter of 56 mm. Next, cold drawing is performed to a diameter of 25 mm (area reduction rate 80%), and then 500 ° C.
Aged for 2 hours, then trimmed to 18mm in diameter,
After that, it was set up in the shape of an electrode, and this was externally cut to form an electrode. The ingot was reheated at 1000 ° C. for 1 hour, hot extruded to a diameter of 60 mm and then trimmed to a diameter of 56 mm. Next, cold drawing is performed up to a diameter of 40 mm (area reduction rate 49%), and then 450 ° C.
After aging treatment for 2 hours, cold drawing is performed again to a diameter of 18 mm (area reduction rate 80%), then temper annealing is performed at 450 ° C for 2 hours, and then it is set up in the electrode shape.
This was trimmed to form an electrode. The ingot was reheated at 1000 ° C. for 1 hour, hot extruded to a diameter of 60 mm and then trimmed to a diameter of 56 mm. Next, cold drawing is performed to a diameter of 18 mm (area reduction rate 90%), and then 650 ° C.
After aging treatment for 2 hours, the electrode shape was set up, and this was externally cut to form an electrode. The ingot was reheated at 1000 ° C. for 1 hour, hot extruded to a diameter of 60 mm and then trimmed to a diameter of 56 mm. Next, cold drawing is performed to a diameter of 18 mm (area reduction rate 90%), and then 350 ° C.
After aging treatment for 2 hours, the electrode shape was set up, and this was externally cut to form an electrode.

The obtained electrodes were examined for (a) conductivity, (b) tensile strength, (c) heat resistance, and (d) electrode life. The results are shown in Table 1. In Table 1, the composition, process (manufacturing method), and shape of crystallized Cr are shown together. For comparison, the same investigation was also conducted for the case where the added amount of Cr was out of the range of the present invention. (B) Conductivity was measured according to JIS H0505. (B) Tensile strength was measured according to JIS Z2241. As the tensile test piece, No. 4 test piece was used according to JIS Z2201. (C) Heat resistance was shown at the maximum heating temperature at which the strength when heated for 2 hours in the temperature range of 180 to 400 ° C. was 90% or more of the strength before heating. (D) Electrode life is 1 mm thick, 30 mm wide, and 200 mm long Al alloy plate
(Al-Mg system, A5182P-O material) was pickled to remove the oxide film on the surface, and two alloy plates were superposed and spot-welded. A single-phase rectification resistance welding machine was used as the spot welding machine. The welding conditions were as follows: welding pressure: 300 kgf, energization time: 5 cycles, welding current: 25000 ± 1000 A (appropriate welding current value at each electrode), welding pitch: 30 mm, and dot speed: 1 point / 2 seconds. The electrode life is measured by peeling the welded part of the spot-welded Al alloy plate with a peel test jig and measuring the major axis and minor axis of the nugget every 10 points with a caliper,
When the average value p becomes less than 4t × 1/2 (however, t is the plate thickness of the material to be welded, 1mm, so p is less than 4mm), or the electrode is cracked or welded and subsequent welding cannot be performed. The number of RBIs until the point In spot welding, the length direction of the crystallized Cr fiber of the electrode is perpendicular to the surface of the Al alloy plate to be welded.

[0016]

[Table 1]

As is clear from Table 1, the products of the present invention (N
o.1 to 9) have electrode life of 5,000 points or more,
It is significantly improved compared to (No.17). In contrast,
In No. 10 of the comparative example product, the crystallized Cr was elongated in the shape of a fiber, but the strength was lowered because the amount of Cr was small. Therefore, the electrode life is better than that of the conventional product, but is clearly inferior to the product of the present invention. Since No. 11 had a large amount of Cr, cracking occurred during cold working and normal processing could not be performed, so production was discontinued. In Nos. 12 and 13, the cross-sectional reduction rate in cold working was less than 90%, the crystallized Cr did not extend into a fiber shape, and therefore the strength was lowered and the electrode life was shortened. In No. 14, the aging temperature was high, and Cr, which had once expanded into a fiber shape, became spherical due to aging, so the strength decreased and the electrode life decreased. N
On the contrary, o.15 had a low aging temperature, so solid solution Cr was not sufficiently precipitated, and therefore the conductivity (heat dissipation) of the electrode was low and the electrode life was shortened. Since No. 16 contained a large amount of B, cracking occurred during cold working and normal processing could not be performed, so production was discontinued. The shape of the fibrous extension of the Cr crystallized product is a string having a substantially circular cross section, and the average value (n = 20) of the ratio L / T of the length L and the diameter T is No. 1 , 2,5
2.7 to 3.0 and other Nos. 3, 4, 6 to 9 were 3.1 to 4.5, and it was recognized that the longer the ratio, the longer the electrode life. Comparative examples Nos. 12 and 13 were about 2.0 to 2.5. A steel plate and a galvanized steel plate were spot-welded using the product of the present invention, and an electrode life of about 20,000 was obtained.

[0018]

As described above, the electrode for spot welding of the present invention contains 10 to 30 wt% of Cr, and the crystallized product of Cr is
Stretched in the pressing direction in a Cu matrix and dispersed in fibers, tensile strength of 800 N / mm ² or more, conductivity of 75% IA
CS or better. Therefore, Al or Al alloy can be spot-welded with a significantly longer electrode life than conventional materials. Further, the electrode can be easily manufactured by defining the conditions. Therefore, it makes a significant industrial contribution.

Claims (4)

(57) [Claims] 1. An electrode for spot welding, which presses a material to be welded and heats it by energizing it for welding, wherein the electrode has a Cr content of 10 to 30.
wt%, the balance consisting of Cu and inevitable impurities.
For spot welding, the crystallized product of is extended in the pressing direction in the pressing direction and dispersed in a fiber shape, and has a tensile strength of 800 N / mm ² or more and an electrical conductivity of 75% IACS or more. electrode. 2. An electrode for spot welding by pressing a material to be welded, heating it by applying electric current, and containing 10 to 30 wt% of Cr, C, B,
0.001 total of 1 or 2 or more selected from N
~ 0.1wt%, the balance consisting of Cu and unavoidable impurities, the crystallized product of Cr in the Cu matrix of the electrode is stretched in the pressing direction and dispersed in a fiber form, the tensile strength is 800 N / mm ² Above, the electrode for spot welding is characterized by having an electrical conductivity of 75% IACS or more. 3. A method for producing an electrode for spot welding, which comprises subjecting a copper alloy containing 10 to 30 wt% of Cr and the balance being Cu and inevitable impurities to hot working, solution treatment, cold working, and aging treatment. A method of manufacturing an electrode for spot welding, wherein the cross-section reduction rate in the cold working is 90% or more, and the aging treatment is performed within a temperature range of 400 to 600 ° C. 4. A total of 0.001 to 0.1 wt% containing 10 to 30 wt% of Cr, and one or more selected from C, B and N.
Including, the hot-working, solution treatment, cold-working, aging treatment on the copper alloy consisting of Cu and unavoidable impurities as the balance is a method for producing an electrode for spot welding, wherein the cross-section reduction rate in the cold working Is 90% or more, and the aging treatment is performed within a temperature range of 400 to 600 ° C.