WO2006004073A1

WO2006004073A1 - Electrode for spot welding

Info

Publication number: WO2006004073A1
Application number: PCT/JP2005/012281
Authority: WO
Inventors: Jun Kurobe; Hiroshi Asada; Shigeo Matsubara; Shuichi Teramoto; Shingo Mukae; Shigeya Sakaguchi; Shigeru Matsuo
Original assignee: Nisshin Steel Co., Ltd.; Nippon Tungsten Co., Ltd.
Priority date: 2004-06-30
Filing date: 2005-06-28
Publication date: 2006-01-12

Abstract

An electrode for spot welding which has a double structure where a core material (3) made of W or Mo is imbedded in a an electrode body (2) wherein the area (S1) of the core material (3) is set to be (0.7 to 3.0) × S0 where S0 is the area of a contacting face (2a) contacting with a material to be welded. Optionally, fine particles are dispersed in the core material (3) made of W or Mo in an amount of 0.5 to 10 volume %. The fine particle comprises an oxide, a nitride, a carbide, a boride or the like of a 2A Group element, a 4A Group element, a 5A Group element, a 6A Group element or a rare earth element. The above electrode for spot welding has the core material made of W or Mo imbedded in the body, which results in the inhibition of the welding or alloying with a plating metal even in the case of the spot welding of a steel plate plated with a zinc-based metal under a high electric current. Consequently, the above electrode can be used as an electrode for spot welding being suitable to the welding of a material being difficult to weld, such as a plated steel plate and an aluminum material, and having a long life.

Description

Specification

Spot welding electrode technology

The present invention relates to an electrode suitable for spot welding of difficult-to-weld materials such as plated steel sheets and aluminum materials. Background art

Spot welding with high work efficiency is frequently used in assembly lines for automobiles, home appliances, etc., and continuous spot welding is performed in mass production lines. For this reason, the electrode for spot welding is subject to repeated high heat and high load and is easily deformed, so a material with high deformation resistance is required. In addition, it is necessary to have excellent electrical conductivity, thermal conductivity, strength, and wear resistance, which are inherent characteristics of resistance welding electrodes.

Against this background, spot welding electrodes are made of copper alloys such as Cu-Cr and Cu-Cr-Zr, and steel materials in which hard particles such as A1203 are dispersed. Cu-Cr alloys are often used with comprehensive consideration of strength and cost. On the other hand, zinc-plated steel plates such as zinc plating and zinc alloy plating are increasingly used as materials for automobiles and home appliances to improve durability. Compared with spot welding of cold-rolled steel sheets, a higher current flows in spot welding of zinc-based plated steel sheets, so that the electrode tip is exposed to more severe conditions. At the tip of the electrode during welding, the plating layer components such as Zn and A1 as well as the base metal component such as Fe alloy with the main component Cu of the electrode to form an alloy reaction with Cu-Zn and Cu-Zn-Al- Intermetallic compounds such as Fe are formed. The produced intermetallic compound is very brittle and peels off by the pressure applied during welding, resulting in an increase in the electrode tip diameter and a decrease in current density. Thus, the disadvantage of welding plated steel sheets is that the electrode life is shorter than when welding cold-rolled steel sheets such as plain steel and stainless steel.

Aluminum material is sometimes used to reduce weight, but in this case assembling The welding line enters the welding line. Aluminum material is a difficult-to-weld material with high thermal conductivity, and it is difficult to maintain the molten state necessary for joining. Therefore, it is necessary to make the molten state with a rapid temperature rise, pressurize at once, and perform spot welding. For rapid temperature rise, it is necessary to increase the welding current. If the temperature rises excessively as the welding current increases, oxides and intermetallic compounds are generated as a result of the chemical reaction between the electrode material Z and the workpiece. In addition, A1 is easily welded to the electrode. Similar welding can be seen in spot welding of A1 plated steel sheets.

Therefore, with the aim of prolonging the life of the electrodes, W-Mo alloys and W-Mo alloy electrodes added with various doping materials, and double-structured electrodes with a core material embedded in the center of the electrode tip have been proposed. Yes.

For example, a welding electrode made of a W-Mo alloy containing 10 to 10 ppm of K in the form of oxide, nitride, simple metal, carbide, boride, etc. is disclosed in Japanese Patent Application Laid-Open No. 10-291078. , Nitrides, simple metals, carbides, borides, etc., rare earth elements such as La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y, etc. ~: A welding electrode produced from a W-Mo alloy containing 10.0% by mass is introduced in JP-A-10-314957. However, even when welding electrodes made of W-Mo alloy containing K or rare earth elements are used for spot welding of sub-sharp steel plates, especially Zn-Al-Mg alloy steel plates, The alloying reaction cannot be sufficiently suppressed, and there is a limit to the extension of electrode life. In addition, an electrode with a single contact surface made of W or Mo is prone to cracking due to heat and impact during repeated use, so the life is greatly extended compared to an electrode made of alumina-dispersed Cu alloy. I can't expect it.

In the welding electrode described in Japanese Patent Publication No. 63-33949, the electrode body is made of a high-strength, high-conductivity copper alloy, and alloyed with the welded material at 20 to 70% by area on the contact surface where the welded material hits. A composite material such as A1 ₂ 0 ₃ dispersed copper alloy that is difficult to weld is embedded. However, if the ratio of the core material to the contact surface is small, Cu or Cu alloy around the core material is easily diffused and alloyed with the plated metal, and the electrode tip diameter is easily increased. Since the core material is also made of a copper alloy, it is difficult to avoid alloying with plated metal even if the core material occupies a large proportion of the contact surface.

The welding electrode disclosed in Japanese Patent Laid-Open No. 4-4984 is a welded body of an electrode body made of Cu or Cu alloy. The core material made of W or Mo, which has excellent electrical and thermal conductivity and higher strength than the electrode body, is embedded in the surface where the material comes into contact at 5 to 20 area%. In this case as well, if the ratio of the core material to the contact surface is relatively small, the Cu or Cu alloy around the core material is likely to diffuse and alloy with the plating metal, and the electrode tip diameter tends to increase. W and Mo are materials that are difficult to wet with the plated metal. However, if the contact surface of the copper alloy around the core is wide, the tip diameter of the electrode as a whole tends to increase.

Japanese Unexamined Patent Publication No. 64-62287 discloses a welding electrode having a double structure comprising an outer peripheral portion made of highly conductive Cu or Cu_Cr alloy and a central portion made of non-conductive material such as ceramics. Has proposed. However, if the ceramic used for the core material is brittle, the nugget formation becomes unstable due to easy peeling due to cracking when the electrode is pressed.

Japanese Examined Patent Publication No. 59-41838 introduces an electrode in which a chip composed of a sintered body of W, W alloy, Mo, Mo alloy is fitted to a retaining ring, but has high strength and toughness precipitation hardening. Type stainless steel is used for the retaining ring, and the electrical conductivity of the retaining ring is poor. Moreover, the manufacturing cost of the electrodes themselves is increasing. Disclosure of the invention

The present inventors investigated and examined various effects of W and Mo embedded in the contact surface of the welding electrode in contact with the material to be welded having a large effect on the diffusion reaction and alloying reaction during spot welding. As a result, we found that diffusion and alloying reactions can be effectively suppressed when a W or Mo core material is embedded in the contact surface of the welding electrode with a large area ratio. The present invention has been completed based on such knowledge, and zinc-plated steel sheets such as Zn-Al and Zn-Al-Mg, aluminum-based plated steel sheets, and aluminum materials are spot-welded at a high current. In particular, an object of the present invention is to provide a spot welding electrode capable of spot welding under stable conditions over a long period of time.

The present invention is an electrode for spot welding in which a core material made of W, W alloy, Mo or Mo alloy is embedded in a contact surface that contacts a workpiece of an electrode body made of Cu or Cu alloy, The area ratio of the core material to the area is set in the range of 0.7 to 3.0.

For the core material W, W alloy, Mo or Mo alloy, 2A group element, 4A group element, 5A A dispersion strengthened material in which at least one kind of fine particles selected from oxides, nitrides, carbides and borides of group elements, group 6A elements or rare earth elements are dispersed can be used. Specifically, one or more fine particles selected from oxides of Be, Mg, Ca, Sr, Ti, Zr, Y, and Ce were dispersed in W, W alloy, Mo, or Mo alloy. A core material is made of a composite material. The dispersion ratio of the fine particles is selected in the range of 0.5 to 10% by volume, and further, fine particles having an average particle diameter of 2 μιη or less are preferably dispersed.

This welding electrode is of course applicable to spot welding of general steel plates, and can also be used for spot welding of aluminum-based steel plates and aluminum materials that are considered difficult to weld. In the spot welding electrode of the present invention, the electrode body is made of Cu or a Cu alloy, and a core material made of W, W alloy, Mo or Mo alloy is provided on the contact surface of the electrode body that contacts the material to be welded. Embedded. By setting the area ratio of the core material to the contact surface to 0.7 to 3.0, the contact area between the electrode body made of Cu or Cu alloy, which is easily alloyed with the plating metal, and the material to be welded is reduced. This suppresses welding and alloying of the electrode and plated metal, prevents cracking due to pressurization and heat generation during welding, extends the life of the electrode, and makes it possible to spot zinc-based plated steel sheets with high productivity. Can be welded. In particular, the life of the electrode can be greatly extended by dispersing fine particles having an average particle size of 2 μιη or less in a proportion of 0.5 to 10% by volume. In addition, the electrode of the present invention is relatively simple in structure, so that the manufacturing cost is low. Brief Description of Drawings

FIG. 1 is a diagram schematically illustrating the structure of the spot welding electrode of the present invention.

Fig. 2 is a graph showing the relationship between the area ratio of the contact surface and electrode life of the electrode for spot welding used in Example 1. BEST MODE FOR CARRYING OUT THE INVENTION

The inventors of the present invention have repeatedly studied various kinds of experiments regarding the material shape of the electrode when spot welding a zinc-based steel sheet. . First, we focused on a double-structured electrode in which a core made of high-strength W or Mo with excellent electrical and thermal conductivity is embedded in the surface of the electrode body made of Cu or Cu alloy that contacts the workpiece. The electrode life was investigated by spot-welding zinc-based steel sheets using welding electrodes with various changes in the size of the electrode constituent material and the core and surrounding materials.

As a result, in the spot welding electrode using Cu or Cu alloy for the electrode body and W, W alloy, Mo or Mo alloy for the core material, the area of the contact surface contacting the material to be welded is So, and the core material When the area is Si, it was confirmed that setting SiZSo = 0.7 to 3.0 is effective for extending the life of the electrode.

The reason why the electrode life of the double-structured embedded electrode is long is that, even if welding points are stacked, the embedded core material secures a current path with a constant area, and a stable nugget can be formed. For this reason, the material of the core material is preferably a hard material such as W or Mo that is difficult to alloy with the plating metal.

Therefore, in the welding electrode in which W is used as the core material and the electrode body surrounding the core material is made of pure Cu, the diameter of the core material is changed variously, and the contact status of the pure Cu surrounding material to the welded material The difference, that is, the relationship between the area ratio of the core Z contact surface and the electrode life was investigated. Since Mo is a metal that behaves almost the same as W, the results obtained with W can be applied to Mo, W alloys, and Mo alloys.

The welding conditions were such that the initial nugget diameter for continuous spot welding, that is, the nugget diameter at the first spot was the same for all electrodes.

The details will be described in the examples described later. In the double-structured electrode 1 (Fig. 1), if the diameter of the contact surface 2a that contacts the material to be welded is a, the area of the contact surface So is So = a ² 4, although the area Si of the diameter of the core 3 embedded in the circumferential囲材2 and b core is represented by Si = JTB ² 4, the area of the area Si to the area So ratio SiZSo (= b ² Za ² ) needs to be set in the range of 0.7 ~ 3.0. When the area Si is larger than the area So, the diameter b of the core material 3 is larger than the diameter a of the contact surface 2a, the tip of the electrode including the core material 3 is ground, and only the core material 3 is present on the contact surface 2a. This means that the tip shape is adjusted.

W, W alloy, Mo or Mo alloy has a lower alloying reactivity to the plating metal than Cu. Therefore, when the diameter b of the core 3 is larger than the diameter a of the contact surface 2a, the Cu surrounding material 2 An alloying reaction occurs between Cu and the metal with no contact with the metal. I don't know. Area of SiZSo≥0.7 If Si core material 3 is used, the surrounding material 2 makes little contact with the metal, but due to the small contact area, deformation due to alloying of the surrounding material 2 with the metal causes an increase in diameter. The tip shape of the electrode as a whole is not deformed.

Moreover, W, W alloys, Mo and Mo alloys are less susceptible to alloying reactions with metal plating than copper materials in which oxides are dispersed, and have high strength at room temperature and high temperature. Therefore, even if SiZ So = 0.7, the electrode life is expected to be extended. However, when the area ratio SiZ So exceeds 3.0, the cooling action of the core material 3 by the surrounding material 2 becomes very small, and the amount of metal deposited on the surface of the core material 3 increases, resulting in an electrode Z welded material. In the meantime, the electrical resistance becomes too high, making it difficult to form nuggets. The area ratio SiZ So is preferably in the range of 1.0 to 2.0.

The double structure in which the core material made of W, W alloy, Mo or Mo alloy is surrounded by the electrode body made of Cu or Cu alloy also prevents cracking and peeling that tends to occur on the contact surface of the welding electrode. It is valid.

That is, the contact surface of the welding electrode generates heat at the time of spot welding and thermally expands around the contact surface, but the thermal expansion is in the vicinity of the contact surface because the temperature change is rapid and the thermal conductivity of W and Mo is low. The thermal expansion does not occur in the vicinity of the outer periphery where heat is not easily transmitted. Thermal expansion that differs between the contact surface and the outer periphery is the cause of the generation of thermal stress, and as a result, it induces cracks and separation near the contact surface. Defects caused by this difference in thermal expansion are prevented by making the contact body and its surroundings W or Mo, which are high melting point materials, and making the electrode body with Cu or Cu alloy with good thermal conductivity. it can.

In the case of an electrode made of an electric current sintered body of W, an electrode made of W in which about 10 to 200 ppm of K (power lium) is doped in the form of oxide, nitride, metal K, carbide or boride is often used. Yes. In this specification, the W core material is also used in the sense of including a K-type electric current sintered body.

W and Mo used as the core material also have a low alloying reactivity with metal plating compared to Cu alloys, but it is not completely absent. In addition, since W and Mo are hard, there are also disadvantages such as cracking due to impact during pressurization, and so on. Therefore, IW alloy, Mo or Mo improved so as to have low alloying reactivity with plating metal and excellent impact resistance. When an alloy is used for the core material, the life of the electrode is expected to be extended.

Improvement measures include: Group 2A elements such as Be, Mg, Ca and Sr; Group 4A elements such as Ti, Zr and Hf; Group 5A elements such as V, Nb and Ta; Group 6A elements such as Cr, Mo and W Alternatively, it is preferable to disperse at least one kind of fine particles selected from oxides, nitrides, carbides and borides of rare earth elements containing Y in a ratio of 0.5 to 10% by volume. The fine particle dispersion is also effective in suppressing fine cracks that tend to occur on the contact surface and in the vicinity of the contact surface. Since these fine particles have poor reactivity with A1 and Zn, the metal attached to the core W or Mo is difficult to wet during spot welding, and the alloying reaction between W or Mo and the metal attached is suppressed. .

In particular, in the welding of Zn-Al-Mg alloy-plated steel sheets containing Mg that easily oxidizes, MgO produced during spot welding accumulates at the electrode tip, increasing the resistance between the electrode and the plated steel sheet. As a result of overheating of the welded part, there is a concern about further MgO generation and deposition. However, with W or Mo electrodes in which fine particles are dispersed, MgO adhesion and deposition can be suppressed, so that welding conditions are stabilized over a long period of time.

In order to reliably suppress plating metal welding, it is necessary to pay attention to the physical properties of both the fine particles dispersed in the electrode and the metal component contained in the plating layer. For example, oxides such as Be, Mg, Ca, Sr, Ti, Zr, Y, and Ce have a standard free energy of formation lower than or equal to that of MgO, so spot the Zn-Al-Mg alloy steel plate. During welding, Mg contained in the molten or semi-molten plating layer is not oxidized by the reduction reaction of the metal oxide. As a result, the formation and deposition of MgO is suppressed, and the core material made of W, W alloy, Mo or Mo alloy is hardly wetted by the molten plated metal, and the welding of the plated metal is surely suppressed.

La203, BeO, SrO, Ce02, Ce203, Zr02, MgO, CaO, Y2O3, TiC, WC, TaC, ZrC, HfC, ZrB2, ZrN, TiN, etc. have a high melting point and react with the plating metal. Due to its particularly low property, the strength of the sintered body can be maintained even when dispersed in W or Mo, and it is suitable for extending the life of the electrode. Furthermore, the fine particles dispersed in W, W alloy, Mo or Mo alloy exert the effect of pinning the propagation of dislocations when the core material is impacted, resulting in excellent impact resistance and cracking. Control the occurrence of In particular, fine particles with a melting point of over 2400 ° C do not melt or segregate during the sintering of the core material, thus improving the quality stability of the core material. It is also effective in

In order to obtain an improvement effect, it is preferable to disperse the fine particles by 0.5% by volume or more. However, excessive dispersion exceeding 10% by volume greatly reduces the electrical conductivity of W, W alloy, Mo or Mo alloy, and during resistance welding. The temperature at the tip of the electrode becomes too high, and on the contrary, an alloying reaction is likely to occur. When a large amount of non-metallic fine particles are contained, the sintered body becomes brittle and it becomes difficult to process into a desired shape by swaging or the like. Preferably, the fine particles are dispersed in the range of 0.8 to 3.0% by volume.

Further, the non-metallic fine particles such as CeC> 2 contained in W or Mo preferably have a particle size of ΙΟμιη or less. If particles larger than ほど μηι are dispersed, they tend to break down due to the difference in thermal expansion coefficient. Considering the action of fine particles that stop the propagation of cracks, the larger the number of fine particles, the more effective even with the same amount of dispersion. When the average particle size exceeds ΙΟμπι or the amount of dispersion is less than 0.5% by volume, the property improvement by fine particle dispersion is not sufficient. In particular, in order to improve the electrode life, a fine particle dispersion having an average particle diameter of 2 μπι or less is suitable.

W or Mo for the core material is used as each metal alone or as an alloy of 5 to 95 mass%.

In general, W, W alloy, Mo or Mo alloy is manufactured by sintering method. The W, W alloy, Mo or Mo alloy used as the core material in the present invention is also manufactured by a sintering method as usual. The sintering raw material is not limited to pure W that does not contain impurities, but can also be doped tungsten containing about 10 to 200 ppm K, which is used for filament electrodes, etc., and a small amount of metal such as Re is alloyed. A W-based alloy may be used.

Reduced atmosphere of oxide powder of W and / or Mo with addition of fine particles of 2A group element, 4A group element, 5A group element, 6A group element, rare earth element oxide, nitride, carbide, boride as required After heat-treating, the obtained powder is formed into an appropriate shape, pre-sintered and electro-sintered, and then subjected to swaging and centerless polishing to obtain a rod having a desired diameter. Instead of the oxide powder, metal W and / or metal Mo powder may be used as a raw material, and if necessary, fine particles may be added and molded as it is.

Alternatively, a powder raw material having a predetermined composition is cold isostatically pressed into a cylindrical shape, and then subjected to current sintering in a hydrogen atmosphere. The obtained sintered body is hot-rotated forged, then cut and processed. A method of forming a core material having a predetermined shape may be used. The powder raw material filled in the sealed container can be cold isostatically pressed, sintered in a hydrogen atmosphere, and further sintered into a sintered body by hot isostatic pressing.

The surrounding material (electrode body) is made of ordinary Cu or Cu alloy such as commercially available pure Cu, Cu-Cr alloy, Cu-Cr-Zr alloy. Furthermore, a dispersion strengthened Cu alloy in which fine particles such as AI2O3 are dispersed can be used as the surrounding material.

Conventional methods can be used for embedding the core material in the surrounding material made of Cu or Cu alloy. For example, the core material may be press-fitted into the hole formed in the surrounding material, or may be inserted through the brazing material. Alternatively, shrink fitting may be used, or cold forging may be performed after the core material is wrapped with steel. As long as the core material and the surrounding material are closely joined, there will be no problem in terms of electrical conduction and heat conduction, but in order to obtain good heat conduction and joining strength, it is preferable to integrate them by the melting method. . ,

After forming a double-structured electrode structure, grind the tip and adjust it to the desired tip shape such as R shape, shape, or CF shape. Next, the present invention will be described specifically by way of examples.

Example 1

An adhesion amount per side: 30 gZm ² and a Zn-Al-Mg alloy-plated steel sheet with a thickness of 0.7 mm provided with a Zn-6% Al-3% Mg alloy-plated layer was used as the material to be welded. The two welded materials were overlapped, and the Zn-Al-Mg alloy-plated steel sheet was welded by spot welding, which was sandwiched between the upper and lower electrodes under the conditions shown in Table 1 and continuously dotted.

For the spot welding electrode, we used a double-structured electrode in which a core material that had been swept and centerless polished after being sintered with current of 99.95% pure W powder was embedded in pure Cu surrounding material. The welding electrode is a DR type with an abutment surface diameter of 6 mm and an overall diameter of 16 mm. An arc with a radius of curvature of 40 mm is placed on the abutment surface diameter of 6 mm, and an arc with a radius of curvature of 8 mm on the other side. It is attached to the part. Table 1: Continuous dot test

The nugget diameter formed by spot welding was measured, and the life of the electrode was determined by assuming that the nugget diameter was less than 4 ^ 3.35 (t: plate thickness) as poor welding.

As shown in the survey results in Table 2, the area ratio between the core material and the contact surface SiZSo is 0.7 to 3.0, and the W core material is embedded in the electrode body made of Cu or Cu alloy. In this case, the shape of the electrode tip shape did not change even after spot welding, and the electrode life was longer than that of the integrated 1% Cr-Cu alloy electrode.

In contrast, in the electrodes of test numbers 1 and 2 with an area ratio Si / So of less than 0.7, the pure Cu of the surrounding material alloyed with the metal and deformed due to an alloying reaction, and the tip surface was enlarged. It was not seen. When the tip of the electrode was observed after spot welding, the plated metal was attached to the surrounding material, and an alloy layer with the plated metal was detected in the cross section of the electrode tip in a wide range of the surrounding material.

Even with the electrodes of test numbers 8 and 9 where the area ratio SiZSo exceeded 3.0, the electrode life was not extended. In this case, the cooling ability of the core material by the surrounding material is small, and it seems that the core material part has become too hot. In the observation of the tip, a large amount of plated metal was detected. Table 2: Effects of core diameter and area ratio on electrode life

Example 2

Except using welding electrode 16 mm,: Various using CeO ₂ powder having a particle diameter 0.5μηι in proportion to the core material a sintered-forging dispersed in W, the entire core diameter was variously changed diameter Under the same conditions as in Example 1, continuous spot welding was performed on a Zn-Al-Mg alloy-plated steel sheet. Table 3 shows the results of obtaining the electrode life by the same evaluation method as in Example 1.

As is clear from Table 3, cores made from W-based composites with Ce02 dispersed in 0.5 to 10% by volume were embedded in Cu electrode bodies with an area ratio of Si / So = 0.7 to 3.0. ： The electrode of 17 and 20-22 has less shape change at the electrode tip after spot welding compared to the electrode made of l% Cr-Cu alloy. It was. The electrode life was also as long as 10,000 points or more.

Ce0 _2: 0.5 area a W-based composite material-made core material of less than% by volume ratio SiZSo: 1.0 Test buried in the Cu electrode body at No.23, in 24 of the electrode, the core material effect of embedding effectively work Itatame The electrode life exceeded 10000 striking points. As for the amount of deposited metal, a larger amount of plated metal was deposited than in Test Nos. 13 to 17 and 17 to 20.

Area ratio Si / So.: be 1.0, in the electrode of the test No.25 with W-based composite material or we fabricated core material CeO ₂ is excessively distributed, than the effect of the core material embedded

Decreasing electric conductivity due to processing dispersion of Ce0 ₂ appears more, and the amount of metal deposited on the electrode tip is larger than that of l% Cr-Cu alloy electrode, and nugget formation is not performed sufficiently The electrode life was short.

Furthermore, even when a core material made of a W-based composite material with 1% by volume of Ce02 embedded in a Cu electrode body, the area ratio SiZSo falls outside the range of 0.7 to 3.0 No.ll -12 and 18 to: in 19 of the electrode, but was shorter electrode life than l% Cr-Cu alloy electrode, youth electrodes life than the CeO ₂ the embedded W-made core material not dispersed electrode (example 1) There was a tendency to extend a thousand.

Table 3: Effects of core material, size, and area ratio on electrode life

The underline indicates that it is outside the scope specified in claim 4. Example 3

For spot welding of the same Zn—Al—Mg alloy-plated steel plate as in Example 1, a welding electrode in which a TaC-dispersed W sintered body was embedded in a pure Cu electrode body was used.

For the core material, we prepared mixed powders in which TaC powder with a particle size of 0.05-3μιη was dispersed in various proportions of W powder with a purity of 99.95%. Diameter produced by centerless polishing: 6mm TaC dispersion W sintered body It was used. Pure Cu melted in a reducing atmosphere and TaC dispersion W sintered body are integrated into a DR type with an abutment surface diameter of 6mm and an overall diameter of 16mni. An arc with a radius of curvature of 40mm is a contact surface diameter of 6mm. In this part, a welding electrode with a radius of curvature of 8mm was attached to the other part.

Two materials to be welded were sandwiched between welding electrodes placed one above the other and spot welded under the continuous spot test conditions shown in Table 1. The nugget diameter formed by spot welding was measured, and the electrode life was determined by assuming that the nugget diameter was less than 4 = 335 (t: plate thickness) as a poor weld. As is apparent from the measurement results in Table 4, when an electrode in which TaC fine particles with an average particle size of 2 μηι or less are dispersed in a proportion of 0.5 to 10% by volume is used, a significantly longer electrode life can be obtained. It was. Even when the electrode cross section was observed, the MgO deposition was very low. Since the deposition of MgO is small, the increase in resistance between the electrode and the plated steel sheet due to MgO can be suppressed, and it seems that welding with the plated metal is difficult to occur. The significant increase in electrode life is due to the synergistic effect of the TaC fine particles dispersed in the W material, which suppresses wetting with the plated metal, and the suppression of crack generation and propagation near the contact surface. Inferred.

On the other hand, in Test No. 34 in which 12% by volume of TaC fine particles were dispersed, the electrode life decreased, and a relatively large amount of MgO was detected in the observation of the electrode cross section. The large amount of MgO deposition is thought to be due to the excessive dispersion of fine particles in the W material, which increases the electrical resistance of the W material itself, increases the amount of heat generated between the electrode steel plates, and reduces the wetting suppression effect due to the dispersion of fine particles. It is done.

In Test No. 29 in which TaC fine particles having an average particle diameter of 3 μιη were dispersed, the electrode life was relatively short as compared with Test Nos. 26 to 28. The short electrode life seems to be because the dispersed fine particles are few in number, so that the effect of suppressing the generation and propagation of cracks in the vicinity of the contact surface could not be fully exhibited.

In Test No. 30, although the electrode life was extended, the amount of fine particles dispersed in the W material was small, so the wetness between the plating component and the electrode was large, and a relatively large amount of MgO was deposited. It is thought that the result of the increase in resistance between the electrode Z-plated steel sheets due to the deposition of MgO appears as a weld with the plated metal.

Thus, the fine particles dispersed in the W material have a suitable size and amount of dispersion, It can be understood that the intended purpose cannot be achieved unless the size and amount of dispersion are appropriate. Table 4: Effects of TaC fine particle dispersion and particle size on electrode life

Underline indicates that it is outside the scope defined in claim 5. Example 4

Instead of TaC, a W-based sintered material in which various fine particles are dispersed is used as a welding electrode embedded in a pure Cu electrode body in the same manner as in Example 3, and two Zn-Al-Mg alloy-plated steel sheets are continuously used. Spot welding was performed and the electrode life was investigated.

As can be seen from the results of the investigation in Table 5, when an electrode in which 0.5 to 10% by volume of fine particles having an average particle diameter of 2 μιη or less were dispersed in W material was used, the electrode life was greatly extended. The extension of the electrode life was effective regardless of the type of fine particles, as long as it was a compound of a Group 2 element, a Group 4 element, a Group 5 element, a Group 6 element, or a rare earth element.

Table 5: Relationship between fine particle type, dispersion, particle size and electrode life

Example 5

A1 plated steel sheet with a thickness of 0.8mm and adhesion per one side of 30gZm ² was used as the material to be welded. Except for the conditions shown in Table 6, continuous spot welding was performed using the same electrode as that used in Example 3, and the electrode life was investigated.

Table 6: Continuous spot test (Welded material: A1 steel plate)

As seen in the survey results in Table 7, TaC fine particles with an average particle size of 2μπι or less When an electrode dispersed in 0.5 to 10% by volume in the material is used, a significantly longer electrode life is obtained even with the A1 plated steel sheet, which is considered difficult to weld, and the effect of dispersing TaC fine particles can be confirmed. Table 7: Effects of TaC fine particle dispersion and particle size on electrode life

(Welded material: A1 plated steel plate)

Example 6

Using the same welding electrode as in Example 3, a 5000 series automotive aluminum plate with a thickness of 1.0 mm was continuously spot-welded under the conditions shown in Table 8, and the electrode life was investigated in the same manner. Even when spot welding of aluminum material, a significant improvement in electrode life is achieved by dispersing fine particles with an average particle size of 2μπι or less in the W material of the core material, as shown in the survey results in Table 9. It was. Table 8: Continuous spot test (Material to be welded: A1 plate)

Table 9: Effect of TaC fine particle dispersion and particle size on electrode life

(Welded material: A1 plate)

Underline indicates that it is outside the scope defined in claim 5.

Claims

The scope of the claims

1. It has a double structure in which a core made of W, W alloy, Mo or Mo alloy is embedded in the contact surface of the electrode body made of copper or copper alloy that contacts the workpiece, and the area of the contact surface Is an electrode for spot welding, characterized in that the area ratio Si / So is in the range of 0.7 to 3.0, where is the core area and Si is the core area.

2. At least one kind of fine particles selected from oxides, nitrides, carbides and borides of 2A group elements, 4A group elements, 5A group elements, 6A group elements or rare earth elements are added to W, W alloy, Mo or Mo alloy. 2. The spot welding electrode according to claim 1, wherein a core material is made of a dispersed composite material.

3. Core with a composite material in which one or more fine particles selected from oxides of Be, Mg, Ca, Sr, ΊΪ, Zr, Y and Ce are dispersed in W, W alloy, Mo or Mo alloy. 2. The electrode for spot welding according to claim 1, wherein the material is made.

4. The electrode for spot welding according to claim 2 or 3, wherein the fine particles are dispersed at a ratio of 0.5 to 10% by volume.

5. The spot welding electrode according to claim 4, wherein the average particle diameter of the fine particles is 2 μπι or less.