JP2015221935A - Tungsten-molybdenum alloy electrode material for resistance welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a W-Mo alloy electrode material for resistance welding which allows life extension of electrodes even when welding is conducted with a large current.SOLUTION: A W-Mo alloy electrode material for resistance welding consists of a sintered body formed by blending pure W particle powder and pure Mo particle powder, preferably with a purity of 99.9% and an average particle size of 0.25-50 μm for the individual powders, so as to yield an Mo content of 37.5-87.5 mass% and sintering the resultant blend e.g. at a pressure of 1 GPa or higher and a temperature of 1,000°C or higher for 10 min. The relative density of the sintered body is 98.5% or higher, and the electrode material for resistance welding allows electrification of a large current, e.g. a 10,000A or higher welding current. The electrode material for resistance welding can be sintered by forming raw powders of a fine W particle and a Mo particle, e.g. of an average particle size of 4 μm or smaller, into a pressure powder molding, heat-treating the pressure powder molding in an atmosphere of a vacuum of 10Pa or lower or an atmosphere replaced with N gas, Ar gas, etc. at 450-1,200°C for 30 min or longer prior to sintering to purify the surface of the particle powders and sintering at relatively low pressure and temperatures.

Description

  The present invention relates to a tungsten (W) -molybdenum (Mo) alloy electrode material used for resistance welding, and in particular, even when welding is performed with a large current, the generation of cracks and deformation due to current impact is suppressed, thereby It is related with the W-Mo alloy electrode material for resistance welding which aimed at lifetime extension.

In resistance welding, welding materials made of metal materials are overlapped, and the overlapped portions are sandwiched between a pair of resistance welding electrodes and a current is applied while being strongly pressed, whereby electricity generated in the overlapped welding materials is generated. This is a welding method using resistance heat as a heat source. The amount of heat generated in this resistance welding is mainly governed by the current value, the energization time and the specific resistance of the material.
As resistance welding electrodes, current flows between the electrodes and presses the material to be welded at a high temperature, so it is difficult to be deformed at high temperatures and pressures, has excellent thermal and electrical conductivity, and has thermoplastic deformation. There are demands for properties such as being less likely to occur, being difficult to alloy with the material to be welded (or the plating material covering it), and being excellent in oxidation resistance.
In order to satisfy these requirements, a number of resistance welding electrode materials have been developed so far.

For example, Patent Document 1 is excellent in thermal conductivity and specific resistance, and excellent in reactivity with galvanizing and the like, but on the other hand, it solves the problem of the tungsten electrode that is brittle and easily cracks. Therefore, a chip main body made of tungsten, molybdenum or an alloy thereof is made of a metal having a relatively high strength and toughness in a temperature range from room temperature to its highest temperature (for example, SUS630 steel which is a precipitation hardening type stainless steel). An electrode for resistance welding provided with an electrode tip fitted to a holding ring has been proposed.

Patent Document 2 describes W-Mo having a weight ratio of W5 to 95% and the balance being substantially made of Mo for the purpose of providing a long-life resistance welding electrode material having strength. In resistance welding electrodes made of an alloy material, it has been proposed that the W-Mo alloy material contains 10 to 100 ppm of potassium.

Patent Document 3 discloses a sintered alloy of any of tungsten and molybdenum in which a fibrous structure is formed by rolling in order to enhance the durability of the electrode and improve the impact resistance and fracture resistance of the electrode. A resistance welding electrode is proposed in which an electrode material for resistance welding is formed and the end surface of the fibrous structure of the electrode material is a welding surface that clamps the workpiece.

Further, Patent Document 4 contains 10 ppm or more and 200 ppm or less of potassium in order to provide an electrode material for resistance welding having excellent durability and high strength, high toughness, and high recrystallization temperature, and the balance is substantially the same. It has been proposed to form a resistance welding electrode from a tungsten alloy, which is typically tungsten.

Moreover, although what is shown by patent document 5 is an electrode for fusing welding, as an electrode for fusing welding to which heating and pressurization are repeatedly applied, it suppresses the degranulation wear and loss at the tip, and has durability. In order to stably increase the electrode, the electrode of the dual structure electrode in which an electrode core material based on W or Mo or an alloy based on them is attached to the tip of an electrode body made of Cu or Cu alloy Fibrous structure that has been subjected to sintering, swaging, and annealing heat treatment as the core material, and has an average particle diameter of 50 μm or more and an axial ratio extending to an aspect ratio of 1.5 or more. It has been proposed to use W or Mo having the above or an alloy based on them as an electrode material for fusing welding.

Japanese Patent Laid-Open No. 55-109583 Japanese Patent Laid-Open No. 10-291078 JP 2000-158178 A JP 2004-277810 A JP 2008-73712 A

As electrode materials for resistance welding, it is difficult to deform at high temperatures and high pressures, it has excellent thermal and electrical conductivity, it is difficult to cause thermoplastic deformation, it has excellent thermal shock resistance, and the material to be welded or this In recent years, in addition to this, in order to increase the efficiency of welding work, improve productivity, etc., it is difficult to alloy with the plating material to be coated and it has excellent oxidation resistance. In resistance welding using a large current, an electrode material that can withstand long-time use has been demanded.
Conventionally, a tungsten-based material has been suitably used as a resistance welding electrode material. However, using a conventional tungsten-based material, for example, a large current of 10,000 A or more (for example, 10,000 to 55000 A) is passed to be welded material. When resistance welding is performed for a long time, deformation of electrode material due to generation of high heat under pressure, breakage / defect of electrode material due to thermal shock, welding phenomenon between welded material and electrode For this reason, the life of the electrode becomes very short, and it is difficult to carry out continuous resistance welding for a long time.
Therefore, there is a demand for a resistance welding electrode material having a long electrode life even in resistance welding using a large current.

  The inventors of the present invention have conducted extensive research to provide a resistance welding electrode material having a long electrode life in resistance welding using a large current. Surprisingly, tungsten (W) produced by sintering has been surprisingly studied. In an electrode material for resistance welding made of an alloy of molybdenum and molybdenum (Mo) (hereinafter also referred to as “W-Mo alloy”), by appropriately adjusting the structure of the sintered body, thermal conductivity / electric conduction Excellent resistance to thermal shock and plastic deformation, no occurrence of welding with the material to be welded, and continuous use for a long time even under high current conditions of 10,000 to 55000 A It has been found that a W-Mo alloy electrode material for resistance welding can be obtained.

  That is, according to the W-Mo alloy electrode material for resistance welding of the present invention, not only is it possible to perform welding in a short time to minimize the thermal effect on the workpiece, but also excellent thermal conductivity, Plastic deformation due to thermal shock is unlikely to occur, it has excellent reactivity with materials to be welded, coatings and rust preventives, and it is difficult to generate welding and oxidation, and stable welding can be performed. It has been found that since it has fatigue resistance due to high pressure / thermal shock and can be mass-produced by continuous shots, the life of the electrode material for resistance welding can be extended.

The present invention has been made based on the above findings,
“(1) Tungsten-molybdenum alloy electrode material for resistance welding comprising a tungsten-molybdenum alloy sintered body obtained by sintering pure tungsten particle powder and pure molybdenum particle powder, and the Mo content in the alloy sintered body Is a tungsten-molybdenum alloy electrode material for resistance welding, wherein the alloy sintered body has a relative density of 98.5% or more.
(2) The tungsten-molybdenum electrode material for resistance welding according to (1) above, wherein the Mo content in the alloy sintered body is 50 to 75% by mass.
(3) The pure tungsten particle powder and the pure molybdenum particle powder have a purity of 99.9% by mass or more and an average particle size of 0.25 to 50 μm, respectively (1) and (2) A tungsten-molybdenum alloy electrode material for resistance welding as described in 1.
(4) The tungsten-molybdenum electrode material for resistance welding is used as a resistance welding electrode material in which a welding current of 10000 A or more is used, according to any one of (1) to (3), Tungsten-molybdenum electrode material for resistance welding. "
It has the characteristics.

The “average particle size” in the present invention means the particle size (cumulative median diameter) at an integrated value of 50% in the particle size distribution obtained by the laser diffraction / scattering method (microtrack method) for the powder before sintering. Means.
The “relative density” in the present invention means the ratio of the density of the sintered tungsten-molybdenum alloy measured by the Archimedes method to the theoretical density of the alloy determined by the content ratio of tungsten and molybdenum.

  The present invention will be described in detail below.

In the present invention, pure W particle powder and pure Mo particle powder are sintered to produce a W-Mo alloy sintered body. When the purity of W or Mo is less than 99.9% by mass, Due to the impurity components contained in W and Mo under the sintering temperature, the sinterability of the W-Mo alloy sintered body tends to vary, and the material of the W-Mo alloy sintered body tends to be heterogeneous. Therefore, when this is used as an electrode material for resistance welding, it tends to cause inconveniences such as breakage, chipping, and welding of the material to be welded. Therefore, the purity of W and Mo may be 99.9% by mass or more. desirable.
Even if an impurity element such as oxygen is present to some extent, the purity of W and Mo can be reduced to 99.9% by mass by removing and purifying by vacuum or heat treatment in an inert gas atmosphere described later. More than that.

In the present invention, the W particle powder having the above purity and the Mo particle powder are blended so that the Mo content is 37.5 to 87.5% by mass, preferably 50 to 75% by mass, and then sintered. W-Mo alloy electrode material for resistance welding made of a W-Mo alloy sintered body having a relative density of 98.5% or more is manufactured.
In the present invention, in order to produce the W-Mo alloy electrode material for resistance welding having the above-mentioned predetermined relative density, the average particle diameters of the W particle powder and the Mo particle powder as the raw material powder are 0.25 to 50 μm, respectively. It is desirable to be.

W particle powder and Mo particle powder having an average particle diameter of 0.25 to 50 μm, respectively, or a mixed green compact of W particle powder and Mo particle powder previously formed from powder, with a predetermined high pressure applied When the sintering is performed within a predetermined temperature range, pressure bonding occurs due to pressurization at the contact surfaces of the W particle powders or the contact surfaces of the Mo particle powders, and the W particle powder and the Mo particle powder are mutually bonded. The sintered body is densified by alloying to obtain a W-Mo alloy sintered body having a relative density specified in the present invention.
When the average particle size of the W particle powder or Mo particle powder is less than 0.25 μm, it becomes difficult to improve the sinterability during sintering and to make the relative density of the sintered body 98.5% or more. On the other hand, when the average particle size exceeds 50 μm, it is difficult to improve the sinterability because the particle gap becomes large. As a result, in order to satisfactorily satisfy the thermal conductivity / conductivity, thermal shock resistance, and thermal plastic deformation required for the electrode material, the W particle powder, which is a raw material powder for manufacturing the tungsten electrode material for resistance welding, The average particle size of the Mo particle powder is desirably 0.25 to 50 μm.

In the present invention, the Mo content in the W-Mo alloy sintered body is determined to be 37.5 to 87.5% by mass. However, when the Mo content is small (Mo content is less than 37.5% by mass) or high. In any case (when the Mo content exceeds 87.5% by mass), if welding is performed 1000 times or more continuously under welding conditions of a large current (for example, 10000 A), Deformation, crack generation, etc. are observed. For example, when the Mo content is less than 37.5% by mass, the current shock resistance is reduced, and cracks are generated in the overload test.
Therefore, in the present invention, in order to perform stable welding and extend the life of the electrode, the Mo content in the W-Mo alloy sintered body is 37.5 to 87.5 mass%, more preferably, It was determined to be 50 to 75% by mass.

The W-Mo alloy electrode material for resistance welding of the present invention comprising the W-Mo alloy sintered body having the predetermined relative density can be manufactured by, for example, the following manufacturing method.
As described above, preferably, the W particle powder and the Mo particle powder having a purity of 99.9% by mass or more and having an average particle size of 0.25 to 50 μm are blended so as to have a predetermined composition. By preparing a raw material powder, charging the mixed raw material powder into a pressure sintering apparatus, and applying a pressing force of 1 GPa or more to the powder, sintering at a temperature range of 1000 ° C. or more for 10 minutes or more, The W-Mo alloy electrode material for resistance welding which consists of a W-Mo alloy sintered compact which has the relative density prescribed | regulated by this invention can be manufactured.
In addition, the mixed raw material powder which mix | blended W particle | grain powder and Mo particle | grain powder so that it might become a predetermined composition can also be produced beforehand as a compacting body before sintering.
In addition, when using a fine W particle powder or a fine Mo particle powder (for example, an average particle size of about 4 μm or less) having a large specific surface area as a raw material powder, this is used as a green compact and prior to sintering, for example, In a vacuum atmosphere of 10 ⁻¹ Pa or less, or in an atmosphere in which the heat treatment container is replaced with nitrogen gas, argon gas, or the like, by performing heat treatment at an ultimate temperature of 450 to 1200 ° C. for 30 minutes or more, the surface of W particles, Mo particles When the surface is cleaned, the sintering reaction is likely to proceed. Therefore, it is possible to increase the density of the sintered body in a short time even under relatively low pressure conditions and low temperature regions.
The average particle diameter of each of the W particle powder and the Mo particle powder is preferably in the range of 0.25 to 50 μm, but there is one peak of the particle size distribution frequency of each particle powder (single The particle size distribution of the peak peak is not necessary), and W particle powder and Mo particle powder having a plurality of particle size distribution frequency peaks (multimodal frequency particle size distribution) can also be used. In this case, since the voids can be reduced by entering the small particles between the large particle gaps, the sintering reaction proceeds even under relatively low pressure conditions and low temperature regions, and the sintering is performed. A further increase in density of the bonded body is achieved, and a sintered body having resistance to thermal shock is obtained.
In any case, by sintering under the above conditions and giving a sufficient sintering time, the mixed raw material powder composed of W particle powder and Mo particle powder under high temperature and high pressure is plastically deformed, By arranging, an alloy sintered body of high-density tungsten and molybdenum can be obtained.
In addition, although the upper limit of sintering pressure and sintering temperature is not particularly defined, from the viewpoint of actual operation, if the sintering pressure is in the range of 1 to 10 GPa and the sintering temperature is in the range of 1000 to 2000 ° C. A sintered body having the characteristics defined in the present invention can be obtained.

The W-Mo alloy electrode material for resistance welding according to the present invention has a sintered body structure with a relative density of 98.5% or more, so that it does not deteriorate thermal conductivity and electrical conductivity without causing thermal shock and heat plasticity. Excellent deformation and suppression of welding with the material to be welded. For example, when used for resistance welding of multiple copper foils and aluminum foil laminates used as electrodes of lithium ion batteries, copper foil or aluminum foil No. 20 to 120 sheets, lamination thickness 420 to 1800 μm, electrode pressing force 350 kg / cm ² , current 10000 A, even under severe welding conditions, with 1000 points or more continuously without causing any special welding failure Number of shots can be welded.

  The W-Mo alloy electrode material for resistance welding of the present invention generates welding, deformation, cracks, and breakage with the material to be welded even when resistance welding is performed under conditions of a larger current than conventional. Without incurring heat, without degrading thermal conductivity / electrical conductivity, excellent thermal shock and heat plastic deformation, enabling continuous welding over a long period of time without causing any special welding defects. The life of the W-Mo alloy electrode material for resistance welding can be greatly extended.

It is a schematic explanatory drawing of the resistance welding implemented for the performance evaluation of the electrode for resistance welding.

  Hereinafter, the present invention will be described in detail by way of examples.

As a raw material, W particle powder and Mo particle powder having the purity and average particle diameter shown in Table 1 are prepared, and this is blended so as to have the Mo content shown in Table 1 to produce a mixed raw material powder. By pressure-sintering the mixed raw material powder under the sintering conditions shown in Table 1, the W-Mo alloy sintered bodies 1 to 19 of the present invention having the relative densities shown in Table 1 (hereinafter referred to as “the present invention sintering”). Body 1-19 ").
In preparing the sintered bodies 16 to 18 of the present invention, as raw material powder, W particle powder and Mo particle powder having a plurality of particle size distribution frequency peaks (multimodal frequency particle size distribution) shown in Table 1 are used. Using.
Subsequently, these sintered bodies were processed to produce W-Mo alloy electrodes 1 to 19 (hereinafter referred to as “present invention electrodes 1 to 19”) having a diameter of 8 (mm) × a length of 50 (mm). .

For comparison, W particle powder and Mo particle powder having the purity and average particle diameter shown in Table 2 are prepared, and this is mixed so that the Mo content shown in Table 2 is obtained. By producing and pressure-sintering the mixed raw material powder under the sintering conditions shown in Table 2, W-Mo alloy sintered bodies 1 to 13 (hereinafter referred to as “ Comparative example sintered bodies 1 to 13 ") were prepared.
In preparation of the comparative sintered bodies 12 and 13, as the raw material powder, W particle powder and Mo particle powder having a plurality of particle size distribution frequency peaks (multimodal frequency particle size distribution) shown in Table 2 were used. Using.
Next, these sintered bodies were processed to prepare W-Mo alloy electrodes 1 to 13 for resistance welding (hereinafter referred to as “Comparative Example electrodes 1 to 13”) having a diameter of 8 (mm) × length of 50 (mm). .
In addition, comparative example sintered compact 1,2,7-10,12,13 and comparative example electrode 1,2,7-10,12,13 have Mo content outside this invention range, and are comparative examples The relative density of the sintered bodies 3-6, 8, 11 and comparative example electrodes 3-6, 811 is a numerical value outside the range of the present invention.

Further, for reference, a reference example having the relative density shown in Table 3 by pressure-sintering the W particle powder having the purity and average particle diameter shown in Table 3 under the sintering conditions shown in Table 3. W sintered bodies 1 to 6 (hereinafter referred to as “reference example sintered bodies 1 to 6”) were prepared.
Subsequently, these sintered bodies were processed to prepare W electrodes 1 to 6 for resistance welding (hereinafter referred to as “reference example electrodes 1 to 6”) having a diameter of 8 (mm) × a length of 50 (mm).
Reference example sintered bodies 1 to 6 and reference example electrodes 1 to 6 are W sintered bodies and W electrodes that do not contain Mo at all.

In order to investigate the performance of the present invention electrodes 1 to 19, comparative example electrodes 1 to 13, and reference example electrodes 1 to 6, copper foil (thickness: 7 μm) and aluminum foil (thickness: 15 μm) were respectively 60 to 120. A welding apparatus schematically shown in FIG. 1 is applied to a laminated welded material of copper or aluminum having a total thickness of 420 to 1800 μm, and the welding current is 18000 to 55000A in the case of copper foil, and 8000 to 20000A in the case of aluminum foil. Electrode resistance welding is performed under the conditions of 350 kg / cm ² , and the electrode is used until the electrode and workpiece are welded and no nugget is formed, or the electrode is cracked, broken, deformed, etc. The number of resistance welding hit points (shots) until it became impossible was measured, and the results are shown in Tables 4 and 5.
In addition, the state of the electrode when the number of resistance welding hit points (shots) was measured, the form of damage, etc. were noted in the remarks column.

According to the results shown in Tables 4 and 5, although the present invention electrodes 1 to 4 and 7 to 10 reach the electrode life due to deformation, generation of cracks, etc., the number of resistance welding hit points (shots) is at least , 1000 times or more.
Moreover, about this invention electrode 5, 6, 11-19, not only deformation | transformation, a crack, generation | occurrence | production of welding, etc., but the resistance welding hit point (shot) frequency | count of 200 times or more is shown, Furthermore, a continuous use is also possible.
And when judging comprehensively the magnitude of the welding current value, the number of resistance welding points (shots), and the electrode damage status, among the electrodes of the present invention, the Mo content is 50 to 75% by mass, and the pure tungsten particles It can be said that the electrodes 2 and 4 to 6 of the present invention in which the purity of the powder and the pure molybdenum particle powder is 99.9% by mass or more and the average particle size is 0.5 to 20 μm have extremely excellent electrode characteristics.
On the other hand, with respect to Comparative Examples 1 to 13 in which at least one of the Mo content and the relative density is a numerical value outside the range of the present invention, resistance welding hit points are caused by the occurrence of deformation, cracks, breakage, and welding. The number of shots is 680 times or less, all of which have a short life, and the W electrodes shown as Reference Example Electrodes 1 to 6 have resistance welding points due to cracks, breakage, and welding. The number of shots was at most 15 times.
That is, the W-Mo alloy electrode for resistance welding made of the W-Mo alloy sintered body of the present invention having the requirements specified in the present invention exhibits excellent characteristics even when used under a large current condition. And it turns out that it has a long lifetime.

The W-Mo alloy electrode material for resistance welding according to the present invention is not limited to the case where the material to be welded is a laminate of copper and aluminum, but is used as a resistance welding electrode for any material to be welded such as a galvanized steel sheet and a copper wire. In addition, it can be used continuously for a long time, and the life of the electrode can be extended.

Claims (4)

  A tungsten-molybdenum alloy electrode material for resistance welding comprising a tungsten-molybdenum alloy sintered body obtained by sintering pure tungsten particle powder and pure molybdenum particle powder, and the molybdenum content in the alloy sintered body is 37.5. A tungsten-molybdenum alloy electrode material for resistance welding, wherein the alloy sintered body has a relative density of 98.5% or more.   The tungsten-molybdenum electrode material for resistance welding according to claim 1, wherein the molybdenum content in the alloy sintered body is 50 to 75 mass%.   3. The resistance welding according to claim 1, wherein each of the pure tungsten particle powder and the pure molybdenum particle powder has a purity of 99.9% by mass or more and an average particle size of 0.25 to 50 μm. Tungsten-molybdenum alloy electrode material. The tungsten for resistance welding according to any one of claims 1 to 3, wherein the tungsten-molybdenum electrode material for resistance welding is used as an electrode material for resistance welding in which a welding current of 10,000 A or more is used. -Molybdenum electrode material.