JPS6195785A - Silicon nitride fiber reinforced copper compound material for electrode - Google Patents

Abstract

PURPOSE:To provide the titled compound material excellent in both mechanism property of wear resistance, strength, etc. and electrical and thermal properties of conductivity, thermal conductivity, etc. by consisting of the silicon nitride fiber in the range of the specified volume factor specified respectively a mean fiber diameter and aspect ratio as a reinforcing material and a pure copper as a matrix. CONSTITUTION:The silicon nitride reinforcing copper compound material for electrode is composed of the silicon nitride fiber of under 1.0mu, especially 0.1-1.0mu mean fiber diameter and 10-300, especially 20-2500 aspect ratio as a reinforcing material and a pure copper of more than 99.5%, especially more than 99.7% purity as a matrix. It is an essential conditions that the volume factor of the silicon nitride fiber in this compound material is to be 2.0-25%, especially 5.0-20%. The density ratio of this compound material is more than 0.90, especially more than 0.92. This compound material is suitable for the formation of electrode for lap resistance welding.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to fiber-reinforced metal composite materials, and more particularly to silicon nitride fiber-reinforced f! for electrodes. 4 Concerning composite paddy.

Conventional technology Electrodes used in lap resistance welding such as spot welding and seam welding apply a large current density and strong pressure to the material to be welded, and therefore have excellent electrical conductivity, wear resistance, and strength. It is necessary that the Furthermore, since a large amount of resistance heat is generated at the welding part, the electrode is required to have excellent high-temperature strength and thermal conductivity. Therefore, electrodes for lap resistance welding have conventionally been generally made of a copper alloy made by adding several percent of chromium or beryllium to pure copper.

Problems to be Solved by the Invention However, when increasing the amount of alloying elements added to pure copper in order to improve wear resistance, etc., the conductivity decreases, leading to problems such as a decrease in current carrying performance and an increase in the amount of heat generated by the electrode itself. Conversely, if the amount of alloying elements added is reduced, wear resistance and strength will decrease, resulting in insufficient durability. Therefore, it is very difficult to improve both mechanical properties such as wear resistance and strength, and electrical and thermal properties such as electrical conductivity and thermal conductivity by adding alloying elements.

Furthermore, in order to improve the wear resistance and strength of copper alloys used for electrodes and the like, particle dispersion-strengthened copper alloys and precipitation-aged copper alloys, in which hard particles are dispersed in copper alloys, are already known. However, these copper alloys have various problems such as being difficult to manufacture, having poor rigidity, and insufficient high-temperature strength.

Furthermore, as disclosed in JP-A No. 55-144386, there is an electrode rod for a spot welder in which at least the tip of the electrode rod is made of copper or a composite material of a metal containing copper as a main component and carbon fiber. is already known. However, in such electrode rods, the performance of carbon fiber at high temperatures is insufficient, so composite materials made of carbon fiber as a reinforcement and pure copper or copper alloy as a matrix have low hardness at high temperatures. There is a problem in that the wear resistance is poor, and therefore, if welding is performed many times using such a composite material electrode, a good weld cannot be obtained.

In view of the above-mentioned problems with conventional electrode materials, the inventors of the present application have conducted various experimental studies and have developed silicon nitride that uses high-purity pure copper as a matrix and satisfies the predetermined requirements! Composite materials that use 11M as a reinforcing material make it possible to produce electrodes that have both mechanical properties, such as wear resistance and strength, and electrical and thermal properties, such as electrical conductivity and thermal conductivity, which are in a trade-off relationship. I found out what can be done.

The present invention is based on the knowledge obtained as a result of various experimental studies conducted by the inventors of the present invention, and has been developed based on the knowledge obtained as a result of various experimental studies conducted by the inventors of the present invention. It is an object of the present invention to provide a silicon nitride fiber-reinforced copper composite material for electrodes which has excellent electrical and thermal properties and is therefore suitable for use in forming electrodes such as electrodes for lap resistance welding.

Means for Solving the Problems According to the present invention, the above-mentioned objects are such that the average [lff1 diameter is 1.0μ or less and the aspect ratio is 10 to 3000].
This is achieved by a silicon nitride fiber-reinforced copper composite material for electrodes, in which silicon nitride fiber is used as a reinforcing material, pure copper with a purity of 99.5% or more is used as a matrix, and the volume percentage of the silicon nitride fiber is 2.0 to 25%. Ru.

Functions and Effects of the Invention Silicon nitride fibers are superior in strength, rigidity, and stability at high temperatures compared to carbon fibers, etc., and are therefore highly effective fibers for improving the cutting stiffness and abrasion resistance of matrix metals. It is. According to the results of experimental research conducted by the inventors of the present application, when the volume fraction of silicon nitride fibers is very small, functions such as strength improvement effects are not fully exhibited, but especially the wear resistance of composite materials. is significantly improved even if the volume fraction of silicon nitride fibers is only a few percent. Therefore, the volume fraction of silicon nitride fibers is preferably 2.0% or more, particularly 5.0% or more. Also, the strength of composite materials is silicon nitride! The higher the volume fraction of lH, the higher the improvement, so from the viewpoint of improving the mechanical properties of the composite material, it is preferable that the volume fraction of the silicon nitride fibers is as high as possible. However, according to the results of experimental research conducted by the inventors of the present invention, if the volume fraction of silicon nitride fibers becomes too high, not only will the electrical conductivity and thermal conductivity of the composite material deteriorate significantly (but also the powder metallurgy When manufacturing composite materials by the method, it is difficult to mix silicon nitride fibers, copper powder, etc. uniformly, and therefore it is difficult to manufacture composite materials in which silicon nitride mH is uniformly dispersed. However, there is a problem that sintering of the copper powder is not performed well, and when manufacturing composite materials by pressure casting, it is difficult to properly infiltrate the molten copper into the IAH molded body with a high volume fraction. Therefore, it is preferable that the volume fraction of silicon nitride fiber is 25% or less, especially 20% or less. Therefore, in the silicon nitride fiber reinforced copper composite material for electrodes, the volume fraction of silicon nitride fiber is is preferably 2.0 to 25%, particularly 5.0 to 20%, and even more preferably 8.0 to 15%.

Silicon nitride m-fibers are currently commercially available with various average diameters and aspect ratios of 111, but silicon nitride altl
When the fiber diameter of f1 is small, it is difficult to separate the individual silicon nitride fibers from the fiber aggregate, resulting in poor workability when manufacturing composite materials, and the strength of the silicon nitride fiber itself is low, resulting in powder In the metallurgical method, when silicon nitride fibers and copper powder are mixed, the silicon nitride fibers are easily broken, and in the pressure casting method, a fiber molded body with a small volume percentage of silicon nitride fibers is formed. It is difficult to do so. On the other hand, if the diameter is large, the contact between silicon nitride fibers and copper powder in the mixture becomes insufficient in the powder metallurgy method, and therefore even after sintering, the silicon nitride fibers do not remain in contact with each other. The adhesion between the fiber material and the matrix metal tends to be insufficient, and in the case of pressure casting, it is difficult to form a homogeneous fiber molded product. In addition, when the fiber length of silicon nitride fiber is short,
Silicon nitride fibers do not function well as fibers, so the strength improvement effect tends to be insufficient. Conversely, when the fiber length is large, it is difficult to combine silicon nitride fibers and copper powder in the powder metallurgy method. During the mixing process, silicon nitride w4r41 tends to become entangled with each other, causing segregation of silicon nitride fibers, making it difficult to form a homogeneous fiber molded body in the pressure casting method. Therefore, according to the results of experimental research conducted by the inventors of the present application, the average II fiber diameter of silicon nitride fibers is 1.0μ or less;
In particular, it is preferably 0.1-1°0μ, and the aspect ratio is 10-3000. Especially 20-2500, even 5
It is preferable that it is 0-2000.

Furthermore, pure copper as a matrix metal has the second highest electrical conductivity next to silver, but its electrical conductivity decreases as its purity decreases. According to the results of experimental studies conducted by the inventors of the present application, the purity of pure copper compositely reinforced with silicon nitride fibers as described above is preferably 99.5% or more, particularly 99.7% or more.

According to the present invention, the size and volume fraction of silicon nitride fibers as a reinforcing material and the purity of pure copper as a matrix metal are set as described above, so that mechanical properties such as wear resistance and strength are excellent, and It is possible to obtain a silicon nitride fiber-reinforced copper composite material for electrodes that has excellent electrical and thermal properties such as electrical conductivity, thermal conductivity, and high-temperature strength.

According to the results of other experimental studies conducted by the present inventors, the conductivity of silicon nitride fiber-reinforced steel composite materials for electrodes is determined by a decrease in the density ratio, that is, the ratio of the true density to the apparent density of the composite material. decreases as the temperature increases. According to one detailed feature of the invention, therefore, the density ratio of the composite material is set to 0.90 or more, in particular 0992 or more, and even 0693 or more.

In addition, when the composite material according to the present invention is applied to an electrode for lap resistance welding, in order to reduce the heat generation of the electrode itself and achieve good resistance welding, the experimental According to research results, the electrical conductivity rAcs of the composite material is preferably 70% or more. According to another detailed feature of the invention, therefore, the electrical conductivity of the composite material IA
CS is set to 70% or more, particularly 72% or more, and even 75% or more.

Furthermore, the aggregate of silicon nitride fibers produced by blowing method etc. contains non-fibrous particles to some extent due to the manufacturing process, and these non-fibrous particles have a hardness) (v
(50 (1>) is 1000 or more, and its size is also very large compared to the m thread diameter of silicon nitride m fibers.According to the results of the research conducted by the inventors of the present application, such a Composite materials that are reinforced by aggregates of silicon nitride fibers containing fibrous particles have very poor processability, and when such composite materials are applied to electrodes, non-fibrous particles tend to fall off from the matrix. This may cause problems such as abnormal wear in the welded material.This problem is particularly noticeable when the content of relatively large non-molecular particles with a diameter of 150μ or more is high.Therefore, the present invention According to yet another detailed feature, the amount of non-fibrous particles with a diameter of 150μ or more contained in the silicon nitride H&tape aggregate is 7.
It is limited to 5 wt% or less, particularly 1 wt% or less.

In addition, when the composite material of the present invention is applied to an electrode of a spot welding device, etc., the entire electrode may be formed of the composite material, or only the part of the electrode in contact with the multiple connecting member is made of the composite material. The other parts may be made of pure copper.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to embodiments with reference to the accompanying drawings.

(1) Casting Example Prepare various silicon nitride fibers shown in Table 1 below that have been treated so that the content of non-fibrous particles with a diameter of 150 μm or more contained in the aggregate is substantially zero, A fiber molded body 2 having a length of 80 m, a width of 8 Q mm, and a height of 20111111 as shown in FIG. 1 was formed using 1 m1 of silicon nitride #1. In this case, the silicon nitride m fiber is white Ox80
They were oriented randomly in a plane parallel to the end face of mm, and were stacked in the height direction. The silicon nitride fibers in each sample in Table 1 were manufactured by Tateho Chemical Industry Co., Ltd.
It was i 3 Nt Whisker J.

Next, after preheating the 4IN molded body 2 to 600°C, it is placed in the lower mold 3 of a high-pressure casting apparatus 6 consisting of a lower mold 3, an upper mold 4, and a knockout bin 5, as shown in FIG. Pour molten metal 7 of pure copper (purity 99.9%) at 1200°C into the lower mold, pressurize the molten metal at a pressure of about 1000 kg/♂, and maintain the pressurized state until the molten metal completely solidifies. did. After the molten metal was completely solidified, the solidified body was taken out from the lower mold 3 using a knockout pin 5, and the solidified body was subjected to mechanical processing such as grinding. The Vickers hardness, electrical conductivity, and density ratio at air temperature and at 500° C. were measured for the portion of the solidified body made of pure copper reinforced with silicon nitride fibers. The results are shown in Table 2 below.

Further, the solidified body formed as described above is subjected to machining such as turning, and the total length is 1-23 mm as shown in FIG.
11111, nominal diameter a-15 mm, diameter of the electrode tip, that is, diameter d-5+u+ of the contact surface 9a with the welded material (not shown in the figure), radius of curvature R-8II of the radial cross section of the outer periphery of the electrode tip and has a substantially truncated conical tip 8
Only the electrode tip 9 for spot welding is compositely reinforced with silicon nitride fiber.

Formed. In FIG. 3, 9b indicates a cooling water passage.

Using the electrode tip 9 formed as described above, as shown in FIG. Spot welding was carried out, and the diameter per electrode was measured until the 100th welding point was performed, and the number of welding points that could form a normal nugget on the welded material 10 was measured as the tip life. The results are shown in Table 2 below.

(2) Sintering example Silicon nitride m fiber 11 and pure copper (I) shown in Table 3 below
4i degree 99.9%) powder 12 respectively silicon nitride ms
Weigh so that the volume ratio of a becomes a predetermined value, and add them to the fifth
Dry powder mixing was carried out using a V-type powder mixer 13 as shown in the figure at a rotation speed of 30 rpm and a powder mixing time of 30 minutes.

The silicon nitride II miscellaneous material for each sample in Shouzoku 3 was rsIaN4 Boyce Force manufactured by Tateho Chemical Industry Co., Ltd.

Next, the mixture obtained by mixing the powders as described above is sequentially placed in the mold 15 of the hot press device 14 as shown in FIG. Pressure force: 200 kg/♂, pressurization time: 10 minutes, atmosphere: 10"'j
Hot pressing was performed under vacuum conditions of orr. After performing mechanical processing such as grinding on the sintered body thus obtained,
Vickers hardness, electrical conductivity, and density ratio were measured at room temperature and at 500°C. The measurement results are shown in Table 4 below.

Further, the sintered body formed as described above is subjected to machining such as turning, and the total length is 1-23 mm as shown in FIG.
mm, nominal diameter a-16111111. The radius of curvature R of the radial cross section of the outer periphery of the electrode tip is 8 mm, and the diameter of the contact surface 9a with the material to be welded is d - 6 + 1L, and the entire area is made of pure copper compositely reinforced with silicon nitride tIN. An electrode chip 9 was formed. Using the electrode tip thus formed, a welding test was conducted in the same manner and under the same conditions as the welding test conducted in the above-mentioned casting example, and the diameter per electrode and The life of the electrode tip was measured. The measurement results are shown in Table 4.

(3) Comparative Example Chromium copper, which is currently used as a constituent material of electrode tips for spot welding, was used (Cu-0.6wt%cr>Sample 1).
The sample was prepared as
The Vickers hardness, electrical conductivity, and density ratio were measured, and a welding test was conducted using the electrode tip made of chromium copper in the same manner and conditions as the welding test described above, and the diameter per electrode and The life of the electrode tip was measured. The results are shown in Table 2 below.

From Group 1 to Table 4 below, especially samples 2.3.5.6.8.
9, the hardness of the electrode tip increases as the volume fraction of silicon nitride fiber increases, but the comparison between sample 4.5.6.20 and sample 8.9 shows that the volume fraction of silicon nitride fiber increases. It can be seen that the life of the electrode tip decreases significantly as the temperature increases. Therefore, the volume fraction of silicon nitride fibers is preferably 25% or less. Moreover, from Samples 10 and 11, it can be seen that the volume fraction of silicon nitride fibers is preferably 2.0% or more. Moreover, from Samples 4 to 7, it can be seen that when the average fiber diameter is relatively large such as 15μ, the life of the electrode tip is short, and therefore it is preferable that the average fiber diameter of the silicon nitride fiber is 5μ or less. However, judging from the fact that the silicon nitride fiber manufactured by Tateho Chemical Industry Co., Ltd. has a large variation in fiber diameter and includes fibers with a diameter of about 1°0μ, the average fiber diameter of silicon nitride fiber is 1.0μ or less. It is assumed that this is preferable.

Also, from the comparison of samples 12 and 13, the aspect ratio is 10.
When the aspect ratio is less than 3,000, the diameter per electrode increases significantly, and from a comparison of samples 16 and 17, it can be seen that when the aspect ratio exceeds 3000, the life of the electrode tip is significantly reduced. Therefore, the aspect ratio of silicon nitride mM is preferably 10 to 3000. Furthermore, from Samples 20 to 23, it can be seen that when the density ratio is less than 0.90, the life of the electrode tip is very short, and when the electrical conductivity is less than 70%, the life of the electrode tip is also short. Therefore, the density ratio and electrical conductivity are preferably 0.90 or more and 70% or more, respectively.

From the above description, it will be understood that according to the present invention, an excellent silicon nitride fiber-reinforced copper composite material for electrodes, which is suitable for forming electrodes for lap resistance welding, can be obtained.

Although the present invention has been described above in detail with respect to several examples of the composite material of the present invention in comparison with several comparative examples, the present invention is not limited to these examples. It will be apparent to those skilled in the art that numerous embodiments are possible within the scope of the invention.

Table 1 Table 2 Table 3 Table 4

[Brief explanation of drawings]

Figure 1 shows a fiber structure made of silicon nitride fibers.
Figure 2 is a cross-sectional view showing the casting process when a composite material is produced using the fiber molded body shown in Figure 1, and Figure 3 is a perspective view showing the composite material according to the present invention. An illustration showing one embodiment of the formed electrode tip for spot welding, FIG. 4 is an illustration showing the procedure for spot welding performed using the electrode tip shown in FIG. 3, and FIGS. FIG. 6 is a cross-sectional view showing a powder mixing step and a hot pressing step in the process of manufacturing a composite material by powder metallurgy. 1... Silicon nitride fiber, 2... Fiber molded body, 3...
- Lower mold, 4... Upper mold, 5... Knockout bin, 6
... High pressure casting device, 7... Molten metal, 8... Tip part,
9... Electrode tip, 9a... Contact surface, 9b... Cooling water passage, 1o... Material to be welded, 11... Silicon nitride m-thread, 12... Pure copper V) powder, 13 ...V-type flour mixing machine,
14... Hot press device, 15... Mold, 16...
・Heater, 17... Upper bunch, 18... O-a punch Figure 1 Figure 2 Figure 3 Figure 4

Claims (3)

[Claims] (1) Silicon nitride fibers having an average fiber diameter of 1.0 μ or less and an aspect ratio of 10 to 3000 are used as reinforcement,
A silicon nitride fiber-reinforced copper composite material for an electrode, which has pure copper with a purity of 99.5% or more as a matrix and has a volume fraction of the silicon nitride fibers of 200 to 25%. (2) In the silicon nitride fiber reinforced copper composite material for electrodes according to claim 1, the density ratio of the composite material is 0.90.
A silicon nitride fiber-reinforced copper composite material for electrodes, which is characterized by the above. (3) In the silicon nitride fiber-reinforced copper composite material for electrodes according to claim 1 or 2, the composite material has a conductivity IACS of 70% or more. Fiber reinforced copper composite material.