Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H1/00—Contacts
  • H01H1/02—Contacts characterised by the material thereof
  • H01H1/021—Composite material
  • H01H1/025—Composite material having copper as the basic material

Definitions

• the present invention relates to copper-based composite materials for highly stressed electrical contacts. It also relates to methods of manufacturing such materials, as well as to highly stressed electrical contact members produced from this composite material.
• the electrical contact members must have not only a high electrical conductivity, but also good mechanical resistance, in particular to compression, both at ambient temperature and at high temperature. These conditions relate in particular to the tools used in spot welding, such as electrodes or rollers, which must at the same time admit high current densities without overheating excessively and withstanding the high pressures imposed to ensure welding.
• the electrical contact members must have as wide a metallurgical inertia as possible with respect to the metal constituting the parts with which they are brought into contact. Spot welding of bare steel sheets does not pose any major problems in this regard. On the other hand, in the increasingly frequent case of welding of galvanized sheets, there is a diffusion of zinc in the copper alloy; this leads to rapid degradation of the contact member as a result of the formation, at the end of this member, of various copper-zinc alloys whose electrical conductivity is poor and whose mechanical properties are poor.
• copper alloys have long been used containing small amounts of certain hardening elements, in particular cadmium, chromium or zirconium.
• the mechanical resistance of these alloys at room temperature is increased compared to that of pure copper, either thermally, namely by precipitation hardening, or mechanically, namely by work hardening.
• the mechanical resistance when hot is poor, however, and the electrical conductivity is significantly reduced by the presence of the hardening elements.
• these alloys are very sensitive to the degradation resulting from the diffusion of zinc during the assembly by resistance of galvanized sheets.
• Copper alloys hardened by dispersion of inert oxides such as zinc or aluminum oxides are also known. These alloys are manufactured by fusion, atomization in powder, internal oxidation of powders, consolidation by extrusion and cold work hardening by drawing.
• the alumina dispersion guarantees remarkable stability of the mechanical properties when hot.
• the electrical conductivity of this alloy is however lower than that of copper.
• this type of material does not provide a remedy for the problem of contamination of the contact member by zinc from a galvanized sheet.
• the object of the present invention is to provide alloys and composite materials based on copper which do not have the aforementioned drawbacks in terms of mechanical, electrical and metallurgical properties. Another object of the invention is to propose methods of manufacturing these alloys and these composite materials. Finally, the present invention also relates to a method for improving the metallurgical inertia of a copper contact member with respect to zinc or a zinc alloy originating from a galvanized part.
• a copper-based composite material for highly stressed electrical contacts is characterized in that it contains at least one reinforcing component dispersed in the copper matrix.
• the reinforcement component can take various forms; a composite material according to the invention may moreover contain several reinforcing elements and / or components having different shapes.
• this reinforcing component can consist of one or more oxides stable with respect to copper, such as yttrium (Y2O3) or aluminum (Al2O3) oxides, which form a dispersion hardening in the copper matrix.
• Y2O3 yttrium
• Al2O3 aluminum
• the proportion of these oxides is preferably between 2% and 5% by volume, but it can be between 1 and 10% by volume without departing from the scope of the invention; these latter values mark markedly the limits beyond which the effects of the dispersion of oxides are no longer clearly perceptible.
• the copper-based alloys thus hardened by oxide dispersion have a high resistance to recrystallization, a high mechanical resistance to hot, as well as a very high electrical conductivity, close to that of pure copper.
• this reinforcing component can consist of one or more elements poorly soluble in copper, such as chromium and zirconium, which give rise to additional hardening by precipitation.
• this reinforcing component can be constituted by short fibers, made of materials stable with respect to copper, distributed in the copper matrix, such as fibers of Al2O de or silicon carbide (Sic).
• fibers By short fibers is meant fibers whose diameter is not greater than 50 ⁇ m and whose length is between 0.1 and 2 mm.
• the proportion of these short fibers in the composite material is between 5 and 25% by volume to ensure high mechanical strength, both at room temperature and at high temperature, as well as very good electrical conductivity.
• a preferential proportion of 12 to 20% by volume has proved particularly favorable for obtaining a high metallurgical inertia of the composite material with respect to zinc.
• a composite material according to the invention can contain at the same time a dispersion of oxides and short fibers in a copper matrix.
• the composite material thus benefits from the combination of hardening of the copper matrix by dispersion of oxides and of its reinforcement by short fibers.
• the composite materials which have just been described are preferably produced by particular methods which constitute another aspect of the present invention.
• a mechanical alloy of a copper powder or copper alloy and of at least one reinforcing component is produced.
• mechanical alloy is meant here the mixture of constituents in the solid state in any suitable device, for example a ball mill or a vibrating mill, for a sufficient time to ensure dispersion.
• the mixing time is advantageously between 1 h and 48 h, preferably between 4 and 24 h, depending on the particle size of the initial powders.
• the mixture thus obtained is preferably consolidated by hot extrusion, then stretched for the manufacture of electrical contact members.
• the principle of mechanical alloying is also applicable; in this case, however, a mixer is used instead of a grinder, so as not to destroy the short fibers.
• a molten charge of copper or copper alloy is prepared, oxides and / or short fibers are added to it in an appropriate quantity, the molten bath is stirred to ensure the dispersion of said components and said charge is poured into ingots which are then rapidly solidified. In general, the ingots are then extruded and optionally drawn.
• the copper-based composite materials according to the present invention have excellent mechanical resistance, both at ambient temperature and at high temperature, as well as an extremely high electrical conductivity, often close to that of pure copper.
• the metallurgical inertia of these materials is also very good, which prolongs their life in appreciable proportions.
• a major advantage lies in the fact that they make it possible to choose, independently of one another, the copper-based matrix and the reinforcing elements and / or components.
• the mixture was ground for 24 h in an attritor with carbide balls, under scanning of argon.
• the quantity of beads used was 10 kg for 2 kg of copper powder; the argon was of the quality known as "welded argon" known under the name N39.
• the ground powder was poured into copper containers with an outside diameter of 80 mm and a wall thickness of 5 mm; these are closed by copper plugs to maintain the filling.
• the containers are preheated to 800 ° C for 1 hour in an air oven and extruded with a liner of bars of approximately 13 mm in diameter. After extrusion and at room temperature, the diameter of the bars is 13 mm. The bars were then subjected to cold deformation by shrinking, in 6 passes, causing a reduction in section of about 48%.
• the resistance of the material to recrystallization was determined by hardness measurements after exposure for 1 h at various temperatures up to 760 ° C.
• the hardness of the material amounted, after exposure for 1 h at 760 ° C, to 64 Rb.
• the hardness of a conventional copper alloy C 18200 (Cu - 1% Cr) was only 10 Rb.
• Example 1 Copper powders and short SiC fibers, 12% by volume, were mixed for 8 h in a vibrating mill. The mixture obtained was consolidated by extrusion and then cold-worked under the same conditions as in Example 1. The thermal stability of the bars obtained was determined as in Example 1.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Composite Materials (AREA)
• Materials Engineering (AREA)
• Manufacture Of Alloys Or Alloy Compounds (AREA)
• Contacts (AREA)
• Conductive Materials (AREA)

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Citations (6)

• 1988
  • 1988-06-29 BE BE8800753A patent/BE1002075A6/fr not_active IP Right Cessation
• 1989
  • 1989-06-23 EP EP19890870101 patent/EP0349515A3/de not_active Withdrawn

Patent Citations (6)

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