Method of joining copper conductors

A method of forming a solid-state weld between a pair of copper conductor bars for an electric motor, the copper conductor bars having facing surface areas to be joined in the solid-state weld, the facing surface areas being substantially the same in shape for the formation of the solid state weld coextensive with each facing surface area and the profiles of the facing surface areas allowing them to lie in substantially full face-to-face contact when they are assembled;

• the method comprising:
• preparing an assembly of the first and second copper conductor bars, with their joining surfaces aligned surface-to-surface but separated with a layer of reactive copper alloy material, the thickness of the copper alloy material being no greater than about 250 micrometers and the composition of the copper alloy material being selected to melt and react with surface material of the copper conductor bars at a temperature below the melting point of either of the copper conductor bars;
• pressing opposing electrical resistance heating electrode members against the first and second copper conductor bars to press the first and second joining surfaces against the reactive copper alloy material and for electrical resistance heating of the reactive copper alloy material by passing an electrical current through the conductor bars and reactive material at the first and second joining surfaces of the workpieces, the opposing electrical heating electrode members having textured surfaces for contacting the first and second copper conductor bars and for reducing the electrical resistance at the contacts of the textured surfaces with the first and second copper conductor bars, the textured surface of each electrode member being characterized by peak-to-peak roughness of no less than ten micrometers and no more than ten-percent of the thickness of the copper workpiece at the region of its contact;
• electrical resistance heating the reactive copper alloy material in the assembly for a predetermined time for the reactive copper alloy material to react with material at the joining surfaces of the copper conductor bars and to form a liquid-containing reaction product;
• the pressure on the assembly acting to force substantially all formed liquid reaction product from between the residual joining surfaces, and, thereafter
• holding the joining surfaces against each other until a solid-state welded joint is formed coextensively with the joining surfaces.