Copper conductor members or other copper-base workpieces are welded using a suitable copper alloy material that is reactive with the joining surfaces of the copper members. The reactive metal material may be applied as a thin metal strip between assembled facing joining surfaces. The members are pressed together against the reactive material and heated. The combined pressure and heat enable the reactive material to react with facing workpiece material, to liquefy and remove oxides or the like that might inhibit the formation of a welded interface. The liquid, containing original reactive metal and byproducts, is squeezed from the interface of the workpieces to enable the formation of a solid-state weld between them without melting of un-reacted workpiece copper material.