Composite wire for electrical discharge machining

Process for producing an electrode wire having a core made of copper, copper alloy or brass, and a brass coating, the brass coating comprising the superposition of a β-brass sublayer and of a surface layer with a fractured γ-brass structure which reveals β-brass in the fractures, the method comprising:

• a) providing the core,
• b) covering the core with a layer of zinc using an electrolytic process in order to produce a preblank,
• c) possibly subjecting the preblank to a first wire-drawing operation,
• d) annealing the wire-drawn preblank in a furnace at a temperature ranging between about 200° C. and about 400° C. and for a time of about 2 h to about 40 h, choosing the temperature and the time so as to produce, as a result of diffusion between the zinc of the covering layer and the copper or brass of the core, a blank that has the β-brass sublayer and a surface-oxidized γ-brass surface layer,
• e) subjecting the blank thus diffused to a second, cold, wire-drawing operation in order to bring it to its final diameter and in such a way as to fracture the γ-brass surface layer such that the β-brass sublayer is revealed in the fractures.