Structure and strength of polycrystalline copper during hydrostatic extrusion with reduction up to R = 100

Abstract

The effect of extrusion ratios in the range 60–100 on the structure and strength of cold hydrostatically extruded. copper of 99.9% purity are reviewed. The final structure is mainly formed as a result of dynamic and static recrystallization and is controlled directly by the temperature generated in the die and the cooling rate at the die exit. Because of the high thermal effect of the process (T/T _m … 0.54), products air cooled are fully recrystallized, the process having no dependence on the value of extrusion ratio used but being a result of the high efficiency of postdynamic recrystallization and secondary grain growth. It is possible to prevent static effects by instantaneous quenching of the extruded wire. Quenched products have microstructures in various stages of plastic deformation. Plots of 0.2% proof stress and elongation v. extrusion ratio exhibit two maxima which are a result of interaction between dynamic recrystallization and strain hardening. Above an extrusion ratio of about 90, the structure and mechanical properties of the quenched and unquenched products are the same.