Formation of spheroidal microstructure in semi-solid state and thixoforming of 7075 high strength aluminum alloy

Abstract

The effects of isothermal holding process on the microstructure evolution of semi-solid 7075 strength aluminum alloy produced by the recrystallisation and partial remelting (RAP) process were investigated. Tensile mechanical properties of as-received and thixoformed alloys at room temperature were examined. The results show that the microstructure of as-received alloy exhibits remarkable orientation along the deformation direction. With the increase of isothermal holding time, the solid particle grain size continuously increases and the degree of spheroidization also improves. Coalescence mechanism is dominant when reheated at 595 °C and Ostwald ripening mechanism is dominant when reheated at 615 °C in the semi-solid state. A lower coarsening rate is observed for 615 °C (coarsening rate K = 391 μm3·s−1) compared with the coarsening rate for 595 °C (coarsening rate K = 501 μm3·s−1). The RAP 7075 aluminum alloy can be successfully thixoformed and the filling of components is good after thixoforming. The thixoformed components exhibit favorite mechanical properties.