An investigation of microstructure evolution of RAP processed ZK60 magnesium alloy

Abstract

The effect of compression ratio on the microstructure evolution of semi-solid ZK60 magnesium alloy produced by the recrystallisation and partial melting (RAP) process was investigated. The microstructure evolution within the semi-solid zone of a ZK60 alloy through a direct isothermal holding process from as-received and as-deformed conditions was also investigated. The results show that as-received alloys reheated to the semi-solid state had solid particles predominantly elongated along original extrusion direction. For as-deformed alloys, the compression deformation gradually refined the recrystallised α-Mg grains by increasing their nucleation to growth ratio. During isothermal holding, intragranular liquid droplets were present in a large number of solid particles, reducing in number and increasing in average size with increasing holding time. The coarsening behavior of solid particles in the semi-solid state obeyed an Ostwald ripening mechanism. The coarsening rate constant obtained was 556 μm 3s −1 at 590 °C.