Microstructural evolution during partial remelting of equal channel angular pressed ZW21 magnesium alloy

The microstructural evolution process was investigated during partial remelting of equal channel angular pressed ZW21 alloy. Simultaneously, the effects of heating temperature, pressing pass and pressing route on its semisolid microstructures were also discussed. The results indicated that equal channel angular pressing followed by partial remelting was an effective method to produce semisolid ingot for thixoforming. The microstructural evolution could be divided into five stages, the coarsening and recrystallization of primary dendrites, structure separation, coarsening of the polygonal particles, spheroidization of the polygonal particles and coarsening of the spheroidal particles, which just corresponded to the phase transformations of W → α-Mg, W + α-Mg → L, weak reaction of α-Mg → L, active reaction of α-Mg → L and two reverse reactions of α-Mg → L and L → α-Mg, respectively. Higher heating temperature resulted in coarser primary particles and larger liquid phase amount. Increasing pressing pass was beneficial for obtaining semisolid microstructure with small and spheroidal primary particles and also increased the amount of liquid phase. The semisolid microstructures produced by different routes changed from good to bad in turn of BC, BA, C and A when the pressing pass was same. These results were mainly theoretically discussed in this paper.