A comparable study of Mg98.15Y1Zn0.85 sheets fabricated by twin-roll casting and direct-chill casting and related annealing behavior

Abstract

The effects of twin-roll casting (TRC) and direct-chill casting (DC) on the microstructure and mechanical properties of Mg98.15Y1Zn0.85 alloys were investigated during homogenization, finish rolling and annealing. Special attention paid on the evolution of central segregation as well as second phase transformation. The central segregation produced by TRC disappeared after homogenization and reappeared through intermediate annealing with final rolling. In the subsequent annealing process, as the annealing temperature increased, the segregation gradually grew, disappeared and finally reappeared. In addition, the disappearance and reappearance of the intermediate segregation simultaneously changed the phase compositions and morphology: the discontinuous W phase in the as-roll state disappeared through homogenization and then reappeared after the intermediate annealing. Increasing the final annealing temperature gradually transformed the long-period stacking-ordered LPSO- and W-mixed network structure into LPSO clusters, dispersed LPSO structures, mixed granular and network like W phase and continuous network-like W phase. Particularly, the chain network of W phase exhibited excellent strain hardening and significantly increased the yield strength of the alloy.