Effect of 1wt.%Bi Addition on Microstructure and Mechanical Property of Mg-3al Alloy by Twin Roll Casting and Hot Rolling

Abstract

The microstructural evolution and mechanical properties of twin-roll casting (TRC) and hot rolling (HR) Mg-3Al-1Bi (in wt.%, TRC-AB31 and HR-AB31) alloys were investigated and compared with AZ31 alloy as benchmark. The addition of Bi in TRCed alloys can not only reduce the central segregation, but also introduce thermally stable Mg3Bi2 phase distributed uniformly in α-Mg matrix. The second phases with larger size leading to particle stimulated nucleation (PSN), which in turn, promoted the dynamic recrystallization (DRX) in HR-AB31 alloy and weaken its basal texture. The second phases play two different roles in AB31 alloy, on the one hand, the grain refinement and uniform microstructure resulted from enhanced DRX by second particles which retarding dislocation movement as well as inhibition of grain growth. On the other hand, such brittle particles can also act as the cracking source and degrade elongation. The strengthening mechanism of both AZ31 and AB31 alloys are discussed and investigated.

Keywords: Mg alloy, twin-roll casting, recrystallization, mechanical property