A new strong and ductile multicomponent rare-earth free Mg–Bi-based alloy achieved by extrusion and subsequent short-term annealing

Abstract

A new multicomponent rare-earth free low-alloyed Mg-1.0Bi-1.0Mn-1.0Al-0.5Ca-0.3Zn (wt.%) alloy is prepared by low-temperature and low-speed extrusion. The as-extruded sample has an ultra-high yield strength (∼425 MPa) but low elongation-to-failure (∼2.1%) mainly due to a bimodal grain structure containing ultra-fine recrystallized (DRXed) grains and large-sized unDRXed regions with a strong basal fiber texture feature, accompanied by a certain amount of micro-scale second phases (Al8Mn5 and Mg2Bi2Ca) and the uniformly distributed nano-scale α-Mn particles. More importantly, the excellent strength-ductility synergy is realized in the annealed samples after appropriate short-term annealing, and the yield strength and elongation-to-failure can reach ∼378 MPa and ∼16.8%, respectively. The effective inhibition of grain growth by grain boundary co-segregation of solutes and pinning effect of α-Mn nanoparticles is crucial for the annealed samples to maintain the relatively high strength. The formation of a new heterogeneous fibrous structure containing fine/coarse DRXed grains and thin fibrous unDRXed regions, along with weak basal fiber texture and low-density residual dislocations, is a key factor for the annealed sample to significantly enhance the ductility. Hence, such a new high strong and ductile low-alloyed Mg–Bi-based alloy will be helpful for enriching high performance low-cost wrought Mg alloy series to achieve extensive applications in industries.