Enhanced strength-ductility synergy achieved through twin boundary pinning in a bake-hardened Mg-2Zn-0.5Ca alloy

Bake-hardening (BH) processing is an efficient way to rapidly increase the strength of solution-treated Mg alloys, which is attributed to GP-zone strengthening or dislocation pinning caused by solute segregation. Here we report a new hardening mechanism of BH in Mg-2Zn-0.5Ca (wt. %) alloy, i.e., twin boundary pinning, which could obtain enhanced strength-ductility synergy, with a flow stress of-200 MPa (increased from-141 MPa) and an elongation to failure of-17% (increased from-12%). Microstructure analyses show that the co-segregation of Zn and Ca atoms at { 1012} twin boundaries can impede twin boundary migration, which effectively suppresses crack propagation and therefore improves the ductility. Meanwhile, the twin boundary pinning obviously in-creases strength in conjunction with the pinning effects of co-segregated Zn and Ca atoms at dislocations. Such a twin boundary pinning mechanism suggests that BH technique can be generally applied to develop high-performance Mg alloys with enhanced strength and ductility.