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 10 1 ¯ 2 twin boundaries can impede twin boundary migration, which effectively suppresses crack propagation and therefore improves the ductility. Meanwhile, the twin boundary pinning obviously increases 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.