Achieving high strength-ductility synergy via Guinier-Preston zone formation in a new Mg–Zn–Al–Ca–Mn–Ce sheet alloy

ZAXME11100 (Mg-1Zn-1Al-0.5Ca-0.4Mn-0.2Ce, wt.%) is a recently developed sheet alloy with excellent formability at room temperature. The yield strength of this alloy is significantly improved by a short 1-hour aging treatment at 210 °C (T6), from 159 MPa in solution-treated state (T4) to 270 MPa in the T6 condition, with a slight reduction in tensile elongation (from 31% in T4 to 26% in T6). In this work, precipitation microstructure was characterized to explain the aging hardening and high strength-ductility synergy of the new alloy. A high density (8×1023/m3) of ordered monolayer Guinier-Preston (GP) zones enriched in Al, Ca and Zn uniformly form on the Mg basal planes after T6 treatment. Grain boundary segregation of Al, Ca and Zn is also observed. Deformation microstructure of T4 and T6 samples tested to various strain levels was examined. At small strain levels, basal and non-basal dislocation slip dominates the deformation process, and cross slip of dislocations between basal and non-basal planes is observed in T6 samples. The GP zones are gradually destroyed by plastic deformation. Based on those results, the strengthening contribution of ordered GP zones was modeled to be 116 MPa. Therefore, formation of GP zones is an effective way to achieve high strength-ductility synergy in wrought Mg alloys.