Effect of minor Ca addition on microstructure and mechanical properties of a low-alloyed Mg–Al–Zn–Sn alloy

Abstract

Due to the lack of secondary phases, low-alloyed Mg–Al series alloys usually exhibit low strength. In this work, by the addition of Ca element, a microstructure consists of a large fraction of fine recrystallized grains, profuse low angle boundaries and dense nano-sized CaMgSn particles has been achieved in a low-alloyed Mg-1.1Al-1.1Zn-0.2Sn-0.3Ca (wt%) alloy via sub-solidification followed by hot rolling and annealing. The addition of Ca introduces a large number of nano-sized CaMgSn particles, which can pin boundaries to inhibit recrystallization and grain growth during rolling and annealing. The annealed dilute Mg-1.1Al-1.1Zn-0.2Sn-0.3Ca alloy exhibits a high strength-ductility synergy with a yield strength (YS) of ∼249 ± 3 MPa, an ultimate strength (UTS) of ∼308 ± 4 MPa and a total elongation of ∼14 ± 1.1%. The fine recrystallized grains and profuse low angle boundaries account mainly for the high YS, which contribute 65% to the total YS. Meanwhile, the precipitation strengthening contributes ∼57 MPa to the total YS. The moderate elongation can be attributed to the activation of <c + a> dislocations due to the fine grain sizes (∼2 μm), as well as Ca and Sn solute atoms in the α-Mg matrix. The present work provides an effective way to fabricate dilute Mg alloys with enhanced mechanical properties at room temperature by the combination of SRS, hot rolling and annealing.