High-strength Mg–Al–Ca alloy with ultrafine grain size sensitive to strain rate

The microstructure, texture and mechanical properties of the 1 wt.% Ca-AZ31 alloy (1CaAZ31) processed by high-ratio differential speed rolling (HRDSR) were examined. After HRDSR, the grain size of the 1CaAZ31 decreased to ∼0.9 μm, and (Al, Mg)2Ca particles were highly refined and uniformly dispersed into the matrix. The significant improvement in strength was attributed to the effective grain-size reduction. Contribution of the particle strengthening was relatively small. Strength of the ultrafine grained (UFG) 1CaAZ31 was sensitive to strain rate. As the result, the yield stress was as high as 412 MPa at 1 × 10−1 s−1, while it was 292 MPa at 1 × 10−5 s−1. The strain-rate-sensitivity of the UFG 1CaAZ31 was 0.031–0.041, which is about twice larger than that of its annealed counterpart having coarse grains (0.018). Uniform elongation of the UFG 1CaAZ31 was small compared to that of the coarse-grained 1CaAZ31 due to the reduced strain hardening ability, but its post-uniform elongation was large due to the increased strain-rate sensitivity.

Research highlights▶ High-strength Mg alloys with ultrafine grains could be fabricated by applying extrusion and high-ratio differential speed rolling to the 1 wt.% Ca-AZ31 alloy. ▶ Strength of the ultrafine grained 1 wt.% Ca-AZ31 was sensitive to strain rate. ▶ Uniform elongation of the UFG alloy was smaller than the coarse grained alloy due to the reduced strain hardening ability, but its post-uniform elongation was larger due to the increased strain rate sensitivity.