Potential of multi-pass ECAP on improving the mechanical properties of a high-calcium-content Mg-Al-Ca-Mn alloy

In this study, the multi-pass equal channel angular pressing (ECAP) was employed on a high-calcium-content Mg-Al-Ca-Mn alloy to tailor its microstructure and mechanical properties. The obtained results showed that the network-shaped Mg2Ca and (Mg, Al)2Ca eutectic compounds in as-cast alloy were gradually crushed into ultra-fine particles after ECAP, which exhibited a bimodal particle size distribution and most aggregated at original grain boundaries. Dynamic recrystallization (DRX) of α-Mg occurred during hot deformation via a particle stimulated mechanism, and the almost complete DRX with an average grain size around 1.5 µm was obtained after 12p-ECAP. Moreover, abundant nano-sized acicular and spherical precipitates were dynamically precipitated within α-Mg grains during ECAP. Tensile test results indicated that the maximum strength and ductility were acquired for 12p-ECAP alloy with ultimate tensile strength of 372 MPa and fracture elongation of 8%. The enhanced strength of the alloy could be ascribed to fine DRX grains, ultra-fine Ca-containing particles and dynamically precipitated nano-precipitates, while the improved ductility was mainly due to the refined and homogeneous microstructure, and weak texture with high average Schmid factors. Keywords: Mg-Al-Ca-Mn alloy, Equal channel angular pressing, Dynamic recrystallization, Precipitates, Mechanical property