Achieving Ultra-Fine Grains and Improved Mechanical Properties in a Mg-Zn-Al-Ca Alloy via Forward Extrusion and Post Decreased-Temperature Equal Channel Angular Pressing

In this work, a Mg-Zn-Al-Ca alloy was processed by the combination of forward extrusion and post ECAP. The evolution and corresponding mechanism of the microstructure and mechanical properties of the Mg-5Zn-2Al-1Ca alloy were systematically investigated. As a result, the decreased-temperature ECAP processing contributes to the significant grain refinement and the production of substructures in the alloy. The minimum average grain size of 1.04 µm is achieved in the alloy after 2 passes of ECAP at 250 °C, followed by 2 passes of ECAP at 170 °C. Moreover, the texture type is changed from conventional basal fiber texture to shear texture after ECAP deformation. Consequently, the Mg-5Zn-2Al-1Ca alloy after the last 2 passes of ECAP at 170 °C exhibits excellent mechanical properties (ultimate tensile strength of ~ 350 MPa and an elongation of ~ 20%). The grain boundary strengthening and the texture strengthening as well as the Orowan strengthening effect are considered as the main contributors to the substantial increase in strength.