Effect of ECAP process on as-cast and as-homogenized Mg-Al-Ca-Mn alloys with different Mg2Ca morphologies

A comparative study on the microstructural evolutions and mechanical properties of as-cast and ashomogenized Mg-3.5A1-4.5Ca-0.4Mn (wt.%) alloys with different Mg2Ca morphologies during equal channel angular pressing (ECAP) is reported herein. The results showed that while the network Mg2Ca phases in the as-cast alloy were broken into ultrafine particles after multipass ECAP, they were still aggregated at original grain boundary regions. After homogenization, large spherical Mg2Ca particles, which were not refined but distributed uniformly through multipass ECAP, were formed. With an increase in ECAP passes, both aggregated ultrafine Mg2Ca particles and large spherical particles stimulated dynamic recrystallization (DRX). The ultrafine Mg2Ca particles introduced incomplete DRX with a finer ccMg grain size, whereas the large spherical particles resulted in almost complete DRX with a coarser grain size after 12p-ECAP. Moreover, nano-sized acicular and spherical precipitates were dynamically precipitated during ECAP. Owing to the fine grain size, weak texture, ultrafine Mg2Ca particles, and nano precipitates, the 12p-ECAP cast alloy exhibited a high ultimate tensile strength of 331 MPa and moderate fracture elongation of 7.4%. The ECAPed homogenized alloys showed lower mechanical properties, which could be attributed to preexisting microcracks within Mg2Ca spherical particles that were introduced by homogenization. (C) 2019 Elsevier B.V. All rights reserved.