Improving toughness of a Mg2Ca-containing Mg-Al-Ca-Mn alloy via refinement and uniform dispersion of Mg2Ca particles

In this work, two wrought Mg-3.66Al-4.25Ca-0.43 Mn (wt%) alloys with different morphology and distribution of Mg2Ca particles were fabricated by hot extrusion and multi-pass (32) equal channel angular pressing (ECAP). The as-extruded alloy exhibits a banded microstructure with alternately arranged Mg2Ca particle bands, fine alpha-Mg dynamically recrystallized (DRX) grain bands, and coarse alpha-Mg deformed grain bands. The Mg2Ca bands are composed of broken Mg2Ca particles which are aggregated and aligned along extrusion direction. The microstructure of ECAP alloy contains complete alpha-Mg DRX grains and refined Mg2Ca particles which are dispersedly distributed at grain boundaries. Tensile test results show that the as-extruded alloy possesses high ultimate tensile strength (UTS) of 420 MPa and poor fracture elongation of 7 %, while the ECAP alloy exhibits improved toughness with UTS of 347 MPa and fraction elongation of 16 %. The higher strength of as-extruded alloy is mainly ascribed to the contribution of coarse deformed grains with strong texture, and its poor toughness is resulted from the formation of Mg2Ca bands within which microcracks could form and extend rapidly. On the contrary, the refined and dispersedly distributed Mg2Ca particles are effective to retard crack initiation and impede crack propagation, thereby enhancing the toughness of ECAP alloy significantly. (C) 2020 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.