Effect of microalloyed Ca on microstructure and mechanical properties of Mg–6Zn–1Mn–4Sn (wt.%) alloy

Abstract

The effect of microalloyed Ca on the microstructure, mechanical properties and aging precipitation of Mg–6Zn–1Mn–4Sn (wt.%, ZMT614) alloy were investigated. The as-cast ZMT614 alloy was mainly composed of α-Mg, Mg–Zn and Mg2Sn phase, and a new CaMgSn phase with high melting point was formed with Ca addition. The CaMgSn phase was easier to form than Mg2Sn during solidification, so the formation of Mg2Sn was suppressed. Undissolved CaMgSn phases after solution treatment played an important role in pinning grain boundary migration and grain growth, and can act as nucleation sites promoting precipitation during aging process. CaMgSn particles also retarded the recovery process and the retained dislocations could act as additional heterogeneous nucleation sites for precipitation. β′ precipitates along [0001]α were finer and disc-like precipitates β'' on (0001)α were denser for Ca-containing alloys after aging treatment. The peak-aged ZMT614-0.5Ca alloy exhibited the optimum mechanical properties and its yield strength, ultimate tensile strength and elongation were 345 MPa, 378 MPa and 6.5%, respectively. The strengthening mechanism was mainly attributed to the grain refinement and precipitation strengthening.