Microstructure and mechanical properties of the sub-rapidly solidified Mg―Zn―Y―Nd alloy prepared by step-copper mold casting

Abstract In this paper, the microstructure and compression mechanical properties of the sub-rapidly solidified Mg‒Zn‒Y‒Nd alloy cylinders with diameters of 2–8 mm prepared by step-copper mold casting were investigated. The cooling rate of samples increased gradually with decreasing the mold diameter. The ϕ2-mm sample consists of α-Mg with the smallest grain size of about 10 μm and spherical T-phase, rod-like I-phase, ribbon-like Mg7Zn3 phase, skeleton-like W'-phase. With a decrease in the cooling rate, the grain size of α-Mg increases and the secondary phases are coarsened. For the ϕ6-mm and ϕ8-mm samples, I-phase and W'-phase disappear, W-phase appears and tends to form network structures. Among these samples, the ϕ2-mm one exhibits the highest ultimate fracture strength of 384 MPa and the largest plasticity of 30 %. The good mechanical properties were attributed to the activation of non-basal slips at the later stage of deformation. This result suggests that the sub-rapid solidification technique would be a promising way to improve the mechanical properties of Mg alloys, which can be used as biodegradable mini-implants.