Influence of 0.6 wt% Sc/Nd on the microstructure, mechanical property and in vitro biodegradation behavior of as-cast Mg-2Zn-0.2Zr alloy

Abstract

The effects of 0.6 % Sc/Nd on the microstructure, mechanical property and in vitro biodegradation behavior of as-cast Mg-2Zn-0.2Zr (ZK20, wt%) alloy were investigated in this work. The 0.6 % Sc addition in ZK20 alloy weakens the segregation of rich-Zr phase and increases the volume fraction and particle diameter of nano-scale rod-like β’(MgZn2) particles in the matrix. It is mainly because of the precipitation strengthening of the nano-scale β’(MgZn2) precipitates that the as-cast ZK20–0.6Sc alloy exhibits good mechanical property (UTS=213 ± 1 MPa; YS=100 ± 4 MPa) with the increasing of the yield strength from 77 MPa to 100 MPa. Compared with ZK20 and ZK20–0.6Nd alloys, ZK20–0.6Sc alloy exhibits the lowest degradation rate in vitro (Dw=0.20 ± 0.04 mm·y–1) because the reduction of rich-Zr phases is beneficial to the electrochemical homogeneity. Adding 0.6 % Nd element in ZK20 alloy induces the MgZn2Nd ternary phase preferentially generated at grain boundary and within grains, resulting in a reduction of the strength and elongation (UTS=201 ± 1 MPa; δ: 27.7 ± 1.8 %). Besides, the large electrochemical inhomogeneity between the MgZn2Nd phase and the Mg matrix triggers severe overall degradation.