Effect of Nd on the microstructure and mechanical properties of Mg–3Zn-0.5Zr alloy

Abstract

The effect of adding trace amounts of Nd to Mg–3Zn-0.5Zr alloy was systematically investigated in this work. With the introduction of Nd, the composition of the second phase changed significantly in the as-cast Mg–3Zn-0.5Zr–x Nd (ZKN) alloy (x=0,0.3,0.6,0.9wt%). The volume fraction of the second phases increased with increasing of Nd content, and the distribution gradually changed from a discontinuous point to a semi-continuous reticular structure and then to a continuous reticular structure. Furthermore, it was found that the degree of dynamic recrystallization (DRX) and the sizes of DRXed grains gradually decreased with increasing Nd content (0 wt% ∼ 0.6 wt%) after extrusion, as well as the texture intensity gradually increased. However, when the Nd content was greater than 0.6 wt%, the DRXed grain sizes and the degree of DRX had not changed significantly. In addition, the volume fraction of the precipitates first increased and then decreased as the Nd content increased. High ultimate tensile strength (450–510 MPa), yield strength (400–476 MPa), and acceptable elongation (4.1% ∼ 11.0%) could be obtained in the extruded ZKN alloys. The prodigious increase in strength was mainly caused by grain boundary strengthening, dislocation strengthening, and Orowan strengthening. Low alloying content and traditional extrusion processes contribute to current low-cost and high-strength alloys that have substantial commercial application potential.