The investigation of microstructure evolution and strength-ductility mechanism of Mg-5Bi-xAl alloys

Abstract

The development of low-cost Mg alloys with excellent strength-plasticity matching is essential to expand their industrial applications. In this study, a new Mg-5Bi-1Al alloy with high performance has been reported. Aluminium with various content was added to investigate the microstructure evolution and mechanical properties of the Mg-5Bi-xAl (0, 1, 3, and 5 wt%) alloys. The results revealed that all the as-extruded Mg-5Bi-xAl alloys exhibited bimodal structure. The dynamic recrystallization (DRX) fraction increased in accordance with the rise in Al content ≤3 wt%, which was attributed to the increased number of DRX nucleation sites and enhanced effect of particle stimulated nucleation (PSN). In Mg-5Bi-5Al alloy, the high-density fine precipitates were found to pin dislocations, resulting in a decrease in the DRX fraction. The grain texture splited in extrusion direction with the addition of Al element, and texture intensity decreased significantly. As-extruded Mg-5Bi-1Al alloy exhibited excellent strength-ductility matching, demonstrating the yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) of 241 MPa, 315 MPa, and 18.9%, respectively. The increase in YS was mainly attributed to the grain refinement and precipitation strengthening. The excellent plasticity was mainly owing to the weakening of basal texture. However, work-hardening rate was decreased as Al content increased to 3 wt% and 5 wt%, which may be related to the presence of numerous undissolved coarse second phases. This study provides an experimental basis for developing medium alloyed Mg alloys with low-cost, excellent strength-ductility matching.