Fast shot speed induced microstructure and mechanical property evolution of high pressure die casting Mg-Al-Zn-RE alloys

Abstract

In this study, the effects of fast shot speeds during high pressure die casting on the microstructure and mechanical properties of Mg-Al-Zn-RE (RE: rare earth) alloys were systematically investigated. The optimum mechanical performance was achieved at a fast shot speed of 6 m/s, and the ultimate tensile strength, yield strength, and elongation of the castings reached 290 MPa, 190 MPa, and 10.5 %, respectively. With an increase in fast shot speed, the yield strength, ultimate tensile strength, and elongation of the Mg-Al-Zn-RE alloy increased by 17 MPa, 82 MPa, and 8.2 %, respectively. These improvements are primarily attributed to the decreased area fraction of externally solidified crystals (ESCs) and the reduced volume fraction of pores. Furthermore, the enhancement in yield strength is due to grain boundary strengthening, solid-solution strengthening, and second-phase strengthening. The reduction in the area fraction of ESCs and porosity are the main contributors to the improvement in plasticity. The findings of this study provide valuable guidance for the intelligent design of novel high pressure die casting Mg alloys.