Effect of Sb doping on microstructure, mechanical and electronic properties of Mg2Si in Mg2Si/AZ91 composites by experimental investigation and first-principles calculation

Abstract

In this work, the effect of Sb addition on the microstructure and mechanical properties of Mg2Si phase in Mg2Si/AZ91 composites are investigated by experimental research and first-principles calculation. The experimental results show that the coarse dendritic shape is modified to blocky polygonal shape, and the size of primary Mg2Si, is successfully refined with the Sb addition. With enhancing Sb addition contents, the doping concentration of Sb in Mg2Si phase keeps increasing, which accounts for the morphology and size modification. Besides, nano-indentation tests reveal that the Young’s modulus of Mg2Si phase exhibits less reduction, while the hardness is significantly improved when introducing 2.0 wt%Sb. The calculated results indicate that the structure stability of Mg2Si crystal is enhanced, and the mechanical modulus including bulk modulus, shear modulus and Young’s modulus of Mg2Si are decreased with the increase of Sb concentration, agreeing well with experimental observation, but the hardness reduces, which is contrary to the experimental results. Mg2Si phase doping with Sb atoms, however, exhibits improved ductile behavior compared with undoped Mg2Si due to the increased Poisson’s ratio and B/G ratio. In addition, Sb doping can weaken the bond strength and reduce the population of Mg-Si covalent bonds, as well as generate new Mg-Sb bonds with lower strength based on the electronic structure analysis, which contribute to the decrease of mechanical modulus.