One-Step Synthesis of Spherical Primary Mg2Si in Ca/Sb-Modified Al-Mg2Si Alloy

One-step synthesis of spherical primary Mg2Si is achieved in 0.5 wt.% Ca/Sb-modified Al-12Mg(2)Si alloy by gravity casting for the first time. The addition of 0.5 wt.% Ca/Sb results in large number density of CaSb2 compounds for the nucleation of primary Mg2Si. Embryos of primary Mg2Si can be formed on these CaSb2 compounds in the hypereutectic areas caused by the composition fluctuations. Low content of Mg/Si reduces the Mg/Si concentration for the growth of primary Mg2Si, which results in the final particle size which is less than the critical size of primary Mg2Si isotropic growth; the spherical primary Mg2Si is formed. Fracture behavior changes from the transgranular fracture of eutectic Mg2Si to intergranular fracture of primary Mg2Si with the formation of primary Mg2Si in Al-12Mg(2)Si alloy. Formation of spherical primary Mg2Si decreases the stress concentration, while the bonding strength between the particle and matrix is enhanced. Ultimate tensile strength of 0.5 wt.% Ca/Sb-modified Al-12Mg(2)Si alloy is improved significantly (from similar to 168 to similar to 230 MPa). The study provides a simple methodology to prepare spherical primary Mg2Si, which is beneficial to improving the mechanical property of Al-Mg2Si alloy.