文摘
The morphology evolution of primary Mg2Si particles in a Al-20Mg2Si-4.5Cu alloy both unmodified and modified with 0.5 wt% Ca-Sb prepared by hot-extrusion followed by T6 heat treatment was investigated in the present study. Interestingly, we found that the combination of hot-extrusion and T6 heat treatment was efficient in transforming truncated octahedral primary Mg2Si into sphere in the modified alloy. In contrast, the primary Mg2Si particles still kept dentritic in the unmodified alloy. It suggested that the formation of truncated octahedral primary Mg2Si particles in as-cast state, the fragmentation of particles by hot-extrusion and the enhanced solid-state diffusion of Si and/or Mg atoms during heat treatment were responsible for the spheroidization of primary Mg2Si. Moreover, the existence of fine (~10–20 µm) spherical primary Mg2Si played an important role in strengthening the alloy, i.e., the ultimate tensile strength (UTS) increased from ~227 MPa in the unmodified alloy to ~303 MPa in the modified one. It is because the fine spherical primary Mg2Si particles can provide a higher fracture stress and strength of the matrix/particle interface. Our study offered a simple methodology to prepare spherical primary Mg2Si in an Al-high Mg2Si alloy, which is beneficial to design novel light-weight Al-Mg-Si alloys with improved mechanical properties.
