Spheroidization of primary Mg2Si in Al-20Mg2Si-4.5Cu alloy modified with Ca and Sb during T6 heat treatment process
Abstract The morphology evolution of primary Mg 2 Si particles in a Al-20Mg 2 Si-4.5Cu alloy both unmodified and modified with 0.5wt% 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 Mg 2 Si into sphere in the modified alloy. In contrast, the primary Mg 2 Si particles still kept dentritic in the unmodified alloy. It suggested that the formation of truncated octahedral primary Mg 2 Si 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 Mg 2 Si. Moreover, the existence of fine (~10–20μm) spherical primary Mg 2 Si played an important role in strengthening the alloy, i.e., the ultimate tensile strength (UTS) increased from ~227MPa in the unmodified alloy to ~303MPa in the modified one. It is because the fine spherical primary Mg 2 Si particles can provide a higher fracture stress and strength of the matrix/particle interface. Our study offered a simple methodology to prepare spherical primary Mg 2 Si in an Al-high Mg 2 Si alloy, which is beneficial to design novel light-weight Al-Mg-Si alloys with improved mechanical properties.
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