Microstructure and Mechanical Properties of High Pressure Die Cast Mg–Al–Sn–Si Alloys

The effect of a small addition of silicon (Si) was studied to increase the mechanical properties of Mg–Al–Sn alloys. Test specimens were produced by a vacuum die casting process which makes it possible to perform various heat treatments on the alloy which was not possible with conventional high pressure die casting (HPDC). The addition of Si leads to the formation of a binary Mg₂Si phase which contributes to an increase in strength in the as-cast condition. Artificial aging treatments were performed to further increase the strength of the alloys by precipitation of fine Mg₂Sn, Mg₂Si, and Mg₁₇Al₁₂ phases. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) techniques were used to observe these fine precipitates at different stages of the heat treatment and mechanical testing was performed to compare strength and ductility to previous magnesium alloys.