Effects of different Al contents on as-cast microstructure and properties of Mg-Al-Si-Sr alloy

Effects of different Al additions (3wt.%,5wt.%, 7wt.%, 9wt.%Al) on as-cast microstructure and properties of Mg-Al-1Si-0.5Sralloy were studied.The average grain size decreases and then increases with the increasing of Al additions.There are polyhedral shape, fine fibers shape, a few Chinese script Mg 2 Si particles and β-Mg 17 Al 12 divorced eutectic phase appeared in the interdendritic area in Mg-3Al-1Si-0.5Sralloys.With the increase of Al content, more and more β-Mg 17 Al 12 divorced eutectic phase appear in semi-continuous distribution.The lamellar-like shape β-Mg 17 Al 12 secondary-precipitated phase emerge with Al addition of 5wt.%, 7wt.% and 9wt.%.The optimum tensile properties of Mg-7Al-1Si-0.5Sralloy can be obtained, where the ultimate strength, yield strength and elongation are 201.1MPa,160.7MPa, 4.8% at ambient temperature and 164.5MPa, 128.0MPa, 7.4% at 150°C respectively.The hardness increased with the increasing of Al content.