Influence of tin addition on the microstructure and mechanical properties of Al-Si-Cu-Mg and Al-Si-Mg casting alloys

This article presents the results of an experimental study of the effects of tin (Sn) additions (less than 0.15 wt pct) on the microstructure and mechanical properties of B319.2 and A356.2 cast aluminum (Al) alloys. The microstructural evolution was examined by means of optical microscopy and electron probe microanalysis (EPMA) techniques. Porosity measurements were also made using image analysis. Alloy hardness, tensile and impact properties were evaluated at room temperature for both as-cast and heat-treated conditions. Experimental results show that in B319.2 alloy, Sn precipitates in the form of Sn particles (beta-Sn) within the Al2Cu network, and as minuscule (300 to 500 nm) Mg2Sn particles on the eutectic Si particles. However, in A356.2 alloy, Sn precipitates mainly as Mg2Sn in the form of Chinese script. Both the ductility and the toughness of as-cast B319.2 and A356.2 alloys are sensitive to variations in Sn content, while the yield strength (YS) remains practically unaffected. The higher ductility and toughness of Sn-containing alloys in the as-cast condition may be attributed mainly to the stress-strain state in the matrix material associated with the fineness of Sn-bearing phases.