Effects of Individual and Combined Additions of Pb, Bi, and Sn on the Microstructure and Mechanical Properties of Al-10.8Si-2.25Cu-0.3Mg Alloy

The effects of individual and combined additions of Pb, Bi, and Sn on the microstructure and mechanical properties of the modified grain-refined Al-10.8 pct Si alloy were investigated. Microstructures were monitored using optical microscopy and electron probe microanalysis (EPMA) techniques. Mechanical properties of as-cast and heat-treated alloys were evaluated using hardness measurements and tensile testing. The results show that Pb alone has no significant effect on the microstructure and mechanical properties in the as-cast and heat-treated conditions; Bi counteracts the modifying effect of Sr, leading to coarsening of the eutectic Si particles; however, Sn precipitates as beta-Sn within the Al2Cu network when added individually. Lead and bismuth combined precipitate as bismuth particles enveloped with Pb3Bi phase, thereby improving mechanical properties in the as-cast and aged conditions contrary to the combined addition of Bi and Sn. Tin and indium combined precipitate as In3Sn phase, thereby providing better mechanical properties in as-cast and aged conditions than may be obtained through the addition of Sn alone.