The effect of Cu, Ag, Sm and Sr additions on the statistical distributions of Si particles and tensile properties in A357-T6 alloy castings

The effect of 1 wt% Cu additions as well as minor alloying additions of Sm, Ag and Sr on the Si particle size and aspect ratio as well as tensile properties was investigated in this study. Results showed that all alloying additions decreased elongation and only Cu addition increased strength slightly whereas others had no adverse effect on yield strength. A correlation between Si particle size and average elongation was found. Sr addition to A357-Cu produced a Weibull mixture in elongation which was interpreted as evidence that this correlation was not due to cause-effect but a third variable affecting both Si particle size and elongation. The Quality Index analysis of tensile data showed that the third variable was most probably the density of bifilms in the melt (melt quality). It is recommended that Quality Index analysis be a part of all new alloy development efforts for cast aluminum alloys.