Effect of melt treatment, solidification conditions and porosity level on the tensile properties of 319.2 endchill aluminium castings

Abstract

An experimental investigation of the tensile properties of endchill castings of 319.2 commercial aluminium alloy was carried out to determine the effect of Sr modifier, TiB₂ grain refiner and hydrogen content, and the resulting porosity on these properties. It was found that with respect to solidification time, the interaction effect of other parameters on the porosity followed the order H₂ > Sr > TiB₂. Pore nucleation and pore morphology were solidification time-dependent, with Sr addition enhancing the sphericity of the pores. Both ultimate tensile strength (UTS) and ductility were sensitive to variations in porosity and solidification conditions, while the yield strength remained practically unaffected. Increase in the porosity volume fraction above 0.5% reduced the ductility to negligible levels in the unmodified, non-grain refined base alloy. It was also observed that Sr modification and grain refining allow for an increase in the porosity level before the same level of degradation in ductility is reached.