EFFECT OF MELT TREATMENT, SOLIDIFICATION CONDITIONS AND POROSITY LEVEL ON THE TENSILE PROPERTIES OF 319.2 ENDCHILL ALUMINUM CASTINGS

An experimental investigation of the tensile properties of endchill ca stings of 319.2 commercial aluminium alloy was carried out to determin e 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 param eters on the porosity followed the order H-2 > Sr > TiB2. Pore nucleat ion and pore morphology were solidification time-dependent, with Sr ad dition enhancing the sphericity of the pores. Both ultimate tensile st rength (UTS) and ductility were sensitive to variations in porosity an d solidification conditions, while the yield strength remained practic ally unaffected. Increase in the porosity volume fraction above 0.5% r educed the ductility to negligible levels in the unmodified, non-grain refined base alloy. It was also observed that Sr modification and gra in refining al low for an increase in the porosity level before the sa me level of degradation in ductility is reached.