Parameters Controlling the Tensile Properties of Non-Modified and Sr-Modified Al-Si-Cu-Mg 319-Type Alloys

The mechanical properties of Al-Si-Cu-Mg 319-type alloys are determined by their microstructures, which are in turn determined by the addition of such hardening elements as Cu and Mg, as well as by the eutectic Si-particle characteristics which are subject to being transformed from their acicular morphology in non-modified alloy to a fibrous form through the addition of modifiers such as Sr to the alloy. Solution heat treatment is also applied so as to obtain homogeneous Si particles in the structure, and to maximize dissolution of Al2Cu and other hardening phases. The results obtained show that the addition of Mg to experimental 319 alloys leads to an increase in strength, but to a reduction in percentage elongation (%El); the higher the Mg content, the greater the decrease in elongation. In unmodified alloys, the loss of elongation is compensated for by the increase in strength, thus the quality of the alloy itself increases. Magnesium may cause a greater increase in yield strength (YS) than it does in ultimate tensile strength (UTS). In Mg-free alloys, the addition of Sr increases strength (YS, UTS) and ductility (%El). When Mg is present, in either experimental or industrial alloys, the effect of Sr in increasing the percent elongation is reduced. In the Mg-free 319 alloys, tensile properties increase with increasing solution treatment time and temperatures.