Effects of strontium on the structure and properties of aluminium-silicon alloys

In this study, modification of aluminium-silicon eutectic alloy by strontium was investigated and shown to improve the tensile properties of the alloy. The evaluation of the modification was done metallographically. The tensile properties were obtained from round, cast to shape and size, test bars which were produced in green sand moulds and cast iron chill moulds. The appearance of the fracture surfaces after tensile testing showed structural differences in the modified and unmodified specimens for both rates of cooling. The effect of magnesium addition to aluminium-silicon eutectic alloy was investigated also. The initial addition of 0.4% magnesium to this alloy increased the strength at the expense of the ductility, but beyond this amount the tensile properties decreased for both rates of cooling. The high-magnesium-content modified specimens showed more porosity than the unmodified specimens, although the tensile properties were higher due to the structural modification.