EFFECT OF STRONTIUM ADDITION ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF ALSI7MG0.3 ALLOY

The effect of Sr on the microstructure and mechanical properties of AlSi7Mg0.3 alloy were investigated over a wide range of Sr additions between 0.01 and 0.2 wt%. Sr modifies not only the eutectic Si particles but also the beta-Al5FeSi needles. While 0.01-0.02 wt% Sr suffices to achieve an adequate level of eutectic modification, it takes higher Sr additions to modify the beta-Al5FeSi needles. The porosity and average grain size increase with increasing Sr additions, but there is no evidence of coarsening of eutectic Si particles, to signal overmodification. Since the adverse and favourable effects introduced by Sr addition balance each other, the impact of Sr additions between 0.01 and 0.2 wt% on the tensile properties of AlSi7Mg0.3 alloy is limited. Nevertheless, tensile properties enjoy some improvement with increasing Sr additions, possibly owing to the modification of beta-Al5FeSi at high Sr additions. The modification of beta-Al5FeSi needles apparently compensates for the increasing porosity as well as grain coarsening, the two adverse effects of Sr addition