Synergistic effect of Gd and Sr on the microstructure and mechanical properties of Al–Si–Mg alloy

Al–Si–Mg alloys have received widespread application in communication, transportation and other fields on account of their attractive properties, e.g. superior castability, high ductility and excellent corrosion resistance. Comprehensive understanding of relationship between morphologies and mechanical performances under combined refiner-modifier condition is the prerequisite for the applications expansion. In this work, effect of Gd and Gd/Sr on the microstructure and mechanical properties of Al-9Si-0.4 Mg alloy was systematically studied. The results indicated that Gd had excellent refinement effect on α-Al but only partial modification on eutectic Si. Whereas simultaneous addition of Gd/Sr resulted in completely refined α-Al and modified eutectic Si. Growth of eutectic Si in untreated alloys show evidence of typical facet step growth mechanism. However, eutectic Si in Gd/Sr composite modified alloy mainly grew through impurity induce twinning mechanism and twin plane re-entrant edge mechanism, and facet step growth gradually weakened until disappearance. Based on these, both ultimate tensile strength (UTS) and elongation (El) of alloys were significantly improved and reasons were explained.