Enhanced comprehensive performance via alloying and rheo-diecasting in a semi-solid Al–Si–Fe–Mg–Cu–Sr alloy

A semi-solid Al alloy with superior comprehensive performance was obtained via alloying design concept and rheo-diecasting (RDC). The semi-solid alloy slurry was obtained via the vibrating contraction sloping plate. As the contents of Cu and Mg elements increased, the secondary dendrite arm spacing (SDAS) decreased and solubility of Cu and Mg elements increased, which improved the mechanical property and decreased the thermal conductivity of as-cast alloys. The effect of microstructure evolution induced by pouring temperature on mechanical properties at room and elevated temperatures, thermal conductivity, and corrosion behavior of the RDC alloy was investigated. The results demonstrated that the low porosity and refined primary α1-Al grains, secondary α2-Al grains, β-Al5FeSi phases, eutectic Si phases played a significant role in enhancing mechanical properties of the alloy at room temperature. Meanwhile, some submicron β-Al5FeSi phases effectively hindered grain boundary sliding, resulting in the increased mechanical properties of the alloy at elevated temperatures. The improvement in thermal conductivity was related to the decreased electron scattering due to the reduced porosity and small-sized secondary phases. The decrease in the potential difference between the β-Al5FeSi phase and matrix helped improve the corrosion resistance of the alloy.