Microstructural evolution and strengthening mechanisms of a novel Al–11Si–3Cu alloy microalloyed with minor contents of Sr and Sc

Alloying technology usually improves the mechanical properties of alloys; however, the high cost of alloying elements limits their wider applicability to conventional cast aluminium alloys. In this work, a novel high-strength, ductile, and low-cost Al–11Si–3Cu alloy microalloyed with minor Sr + Sc was developed and shown to improve the ultimate tensile strength and elongation relative to the majority of developed Al–Si-(Cu) alloys to date. Atom probe tomography (APT) reconstruction showed that Sc atoms existed separately instead of being enriched with Al and Sr atoms in eutectic Si, which indicated that the growth of eutectic Si in different crystallographic directions was inhibited. Many interactive stacking fault planes were formed in the novel alloy, which, as a series of barriers, effectively prevented dislocations from passing through, thereby providing a significant boost to the alloy strength. Moreover, a large number of Al3Sc and AlSi2Sc2 nano-precipitates exerted positive effects on the alloy strength by effectively slowing the dislocation movement. In addition, the strengthening mechanisms of the novel high-strength ductility Al–11Si–3Cu alloy are discussed. •A novel high strength-ductility Al alloy was developed by minor content of Sr and Sc micro-alloying.•The distribution of micro-alloyed atoms in the novel alloys were analyzed by APT.•The Sc and Sr atoms inhibited the growth of eutectic Si in different directions.•Many stacking faults, Al3Sc and AlSi2Sc2 nanoparticles are formed in the alloy.•Effect of eutectic refining, stacking fault and nanoparticle strengthen are discussed.