Multilevel microstructure control of cast Al–7.0Si–4.0Cu alloy with high strength–toughness synergy via micro-alloying combined with manipulation by in-situ nano-ceramics

Abstract

Incident Ti–Si poisoning when applying traditional agents of microstructure manipulation in Al–Si alloys is always adverse to realize multilevel microstructure control. This work combined the manipulation by physically formed in-situ nano-ceramics from Fe79.58B11.26Si9.26 amorphous alloy and the micro-alloying to comprehensively improve the microstructure configuration of Al–7.0Si–4.0Cu alloy. It was suggested that micro-alloying of Mg and Sb prominently refined α-Al dendrites and eutectic silicon. Micro-alloying with Mg increased the nucleating temperature of α-Al, meanwhile Mg atoms can hinder the growth of α-Al and eutectic silicon. Sb atoms can also be adsorbed to the growth interfaces of eutectic silicon hindering the growth process. On this basis, trace Fe79.58B11.26Si9.26 amorphous alloy brought further optimization on α-Al dendrites and eutectic silicon, especially Al2Cu and Mg2Si, realizing the multilevel microstructure control. In-situ Fe2B and Fe3Si nano-ceramics were confirmed to have low lattice misfits with α-Al and silicon, serving as efficient nucleation sites and growth retardants. After combined micro-alloying and manipulation, the mean sizes of α-Al and eutectic silicon were significantly refined by 72.7% and 79.9%, respectively, meanwhile, the ultimate tensile strength (UTS) and plastic strain (δ) were improved to 480 MPa and 9.4%, corresponding to 30.1% and 77.4% improvement, respectively. This work provides new mentality to realize multilevel microstructure control and improvement of strength–toughness synergy in Al–Si alloys.