The formation of (Al, Si)3(Ti, Sc) through microalloying and solidification control synergy in Al-7Si-0.7Mg refines α-Al greatly

The grain refinement mechanism of Al-7Si-0.7Mg alloy by Sc and Ti have been systematically investigated at different cooling rate. The Si-poisoning effect have been avoided by synergistic inoculation of Sc and Ti at special where slow cooling rate before solidification is required. The inoculation of Sc and Ti avoid the Si-poisoning effect by forming a new phase of (Al, Si)3(Ti, Sc). The gradient solidification is adopted to make the (Al, Si)3(Ti, Sc) phase reappear at fast cooling rate to avoid Si-poisoning. The average grain size of Al-7Si-0.7Mg-0.15Ti-0.5Sc alloy solidified through gradient solidification is refined to 131 µm decreased 45 % compared with traditional cast. The mechanism for anti Si-poisoning is also investigated using first-principles calculation and High-Angle Annular Dark-Field STEM. Data will be made available on request. •The poisoning effect of Si on Al3Ti have been tackled.•D022-(Al, Si)3(Ti, Sc) are observed in Al-Si-Mg-Sc-Ti alloy.•D022-(Al, Si)3(Ti, Sc) can act as the heterogeneous nucleus of α-Al.•A new casting technology, gradient solidification, makes grain finer.•The mechanism for anti Si-poisoning is investigated.