Refinement Mechanism of the Hypoeutectic Al–7Si Alloy by Adding a Novel La-Rich Rare-Earth Grain Refiner

Refining the grain size of the as-casted hypoeutectic Al–Si alloys is an established technique for improving their mechanical properties. This work is based on the development of a novel La-riched grain refiner, i.e., Al–3Ti–4.35La, which exhibited remarkable efficiency for grain refinement from 1.46 mm into ~ 0.1 mm (with 0.2 wt pct of the refiner), increasing both tensile strength, yield strength, elongation and hardness from 154.3 MPa, 64.5 MP, 5.83 pct, and 54.8 HV to 178.3 MPa (an enhancement of 15.6 pct), 77.5 MPa(an enhancement of 20.2 pct), 12.02 pct (an enhancement of 106.0 pct), and 58.4 HV (an increase of 6.6 pct), respectively. The in situ formation of the Ti₂Al₂₀La phase served as the nucleus for α-Al during solidification. The segregation of trace Si and La atoms at the interface indicates their chemical affinity with a relatively lower energy configuration, which is consistent with the first-principles calculations. The results of this study offer an innovative approach for attaining considerable grain refinement in Al–7Si alloys by constructing rare-earth grain refiners.