Minimizing detrimental impacts of β-Fe in Al-Mg-Si alloy by combining thermal and compression processes

When Al alloy is recycled, it will continue to enrich Fe, Si impurities and form coarse plate-like β-Fe upon solidification, which is very detrimental to the conductivity and mechanical properties of the final components. In this study, a multi-object optimization method was developed to achieve the combination of high-strength and high-conductivity of Al-Mg-Si alloys by optimizing homogenization and hot deformation process. The homogenized elongation reached 14%, which is 50.5% higher than the as-cast state at 9.3% simply by increasing the relative α-Fe fraction f_α (α/(α + β) %) from 0.56 to 0.81. By inventing two new thermo-mechanical processing paths: route 1 and 2, a superior combination of strength and conductivity has been achieved. The strength and conductivity of route 1 process are 292.04 MPa and 51.10%IACS, respectively, with f_α at 85%; for route 2 process, they are 299.26 MPa and 50.66%IACS, respectively, with f_α at 96%. That means the transformation from β-Fe to α-Fe is almost complete. Therefore, the quantitative characterization of β-Fe and α-Fe fractions enables the design of Fe tolerable recycled Al-Mg-Si alloys at high strength, high conductivity, and high ductility.