Abstract:To fabricate Al-Si-Fe-Mg-Cu alloys with superior comprehensive performances, Sr and Mn elements were used to modify secondary phases, i.e., eutectic Si and Fe-rich phases. As the Sr element content increases from 0 to 0.02 wt.%, the morphology of eutectic Si phases changes from coarse lamellar to fine fibrous. However, due to the increased porosity caused by Sr, the mechanical properties and thermal conductivity of the as-cast alloy with Sr content of 0.03 wt.% are weakened. Under the optimized Sr content, Mn element was added to further tailor the properties of the as-cast alloy. With the increase in Mn content from 0.2 to 0.6 wt.%, the needle-like β-Al₅FeSi phases transform into Chinese-script α-Al₁₅(Fe,Mn)₃Si₂ phases, and the mechanical properties of the alloy are initially enhanced, then weakened. The thermal conductivity is decreased owing to the solution of Mn atoms in the alloy. In comparison, Al-Si-Fe-Mg-Cu alloy with addition of 0.02 wt.% Sr and 0.4 wt.% Mn exhibits a satisfactory comprehensive performance, with thermal conductivity of 168.5 W/(m·K), ultimate tensile strength of 201.9 MPa, yield strength of 115.3 MPa, and elongation of 9.0%.

Key words: Al-Si alloy; modification treatment; secondary phases; mechanical properties; thermal conductivity