Tailoring the mechanical properties of the multicomponent lightweight alloy Al58Zn28Mg6Si8 via composition and processing-route engineering

In this study, the multicomponent (medium entropy) lightweight alloy Al 58 Zn 28 Mg 6 Si 8 was systematically improved through a dual optimization strategy. First, the chemical composition was adjusted using the CALPHAD methodology, reducing the Si content and incorporating Sr and Sb as modifying elements to control intermetallic phase formation. This optimization led to the new composition Al 60 Zn 27 Mg 11 Si 2 , effectively suppressing the formation of primary Si and altering the morphology of the Mg 2 Si phase. Second, the alloy microstructure was modified using two processing techniques—Directional Solidification (DS) and Near-Solidus Forming (NSF)—followed by heat treatment. These methods were selected to refine the microstructure, improve phase distribution, and enhance mechanical performance. Microstructural characterization and mechanical testing, including uniaxial compression and nanoindentation, were performed on both as-cast and heat-treated samples. The results revealed that the combination of chemical and microstructure optimization significantly enhanced the compressive strength, increasing from 471 MPa to 769 MPa—a 61 % improvement. Additionally, directional solidification produced the finest lamellar-dendritic microstructure, resulting in the highest yield strength. However, the alloy remained brittle, with limited ductility despite structural refinement. Overall, this work highlights the strong interdependence between composition, processing, and microstructure in determining the mechanical performance of multicomponent lightweight alloys. The findings provide a pathway for designing high-strength multicomponent systems tailored for structural applications.