Effect of heat treatment on microstructure modulation and aging precipitation behavior of Al-6Si-0.75Mg-0.2Sc-0.15Zr-0.12Sb alloy

The Al-6Si-0.75Mg-0.2Sc-0.15Zr-0.12Sb alloy is prepared using the smelting process. This study investigates the impacts of solution and aging temperatures， as well as their durations， on the microstructure and mechanical properties of the alloy. Additionally， it analyzed the morphology， size， and distribution of Si and precipitated phases.It is observed that the as-cast microstructure comprises α-Al， eutectic Si， Mg₂Si， Al₃Sc， and Al₃（Sc， Zr） phases. As the solution and aging temperatures and times increase， the morphology of the Si phase transforms from plate-like and fibrous to worm-like and nearly spherical. Prolonged holding times lead to the segregation and coarsening of the Si phase， which turns into short rod-like structures. The tensile strength and elongation initially rise and then decline with increasing solution temperature. During single-stage aging at 170 °C， the strength and hardness first increase and then decrease with the extension of the holding time， eventually reaching a stable state. The interface between the β´´ and α-Al phases evolves from coherent to semi-coherent and then incoherent， and the fracture mechanism shifts from intergranular fracture to typical dimple fracture.Pre-aging at 110 ℃ promotes the precipitation of β´´ and Al₃（Sc， Zr） phases， significantly spheroidizes the morphology of the Si phase， and refines its size. The length and precipitated surface density of the β´´ phases are （29 ± 1.8） nm and 3.52 × 10³ μm⁻²， respectively. After dual-stage aging at 110 °C/2 h + 170 °C/6 h， the tensile strength， yield strength， and elongation can reach 363， 301 MPa， and 7.9%， respectively.