A novel semi-solid rheo-squeeze strategy for optimizing the microstructure and mechanical properties of A356 aluminum alloy

This study introduces an innovative method that integrates instantaneous undercooling-induced nucleation, semi-solid rheological squeeze casting, and T6 heat treatment (525 °C solution treatment for 3 h followed by 155 °C artificial aging for 8 h) to produce A356 alloy castings with enhanced strength and plasticity. The investigation examines the impact of key structural components—single-waved protrusion (L = 225 mm) and double-waved protrusion (L = 400 mm)—on the microstructure and mechanical properties of A356 alloy castings. The results demonstrate that when L = 400 mm (referred to as RSC-400), the primary α-Al grains are small and uniform, secondary nucleation of the α2-Al phase is nearly absent, and the eutectic Si phase transitions from sharp dendritic forms to fine rod-like or nearly spherical shapes. In contrast, the RSC-225 sample exhibits coarser grains, significant agglomeration of the eutectic Si phase, and the presence of harmful Fe-rich β-Al 5 FeSi and π-Al 8 Mg 3 FeSi 6 phases. After a T6 heat treatment, the microstructure of the RSC-400-T6 sample further improves in sphericity, with the eutectic Si phase passivated and a notable reduction in the Fe-rich β phase. The precipitation strengthening mechanism is effectively activated. Tensile tests reveal that the RSC-400-T6 sample achieves a tensile strength of up to 260.74 MPa and an elongation of 10.03 %, outperforming other samples processed by different methods in this study. This research demonstrates that the synergistic effects of cooling channel length, semi-solid rheological squeeze casting, and T6 heat treatment can effectively control microstructural development and optimize the mechanical properties of A356 alloys, providing a theoretical and practical foundation for the efficient, low-energy, and precise manufacturing of high-performance aluminum alloy components.