Effects of secondary phase and coarse grain defects on mechanical behavior of near-equiatomic Al alloy during extrusion at different temperatures and speeds

This study investigates the microstructural characteristics and mechanical properties of a novel near-equiatomic AlZnCuMgSi alloy under various extrusion conditions. The alloy demonstrates favorable mechanical properties, at the extrusion temperature of 250 °C and the extrusion speed of 1.0 mm/s, with a yield strength of 233.07 MPa, a tensile strength of 306.90 MPa, and an elongation of 15.70%. Under this condition, the secondary phases are small and uniformly distributed, promoting recrystallization. The lattice mismatch between the secondary phases and the matrix impedes dislocation movement, resulting in dislocation pile-up, which generates regions of high dislocation density and facilitates the formation of high-angle grain boundaries, thereby enhancing the mechanical properties of alloys. The microstructure characteristics reveal that the alloy comprises coarse grains distributed in the extrusion direction and fine recrystallized grains. The contribution of the fine grains to the stress is minimal, whereas the coarse grains serve as the primary stress concentration zones, rendering them more susceptible to fracture during deformation and adversely impacting the strength and ductility of the as-extruded AlZnCuMgSi alloy.