Effect of Solution Treatment on Microstructure and Properties of Rheo-Squeeze-Cast AA7075 Alloy

7xxx series aluminum alloys exhibit high strength and low density; however, their high degree of alloying results in a pronounced hot-cracking tendency, making direct casting forming challenging. In this study, a rheo-squeeze-cast AA7075 alloy was investigated. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and room-temperature tensile testing were employed to systematically examine the effects of the solution treatment window on the microstructure and mechanical properties of the castings. The distinctive contribution of this work is the quantitative correlation of solution-time-dependent second-phase evolution and porosity with the tensile behavior of ECSC-assisted rheo-squeeze-cast AA7075. The results show that, with increasing solution treatment time, the intergranular eutectic phases gradually dissolved, and their morphology evolved from lamellar structures into fine rod-like features. When the solution treatment time was extended to 12 h, a small number of pore defects appeared in the microstructure. Under the conditions of solution treatment at 470 °C for 8 h followed by aging at 120 °C for 24 h, uniformly distributed Zn–Mg-rich aging precipitates were observed in the matrix, resulting in the best comprehensive mechanical properties, with an ultimate tensile strength, yield strength, and elongation of 498.1 MPa, 413.7 MPa, and 8.2%, respectively. The optimized heat-treatment condition provides a practical route for achieving a favorable strength–ductility balance in rheo-squeeze-cast AA7075 components.