The alloy design and homogenization processes are intimately associated with the microstructure, phase composition and performance for Al-Zn-Mg-Cu alloys. The microstructures and phase composition of a series of Al-Zn-Mg-Cu alloys before and after the homogenization treatments were investigated along with thermodynamic calculation to understand the underlying relationship. The eutectic microstructures (α-Al + M (Mg(ZnAlCu)₂)) are dominating with Cu-enriched [AlCuMgZn] particles, both depending on the Zn:Mg ratio and (Cu + Mg) content, in addition to minor constituent θ (Al₂Cu) and Al₇Cu₂Fe phases in the as-cast alloys. The optimal homogenization process was suggested based on the analysis of the residual phases (i.e., the S (Al₂CuMg) phase) since all (for low/mediate-(Cu + Mg) alloys) or partially (for high-(Cu + Mg) alloys (∼>4.24 wt%)) S (Al₂CuMg) particles were dissolved during the homogenization. This residual S phase may be transformed from the primary M and/or Cu-enriched [AlCuMgZn] phases. The homogenization kinetics calculation results agreed well with above experimental results. A critical (Cu + Mg) level and a linear correlation between Cu and Mg concentrations were revealed based on the thermodynamically modelling, which can be conductive to determine the optimal homogenization process. Furthermore, the solubility limit and stoichiometric balance principles based on controlling the homogenized microstructures can guide the composition design for advanced high-strength aluminum alloys.

AA7050 is an aluminum alloy with superior mechanical properties; however, it is prone to hot tearing (HT) during its production via direct-chill casting. This study focuses on extracting constitutive parameters of the alloy thermomechanical behavior in semi-solid state as well as gaining insight in its failure behavior. Tensile tests were performed using an Instron 5944 at solid fractions between 0.85 (550 °C) and 1.0 (465 °C), at deformation rates of 0.2 and 2 mm/min. The results showed that there are three mechanical behavior regimes in this solid fraction range: ductile at 1.0 (T = 465 °C) ≤ f_s < 0.97 (T = 473 °C), brittle at 0.97 (T = 473 °C) ≤ f_s ≤ 0.9 (T = 485 °C) and then ductile again (at 0.9 (T = 485 °C) < f_s ≤ 0.85 (T = 550 °C)). Fracture surface analysis revealed that the fracture mode was mostly intergranular with fracture propagating through solid bridges as well. Semi-solid constitutive parameters were obtained by making a simple thermal model and numerical tensile tests in ALSIM software package and comparing the simulation results with experimental mechanical tests. The extracted constitutive parameters and available information from the literature support the fact that AA7050 is more susceptible to HT than AA5182 and Al-2 wt pct Cu alloys. The obtained parameters can further enhance the predictive capability of computer simulations of direct-chill casting.