Semi-solid Constitutive Parameters and Failure Behavior of a Cast AA7050 Alloy

Abstract

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.