Depth-dependent microstructure and mechanical properties of hot rolled AA7075

In this study, the through-thickness mechanical properties of a 32 mm thick hot rolled 7075 aluminum plate were measured with microscale uniaxial tensile tests. The mechanical strength across the thickness of the plate exhibited a complex M-shaped profile, with the maximum yield strength and ultimate tensile strength of 440.45 MPa and 493.81 MPa respectively attained at 11 mm depth from the surface of the plate. Representative samples from 0, 4, 11 and 16 mm depths were investigated to understand the influence of the precipitate distribution on the evolution of through-thickness mechanical properties in this alloy. The size and distribution of the microscale (>50 nm) and nanoscale (<20 nm) precipitate phases were quantified with a combination of large area scanning electron microscopy (SEM) and small angle x-ray scattering (SAXS) techniques and correlated with through-thickness mechanical properties obtained through microscale tensile testing. The nanoscale precipitate density as investigated with SAXS showed that the 11 mm depth had the highest volume fraction (0.0086) in comparison to the other representative depths. Moreover, the quench and temper processes were modeled using the precipitation module of Thermo-Calc with various assumptions about cooling rate and microstructure and they were found to be in good agreement with the experimental findings.