Phase Transformations in Thermally Treated Gas-Atomized Al 7075 Powder

Abstract

Al 7075 is a heat-treatable Al–Mg–Zn alloy widely used in the aerospace industry. Recently, it has found application as feedstock for metal additive manufacturing (MAM). It has been shown that wrought alloy compositions in powder form differ in microstructure and properties from their conventional form. Given this, it is important to understand the microstructure of the powders prior to use in MAM processes. This work studies as-atomized gas-atomized Al 7075 powders and the effect of thermal treatments on microstructure. Extensive electron microscopy revealed the presence of T-phase, Al7Cu2Fe, and Mg2Si in the as-atomized condition. Thermal treatments were performed at 465 °C and 480 °C to homogenize the microstructure; however, S-phase was unexpectedly present in the samples treated at 465 °C. In both 465 °C and 480 °C treatments, T-phase was not fully dissolved after the 60-min treatment. Guided by thermodynamic modeling, these results indicate a shift in local equilibria in these powders.