Microstructural Evolution of an Al–Zn–Mg–Cu Aluminum Alloy During an Optimized Two-Step Homogenization Treatment

The microstructural evolution of an Al–Zn–Mg–Cu aluminum alloy during an optimized two-step homogenization treatment was investigated by optical microscopy (OM) and scanning electron microscopy (SEM) equipped with energy-dispersive spectrometer (EDS) and differential scanning calorimetry (DSC). It mainly focused on secondary phase transformation and dissolution. Methods such as and differential scanning calorimetry (DSC) was used to investigate the heat change of each specimen as an indication of phase transformation involved in the homogenization. The results showed that the lamellar eutectic phase had the trend of spheroidizing during the treatment at 400 °C, and the T-Al2Mg2Zn3 phase was transformed into S-Al2CuMg phase. Further dissolution of T phase was not obvious at second step homogenization even after the holding time was extended to more than 24 h.