Homogenization heat treatment of 2099 Al–Li alloy

The microstructure evolution and composition distribution of as‐cast and homogenized 2099 aluminum–lithium (Al–Li) alloy were studied by optical microscopy (OM), differential thermal analysis (DTA), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), area and line scanning, X‐ray diffraction (XRD), and Vickers microhardness test methods. The results show that severe dendrite exists in the as‐cast alloy. Cu, Zn, Mn, and Mg distribute unevenly from the grain boundary to inside. The low‐melting point nonequilibrium eutectic phases dissolve into the matrix during the first‐step homogenization, whereas the melting point of residual eutectic phases is elevated. After the second‐step homogenization, most of the remaining eutectic phases dissolve into the matrix, except a small amount of Al–Cu–Fe phases. An optimized homogenization process of the 2099 Al–Li alloy is developed (515 °C × 18 h + 525 °C × 16 h), which shows a good agreement with the homogenization kinetic analysis results.