Microstructure evolution of spray deposited and as-cast 2195 Al-Li alloys during homogenization

Abstract In this paper, a comparative study on the spray deposited and as-cast 2195 alloy was carried out to reveal their microstructure evolutions and differences during the homogenization process. The dissolution of the secondary particles and the diffusion of solute were studied based on microstructure characterization and kinetics analysis. The precipitation behavior of Al3Zr dispersoids and its influence on recrystallization were investigated by using TEM and EBSD characterization. It was found that the large-size particles at triangular grain boundaries dissolve slower than the intragranular phases and other grain boundary phases. The required homogenization time depends on the dissolution processes of the large-size phases at grain boundaries. The size of grain boundary phases in the spray deposited alloy is much smaller than that in the as-cast alloy, so the homogenization time required for the spray deposited alloy is significantly shorter. Two-stage and ramp heating homogenization processes can promote the precipitation of Al3Zr dispersoids in the two alloys. In the spray deposited alloy, the dispersoids tend to precipitate at the positions of the T1 plates dissolved, which causes a non-uniform distribution and decreases the recrystallization resistance of the alloy. However, the distribution of the dispersoids in the as-cast alloy is more uniform after the homogenization, which brings a stronger inhibition on the recrystallization. According to the microstructural characterization and kinetics analysis results, it can be concluded that the homogenization with a slow ramp heating is suitable for the two 2195 alloys, and a shorter holding time can be used for spray deposited alloy, e.g. 12 h at 500 °C, while the holding time for the as-cast alloy is no less than 35 h at 500 °C.