Homogenization Treatment and Kinetic Analysis of 2297 Al-Li Alloy

The microstructure evolution and composition distribution of the industrially cast 2297 Al-Li alloy during single-stage and double-stage homogenization were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and differential scanning calorimetry (DSC). The results show that severe dendrite segregation exists in the as-cast alloy. Cu, Fe and Mn elements have obvious segregation at grain boundaries, and the degree of enrichment decreases gradually from grain boundary to intracrystal. The undissolved phases in the grain boundaries are mainly Al2Cu phase and Fe and Mn containing phase. The optimal single-stage homogenization treatment system is 525 degrees C x 24 h. And the optimal double-stage homogenization system is 460 degrees C x 20 h + 525 degrees C x 24 h. After double-stage homogenization treatment, non-equilibrium eutectic phase on the grain boundary fully dissolved, and the segregation of dendrite is eliminated. At the same time, the size of Al3Zr particles is uniform and distributed dispersion, while no dissolved Fe and Mn containing phase is found at grain boundaries. The mechanism of the double-stage homogenization treatment agrees with the results of kinetic analysis.