Homogenization Treatment Parameter Optimization and Microstructural Evolution of Al-Cu-Li Alloy

The microstructure evolution and composition distribution of the industrially cast Al-Cu-Li alloy during single-step and tow-step homogenization were investigated by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The results show that severe dendrite segregation exists in the Al-Cu-Li as-cast alloy. Cu distributes unevenly from the grain boundary to inside. But the changes of Mg, Zn, Mn and Ag are not obvious. At the grain boundary, there are a large amount of coarse nonequilibrium eutectic phases Al2Cu, Al2Cu containing a trace of Mg and Al2CuMg phase. After the optimized two-step homogenization treatment, most of the nonequilibrium eutectic phase and second phase (Al2CuMg and Al2CuLi) dissolve into α(Al) matrix. A small amount of Fe-rich and Mn-rich phase are still distributed at the grain boundaries. Al2CuMg phase melting point is lower than that of Al2Cu phase. Al2CuMg and Al2Cu phase gradually dissolve into the matrix at 495 and 515 °C, respectively. The suitable homogenization treatment for the Al-Cu-Li alloy is 495 °C/24 h + 515 °C/24 h. The results of homogenization can be described by homogenization kinetic analysis, which agrees well with experimental observation.