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

Abstract

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 Al 2 Cu, Al 2 Cu containing a trace of Mg and Al 2 CuMg phase. After the optimized two-step homogenization treatment, most of the nonequilibrium eutectic phase and second phase (Al 2 CuMg and Al 2 CuLi) dissolve into α(Al) matrix. A small amount of Fe-rich and Mn-rich phase are still distributed at the grain boundaries. Al 2 CuMg phase melting point is lower than that of Al 2 Cu phase. Al 2 CuMg and Al 2 Cu 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.