Homogenization treatment parameter optimization and microstructural evolution of Al-Cu-Li alloy

Abstract:

Abstract: The microstructure evolution and composition distribution of the industrially cast Al-Cu-Li alloy during single-step and tow-step homogenization were investigated in detail by means of 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 distribute unevenly from the grain boundary to inside. But the change of Mg, Zn, Mn and Ag are not obvious. In the grain boundary, there are distributed a large number of coarse nonequilibrium eutectic phases Al2Cu, Al2Cu dissolved a small amount of Mg and Al2CuMg phase. After?optimized two-step?homogenization treatment, most of the nonequilibrium?eutectic?phase and second phase(Al2CuMg and Al2CuLi)?dissolved?into ɑ(Al) matrix. A small amount of Fe-rich and Mn-rich phase are still distributed at the grain boundaries. Al2CuMg phase melting point lower than?the melting point of Al2Cu phase. Al2CuMg and Al2Cu phase gradually dissolved into matrix at 495℃ and 515℃, respectively. The suitable homogenization treatment for the Al-Cu-Li alloy is 495℃×24h 515℃×24h. The results of homogenization can be described by homogenization kinetic analysis, which agrees well with experimental observation.

Key words:Al-Cu-Li alloy; Homogenization treatment; Nonequilibrium eutectic phases; Kinetic analysis