Microstructural evolution during homogenization of DC cast 7085 aluminum alloy

The microstructural evolution of a DC cast 7085 alloy during homogenization treatment was investigated by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry (EDS), differential scanning calorimeter (DSC) and X-ray diffraction (XRD). The results showed that serious dendritic segregation existed in the as-cast 7085 alloy. Numerous eutectic microstructures and phases were observed at the grain boundary. During homogenization process, eutectic alpha(Al)+T(AlZnMgCu) microstructure gradually was dissolved into matrix. Intermetallic S(Al2CuMg) phase formed and grew along the eutectic microstructure and disappeared into the matrix completely when it was homogenized at 460 degrees C for 24 h. It could be found that the evolution of primary eutectic structure of 7085 alloy consisted of three processes, dissolution of eutectic alpha+T microstructure, phase transformation from T phase to S phase and the dissolution of S phase. The optimum homogenization parameter was at 470 degrees C for 24 h.