Research on microstructure in as‐cast 7A55 aluminum alloy and its evolution during homogenization

The microstructure of the as‐cast 7A55 aluminum alloy and its evolution during homogenization were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X‐ray diffraction (XRD), and differential scanning calorimetry (DSC) analysis. The results indicate that the microstructure of the as‐cast 7A55 aluminum alloy mainly consists of the dendritic network of aluminum solid solution, Al/AlZnMgCu eutectic phases, and intermetallic compounds MgZn 2 , Al 2 CuMg, Al 7 Cu 2 Fe, and Al 23 CuFe 4 . After homogenization at 470°C for 48 h, Al/AlZnMgCu eutectic phases are dissolved into the matrix, and a small amount of high melting‐point secondary phases were formed, which results in an increasing of the starting melting temperature of 7A55 aluminum alloy. The high melting‐point secondary phases were eliminated mostly when the homogenization time achieved to 72 h. Therefore, the reasonable homogenization heat treatment process for 7A55 aluminum alloy ingots was chosen as 470°C/72 h.