Microstructural evolution of high strength 7B04 ingot during homogenization treatment

The evolution of the microstructure and phases of the direct chill semicontinuous casting ingot of 7B04 super-high strength aluminum alloy during homogenization treatment was studied with metallographic analysis, scanning electron microscopy(SEM), energy spectroscopy and differential scanning calorimetry(DSC). The results show that a considerable amount of non-equilibrium eutectics containing Al, Zn, Cu and Mg exist in the direct chill semicontinuous casting ingot of 7B04 super-high strength aluminum alloy, and their melting point is 478 °C. During homogenization treatment at 470 °C, these eutectics dissolve into the matrix partly, coarsen and also transform into Al2CuMg phase whose equilibrium melting point is 490 °C in the alloy. Moreover, the homogenization treatment at 470 °C for 72 h results in the disappearance of the non-equilibrium eutectics though Al2CuMg phase can not dissolve completely.