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 71304 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 71304 super-high strength aluminum alloy, and their melting point is 478 degrees C. During homogenization treatment at 470 degrees C, these eutectics dissolve into the matrix partly, coarsen and also transform into Al2CUMg phase whose equilibrium melting point is 490 degrees C in the alloy. Moreover, the homogenization treatment at 470 degrees C for 72 h results in the disappearance of the non-equilibrium eutectics though Al2CuMg phase can not dissolve completely.