Microstructural evolution of new type Al–Zn–Mg–Cu alloy with Er and Zr additions during homogenization

A comprehensive study on the microstructural evolution of a new type Al–Zn–Mg–Cu–Er–Zr alloy during homogenization was conducted by optical microscope, scanning electron microscope, transmission electron microscopy and X-ray diffraction analysis. The results show that serious segregation exists in as-cast alloy, and the primary phases are T(AlZnMgCu), S(Al₂CuMg) and Al₈Cu₄Er, which preferentially locate in the grain boundary regions. The soluble T(AlZnMgCu) and S(Al₂CuMg) phases dissolve into the matrix gradually during single-stage homogenized at 465 °C with prolonging holding time, but the residual Al₈Cu₄Er phase cannot dissolve completely. Compared with the single-stage homogenization, both a finer particle size and a higher volume fraction of L1₂-structured Al₃(Er, Zr) dispersoids can be obtained in the two-stage homogenization process. A suitable homogenization scheme for the present alloy is (400 °C, 10 h)+(465 °C, 24 h), which is consistent with the results of homogenization kinetic analysis.