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 degrees 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 L1(2)-structured Al-3(Er, Zr) dispersoids can be obtained in the two-stage homogenization process. A suitable homogenization scheme for the present alloy is (400 degrees C, 10 h)+(465 degrees C, 24 h), which is consistent with the results of homogenization kinetic analysis.