Aging behavior and precipitate characterization of a high Zn-containing Al-Zn-Mg-Cu alloy with various tempers

In the present work, the influence of one-step and two-step aging treatments on hardness, electrical conductivity and mechanical properties of a high Zn-containing Al-Zn-Mg-Cu alloy is investigated and detailed aging parameters subjected to various aging tempers, i.e., T6, T79, T76, T74 and T73, are proposed. The nanoscale precipitates under different tempers are qualitatively investigated by means of transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HREM) techniques. Based on the precipitate observations, precipitate size distributions and neighbor precipitates distances are extracted from bright-field TEM images projected along 〈110〉 Al orientation with the aid of an imaging analysis. The results show that with the deepening of aging degree, the conductivity of one-step and two-step aging increase continuously while the hardness increases for one-step aging and decreases for two-step aging at the second preservation. The tensile strength decreases as the aging degree deepens and the yield strength shows a similar trend. In addition, as the degree of over-aging deepens, the precipitate size distribution interval becomes broader, the average precipitate size turns larger and the average distance of neighbor precipitates also becomes greater. The influence of precipitates on mechanical properties is discussed.