Effects of natural aging on the formation and strengthening effect of G.P. zones in a retrogression and re-aged Al–Zn–Mg–Cu alloy

Abstract In this work, a new four-stage aging treatment by employing a natural aging prior to re-aging is designed to promote GP zones formation and subsequent shear-able strengthening effect in an Al–Zn–Mg–Cu alloy. The effects of natural aging on the microstructural evolution, tensile properties and stress corrosion cracking (SCC) behavior of Al–Zn–Mg–Cu alloy are carefully explored by atom probe tomography (APT) technique, transmission electron microscope (TEM) and differential scanning calorimetry (DSC) analysis. The results show that increased GP zones distributed in the matrix of the alloy subjected four-stage aging processing, finally contributing to the greater tensile strength properties and elongation of four-stage aging treated alloy. The SCC test results reveal that four-stage aging condition can enhance the corrosion resistance of the Al–Zn–Mg–Cu alloy without sacrificing much strength.