Effects of retrogression and re-aging treatment on precipitation behavior, mechanical and corrosion properties of a Zr+Er modified Al-Zn-Mg-Cu alloy

Abstract

The microstructure, mechanical properties, and corrosion resistance of a Zr + Er modified Al-Zn-Mg-Cu alloy after different retrogression and re-aging (RRA) treatments were investigated. Results show that the main precipitates after different heat treatment change from GP zones + η’ + Al 3 (Er, Zr) phase (T6) to η’ + Al 3 (Er, Zr) phase (RRA180–30) and then to η + T phase (RRA200–30). The component, size, and distribution of precipitated phases would be affected by the regression time and temperature during RRA treatment. It is concluded that the uniformly dispersed precipitate phase in matrix and narrow precipitate-free zones (PFZs) could significantly improve the strength of Al-Zn-Mg-Cu alloy, and the grain boundary precipitated phase (GBPs) with moderate size and large interparticle distance could improve the alloy's corrosion resistance. Besides, a wider PFZ within a certain range is beneficial to improve the intergranular corrosion (IGC) performance. Therefore, it is important to accurately control the heating temperature and retrogression time during the retrogression stage to regulate the characteristics of precipitated phases and achieve the best balance of mechanical properties and corrosion resistance. • The precipitates size of RRA sample was larger and discontinuously distributed in GB. • Uniform precipitates in matrix and narrow PFZ are beneficial to the alloys' strength. • Corrosion resistance was improved with increasing retrogression temperature and time. • The wide PFZ and discontinuous GBP could improve the IGC resistance of the alloy.