Effect of retrogression re-aging on the properties and microstructure of AA7050

The effect of retrogression re-aging on the mechanical properties, electrical conductivity and the microstructure of AA7085 has been investigated. Transmission electron microscope was used to analyze the microstructures. Through the investigation of the effect of the retrogression time on the properties and microstructure of AA7050, the optimized retrogression time was confirmed. After pre-aging at 135°C for 12h, the peak of hardness and strength were achieved after 2 hours´ retrogression treatment at 170°C. The results of comparing retrogression aging and retrogression re-aging treatment showed that through RRA treatment, higher conductivity and mechanical properties were gained. The results show that the change of the properties are closely related to the re-dissolution of G.P zones and the transformation between G.P zones, ή and η. During the re-aging treatment, the re-precipitation and nucleation of G.P zones and ή result in the increase of the mechanical properties of AA7050. Through the optimized RRA treatment based on appropriate retrogression time, the ultimate tensile strength, the tensile yield strength, elongation and conductivity of AA7050 were raised to 643MPa, 629MPa, 11.76%, and 37.3%IACS.