Microstructural Characteristics and Heat Treatment Response of Al-Zn-Mg-Cu Alloy Fabricated by Additive Friction Stir Deposition

The development of aluminum alloys with high specific strength and excellent toughness is of strategic significance to meet the lightweight requirements of next-generation high-performance equipment. In this study, Al-Zn-Mg-Cu alloy (7055) with outstanding mechanical properties is selected as the research object. To address the solidification defects formed in the conventional fusion-based additive manufacturing (AM) techniques, the solid-state additive friction stir deposition (AFSD) is innovatively employed to prepare 7055 alloy. A systematic characterization of microstructure evolution is conducted in different regions (advancing side Region A, central Region B, and retreating side Region C) of both as-deposited and heat-treated samples. The results demonstrate that the AFSD process can successfully achieve defect-free deposition of 7055 alloy, effectively dispersing the banded secondary phases in the raw material and transforming elongated grains into fine equiaxed grains, and that the recrystallization degrees in different regions are different. After heat treatment, noticeable grain coarsening and recrystallization occur in Regions B and C. Moreover, the heat treatment effectively dissolves coarse η phases and promotes the precipitation of high-density nanoscale GPII zones and η' phases.