Microstructure evolution and mechanical properties of high-strength aluminum alloy prepared by additive friction stir deposition

Additive friction stir deposition (AFSD) is a solid-phase additive technology with promising development and application prospects. In this paper, the final AA7075 builds with five layers were successfully prepared using the AFSD process under both room and low temperature conditions, and the microstructure evolution and mechanical properties of the final builds were systematically studied. The build produced at room temperature exhibited an average grain size of 4.2-4.5 mu m, primarily influenced by the rotated Cube texture. Whereas, the build produced at low temperature had an average grain size of 3.9-5.0 mu m, dominated by the Brass, rotated Cu and rotated Goss components. The dislocation restoration was suppressed by the lower temperature environment, resulting in an increase in geometrically necessary dislocation density and a drop in recrystallization fraction. Due to the overgrowth of the strengthening phase, the hardness and tensile strength of the final builds decreased from the top layer to the bottom layer. Moreover, the lower temperature environment also inhibited the precipitation of the strengthening phase. This led to lower hardness and tensile strength compared to the build produced at room temperature. However, the elongation of the both builds exceeded 16 %, surpassing that of the AA7075-T6 feed bar. This study enhances the understanding of the relationship between microstructure and mechanical properties of additive friction stir deposited age-hardenable aluminum alloys, and provides an experimental reference and theoretical foundation for industrial additive manufacturing of high-performance aluminum alloys.