Microstructure and anisotropy of mechanical properties in 7055 aluminum alloy fabricated by additive friction stir deposition: effects of heat treatment

Additive friction stir deposition (AFSD) technology provides a solution by enabling near-net-shape part production, imparting forging-like qualities with minimal machining requirements, thereby emerging as a rapidly evolving manufacturing method. This study thoroughly investigated the micro-structural evolution, mechanical properties, and strength anisotropy of large 7055 aluminum alloy specimens fabricated by the AFSD technology. The concrete results revealed that the as-deposited material indicated a fine grain structure (approximately 3 μm), with residual Zn/Cu-rich precipitates, resulting in low yield strength anisotropy, but poor ductility in the structural (ST) direction due to porosity defects. Solution heat treatment (SHT) dissolved these precipitates, achieving solid solution strengthening with a 116.1% increase in micro-hardness (reaching 220.4 HV 0.2 ). Subsequent aging treatment (120 °C/6 hours + 160 °C/6 hours) resulted in the formation of nanoscale GP zones and η' precipitates, leading to ultimate tensile strengths of 500.9 MPa and 493.0 MPa in the L and LT directions, respectively, with increases of 68.7% and 61.4%. Nevertheless, grain boundary precipitation and pre-existing voids lead to reduce ductility and brittle fracture in the ST direction. Ultimately, the paper demonstrates that post-deposition heat treatment can effectively restore the strength potential of AFSD 7055.