Abstract: FSAM is a solid-state, non-melting additive manufacturing technique that avoids defects such as cracks, porosity, and inclusions commonly encountered in melting-based additive manufacturing methods. Using T2 copper as the material, the FSAM technique was employed through a layer-by-layer plate stacking approach for additive manufacturing. This study investigated the microstructural and property variations in the additively manufactured components. The results indicated that the macro-forming quality of the additively manufactured zone was excellent, with no significant surface or internal defects. The interface between layers exhibited good bonding due to improved interfacial migration. The grain size in the AZ increased gradually from the top to the bottom along the additive thickness direction, while the trends in tensile strength and microhardness were the opposite. The formation of subgrains and subgrain boundaries at the top and middle of the AZ significantly enhanced tensile strength. The density of nanolayered superstructures distributed between the substrate and the AZ influenced the distribution of microhardness. The elongation of the top, middle, and substrate layers of the AZ was comparable. The formation of nanometer twin boundaries at the bottom of the AZ not only impeded dislocation motion, enhancing tensile strength, but also interacted with dislocations to absorb them and improve plasticity. The substrate exhibited characteristics of brittle intergranular fracture and ductile fracture. In contrast, fine grains formed by dynamic recrystallization resulted in ductile fracture behavior in tensile samples across different layers of the AZ.

Key words: T2 copper, friction stir, additive manufacturing, microstructure, mechanical properties, X-ray detection