Microstructure evolution and mechanical properties of ultrafine-grained Al–Li alloy fabricated via friction stir additive manufacturing

High-strength laminated blocks of 2060 Al–Li alloy were fabricated by friction stir additive manufacturing (FSAM) in this study, and a comprehensive analysis of their microstructural evolution and mechanical properties were investigated. The microstructure of the alloy produced by FSAM exhibited ultrafine equiaxed grains ranging from 2 to 5 μm. Dislocation multiplication can be observed after FSAM, which is formed due to plastic deformation. Both the geometrically necessary dislocations density and the proportion of low angle grain boundaries show a decreasing trend from top to bottom. The reprecipitated θ’ and Al₆Mn precipitates at grain boundaries was observed, exhibiting a coarsening phenomenon along the building direction. Additionally, the mechanical properties of the FSAM-produced 2060 Al–Li alloys were assessed, revealing YS, UTS, and EL values of 290.4 MPa, 443.1 MPa, and 11.06%, respectively. And the microhardness exhibited a range from 110.8HV_0.2 to 139.6HV_0.2. In summary, this work offers practical guidelines for optimizing the additive manufacturing quality of Al–Li alloys.