Microstructure Evolution and Mechanical Properties of Single-Layer Multipass Overlapped Al-Mg-Mn-Sc-Zr Alloy Fabricated via Additive Friction Stir Deposition

A single-layer of three-pass overlapped Al-Mg-Mn-Sc-Zr alloy was successfully fabricated by additive friction stir deposition (AFSD). Microstructures of the deposit were analyzed using optical microscope, scanning electron microscope and electron backscatter diffraction. Vickers hardness was evaluated over the whole cross-section of the deposit. Tensile tests were performed on the deposit as well as the base material using digital image correlation technique. The results indicated that dynamic recrystallisation occurred in the deposit, producing fine and equiaxed grains whose average grain sizes in overlapped zones were reduced to approximately 2–5 μm. The high-angle grain boundaries in the upper regions of the first-third and the first-second passes overlapped zones are 85% and 76%, respectively. The hardness distribution is non-uniform throughout the cross-section of the deposit, with minimum hardness of about 90% of the BM on the retreating side of the second pass and the two overlapped zones. The ultimate tensile strengths of specimens on the first-third and the first-second passes overlapped zones are 343 MPa and 308 MPa. The elongation of the specimens on the first-third passes overlapped zone is 22.2%, higher than that of the base material (19.5%), while the elongation of the specimens on the first-second passes overlapped zone drops to 10.4%.