Microstructure evolution and strengthening mechanisms of an additive friction stir deposited multi-layer Al-Mg-Sc-Zr alloy

In recent years, additive friction stir deposition (AFSD) has emerged as a promising solid-based additive manufacturing method with applications with lightweight materials such as aluminum alloys. In this study, a three-layer Al-Mg-Sc-Zr alloy deposit was produced with AFSD. The mechanism of continuous dynamic recrystallization in the deposit was identified, revealing average grain sizes of 9.9 μm at the top and 8.8 μm at the bottom. The phase boundaries between micron-sized and nano-sized Al₃Sc reinforced phase particles and the alloy matrix were studied which confirmed orientations of {1 1 1} Al∥{1 1 1} Al₃Sc and [1 1 2] Al∥[1 1 2] Al₃Sc. The yield strength of the deposit in the longitudinal direction reached 314 MPa (90 % of the substrate), and in the transverse direction was 343 MPa, equal to that of the substrate (342 MPa). Second-phase strengthening, dislocation strengthening, and solid solution strengthening affected significantly yield strength.