The effect of heat treatment on microstructure and mechanical properties of a high-strength Al–Mg–Mn-Sc-Ti alloy fabricated by wire arc directed energy deposition

The lower strength of Al–Mg-Sc-X alloys manufactured by wire arc directed energy deposition (WA-DED) was challenging to solve. In this study, three different heat treatments were taken to the Al–Mg–Mn-Sc-Ti alloy deposited by WA-DED with CMT + Adv mode, and the microstructure and mechanical properties were comprehensively discussed, which achieved a breakthrough in strength and good heat resistance at 325 °C-2 h. The results indicated that the microstructures were all equiaxed grains with an average grain size of about 9.13 ± 3.42 μm. After treatment at 325 °C-2 h, the yield strength (YS) and ultimate tensile strength (UTS) were about 302 ± 4 and 449 ± 1 MPa, and the YS and UTS were 208 ± 2 and 251 ± 3 MPa respectively at 200 °C, which exhibited excellent tensile performance. Theoretical calculation results showed that the synergistic strengthening effects of fine grain strengthening (Sc and Ti elements), precipitation strengthening (Al3Sc and Al19Mn4 phases) and solid solution strengthening (Mg and Mn elements) significantly improved the strength. At 325 °C - 2 h + 350 °C - 10 h, the precipitation of Al19Mn4 phase transformed from heterogeneous nucleation on dislocations to homogeneous nucleation within the grain and the morphology evolved from spherical to spherical and block, and finally sheet and rod which significant decreased the strength. This work provided a theoretical basis and data for fabricating high-strength Al–Mg-Sc-X alloys.