An Al-Mg-Mn-Ni-Sc-Ti alloy fabricated by wire arc directed energy deposition: Composition design and strength breakthrough

Al-Mg-Sc alloys exhibited excellent strength, ductility, and weldability, making them one of the most ideal materials for wire arc directed energy deposition (WA-DED). However, the insufficient strength of WA-DED Al-Mg-Sc alloys severely limited their widespread application in aerospace. Therefore, in this work, the authors designed Al-Mg-Mn-Ni-Sc-Ti alloy wires with Sc contents of 0.15, 0.35, and 0.55 (wt.%), analyzing the influence of Sc content on the microstructure and mechanical properties. The results indicated that in the as-deposited alloy, as the Sc content increased from 0.15 to 0.55, the coarse equiaxed grains (CEGs) were significantly refined, leading to a more uniform distribution. During aging at 320 °C for 50 h, the Al 3 Sc phase precipitated prior to the AlMnNi 2 phase, and the Al 3 Sc could induce the nucleation and precipitation of the AlMnNi 2 , resulting in an increase in the number density and volume fraction of the AlMnNi 2 phase. At a Sc content of 0.35, the alloy achieved optimal performance, with yield strength, ultimate tensile strength (UTS), and elongation reaching 298 ± 3 MPa, 472 ± 4 MPa, and 18 ± 2%, respectively. Theoretical calculation showed that solid solution strengthening (Mg and Mn), precipitation strengthening (Al 3 Sc and AlMnNi 2 ) were the primary strengthening mechanisms. Additionally, the extensive entanglement of dislocations and the interactions between twins and dislocations significantly enhanced the UTS, achieving a breakthrough in the strength of WA-DED Al-Mg-Sc alloys.