Achieving uniform plasticity in a high strength Al-Mn-Sc based alloy through laser-directed energy deposition

The recently-developed Al-Mn-Sc based alloys fabricated by laser-powder bed fusion (L-PBF) have achieved a yield strength of 560 MPa and a ductility of 18%. However, these high strength Al alloys normally exhibit severely non-uniform plasticity due to the strain incompatibility of bimodal grain structure, which hinders their practical application. In this work, an Al-Mn-Sc based alloy has been fabricated through laser-directed energy deposition (L-DED). The results revealed that during deposition, the precipitation of primary Al-3(Sc, Zr) particles can be more homogeneous in the entire melt pool due to the relatively low cooling rate and temperature compared with that of L-PBF, fully exploiting the ability of Al-3(Sc, Zr) particles to promote alpha-Al nucleation. Therefore, fully equiaxed grains of 5-6 mu m in diameter without preferential crystallographic orientation have been obtained. This leads to excellent strength and ductility with a good strain hardening capacity without the need for subsequent forming processes, which has successfully tackled the non-uniform plasticity issue associated with the L-PBF counterparts. This alloy possesses a yield strength and ultimate tensile strength of 230 and 331 MPa, respectively, with a uniform elongation of 8.3% at the as-fabricated stage. After a simple post-heat treatment at 300 ? for 3 h, the yield strength and ultimate tensile strength can reach up to 425 and 519 MPa, respectively, accompanied with 6.2% uniform elongation. The yield strength in the direct-aged state ex-ceeds all the existing Al alloys manufactured by various DED methods. The current results bode well for the achievement of high strength Al alloys engineering components fabricated by L-DED for future industrial adoption.