Developing a novel lightweight Al–Mg–Li alloy for laser powder bed fusion additive manufacturing: Parameter optimization, microstructure evolution, and mechanical performance

With the advancement of laser powder bed fusion (LPBF) for aluminum alloys, developing novel lightweight Al–Li alloy systems present enormous potential for aerospace applications. Conventional Al–Mg–Li alloys exhibit low densities but suffer from poor strength due to the lack of inherent strengthening phases. In the present work, a novel lightweight Al–Mg–Li–Ag-Sc-Zr alloy was developed for LPBF after optimizing the processing parameters. The as-built alloy featured a bimodal microstructure consisting of fine equiaxed grains and columnar grains. The submicron primary Al3(Sc, Zr) phases with a cubic L12 structure served as inoculants for grain refinement and exhibited good coherency with the α-Al matrix. Besides, submicron spherical quasicrystalline T-Mg32(Al, Ag)49 phases of and nanometer rod-shaped S1–Al2MgLi phases were scattered inside the grains. These results produced a yield strength (σy) of 286 ± 8 MPa, ultimate tensile strength (σUTS) of 406 ± 3 MPa, and elongation at fracture (εf) of 12.5 ± 0.3%. The direct aging at 325 °C for 12 h led to an increase in hardness to a peak value of 170 HV. The secondary phases at the grain boundaries were breached and a large amount of submicron T and S1 phases within the grains were prominently increased. Besides, spherical Al3(Sc, Zr, Li) and tiny δ′-Al3Li precipitates were observed in the α-Al matrix. A considerably enhanced σy of 375 ± 12 MPa and σUTS of 469 ± 4 MPa were achieved mainly due to the particle strengthening but decreased εf to 5.8 ± 0.2%. The alloys in both states exhibited a moderate work-hardening capability. The feasibility of LPBF for lightweight Al–Li alloy was successfully established but required further optimization of the alloy composition.