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 & alpha;-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 (& sigma;y) of 286 & PLUSMN; 8 MPa, ultimate tensile strength (& sigma;UTS) of 406 & PLUSMN; 3 MPa, and elongation at fracture (& epsilon;f) of 12.5 & PLUSMN; 0.3%. The direct aging at 325 degrees 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 & delta;& PRIME;-Al3Li precipitates were observed in the & alpha;-Al matrix. A considerably enhanced & sigma;y of 375 & PLUSMN; 12 MPa and & sigma;UTS of 469 & PLUSMN; 4 MPa were achieved mainly due to the particle strengthening but decreased & epsilon;f to 5.8 & PLUSMN; 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.