ON THE DEVELOPMENT OF A DISPERSOID-STRENGTHENED ALUMINUM ALLOY FOR LASER POWDER BED FUSION ADDITIVE MANUFACTURING

Abstract

The scope of aluminum alloys available for laser powder bed fusion (L-PBF) is limited as conventional chemistries are prone to processability issues and solidification cracking. In recent times, researchers and stakeholders have worked to address this shortfall by developing aluminum alloys tailored specifically to the process. In keeping with this, the objective of this work was to develop a novel dispersoid strengthened aluminum alloy with enhanced thermal stability and adequate resistance to solidification cracking as required for L-PBF processing. Here, the Al–Zr–Y system was identified as a promising domain and specific formulations from it were subjected to a comprehensive investigation emphasizing solidification behavior, L-PBF processing, post-build aging, and mechanical performance. To expediently evaluate the effects of rapid solidification on this system, cast Al-Zr-Y plates with varying Zr and Y contents (0-2 wt.%) were subjected to laser remelting (LRM) and microstructural characterization. Zr-containing chemistries developed a high density of metastable L12–Al3Zr dispersoids, which promoted to the formation of equiaxed α-Al grains near the melt pool boundaries. Yttrium additions manifested as a Y-rich phases in the grain boundaries. Ultimately, the Al–2Zr–1Y chemistry (wt.%) was selected for L-PBF processing as it exhibited the highest dispersoid density and contained no metallurgical defects. Al–2Zr–1Y was found to be highly amenable to L-PBF and could be processed to near full-density (≥ 99.5%). Density correlated with laser power and scan speed. Notably, the as-built microstructure was highly similar to those seen in LRM. Al–2Zr–1Y exhibited a strong response to direct aging with peak hardness (~125 HV0.3) achieved when holding at 350 ˚C for 50 hours or 400 ˚C for 5 hours. Rapid overaging transpired at 450 ˚C in times as short as 1 hour. Hardness trends aligned with microstructural transformations, including precipitation of nanoscale precipitates in the α-Al matrix, the formation of precipitate free zones (PFZs), and growth of grain boundary particles. Despite this, minimal grain growth was apparent. Ultimately, Al–2Zr–1Y demonstrated tensile properties that were significantly superior to the most prevalent alloy utilized in commercial L-PBF operations (AlSi10Mg) as well as an exceptional resistance to thermal softening.