Development of Al-Cu-Mg and Al-Mg-Si-Zr Alloys with Improved L-PBF Processability

Many Al alloys are susceptible to hot cracking when manufactured by Laser Powder Bed Fusion (L-PBF). In this study, small batches of Al powders were processed using a Reduced Build Volume device to target the optimal chemical composition of the alloy able to suppress hot cracks during solidification. Specifically, batches with increasing content of Cu and Zr were obtained through mechanical mixing of Al-4wt.%Cu-Mg and pure Cu and Al-Mg-Si and Al-Mg-Si-2wt.%Zr powders, respectively. The design strategy based on Cu relies on the segregation of an abundant Al-Al2Cu eutectic phase mixture during final stages of solidification, whereas the Zr addition promotes a fine equiaxed microstructure induced by heterogeneous nucleation of grains triggered by the precipitation of L1(2)-Al3Zr crystal nuclei in the liquid phase. The design of the new alloys was supported by thermodynamic simulations. The microstructures and phase transformations of the alloys were investigated through electron microscopy, X-ray diffraction, and differential scanning calorimetry.