Single-track study of A20X aluminum alloy fabricated by laser powder bed fusion: Modeling and experiments

Optimum process parameter window for recently developed metal powders used for laser powder bed fusion (LPBF) is strongly correlated with characteristics of each single track and single layer. In the present research, the influence of LPBF process parameters on geometrical and microstructural characteristics of A20X aluminum single tracks was studied theoretically and experimentally. Increasing the laser scan speed led to formation of non-homogenous, irregular single tracks. Moreover, enlarging the powder layer thickness to 120 mu m induced balling phenomenon owing to a poor wetting of substrate by melt pool. Experimental measurements indicated that width and depth of melt pools decreased up to 53 % and 68 %, respectively by increasing the scan speed from 500 to 1700 mm/s and layer thickness from 40 to 120 mu m. These findings were in agreement with pre-dictions of an exponentially decaying heat input model used in this study. The model took into account thermo-physical properties of the alloy at different states. Bead height was observed to increase with the powder layer thickness, but remain unchanged with the scan speed. The process parameter window (energy density range) resulting in the conduction melting mode for the A20X alloy was found to be more than two times wider compared to conventional LPBF aluminum alloys. For all process parameters, a fine equiaxed grain structure was observed in the vertical section of the single tracks. Enhancing the scan speed and reducing the powder layer thickness resulted in a substantial grain refinement. This was well explained by the simulated cooling rates. In contrast to cast Al-Cu alloys, shape, size, and volume fraction of the second phase precipitates were determined to be independence of cooling rate over the investigated cooling rate range (1.4 x 106 to 7.5 x 106 degrees C/s).

Automated summary

This research investigates the influence of LPBF process parameters on the geometrical and microstructural characteristics of A20X aluminum single tracks. Experimental measurements show that increasing the scan speed and reducing the layer thickness result in a decrease in the width and depth of the melt pools. Additionally, increasing the scan speed leads to a decrease in the bead height, while the powder layer thickness has the opposite effect.