The influence of beam focus during laser powder bed fusion of a high reflectivity aluminium alloy-AlSi10Mg

摘要

The laser powder bed fusion (LPBF) of aluminium alloys is associated with numerous challenges when compared to other commonly used alloys (e.g., steels and titanium alloys) due to their higher reflectivity and thermal conductivity. This leads to a higher defect density in the final parts, commonly related to melt pool instabilities in the transition and keyhole melting modes. In this work, processing diagrams, temperature prediction models, X-ray computed tomography (XCT), and metallography are used for establishing criteria in process parameter optimization of high reflectivity aluminium alloys based on AlSi10Mg response in using 57 different power, velocity, and beam diameter combinations. For LPBF systems with focused beam diameters 99.98%, with effectively no porous defects in the subsurface regions. Additionally, an analytical model guided selection of laser power and velocity settings for a focused beam help in stabilizing melt pool and spatter dynamics in the transition melting mode thereby enabling a potential to obtain density values close to conduction mode densities (similar to 99.98%). A dimensionless keyhole number (Ke) was used in this work to identify distinct regions of conduction (Ke of 0-12), transition (Ke of 12-20), and keyhole (Ke > 20) mode melting during LPBF of AlSi10Mg. Lastly, a melt pool aspect ratio (ratio of melt pool depth to width) of similar to 0.4 is observed to be the threshold between conduction and transition/keyhole mode melt pools for AlSi10Mg, different from the conventionally assumed 0.5. This work demonstrates a dimensionless-process map method to obtain near fully dense parts that can be generalized for LPBF of high reflectivity alloys.