Sagar Patel (1), Haoxiu Chen (2), Mihaela Vlasea (1), Yu Zou (2)
arXiv, May 2021. DOI: arXiv:2105.07920

Keywords

Additive manufacturing; Laser powder bed fusion; Selective laser melting; Aluminium alloy; Defects; AlSi10Mg

Abstract

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, a laser beam defocusing strategy using a divergent beam is proposed to achieve a stable conduction mode microstructure in AlSi10Mg, a eutectic Al composition that is most studied in LPBF. The effects of conduction, transition, and keyhole melting modes on the final part are studied in detail using processing diagrams, metallography, and X-ray computed tomography. The conduction mode LPBF of AlSi10Mg leads to parts with densities of over 99.98%, with close to no porous defects in the subsurface regions, which are known to directly affect the fatigue life of the final parts. The threshold between conduction and transition mode melt pools is also observed to be at a melt pool aspect ratio (ratio of melt pool depth to width) of about 0.4, which differs from the conventionally assumed 0.5. Additionally, a significant difference is observed in the standard deviation of the melt pool depths for the transition and keyhole mode melt pools, when compared to the conduction mode melt pools. This points to the large differences in laser absorptivity between melting modes, that are exaggerated by the onset of vaporization expected for transition and keyhole mode melting during LPBF of high reflectivity aluminium alloys.

How Our Software Was Used

Dragonfly was used to analyze CT data.

Author Affiliation

(1) University of Waterloo, Department of Mechanical and Mechatronics Engineering, Waterloo, ON N2L 3G1, Canada.
(2) University of Toronto, Department of Materials Science and Engineering, Toronto, ON M5S3E4, Canada.