The effect of powder reuse on the surface chemical composition of the Scalmalloy powder in Powder Bed Fusion – Laser Beam process

Abstract

The powder quality is one of the main factors to be considered in laser powder bed fusion (PBF-LB/M) production closely connected with the performance of the final component. Only powders with spherical particles, a low percentage of satellites, a narrow particle size distribution, controlled internal defects and a strongly limited surface oxide layer are acceptable for PBF-LB/M production. Gas atomisation is the main production method that permits to achieve the restrictive standards of the PBF-LB/M powder; however, it is energy-intensive and characterised by limited productivity. These considerations justify the key role of the reuse of the unmelted metal powder in obtaining a more sustainable PBF-LB/M process. Nevertheless, the reuse of the powder leads to significant changes in the particle morphology, particle size distribution and surface chemical composition, which can compromise the bulk properties. Powder surface oxide is one of the most impactful problems for the PBF-LB/M production, and Al-based alloys are particularly prone to this phenomenon.With the aim to study the effect of the powder reuse, a surface chemical analysis on gas atomised Scalmalloy powder was performed through the X-ray photoelectron spectroscopy investigation before and after seven jobs with 32 h as overall build time. Results obtained for virgin and recycled Scalmalloy powders revealed remarkable differences in depth and composition of the surface oxide layer. The 57% increase in the oxide layer thickness and the formation of carbides during PBF-LB/M production can have harmful effects on bulk properties.

Ongoing Challenges of Laser-Based Powder Bed Fusion Processing of Al Alloys and Potential Solutions from the Literature—A Review

“…The tendency of hydroxide and oxide formation is correlated with the high oxygen affinity of the Al matrix and the alloying elements. In fact, Al-based powders tend to oxidise and form Al 2 O 3 and other oxides depending on the other alloying elements [ 45 , 46 ]. The thermodynamic stability of the oxides and the thermal history of the metal surface determine the characteristics of the surface oxide [ 47 ].…”

Microstructural Evaluation and Tensile Properties of Al-Mg-Sc-Zr Alloys Prepared by LPBF

“…The commonly used powder had a D50 of approximately 38-48 µm [34,40,41]. To reduce costs, researchers have developed several methods for alloy production, including the partial or complete substitution of Zr for Sc [26,[42][43][44], the substitution of Er or Hf for Sc [27,45,46], and the reuse of recycled powder [47,48]. In this work, we attempted to reduce the cost of the powder by appropriately reducing the Sc content and using small atomization equipment to produce fine powders.…”