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

Abstract

Their high strength-to-weight ratio, good corrosion resistance and excellent thermal and electrical conductivity have exponentially increased the interest in aluminium alloys in the context of laser-based powder bed fusion (PBF-LB/M) production. Although Al-based alloys are the third most investigated category of alloys in the literature and the second most used in industry, their processing by PBF-LB/M is often hampered by their considerable solidification shrinkage, tendency to oxidation, high laser reflectivity and poor powder flowability. For these reasons, high-strength Al-based alloys traditionally processed by conventional procedures have often proved to be unprintable with additive technology, so the design and development of new tailored Al-based alloys for PBF-LB/M production is necessary. The aim of the present work is to explore all the challenges encountered before, during and after the PBF-LB/M processing of Al-based alloys, in order to critically analyse the solutions proposed in the literature and suggest new approaches for addressing unsolved problems. The analysis covers the critical aspects in the literature as well as industrial needs, industrial patents published to date and possible future developments in the additive market.

Keywords: PBF-LB/M; additive manufacturing; al-based alloys; ongoing challenges; processability.

Figure 1

Graphical overview of the review.

Figure 2

Literature trends on the development of computational models for the novel composition design related to the growth of the PBF-LB/M process, according to the Scopus database.

Figure 3

The best scenario for the highest powder packability (a) and the best scenario for powder flowability (b).

Figure 4

The mechanism of oxide film formation, its disruption and resulting defects.

Figure 5

Different process parameter optimisation procedures.

Figure 6

The absorption variation of laser emission at different wavelengths for the main material categories [69].

Figure 7

Physical phenomena involved in the PBF-LB/M process.

Figure 8

Causes and solutions in the formation of the main defects in the PBF-LB/M process according to the literature.

Figure 9

Strengths and weaknesses of the main methodologies for evaluating the level of densification achieved in PBF-LB/M production.

Figure 10

Thermal post-processing and its effects on melt pool morphology and microstructure in Al–Si alloys.

Figure 11

Plot of surface roughness as a function of the main categories of commercially available materials for PBF-LB/M production [130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159,160,161,162,163].

Figure 12

Schematic representation of the SP (a) and UNSM (b) processes (c) and how they affect the surface morphology, grain refinement, surface hardening and residual compressive stresses induced in the surface layer [102].