Among aluminium alloys, Scalmalloy® has been designed for Additive Manufacturing (AM) Selective Laser Melting (SLM) technology, in order to provide a material uniquely light and yet ductile and resistant [1,2]. Due to its interest for the aeronautical industry, extensive research has been performed on the mechanical properties of SLM-fabricated Scalmalloy® in the last few years. SLM inducing inherently some defects, connections have been proposed between fracture mechanisms and main SLM defects in the literature [3]. However, very few studies have really focused on the impact of process-induced defects on mechanical properties and tackled their real harmfulness.

The present study gives insights into the negative impact of typical process-induced defects – namely, keyholes and lacks of fusion – on SLM-Scalmalloy® mechanical properties. The main long-term goal is to propose a new paradigm for aeronautical quality control, shifting from a “zero defect tolerance” policy, which is very costly, towards accepting unharmful defects, inherent to the process, and focusing on critical defects only. In this work, the effect of selected defect configurations (defect type & position) on tensile properties was investigated. Defects were introduced on purpose within different specimens during manufacturing. Such defects were characterized prior to tensile tests, via Computed Tomography (CT), to be related to the fractured surface characteristics, as illustrated in Figure 1. Tensile results were scrutinized and more specifically related to the different defects, to investigate critical configurations. A particular attention was given to the identification of the main damage mechanisms, through Scanning Electron Microscope (SEM) fractography. A first attempt was carried out to compare the harmfulness of the controlled defects observed during tensile testing to dynamic tests, such as fatigue testing. This study comes along with a critical discussion of the possibility to reduce the number of test samples necessary to obtain statistically relevant data on AM samples containing defects.

References

[1] Schmidtke, K., Palm, F., Hawkins, A., & Emmelmann, C. (2011). Process and mechanical properties: applicability of a scandium modified Al-alloy for laser additive manufacturing. Physics Procedia, 12, 369-374.

[2] Spierings, A. B., Dawson, …, & Uggowitzer, P. J. (2016). Microstructure and mechanical properties of as-processed scandium-modified aluminium using selective laser melting. Cirp Annals, 65(1), 213-216.

[3] Schneller, W., Leitner, M., Pomberger, S., Grün, F., Leuders, S., Pfeifer, T., & Jantschner, O. (2021). Fatigue strength assessment of additively manufactured metallic structures considering bulk and surface layer characteristics. Additive Manufacturing, 40, 101930.