PSI - Issue 76

Vladimír Mára et al. / Procedia Structural Integrity 76 (2026) 123–130

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1. Introduction

For AlSi10Mg alloy, laser powder bed fusion (LPBF) is the most used additive manufacturing (AM) technology . It is an expanding technology based on the powder melting process that receives energy from a high-energy laser. Consequently, a microstructure with a cellular hierarchy and melting pool (MP) morphology is formed. The size and arrangement of MPs in combination with the presence of manufacturing-induced defects and residual stresses have a fundamental influence on the achieved physical/mechanical properties and the overall anisotropy of the material (Bisht et al., 2022). The quality of the surface and the amount, type and distribution of defects in the microstructure of the printed material usually have the greatest impact on fatigue properties. Depending on the selected processing parameters and quality of the feedstock powder, porosity (e.g. gas and keyhole pores, lack of fusion, oxide membranes or oxide particles) may form during the LPBF process (Matuš ů et al., 2024b). Defects act as stress concentrators, promoting the initiation and propagation of fatigue cracks and resulting in a significant decrease in fatigue life. (Wu et al., 2021). The mechanical, physical and fatigue properties can be improved through suitable post-processing, which is often in the form of heat treatment (Miyajima et al., 2023; Roveda et al., 2024). The most commonly used type of heat treatment is stress-relieving annealing. Based on temperature, the β -Si eutectic network partially disintegrates. This is often followed by a noticeable decrease in strength, though plastic properties usually increase. To achieve a balance between strength and plasticity, a T6 heat treatment (solution annealing and artificial ageing) is typically employed (Lehner et al., 2024). This involves dissolving MPBs (Melting Pool Boundaries), transforming the cellular structure into coarse, equiaxed grains and completely disrupting the as-built Si network. New equiaxed and partially globularised Si particles then segregate at the grain boundaries. Structural changes reduce the anisotropy of the properties, which has a positive impact on fatigue resistance. (Lehner et al., 2024). This study focuses on analyzing the impact of the combined influence of microstructural features induced by various heat treatment regimes, as well as existing inhomogeneities in the form of defects, on the fatigue life and fatigue crack propagation of an LPBF AlSi10Mg alloy. The material used in this study was an AlSi10Mg alloy in the form of powder, supplied by GE Additive (USA) under the CL 31AL company designation. All specimens were built from fresh unused powder. Analysis of the powder morphology showed that the particles are mostly circular (see Fig.1a). However, irregular shapes, splats and satellite agglomeration can also be observed. The De Brouckère diameter (volume of mean) of the particles is D[4,3] = 45.4 µm, with an average circularity of 0.85. The HCF testing specimens were preprinted using the LPBF method and a Concept Laser M2 metal printer (GE Additive, USA), with the Z-axis as the building direction (see Fig 1b). For the LPBF specimen preprint, the skin-core building strategy was utilized. The skin (outer shell) was printed with every layer with lower parameters of the energy input, while the core (infill) was printed with every second layer with higher parameters (see Table 1). This strategy reduces printing time significantly and produces parts that are less susceptible to warping and dross formation. A total of three batches were printed, each containing 30 HCF testing specimens. The printed samples were then machined to give the specimen its final hourglass shape (see Fig 1c). 2. Experimental setup and testing

Fig. 1. (a) SEM micrographs of as-received AlSi10Mg powder morphology; (b) specimen arrangement on the building platform; (c) the geometry of HCF testing specimens with dimensions provided in mm.