PSI - Issue 76

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

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Table 1. Summary of processing parameters utilizing skin-core strategy Parameter Laser Power (W)

Scanning speed (mm/s)

Spot size (µm)

Hatch distance (µm)

Skin

200

1250

3

25

Core

370

1400

5

25

Subsequently, each half of the batch (i.e., 15 specimens) was subjected to a different type of heat treatment. These modes utilize lower temperatures with low to medium impact on eutectic β -Si network (variations of stress relief annealing) and higher temperatures for complete β -Si network decomposition and transformation (solution annealing, water quenching and artificial aging). The parameters of the heat treatments were selected based on the results of previous studies (Mára et al., 2022; Lehner et al., 2024; Matuš ů et al., 2024b; Roveda et al., 2024). Table 2 summarizes the individual heat treatment processes and their corresponding parameters.

Table 2. Heat treatment parameters with assigned color coding Specimen batch 1

2

3

Heat treatment

noHT

T240

T200

T300

T6

T6mod

Parameters

as-built

240 °C/6h 200 °C/2 h

300 °C/2h

510 °C/6h + 170 °C/4h 520 °C/1h + 160 °C/6h

After each stage of the manufacturing process (3D printing, machining, heat treatment) and before the HCF testing of individual batches, samples and testing specimens were stored at -20°C to avoid natural precipitation and thus undesirable alteration of mechanical properties. Fatigue testing with fully reversed tension compression cycle (stress ratio R = -1) at 113-116 Hz frequency was performed using Amsler HFP 422 resonant pulsator equipped with a 100 kN load cell. The conditions for the experiment end were set as follows: a frequency drop by 10 Hz, a change in load amplitude or static load by ± 0.5 kN or reaching 10 7 cycles (sample classified as a runout). Hardness of heat-treated specimens was determined by the Struers Duramin 40AC3 hardness tester utilizing Vickers HV1 test. The as-received powder, microstructure, and macro- and microfractography were analyzed using light optical microscopy (LOM), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDXS), and electron backscattered diffraction (EBSD). Macro fractographic analysis of fracture surfaces was done by using a digital, high-resolution Olympus DXS 1000 optical microscope with dark-field (DF) illumination. Micro-fractography and the study of microstructural features used a field emission gun–scanning electron microscope (FE-SEM) equipped with an EDAX SDD Octane Elite EDXS detector and an EDAX Velocity Pro EBSD camera. Microstructural analyses were performed on metallographic samples made using the standard procedure: grinding with SiC papers with grits from P240 to P4000, polishing with Struers OP-S colloidal silica suspension (0.25 µm), and final polishing with Struers OP-U NonDry colloidal silica suspension (0.04 µm). Specimens were chemically etched by immersion in Keller's reagent (1 ml HF + 1,5 ml HCl + 2,5 ml HNO 3 + 95 ml H 2 O). EBSD data were collected at an accelerating voltage of 20 kV, tilt angle of 70°, and step size of 0.65 µm. RAW EBSD data processing and post-processing was done using EDAX OIM Analysis TM and ATEX software (Beausir and Fundenberger, 2017). The analysis of defects was conducted through the implementation of image analysis (IA), which entailed the utilization of a combination of NIS Elements AR and Fiji software. The porosity fraction was evaluated for each printed batch on a total of nine micrographs of the microstructure. The highest porosity was measured for batch no. 3 (1.38%), while batches no. 1 and no. 2 exhibited porosities of 0.28% and 0.18%, respectively. The killer defects were identified, and their dimensions (eqDiameter, area and circularity) were measured using SEM micrographs of the fatigue crack initiation area.

3. Results and discussion

3.1. Microstructure evolution

Microstructure of AlSi10Mg in the as-built state consists of MPs structure with fine α -Al cells and eutectic Si network in the skeletal form along the cell boundaries (see Fig.2a). The subsequent heat treatments have major