## 2 Materials and Methods  
Various AM metal powder suppliers have recently enriched their offerings with high-strength Al alloys (for example, Elementum3D, M4P, and EOS); however, in most cases, the TRLs declared by manufacturers are still rather low. In the frame of this project, the raw material chosen was commercially available as forAM(r) Al-HS1, supplied in the form of gas-atomized powder, from Hoganas AB, Sweden. The particle size distribution for this material is 20-53 [m]. The chemical composition of the powder is shown in Table 1.  
The raw material was processed in a PBF-LB machine (EOS M290, EOS GmbH, Krailling, Germany [61]) at Chalmers University of Technology, Sweden. All samples \begin{table}
\begin{tabular}{c c} \hline \hline
**Alloy** & **Chemical Composition** \\ \hline Al-HS1 & Al 5 Mn 0.8 Cr 0.6 Zr 0.17 Fe 0.24 Si \\ \hline AlSi10 Mg & Al 9.8 Si 0.33 Mg 0.15 Fe \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical compositions of the materials used in this study [62; 63]. All compositions are in wt%. Fe and Si are considered impurities from the atomization process. Figure 2: Engineering end-to-end process addressed for Al-HS1 qualification. were produced with 370 [W] laser power, 1300 [mm/s] laser speed, 0.13 [mm] hatch distance, and 0.03 [mm] layer thickness. A scan rotation of 67\({}^{\circ}\) was applied between consecutive layers. These processing parameters led to >99.7% relative density, as discussed within [62; 63]. All samples were cut directly from the build plate with a cold saw, and 10 [mm] side cubes were produced for the microstructural analysis. The bending fatigue samples were printed as rectangular specimens of 95 [mm] \(\times\) 12 [mm] \(\times\) 6 [mm], which were then machined into the dimensions as shown in Figure 3.  
The samples for characterization were prepared by cutting them along the building direction (Z), followed by grinding and polishing, in line with the procedure described in [62]. After polishing, a final step using an OP-S silica suspension was used. All of the samples' preparations were conducted using a Struers TegraPol 31 machine. Light optical microscopy was conducted using a Zeiss Axioscope 7 microscope, and the stereo optical microscopy was performed using a Zeiss stereo discovery V.20 microscope. Microstructural characterization was conducted on a Zeiss Gemini 450 SEM equipped with a field-emission gun source. The SEM was fitted with an Ultimax energy-dispersive X-ray spectroscopy (EDX) detector from Oxford Instruments, which enables elemental mapping of microstructures at submicron resolutions. A voltage of 5 [kV] and probe current of 1 [nA] were used. For mechanical testing, most of the samples were heat treated to achieve precipitation hardening. A direct aging heat treatment was conducted by introducing the samples in a resistance furnace, with a secondary thermocouple close to the samples to ensure temperatures of \(\pm\)2 \({}^{\circ}\)C. Samples were treated at 375 \({}^{\circ}\)C at a heating rate of 10 \({}^{\circ}\)C/min, followed by air cooling. The bending fatigue tests were conducted on 30 samples, which were printed along the building direction (Z), heat treated at 375 \({}^{\circ}\)C for 8 h. The samples were tested in a four-point bending test rig at Hoganas AB, Sweden. The load ratio was set to fully reversed bending (R = \(-\)1.0). The test sequence used the so-called staircase method of evaluation. This method determines the average fatigue strength, i.e., the level at which 50% of the specimens survive until the run-out limit (which was set to 2 \(\times\) 10\({}^{6}\) cycles) was reached. In addition to the staircase samples, a few specimens were tested in the low cycle regime. These points suggest reasonable indication of how steep is the Wohler curve (S-N curve). Furthermore, the runouts were distributed in the X-direction for visibility later. They were all stopped at around 2 \(\times\) 10\({}^{6}\) cycles.