PSI - Issue 53

Martin Matušů et al. / Procedia Structural Integrity 53 (2024) 29 – 36 Author name / Structural Integrity Procedia 00 (2019) 000–000

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All specimens were printed in a single batch in the vertical direction on a Concept Laser M2 printer. Four groups of specimens (differing by heat treatment conditions) were tested, with each group consisting of 14 specimens designated for fatigue experiments and 3 for tensile tests. Eleven specimens were used to establish the S-N curve, while the remaining 3 were used for SH tests (see Sec. 2.3). Throughout the text, the series are described using IDs and color coding according to Table 1.

Table 1. Description of series using color coding to distinguish the heat treatment of the specimens.

ID-code

Heat Treatment

Color coding

NoHT

Left as built without any additional heat treatment.

Red

Heat treatment recommended by the supplier of the printing powder (GE), which also manufactures the used printer. Specimens were heated to 240 °C and held for 6 hours in the furnace, followed by cooling on air. Blue

T240

T200 T300

Heated to 200 °C for 2 hours in the furnace, followed by air-cooling to ambient temperature.

Green

Heated to 300 °C for 2 hours in the furnace, followed by water-cooling.

Orange

Experiments were conducted at two testing facilities with similar equipment, at CTU in Prague and at OTH Amberg-Weiden. The surface temperature of the specimens was measured using an infrared thermal camera. The Flir A315 was used at CTU in Prague, while the Fluke RSE600 was used at OTH Amberg-Weiden. Both cameras had a NETD (thermal sensitivity) of 50mK and 40mK, respectively. To ensure accurate temperature measurement on the specimen's surface, a high emissivity (0.963 at ambient temperature) paint from LabIR was applied. To assess the surface quality of the specimens, surface roughness measurements were conducted using the Perthometer M1 from Grant for tensile specimens ( R a = 2.11 μ m, R z = 14.19 μ m) and MarSurf LD 120 drive unit for fatigue specimens ( R a = 3.09 μ m, R z = 24.28 μ m). Surface quality is generally good for this method of printing and no visible differences were found between different HTs as it was expected. Tensile tests were conducted at OTH using a Hegwald & Peschke tensile testing machine with an extensometer and 20 kN load cell to assess the tensile properties of AlSi10Mg subjected to all four different heat treatments. 2.2. Experimental results Table 2 provides clear evidence of significant distinctions among the four configurations. The NoHT state serves as a baseline for comparing the impact of heat treatments. As anticipated, the T200 case displays higher yield strength and ultimate tensile strength compared to NoHT, but a decrease in ductility. This outcome can be attributed to the employed HT temperature, which falls within the range of age hardening temperatures for the AlSi10Mg. Table 2. Results from tensile tests in Young’s modulus of elasticity, yield strength, ultimate tensile strength and elongation. Designation E [GPa] R p 0.2 [MPa] R m [MPa] A [%] No HT 44.9 244.2 436.8 5.4 T240 66.0 224.8 387.3 4.7 T200 63.1 270.7 447.8 4.6 T300 69.9 209.5 347.4 4.8 On the other hand, the T240 variant employs a heat treatment temperature that lies above the age hardening limit but has not reached the annealing temperature yet. Consequently, there is a reduction in tensile and yield strengths, reminiscent of the effects of annealing, as well as a decrease in ductility, which can be attributed to the age hardening process. The interplay of these temperature zones creates opposing effects within the material, resulting in decreased yield strength, ultimate tensile strength, and ductility. In the case of the annealing T300 configuration, a noticeable decrease in strength and yield strength is observed. However, it is important to highlight an intriguing deviation from the commonly observed increase in ductility, which did not manifest here, and is a focus of future ongoing research. One possible factor to consider is the rectangular critical cross-section of 6x3 mm of the specimen. It is plausible that the skin and core printing technology specific to Concept Laser M2 machine could affect these results.