PSI - Issue 57

Martin Matušů et al. / Procedia Structural Integrity 57 (2024) 327 – 334 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Considering that the values refer to as-built surface,its quality is generally good for this method of printing. The probable reason is the used AM setup of the printer, differentiating the laser parameters in contour and in the core of specimens. No visible differences were found among different HTs. Two testing facilities were used: CTU in Prague and OTH Amberg-Weiden (Fig. 2). The specimens were divided between these facilities to utilize the similar testing equipment for each group regarding the fatigue experiments. Testing frequency at CTU and at OTH were 120 Hz and 90 Hz, respectively. Tensile tests of all four groups of specimens with varying HT were conducted at OTH using the Hegewald & Peschke tensile testing machine with an extensometer and 20 kN load cell.

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Fig. 2. (a) Amsler resonant pulsator with fixed specimen and Fluke RSE600 infrared thermal camera; (b) Tensile test set-up with the specimen fixed in the lower jaws of Hegewald & Peschke machine.

2.2. Experimental results Table 2 clearly shows a significant difference between the four configurations. The non-heat treatment state NoHT serves as a reference value for comparing the effects of heat treatment. As expected, T200 case shows an increase in yield strength and ultimate tensile strength compared to NoHT and a decrease in ductility. This fact stems from the HT temperature used, which is still in the range of age hardening temperatures for AlSi10Mg alloy. With T240 variant on the other hand, HT temperature is in a certain range beyond the age hardening limit but has not yet fully reached the annealing temperatures. Therefore, there is a decrease in strength and yield strength, which corresponds to the application of annealing, but also a decrease in ductility, which would be one of the consequences of the age hardening process. Due to the transition of these temperature zones, the processes inside the material work against each other with the result of a decrease in the yield strength, ultimate tensile strength, and ductility. For T300 case, where stress relief annealing is already taking place, a decrease in strength and yield strength is clearly visible. However, it is necessary to draw attention to a fact that normally occurs with this heat treatment, namely a significant drop in ductility, which did not occur in this case. Investigating why this happened will be the subject of further research. For example, the shape and size of the samples with a rectangular critical cross-section of 6x3 mm, can be to blame, where the different skin and core printing technology can manifest itself on a much larger scale. Table 2. Results from tensile tests including the 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