PSI - Issue 34

Benjamin Möller et al. / Procedia Structural Integrity 34 (2021) 160–165 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

162

3

2. Manufacture of specimens and experimental fatigue investigation Laser Powder Bed Fusion of Metallic materials (PBF-LB/M) of AlSi10Mg powder is used in order to manufacture aluminum sheet metal with 2 mm thickness (measured values are higher than 2.00 mm) on a Concept Laser M2 cusing system applying the parame ter set ‘AlSi10Mg performance’ from 2016. For each layer, first the contour scan and afterwards the core material has been melted in this layer-by-layer process. AM AlSi10Mg already shows differences in the microstructure between the contour and the core material due to different cooling rates resulting from different process parameters, cf. Schnabel et al. (2021). AM plates have been subjected to a stress relief heat treatment afterwards. As it has already been documented by Wagener et al. (2019), Möller et al. (2019) and Möller et al. (2020), microsections show clusters of larger pores, especially in the transition from the surface to the inside. The additively manufactured sheet metal is joined to conventional rectangular (for lap joints) and L-shaped (for peel T-joints) extruded sections made of EN AW-6082 (AlMgSi1, 3.2315) with a T6 heat treatment. These sections also have a nominal thickness of 2 mm, which reduces to approx. 1.90 mm as a real value. In this work, lap joints with I-shape seam welds (laser beam driven through the sheets), lap joints with fillet welds on both sides and peel T-joints (I-shape seam welds again) have been chosen in order to investigate the influence of the fatigue notch effect due to laser beam welding of additively manufactured AlSi10Mg and conventional manufactured EN AW-6082 T6 (Figure 1). The idea to make use of the advantage of thin and deep welding by lap joining with a single pass through the AM sheet and sheet metal, Figure 1(a), is faced to the lap joint with two fillet welds at the ends of the sheets in the overlap area, Figure 1(b). The T-joint has been designed to show the influence of a peel loading, which is realized by L-shape of the AlSi10Mg sheet using a 90° angle and therefore shift of the loading direction according to Figure 1(c). For lap joints, a gap in the range of 0.19 mm to 0.35 mm has been found. For fillet welds of the lap joints, a throat thickness of about 1.6 mm to 1.7 mm has been evaluated. While a tactile LBW system has been applied for the lap joints with fillet welds and AlSi12 filler wire, a remote LBW system has been used for the manufacture of I-shape weld seams in two different lengths, prior to extraction of specimens: • Two long weld seams of ~ 120 mm with a weld seam overlap in the middle part to produce an seam length of ~ 230 mm by deflection of the laser beam • Quilted short weld seams of approximately 40 mm (also by deflection of the laser beam) The weld starts, weld ends and weld overlaps have always been excluded, when straight specimens of 30 mm width have been extracted from all types of welded sheets by water cutting. Edges of the specimens have been chamfered. Further information on the chemical composition of the AlSi10Mg powder, the parameters used for the manufacture of the specimens, the stress-relief heat treatment, the mechanical properties of the base materials and the welding process can be found in Möller et al. (2020). The fatigue life was derived from stress-controlled testing under constant amplitude loading (Wöhler tests) with a stress ratio of R = 0.1 on servo-hydraulic driven test rigs at test frequencies of 20 Hz to 50 Hz. The free length of the lap joints between upper and lower clamping was 120 mm. The load axis was located between the two sheets for lap joints. Peel T-joints were fixed on one side of the base sheet at a distance of 13.6 mm from the load axis, which is in line with the mid axis of the AM-sheet. Loading directions are shown by the arrows in Figure 1.

Fig. 1. LBW joints: (a) lap joint with I-shape seam weld; (b) lap joint with fillet welds (c) peel T-joint (with I-shape seam weld).