PSI - Issue 83

Ahmad Issmail et al. / Procedia Structural Integrity 83 (2026) 229–238

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efficient melting of the surface powder. Moreover, as also observed in [16], the higher heat accumulation in the miniature specimens promotes larger MPs and, consequently, fewer solidification interfaces at the surface and a more even roughness profile. Regardless of the specimen size, the surface roughness also showed an increase with decreasing build angle (Fig. 2(b,c), registering its maximum values for the H orientation. While the surface roughness measurements of the H orientation are affected by support remnants and unfused powder particles, the increase in roughness of 45° compared to V is attributed to the stairstep effect.

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Fig. 2: Surface roughness profiles of (a) 45° specimens; (b) standard specimens; and (c) miniature specimens

Table 1: Average roughness (Ra), mean peak to valley height (Rz), and maximum valley depth (Rv) of the roughness profiles of each category. Specimen Category S|V S|45° S|H m|45° m|H R a [µm] 5.3 33.6 49.3 12.6 45.9 R z [µm] 40.5 208.2 328.5 86.7 324.6 R v [µm] 22.6 109.8 235.2 48.8 196.9 3.2. Monotonic Behavior The stress-strain curves illustrated in Fig. 3(a) demonstrate identical monotonic behavior before fracture across the different build orientations. The orientation-independent tensile behavior before fracture highlights the success of the employed heat treatment in eliminating micro- and meso-structural bulk-material directional anisotropy, as reflected by a maximum difference of 1.2% in UTS across the different build orientations (Fig. 3(b)). This can be explained by the fact that the employed T6 HT homogenizes the microstructure by erasing the MPs, which are a main source of tensile orientational anisotropy in AM materials [19]. Furthermore, T6 HT removes an additional degree of anisotropy presented by the subgrain cellular microstructure [5], which is decomposed and replaced by coarse Si embedded in an Al matrix [18]. On the other hand, the elongation at break (EaB) exhibited a significant decrease (up to 42%) with decreasing build orientation (Fig. 3(c)), which is attributed to the early fractures determined by the higher surface roughness in S|45° and S|H (Table 1). This trend differs from the reported cases where surface roughness is removed, in which the horizontal orientation often displays the highest ductility [5, 19, 20]. In such a case , the greater misalignment between the MPBs and load direction in horizontal specimens leads to consumption of a portion of the tensile load into shear stresses at the MPB, resulting in inter-MP slipping and enabling the material to withstand higher deformations [19].