PSI - Issue 76

Vladimír Mára et al. / Procedia Structural Integrity 76 (2026) 123–130

126

influence on the Si network’s morphology. Conventional annealing (T200, T240 and T300) leads to the gradual decomposition of Si network and precipitation of fine globular and needle-like Si/Mg 2 Si based nanoparticles inside the cells. T200 alone has a minimal influence on the Si network and the precipitation inside the cells is low overall (see Fig.2b), while at T240 the Si network increases its thickness and precipitation is reaching its peak (see Fig.2c). T300 disrupts interconnected Si network which results in formation of fine globular and polyhedral Si particles and partially spherodized blocks of residual Si network (see Fig.2d). Conventional T6 heat treatment is leading to the complete dissolution of eutectic network and reprecipitation in the form of coarse polyhedral Si particles followed by the precipitation of plate and needle-shaped Fe-rich intermetallics ( β -Al 5 FeSi phase) due to the diffusion and segregation of Fe and Si atoms (see Fig.2e). The precipitation of brittle β -Al 5 FeSi has negative impact on alloys ductility and fatigue resistance (Bisht et al., 2022; Mára et al., 2022). By modifying the heat treatment parameters (T6mod), the microstructure partially retains as-built MP contours, while the growth of Si particles is retarded and the precipitation of brittle Fe-based intermetallics is significantly reduced (see Fig.2f).

Fig. 2. (a) Cellular structure with Si network in as-built state; (b) occasional precipitation after T200; (c) Si network coarsening and extensive particle precipitation after T240, (d) Spherodization and Si network decomposition after T300; (e) Precipitation of coarse Si particles and Fe based intermetalics after T6 (different magnification was used due to the size of coarse Si particles); (f) Fine Si particles after T6mod. The results of EBSD analysis in the form of inverse pole figure (IPF) maps along the build direction (BD) can be observed in Fig. 3. Individual MPs of AlSi10Mg as-built specimen consists of equiaxed and coarse columnar grains. Part of the columnar grain exhibits epitaxial growth in <001> direction parallel to the BD, which is typical for the LPBF process (see Fig. 3a). The <001> epitaxial growth is forming stronger {011} <100> GOSS and weaker {001} <100> Cube crystallographic texture components with fractions of 12 % and 10 % respectively. The annealing processes (T200, T240 and T300) do not significantly change grain morphology and crystallographic orientation (see example in Fig. 3b), however, the intensity and mainly the fraction of GOSS and Cube texture components is gradually decreasing to 7.8 and 10% respectively. The impact of annealing is more pronounced in terms of the density of geometrically necessary dislocations (GND). The density of GND is not changing after T200, the value of 5.2×10 13 m -2 remains the same as for the as-built. However, after T240 the density decreases to 4.9×10 13 m -2 , which is tied to the effective reduction of residual stresses. After T300 however, there is only a slight decrease of GND density to 5.1×10 13 m -2 . The fraction of 30% low- and 70% high-angle grain boundaries (LAGBs and HAGBs) remains mostly the same regardless of heat treatment. Significant microstructural changes can be observed after T6 and T6mod heat treatments. The <001> crystallographic orientation decreases which is the result of ongoing softening process – static recrystallization (SRX) during the heat treatment. Majority of columnar grains disappear and are replaced by fine equiaxed grains which effectively increase anisotropy of the material. The fraction of GOSS and Cube texture components is further reduced to 4 % and 5.3 % respectively after conventional T6 and to 5.7 % and 6.5 % respectively after T6 mod. Due to the microstructural transformation, GND density is decreasing to 4.1×10 13 m -2 after T6 and 4.7×10 13 m -2 after T6 mod. The effect of SRX is further manifested in the increase of HAGBs to 82 % after T6 heat treatment. Structural changes have a direct impact on the overall mechanical and fatigue properties and are mainly tied to the diffusion of the Si and changing in lattice parameter during the heat treatment (Yaru et al., 2023). Hardness is mostly decreasing along with the gradual decrease of the concentration of Si in the α -Al matrix (see Fig.3d). The exception is T240, where fine Si/Mg particles in the cells have positive strengthening effect, and the T6 mod, where