PSI - Issue 68

V. Milani et al. / Procedia Structural Integrity 68 (2025) 1181–1187 V. Milani, G. Angella, G. Timelli/ Structural Integrity Procedia 00 (2025) 000–000

1186

6

Despite the higher porosity, the AlSi9Cu3(Fe) alloy treated at 760 °C exhibited greater average values of ductility as well as higher threshold values in the three-parameter Weibull analysis. This result is strictly related to different microstructure of the alloy as shown in Figure 4. While a casting temperature of 720 °C produced a microstructure rich in β-Al 5 FeSi platelets (Figure 4a), characterized by needle-like morphology, the casting temperature of 760 °C led to the formation of the α-Al 8 Fe 2 Si phase with a script-like morphology (Figure 4b). The cooling rate during solidification influenced the morphology of Fe-bearing phases. Higher casting temperatures led to a reduction of the β-Fe phase and an increase in α-Fe intermetallic compounds, consequently reducing the brittleness of the alloy. This result is in agreement with the findings from Haghayeghi et al. (Haghayeghi et al., 2022), who investigated the effect of the casting temperature on the microstructure of an AlSi9Cu3(Fe) alloy and found that an increasing casting temperature progressively reduced the β-phase content in the alloy. The reduction of the β-Fe phase in the alloy treated at 760 °C led to higher average values of elongation, as shown in the individual value plots in Figure 1, and thus to a shift of the threshold parameter λ towards higher values of elongation, as displayed in Figure 2. Therefore, controlling the processing temperature is crucial to minimize porosity and avoid harmful intermetallic particles in AlSi9Cu3(Fe) alloys.

Fig. 4 Microstructures showing the precipitation of Fe-rich compounds in the AlSi9Cu3(Fe) alloy processed without flux at (a) 720 and (b) 760 °C.

Figure 5a shows the typical fracture surfaces of the tensile AlSi9Cu3(Fe) alloy specimens, which exhibited a mixed morphology. Uniformly distributed dimples indicate the occurrence of plastic deformation, whereas the presence of cleavage facets is related to the presence of the brittle precipitates. Upon closer inspection, oxide films were encountered on the fracture surface of the examined samples (Figure 5b), obtained under different processing temperatures and fluxing conditions.

Fig. 5 Typical FEG-SEM images of the fracture surfaces of the tensile samples showing (a) cleavage facets and dimples and (b) oxide films.