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

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The casting bars were heat treated. The heat treatment involved a solutionizing stage at 490 ± 2 °C for 24 h inside an air-circulating resistance furnace, water quenching at 70 ± 2 °C, and artificial ageing at 140 ± 1 °C for 2 h. The specimens were then machined to gauge diameter and length of 8.50 and 55.8 mm, respectively. At least 11 specimens for each experimental condition were tested using an MTS 810 tensile testing machine, with a crosshead speed of 2 mm/min. The strain was measured using a 25-mm extensometer. Experimental data were collected and processed to provide yield stress (YS, actually 0.2% proof stress), ultimate tensile strength (UTS), elongation to fracture (El%) The tensile results were analysed using a Weibull statistical approach to assess the impact of the fluxing condition and processing temperature on the scattering of the elongation to fracture. The samples were cut transversally near the fracture zone, prepared to a 6-μm finish using a diamond paste, and polished with a fine silica slurry. Fe-rich intermetallic phases were analysed by etching samples in a 20% vol. H 2 SO 4 aqueous solution at 70 °C for 50 s. The microstructure of the tensile specimens was examined with an optical microscope (Leica DM6M) equipped with a quantitative image analyser and the fractured surfaces were investigated using a field-emission gun scanning electron microscope (Quanta FEG 250). 3. Results and Discussion The individual value plots of the elongation to fracture of the specimens show that data scattering depends both on the fluxing conditions and the processing temperatures (Figure 1a). The elongation to fracture shows greater dispersion at higher processing temperatures. Conversely, using Flux A at 720 °C minimizes the scattering. The dispersion of UTS values does not significantly show differences at varying processing temperatures or fluxing conditions (Figure 1b). As regards the average tensile parameters, the processing temperature has little effect on the yield strength, but significantly affects the ultimate tensile strength and elongation to fracture. A one-way ANOVA confirmed no statistically significant difference in YS averages, of 184 MPa, at different processing temperatures ( p value = 0.786, 95% Confidence Interval). However, significant differences in UTS and El% are shown between 720 and 760 °C ( p -value = 0).

Fig.1 Individual value plots of the (a) elongation to fracture and (b) ultimate tensile strength of the tensile AlSi9Cu3(Fe) samples obtained under different experimental conditions of fluxing and melt-processing temperature.

The analysis of the Weibull statistical distribution aids in further investigating the dispersion of the mechanical data. The analysis focused on the elongation to fracture, which is more sensitive to the effect of casting defects (Timelli & Bonollo, 2008). Table 2 reports the Weibull moduli, β , and the scale parameters, η , i.e. the characteristic strain at which 63.21% of the specimens has failed, from the two-parameter Weibull analysis for the different experimental conditions. The analysis reveals that the Weibull modulus β is affected both by the processing temperature and the fluxing condition.