Issue 43

M. Tocci et alii, Frattura ed Integrità Strutturale, 43 (2018) 218-230; DOI: 10.3221/IGF-ESIS.43.17 226 Figure 10: Eroded surfaces after 5 minutes of cavitation test for a) AlSi3, b) AlSi9, c) AlSi9 T6 alloys. Figure 11: Eroded surfaces after 30 minutes of cavitation test for a) AlSi3, b) AlSi9, c) AlSi9 T6 alloys. Images at lower magnification are provided in Fig. 12 in order to appreciate the degree of damage after 8 h of testing. Large craters are visible for all the alloys. AlSi3 alloy exhibited the largest craters, while AlSi9 T6 sample was less damaged. The craters likely originated in correspondence of casting defects and then grew with consequent material removal due to fracture of the rim of the craters or flaking [1]. Figure 12: Eroded surfaces after 8 h of cavitation test for a) AlSi3, b) AlSi9, c) AlSi9 T6 alloys. To summarize, at initial stages of erosion, the Al matrix is more prone to deformation, and subsequently erosion, in comparison with the eutectic phase, which is less affected by the load condition due to cavitation. This is especially evident for AlSi3 alloy since it is characterized by the highest area fraction of Al matrix. This is responsible for a larger material removal for AlSi3 alloy in comparison with AlSi9 alloy, despite their similar hardness and grain size. On the other hand, when the Al matrix is strengthened by the formation of precipitates due to heat treatment, the erosion process is delayed, resulting in an increase in incubation period and a decrease in total mass loss and maximum erosion rate. Investigation of eroded surfaces: Effect of intermetallic particles. Analogously, the eroded surfaces of AlSi9CuFe alloy in as-cast and heat-treated condition were evaluated in order to investigate the role of intermetallic particles. Since these compounds are characterized by the presence of elements with high atomic weight, images acquired in back-scattered mode are shown for easier detection of intermetallic particles.