Issue 57

A. Basiri et alii, Frattura ed Integrità Strutturale, 57 (2021) 373-397; DOI: 10.3221/IGF-ESIS.57.27

Figure 5: Optical micrograph images of AlSi_N_T6 samples with 1000X magnification.

To study the material microstructures more accurately, the FE-SEM images were depicted in Fig. 6-7 for both AlSi alloys and AlSi_N_T6. The Intermetallic phases could be distinguished easily from the rest of the microstructure. As it could be observed, the intermetallic phases in AlSi_N_T6 have a nearly needle-shaped morphology, which could act as stress- concentration sites and eventually reduce mechanical properties [47]. For the determination of the dominant chemical element of intermetallic phases, the EDS results for AlSi_N_T6 were depicted in Fig. 8. Both Si and intermetallic phases could be found through the aluminum matrix. The elements, which have percentages of more than 1% including Al, Si, Cu, Mg, and O according to Tab. 1, were presented. As it could be observed, two main intermetallic phases including Cu-rich and Mg-rich could be distinguished. The presence of such intermetallic phases could result in the improvement of mechanical properties [48].

Figure 6: FE-SEM images of AlSi with low magnifications.

It is widely accepted that nano-particles have a high tendency to attract each other and create agglomerations as a result of their high surface to volume ratio. The agglomerations are a possible site for the crack nucleation and therefore, could be the reason for achieving undesirable mechanical properties compared to the original metal matrix. Nevertheless, reaching completely distributed single nano-particles is quite impossible in most cases [7]. The dispersion of nano-particles in the metal matrix is highly dependent on the processing route. Fig. 9-10 demonstrates the FE-SEM images of the surface of

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