PSI - Issue 57

C2 - Confidential

Hayder Y Ahmad et al. / Procedia Structural Integrity 57 (2024) 478–486 Ahmad et al./ Structural Integrity Procedia 00 (2023) 000 – 000

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Figure 6: Example of the EDX analysis results showing the elements from the fracture surface. The EDX analysis approve the alloy used in this work complies with Mg alloy.

5. Fractography The fracture surfaces were examined under a light microscope and in depth examinations were carried out using SEM. 5.1. Light Microscopy Figure 7 (a and b) shows the fracture surface of the outer cylinder. This figure shows there are two cracks initiated from two different location, right and left of the fixing hole. Both cracks propagate and join approximately 10mm away from the edge of the hole. The fracture surface has distinct chevron markings indicating the direction of the fracture propagation. The chevron markings indicate the crack nucleated either at the black particle on the fracture surface or on the boundary of the fixing hole. Figure 6a shows the starburst region indicated by the white arrow, the centre of the fixing hole indicted by the black arrow and a large particle indicted by the grey arrow. This figure also shows the crack had nucleated at a starburst like feature on the fracture surface, which is the lighter grey colour than the rest of the fracture surface. The initiation of the crack on the right side of the fixing hold shows a darker grey region, shown in figure 6b, although the crack pattern was unaffected by the particle.

(a)

(b)

Figure 7: Section of failed magnesium casting with millimetre scale: (a) section a showing the starburst region indicated by the white arrow, the centre of the fixing hole indicated by the black arrow and the large particle indicated by the grey arrow (b) section b showing some discoloration of the fracture surface Further investigation on the fracture surface reported in this paper can be found in figures 8 and 9. These figures identified a brittle fracture; confirming a circular ‘starburst’ feature having a small inclusion in the centre, adjacent to the fixing hole.