PSI - Issue 57

C2 - Confidential

8

Ahmad et al./ Structural Integrity Procedia 00 (2023) 000 – 000

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

485

Inclusion

(a)

(b)

Figure 11: (a) Inclusion found at the centre of the starburst feature, (b) EDX shows the Magnesium and Silicon elements

The sand particle probably originated from the sand mould and had been washed throughout the casting on the advancing metal stream. The inclusion measured 0.3mm in diameter and it was therefore considered that the size of the individual particle was unlikely to be detected with most radiographic inspection techniques. The SEM examination revealed that there is no evidence of Stress Corrosion Cracking (SCC) as well as there being no sign of hydrogen embrittlement given the low susceptibility of this class of alloy to this type of failure. Conclusion 1. The crack was brittle and appeared to have initiated from a subsurface casting flaw. 2. No other flaws were revealed during the examination. 3. Cracking is most likely to have occurred as a result of the low temperature and stresses experienced during thermal cycling. 4. Cracking is also likely due to the change in local alloy chemistry (Zirconium and Neodymium rich phase) that will increase in the brittleness of Magnesium Alloy Recommendation 1. Reduce the flow turbulence of the melted Mg alloy during the pouring process. 2. Ensure the alignment of the downsprue, runner and riser to avoid the erosion of sand in these three regions. 3. Non-destructive testing procedures should be reviewed to determine whether a 0.3mm diameter subsurface casting flaw could be detected. If such features cannot be detected, the design of the part might need to be reviewed.

References Kielbus, A., 2006. Structure and mechanical properties of casting MSR-B magnesium alloy, JAMME, Vol 18, 131-134. Luo, A. A., 2013. Magnesium casting technology for structural applications, Journal of Magnesium and Alloys Vol. 1, 2 - 22 Pashkova, O., Ostrovsky, I., Henn, Y., 2007. Present State and Future of Magnesium Application in Aerospace Industry, in: Presentation at New Challenges in Aeronautics, Moscow.