PSI - Issue 18

Mirco Peron et al. / Procedia Structural Integrity 18 (2019) 538–548 Author name / Structural Integrity Procedia 00 (2019) 000–000

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4. Discussion From the experimental results reported in Figure 6 and from the I SCC indices in Figure 7 it can be seen that the presence of a 100 nm thick ZrO 2 coating highly increased the mechanical performances in presence of a corrosive environment. In fact, the coating reduced the I UTS and I ε of 70.1% and 75.6%, respectively. This can be explained considering the corrosion performances. SCC in Mg alloys has in fact been generally attributed to the combination of anodic dissolution and hydrogen embrittlement (HE) induced cleavage. In particular, the former leads to the local breakdown of the partially protective Mg(OH) 2 surface film that allows the hydrogen evolved from the corrosion process to embrittle the material. In light of these considerations, it is easily understandable why the coated samples are characterized by a lower SCC susceptibility. Being in fact less hydrogen evolved and being the corrosion less pronounced in the coated samples (Figures 4 and 5), the HE is less pronounced in this samples and thus the material is characterized by a more ductile behavior (Figure 6), providing lower I SCC indices (Figure 7). To provide further evidences of this statement, fracture surfaces analyses that are now undergoing and will be provided in the future 5. Conclusion In this study, the effect of a 100 nm thick ZrO 2 coating on the SCC susceptibility of the AZ31 Mg alloy was assessed. To this regard, SSRTs were carried out in SBF at 37 °C on bare and coated samples, and potentiodynamic polarization curves and hydrogen evolution experiments have been carried out to provide an explanation of the observed behavior. The coated samples are characterized by a lower SCC susceptibility, in particular the elongation to failure is more than two times higher than the bare counterparts. 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