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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Mg alloys from corrosion, which is consistent with previous reports (F. Liu et al. 2011; X. Liu et al. 2018; Yang et al. 2017a).

Figure 4. Potentiodynamic polarization curves of bare (blu) and coated (red) AZ31 alloy in SBF. Table 2. The results of corrosion potentials (E corr ) and corrosion cuttent densities (i corr ) for bare and coated AZ31 samples in SBF. Bare ZrO 2 coating E corr (V) -2.0 -2.02 i corr (A/cm 2 ) 3.0 10 -3 1.2 10 -6 3.2. Immersion tests The immersion tests were carried out in SBF at 37 °C. During the immersion tests, the chemical reaction between Mg and electrolyte occurs as shown in the following equation (Peron, Torgersen, and Berto 2017):   2 2 2 2 Mg H O Mg OH H    (3) From the above equation it can be easily understood that the dissolution of one magnesium atom generates one hydrogen gas molecule. In other words, the evolution of one mole of hydrogen gas corresponds to the dissolution of one mole of magnesium. Therefore, measuring the volume of hydrogen evolved allows to assess the corrosion rate of Mg and its alloys in a way that allows to overcome the drawbacks of the weight loss method and of the electrochemical techniques (Song, Atrens, and StJohn 2013). The hydrogen evolution of bare and coated samples are reported in Figure 5, and the results further suggest that a 100 nm thick ZrO 2 coating can prevent the degradation of AZ31 alloy.

Figure 5. Hydrogen evolved from the immersion of bare and coated AZ31 alloy in SBF