Fig. 1 Schematic diagram of the breakdown process of coatings on Mg alloys

Fig. 2 Schematic diagram interpreting the breakdown of coatings on Mg alloys

Fig. 3 Schematic diagram of the four-point flexural test a and the real image of the loader b

Fig. 4 Schematic diagram of the dissimilar joints

Fig. 5 Schematic diagram of closely-arrayed electrodes a and the picture of real electrodes demonstrating the formation of an electrolyte water bridge on the surface b

Fig. 6 Surface and cross-sectional morphologies of PEO coatings prior to a and d, after b and e micro-creep loading, and the surface and cross-sectional observations of composite coatings c and f

Fig. 7 Impedance spectra of PEO coated Mg alloy in a 70 ppm NaCl electrolyte with a temperature of 20 ℃ a and b; the linear c and logarithmic plot d of the calculated Rp values as a function of immersion time

Fig. 8 Calculated ${{L}}_{2}$ values for the diffusion kinetic models: the relationship of ${{L}}_{2}$ value as a function of Cl− concentration at 20 ℃ prior to a and after c micro-creep loading, and the relationship of ${{L}}_{2}$ value as a function of Cl− concentration at 40 ℃ prior to b and after d micro-creep loading

Fig. 9 Degradation of adhesive force of PEO coating a and composite coating b as a function of immersion time in NaCl electrolyte

Fig. 10 Measured (dots) and predicted (dash lines) values of hydrogen evolution volume (HEV) as a function of time for bare Mg alloys a and b and dissimilar joints c and d

Fig. 11 Calculated breakdown time of PEO coating a and composite coatings b

Fig. 12 Measured surface resistance changes as a function of time a and the calculated factor under various relative humidity b

Fig. 13 Comparison of the measured and predicted results for PEO coatings and composite coatings in a 110 ppm NaCl electrolyte and the PEO coatings in an accelerated test

Fig. 14 Weibull probability distribution for the PEO coating and the composite coating, respectively