The AZ31B magnesium alloy has a low density, appreciable strength, and engineering deformability; however, the alloy’s resistance to aqueous corrosion is compromised by fast anodic dissolution, hydrogen gas evolution, and poor formation of stable passive film. The process of micro-arc oxidation creates a protective coating with a ceramic structure, which enhances corrosion resistance, while pores and microcracks are still available for contact with highly-chlorinated and acidic electrolytes. The performance of three AZ31B magnesium alloy surfaces under consideration: unmodified AZ31B alloy (AZ31B); micro-arc oxidation modified AZ31B (AMAO); and zinc-phosphate nanoflowers with a hydrophobic surface treatment on the basis of micro-arc oxidation coating (AMAO@P-ZPNF), will be analyzed in terms of corrosion potential, corrosion current density, coating resistance, charge transfer resistance, anti-corrosive efficiency, acid retention, and dual-environment barrier score in 3.5 wt\% NaCl and 0.5 mol L${}^{-1}$ H${}_2$SO${}_4$. In 3.5 wt\% NaCl, the corrosion current densities decrease from $4.862\times {10}^{-5}$ A cm${}^{-2}$ (AZ31B) to $1.478\times {10}^{-6}$ A cm${}^{-2}$ (AMAO) to $3.775\times {10}^{-8}$ A cm${}^{-2}$ (AMAO@P-ZPNF). The values for the same conditions in 0.5 mol L${}^{-1}$ H${}_2$SO${}_4$ are $2.747\times {10}^{-4}$ A cm${}^{-2}$, $8.029\times {10}^{-6}$ A cm${}^{-2}$, and $9.497\times {10}^{-8}$ A cm${}^{-2}$. The charge-transfer resistance in 3.5 wt\% NaCl increases to $3.517\times {10}^6$ $\Omega$ cm${}^2$. For the acid solution, the corresponding value is $2.534\times {10}^6$ $\Omega$ cm${}^2$. The dual-environment barrier score in the case of AMAO@P-ZPNF is $1.067\times {10}^4$. The value of the score for the AMAO coating is 82.58, while for the uncoated AZ31B alloy, it is 1. It was demonstrated that the additional treatment with zinc phosphate nanoflowers increases the anti-corrosive protection level due to sealed pore openings, decreased conductivity of the electrolyte, increased diffusion pathways, and maintained strong resistance to the charge transfer across the interface.

AZ31B magnesium alloy,micro-arc oxidation,zinc phosphate nanoflowers,superhydrophobic coating,electrochemical impedance spectroscopy,corrosion current density,acidic sulfate corrosion