Effect of ECAP Processing and a PEO Coating on the Corrosion Behavior of a Bioresorbable Mg–Zn–Zr Alloy

Abstract

In this paper, the effect of deformation by equal-channel angular pressing (ECAP) and subsequent coating formation using various regimes (pulsed unipolar polarization—PUP and pulsed bipolar polarization—PBP) of plasma electrolytic oxidation (PEO) on the corrosion behavior of a bioresorbable Mg–Zn–Zr magnesium alloy was studied. Structural studies, gravimetric and electrochemical corrosion tests were performed to evaluate the alloy’s resistance to corrosion in Ringer’s solution. It was found that the use of ECAP contributes to structure refinement and a decrease in the corrosion rate, as compared to the initial state, to 7.6 ± 0.7 mm/year. The best corrosion resistance of the alloy in both the initial and deformed states is ensured by applying the PEO coating using the PUP regime; the corrosion rate was 2.8 ± 0.2 and 3.8 ± 0.4 mm/year, respectively. This may be due to the fact that this regime exhibits a higher content of the high-temperature forsterite Mg₂SiO₄ phase_. Electrochemical tests indicate a decrease in the corrosion current density for the PEO-coated samples by 3–4 orders of magnitude. ECAP processing leads to an increase in the polarization resistance to corrosion for the samples with a PEO coating produced in the PUP and PBP regimes.