Anticorrosive lanthanum embedded PEO/GPTMS coating on magnesium alloy by plasma electrolytic oxidation with silanization

Abstract

The different amount of lanthanum doped PEO coatings with and without 3-glycidyloxypropyltrimethoxysilane (GPTMS) layer were prepared on the AZ31 magnesium alloy to investigate the corrosion resistance of the resulting coatings. The SEM results revealed that the porosity of the PEO coating structure decreased with increase in La(NO3)3 content. The corrosion analysis of prepared coatings was performed using potentiodynamic polarization (PDS) and electrochemical impedance spectroscopy (EIS) methods. As a result of the PDS test, an anti-corrosion property of the coatings was sufficiently improved with the presence of La nanoparticle. The concentration of 0.7 g/l La(NO3)3 in PEO electrolyte produced coatings with lower porosity and higher anticorrosion property. The corrosion resistance of the coatings further improved with GPTMS layer. Corrosion current density for the PEO/GPTMS coating decreased by eight orders of magnitude compared to bare alloy. In addition, the noble potential of − 0.25 V/Ag/AgCl was observed in the PEO/GPTMS coating. 0.7 g/l lanthanum contained and silane sealed P7LaS coating exhibited the highest corrosion resistance, which was 1.79 × 1010 Ω.cm2. According to the EIS test, P7LaS coating showed higher resistance after 7 days of immersion in the corrosive solution compared to other coatings. Moreover, PEO/GPTMS coatings presented better resistance during the immersion due to their proper GPTMS barrier layer in compared to GPTMS-free PEO coatings. Adding a higher concentration of La in PEO electrolyte and consequent GPTMS sealing was an efficient approach for enhancing the corrosion protection properties of PEO coating. © 2022 Elsevier Ltd