Smart functionalization of PEO coating on AZ31B magnesium alloy by a novel facile one-step sealing method

Abstract

Plasma electrolytic oxidation (PEO) coating has been widely applied for the magnesium alloys to resist the corrosion. However, the defaults on the PEO surface greatly weaken its long-term anti-corrosion performance. To fill the micropores is an efficient and feasible strategy to refine the compactness and anti-corrosion of PEO coating and achieve the additional function. Although various sealing pathways are reported in past decades, the leakage of filler and long-term anti-corrosion performance are still the perplexing issues. The corrosion inhibitor 1-methyl-3-(carboxyundecyl)imidazolium bis(trifluoromethylsulfonyl)imide ([MCIM][NTf2], MN), is grafted on the clinochrysotile-like magnesium silicate nanotubes (MSNTs) by the post-synthesis method, then, the MSNTs@MN is filled into the micropores on the PEO surface by the post-sealing process to form PEO/MSNTs@MN. According to the electrochemical results in 3.5 wt% NaCl solution, the log |Z|0.01Hz is increased by 1.26 times after the sealing. After immersion in 3.5 wt% NaCl solution for 120 h, the log |Z|0.01Hz of PEO/MSNTs@MN is still the 1.56 times larger than that of PEO. The PEO coating filled by the MSNTs@MN offers the consistently superior corrosion resistance up to 336 h of salt spray tests with 5.0 wt% NaCl solution. The superior anti-corrosion performance of PEO/MSNTs@MN is associated with the cooperation of physical barrier of PEO coating and protection from MSNTs@MN. The grafted corrosion inhibitor would not leak easily, which is favorable to achieve the long-term anti-corrosion performance. The immobilized MN provides the active anti-corrosion in the initial corrosion stage achieving the self-healing function. Moreover, the release of corrosion inhibitor, MN, does not rely on the smart trigger, which broadens the scope of immobilized materials. This work introduces a facile and one-step strategy to seal the pores on the PEO surface with the self-healing function and improved anti-corrosion capability.