Degradation and structure evolution in corrosive LiOH solution of microarc oxidation coated Zircaloy-4 alloy in silicate and phosphate electrolytes

Abstract To improve the corrosion resistance of zirconium alloys, two separate coatings with distinct structure were prepared on Zircaloy-4 alloy by microarc oxidation in alkaline phosphate and silicate electrolytes, respectively. The coating formed in silicate solution has more dense and homogeneous structure than the other, thus it shows better corrosion resistance. According to the electrochemical impedance spectroscopy of the two samples immersed in LiOH solution for different time periods, the coating formed in phosphate solution is able to protect the substrate alloy from corrosion for 30 days, while the coating formed in silicate can provide sufficient protection to the substrate up to 50 days.