Effect of potassium fluoride in electrolytic solution on the structure and properties of microarc oxidation coatings on magnesium alloy

Abstract

Oxide coatings were produced on AM60B magnesium alloy substrate making use of microarc oxidation (MAO) technique. The effect of KF addition in the Na 2SiO 3–KOH electrolytic solution on the microarc oxidation process and the structure, composition, and properties of the oxide coatings was investigated. It was found that the addition of KF into the Na 2SiO 3–KOH electrolytic solution caused increase in the electrolyte conductivity and decrease in the work voltage and final voltage in the MAO process. Subsequently, the pore diameter and surface roughness of the microarc oxidation coating were decreased by the addition of KF, while the coating compactness was increased. At the same time, the phase compositions of the coatings also varied after the addition of KF in the electrolytic solution, owing to the participation of KF in the reaction and its incorporation into the oxide coating. Moreover, the coating formed in the electrolytic solution with KF had a higher surface hardness and better wear-resistance than that formed in the solution without KF, which was attributed to the changes in the spark discharge characteristics and the compositions and structures of the oxide coatings after the addition of KF.