Effect of adding K₃[Fe(C₂O₄)₃] on the characteristics of the magnesium alloy micro-arc oxidation coating

Abstract

The black micro-arc oxidation (MAO) thermal control coating was prepared in the electrolyte containing Na₃PO₄, K₃[Fe(C₂O₄)₃], C₆H₁₁KO₇ and NaOH. The complexion mechanism of iron(III) complexes was studied. The effect of adding K₃[Fe(C₂O₄)₃] on electrolyte and MAO coating morphology, element composition, phase composition and thermal control properties were investigated. The results showed that K₃[Fe(C₂O₄)₃] hydrolysis to produce Fe(OH)₃ colloidal particles that negatively charged, gluconate and oxalate complexing with iron(III). Discharge channels and molten oxides particles in bigger size were discovered in the MAO coating prepared in the electrolyte containing K₃[Fe(C₂O₄)₃]. Fe₂O₃ and Fe₃O₄ were found in the MAO coating surface prepared in the electrolyte with K₃[Fe(C₂O₄)₃] and the content of Fe in the outer layer was higher than that in the inner layer. The addition of K₃[Fe(C₂O₄)₃] could significantly improve the thermal control property of the MAO coating, and make it black.

Graphical Abstract

Keywords:

• Mg alloy
• micro-arc oxidation (MAO)
• black MAO coating
• thermal control property

Additional information

Funding

This work was financially supported by the National Key Research and Development Program of China [grant number 2016YFB0301105 and 2017YFB0702100].