Effects of NaOH Concentration on the Structure of PEO Films Formed on AZ31 Mg Alloy in PO43- and SiO32- Containing Aqueous Solution

인산 및 규산 이온이 포함된 수용액에서 AZ31 마그네슘 합금의 플라즈마 전해산화 피막의 구조에 미치는 수산화나트륨 농도의 영향

  • Received : 2016.02.16
  • Accepted : 2016.02.29
  • Published : 2016.02.29


The structure of plasma electrolytic oxidation (PEO) coatings was investigated as a function of NaOH concentration in 0.06 M $Na_2SiO_3$ + 0.06 M $Na_3PO_4$ solution by using SEM and epoxy replica method. The PEO film was formed on AZ31 Mg alloy by the application of anodic pulse current with 0.2 ms width and its formation behavior was studied by voltage-time curves during the formation of PEO films. It was found that the addition of NaOH into $PO_4{^{3-}}$ and $SiO_3{^{2-}}$ containing aqueous solution causes a decrease in the PEO film formation voltage, suggesting that dielectric breakdown of the PEO becomes easier with increasing $OH^-$ ion concentration in the solution. With increasing $OH^-$ ion concentration, thickness of the PEO film increased and surface roughness decreased. The size of pores formed in the PEO layer became smaller and the number of cracks in the PEO layer increased with increasing $OH^-$ ion concentration. Based on the experimental results obtained in the work, it is suggested that $OH^-$ ions in the solution can contribute not only to the dielectric breakdown but also to the formation of PEO films in the presence of $PO_4{^{3-}}$ and $SiO_3{^{2-}}$ ions in the solution.


Mg alloy;Plasma electrolytic oxidation;Pore;Coating


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