인산 및 규산 이온이 포함된 수용액에서 AZ31 마그네슘 합금의 플라즈마전해산화 피막의 구조에 미치는 수산화나트륨 농도의 영향
Effects of NaOH Concentration on the Structure of PEO Films Formed on AZ31 Mg Alloy in PO4 3− and SiO3 2− Containing Aqueous Solution
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초록
The structure of plasma electrolytic oxidation (PEO) coatings was investigated as a function of NaOH concentration in 0.06 M Na2SiO3 + 0.06 M Na3PO4 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 PO4 3- and SiO3 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 PO4 3- and SiO3 2- ions in the solution.
Abstract
The structure of plasma electrolytic oxidation (PEO) coatings was investigated as a function of NaOH concentration in 0.06 M Na2SiO3 + 0.06 M Na3PO4 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 PO4 3- and SiO3 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 PO4 3- and SiO3 2- ions in the solution.
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