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인산 및 규산 이온이 포함된 수용액에서 AZ31 마그네슘 합금의 플라즈마 전해산화 피막의 구조에 미치는 수산화나트륨 농도의 영향
권두영(Duyoung Kwon),문성모(Sungmo Moon) 한국표면공학회 2016 한국표면공학회지 Vol.49 No.1
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<SUP>3-</SUP> and SiO₃ <SUP>2-</SUP> 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<SUP>3-</SUP> and SiO₃<SUP>2-</SUP> ions in the solution.
AZ91 마그네슘 합금의 플라즈마 전해산화 피막 형성 및 물성에 미치는 0.1 M NaOH + 0.05 M NaF 용액 중 Na₂SiO₃ 농도의 영향
권두영(Duyoung Kwon),송풍근(Pung-Keun Song),문성모(Sungmo Moon) 한국표면공학회 2020 한국표면공학회지 Vol.53 No.2
Effects of Na₂SiO₃ concentration added into 0.1 M NaOH + 0.05 M NaF solution on the formation behavior and properties of PEO films on AZ91 Mg alloy were investigated under 1200 Hz of alternating current (AC) by voltage-time curves, in-situ observation of arc generation behavior and measurements of film thickness, surface roughness and micro vickers hardness. In the absence of Na₂SiO₃ in the 0.1 M NaOH + 0.05 M NaF solution, about 4 μm thick PEO film was formed within 1 min and then PEO film did not grow but white spots were formed by local burning. Addition of Na₂SiO₃ up to 0.2 M caused more increased formation voltage and growth of PEO film with uniform generation of arcs. Addition of Na₂SiO₃ from 0.2 M to 0.4 M showed nearly the same voltage-time behavior and uniform arc generation. Addition of Na₂SiO₃ more than 0.5 M resulted in a decrease of formation voltage and non-uniform arc generation due to local burning. PEO film growth rate increased with increasing added Na₂SiO₃ concentration but maximum PEO film thickness was limited by local burning if added Na₂SiO₃ concentration is higher than 0.5 M. Surface roughness of PEO film increased with increasing added Na₂SiO₃ concentration and appeared to be proportional to the PEO film thickness. PEO film hardness increased with increasing added Na₂SiO₃ concentration and reached a steadystate value of about 930 HV at more than 0.5 M of added Na₂SiO₃ concentration.
아연계 인산염 피막용액에서 Fe(NO₃)₂ 농도가 SCM430 합금의 전기화학적 거동에 미치는 영향
권두영(Duyoung Kwon),송풍근(Pung-Keun Song),문성모(Sungmo Moon) 한국표면공학회 2019 한국표면공학회지 Vol.52 No.4
The formation behavior of zinc phosphate conversion coating (ZPCC) on SCM430 alloy was investigated in 25 vol.% of 1M ZnO + 170 ml/L solution containing various Fe(NO₃)₂ concentrations, using open-circuit potential(OCP), electrochemical impedance spectroscopy(EIS), cyclic polarization(CP) curve and tape peel test. OCP of SCM430 alloy and corrosion current density increased with increasing Fe(NO₃)₃ concentration. Resistance of films formed on SCM430 alloy by chemical conversion treatment decreased with increasing Fe(NO₃)₃ concentration. Color and adhesion of chemical conversion coatings became darker and worse, respectively, with increasing Fe(NO₃)₃ concentration. It is concluded that addition of Fe(NO₃)₃ into a zinc phosphating bath leads to faster reaction to form porous surface coatings with poor adhesion and corrosion resistance.
AZ91 마그네슘 합금의 PEO 피막 형성거동에 미치는 HF전처리의 영향
권두영(Duyoung Kwon),송풍근(Pung-Keun Song),문성모(Sungmo Moon) 한국표면공학회 2021 한국표면공학회지 Vol.54 No.4
This study demonstrates formation behavior and morphological changes of PEO (Plasma Electrolytic Oxidation) films on AZ91 Mg alloy as a function of pre-treatment time in 1 M HF solution at 25 ± 1 ℃. The electrochemical behavior and morphological changes of AZ91 Mg alloy in the pre-treatment solution were also investigated with pre-treatment time. The PEO films were formed on the pre-treated AZ91 Mg alloy specimen by the application of anodic current 100 ㎃/㎠ of 300 ㎐ AC in 0.1 M NaOH + 0.4 M Na₂SiO₃ solution. Vigorous generation of hydrogen bubbles were observed upon immersion in the pre-treatment solution and its generation rate decreased with immersion time. It was also found that β-Mg17Al12 in AZ91 Mg alloy was dissolved and a protective thin film of MgF₂ was formed on the AZ91 Mg alloy surface during the pre-treatment process in the 1 M HF solution. PEO film did not grow on the AZ91 Mg alloy specimen when the surface was not pre-treated and irregular PEO films with nodular defects were formed for the specimens pre-treated up to 1 min. Uniform PEO films were formed when the AZ91 Mg alloy specimen was pre-treated more than 3 min. The growth rate of PEO films on AZ91 Mg alloy increased significantly with increasing pre-treatment time.