Lateral growth of PEO films on Al7050 alloy in 0.1 M NaAlO₂

Sungmo Moon(문성모),Gi Yeob Kim(김기엽) 한국표면공학회 2021 한국표면공학회지 Vol.54 No.4

This paper investigated generation behavior of micro-arcs and growth behavior of PEO films on the AA7050 disc specimen in 0.1 M NaAlO₂ solution under the application of 1200 ㎐ anodic pulse current. Morphologies, thickness and surface roughness of PEO films were examined at the edge part and central part separately. Micro-arcs were generated first at the edge part and then moved towards the central part with PEO treatment time, indicating lateral growth of PEO films. The lateral growth resulted in uniform PEO thickness of about 5 ㎛ and surface roughness of about 0.5 ㎛. Moving of the arcs from the edge towards the central part appeared only one time and large size arcs were generated at the edge before completing the central part with small size micro-arcs. This suggests that vertical growth starts before completing the lateral growth. Large size arcs generated at the edge resulted in the formation of relatively large size pores within the PEO films on the AA7050 disc specimen.

Anodizing science of valve metals

Sungmo Moon(문성모) 한국표면공학회 2017 한국표면공학회 학술발표회 초록집 Vol.2017 No.5

알루미늄 합금 양극산화피막의 표면경도 측정법

문성모(Sungmo Moon) 한국표면공학회 2020 한국표면공학회지 Vol.53 No.1

In this study, two novel methods to measure the surface hardness of anodic oxide films on aluminum alloys are reported. The first method is to impregnate oil-based ink into pores in the anodic oxide film and then to clean the ink on the surface using ethanol, resulting in an impregnation of inks only inside of the pores in anodic oxide film. The second method is to coat the anodic oxide film surface with thin Au layer less than 0.1 ?. Both the ink-impregnating method and Au-coating method provided clear indentation marks on the anodic oxide film surface when it was indented using a pyramidal-diamond penetrator. Thus, Vickers hardness of anodic oxide films on aluminium alloy could be measured successfully and precisely from the anodic film surface. In addition, advantages and disadvantages of the ink-impregnating method and Au-coating method for the measurement of surface hardness of anodic oxide films are discussed.

Surface hardness measurement of NiP-plated AA7050

Sungmo Moon(문성모),Juseok Kim(김주석) 한국표면공학회 2021 한국표면공학회지 Vol.54 No.4

This paper is concerned with the surface hardness measurement of NiP-coated AA7050 using different loads from 10 to 100 g. The surface hardness was observed to increase from 180 to 600 Hv with increasing NiP layer thickness, depending on the load applied for indentation. When NiP coating thickness is thinner than 2 ㎛, the surface hardness of NiP-coated AA7050 was mainly determined by AA7050 substrate, while it was significantly increased by NiP coating layer when NiP coating thickness is thicker than 2 ㎛. Hardness of AA7050 substrate itself was not dependent on the applied load but the hardness of NiP-coated AA7050 was largely influenced by the load applied for indentation. The largest difference of hardness between 10 g and 100g of applied loads, was obtained at the NiP thickness of about 8 ㎛ above which the measured hardness at 10 g reached a maximum value of about 600 Hv. It was also observed that indentation-induced plastic deformation next to the indented zone occurs when NiP layer is 5.64 times thicker than the depth of impression formed by indentation.

알루미늄 프라이팬에 부착된 스텐리스판의 패턴이 열 변형 및 표면온도에 미치는 영향

문성모(Sungmo Moon),윤명식(Myungsik Yoon) 한국표면공학회 2020 한국표면공학회지 Vol.53 No.5

This article investigated the effects of stainless steel plate-patterns bonded to aluminum frypan on the thermal distortion and surface temperature of the frypan during gas or induction heating. Two different stainless steel plate-patterns were employed: type A contains only circular holes and type B has not only circular holes but also vacant spaces of 0.5 mm thick and 40 mm long straight line crossing 60 mm long curved line. The bottom of the frypan was distorted during heating when type A stainless steel plate-bonded frypan while no significant thermal distortion was observed for type B stainless steel plate-bonded frypan during heating. Temperature of the frypan surface showed the same trend during gas heating, irrespective of stainless steel plate-patterns. During induction heating, however, the frypan with type B stainless steel plate-pattern showed lower surface temperature than the frypan with type A stainless steel plate-pattern. It is concluded that Type B stainless steel plate-pattern with circular holes and vacant spaces of lines is very effective for minimizing a thermal distortion and lowering the surface temperature of an aluminum frypan during induction heating.

AZ31 Mg합금의 PEO피막 형성거동에 미치는 인산나트륨 농도의 영향

문성모(Sungmo Moon),김주석(Juseok Kim) 한국표면공학회 2019 한국표면공학회지 Vol.52 No.5

Formation behavior of PEO (Plasma Electrolytic Oxidation) films on AZ31 Mg alloy was investigated under application of 310 Hz AC as a function of Na₃PO₄ concentration from 0.02 M to 0.2 M. Film formation voltage and in-situ observation of arcs generated on the specimen surface were recorded with time, and surface morphologies of the PEO films were investigated using optical microscopy, confocal scanning laser microscopy and scanning electron microscopy. PEO film formation voltage decreased linearly with increasing Na₃PO₄ concentration which is attributed to the increase of solution pH. PEO films were grown uniformly over the entire surface in Na₃PO₄ solutions between 0.05 M and 0.1 M. However, non-uniform PEO films with white spots were formed in Na₃PO₄ solutions containing more than 0.1 M. Thickness and roughness of PEO films on AZ31 Mg alloy increased linearly with increasing Na₃PO₄ concentration and their increasing rates appeared to be much higher under 1 M than above 1 M. The experimental results suggest that phosphate ions can contribute to the formation of PEO films but higher Na₃PO₄ concentration more than 1 M results in local damages of PEO films due to repeated generation of white arcs at the same surface site of AZ31 Mg alloy.

금속의 양극산화처리 기술

문성모(Sungmo Moon) 한국표면공학회 2018 한국표면공학회지 Vol.51 No.1

Anodic oxidation treatment of metals is one of typical surface finishing methods which has been used for improving surface appearance, bioactivity, adhesion with paints and the resistances to corrosion and/or abrasion. This article provides fundamental principle, type and characteristics of the anodic oxidation treatment methods, including anodizing method and plasma electrolytic oxidation (PEO) method. The anodic oxidation can form thick oxide films on the metal surface by electrochemical reactions under the application of electric current and voltage between the working electrode and auxiliary electrode. The anodic oxide films are classified into two types of barrier type and porous type. The porous anodic oxide films include a porous anodizing film containing regular pores, nanotubes and PEO films containing irregular pores with different sizes and shapes. Thickness and defect density of the anodic oxide films are important factors which affect the corrosion resistance of metals. The anodic oxide film thickness is limited by how fast ions can migrate through the anodic oxide film. Defect density in the anodic oxide film is dependent upon alloying elements and secondphase particles in the alloys. In this article, the principle and mechanisms of formation and growth of anodic oxide films on metals are described.

시편의 준비 방법 및 접촉저항이 알루미늄 합금의 아노다이징 피막 형성에 미치는 영향

문성모(Sungmo Moon) 한국표면공학회 2020 한국표면공학회지 Vol.53 No.1

In this study, five different specimen preparation methods were introduced and their advantages and disadvantages were presented. One of them, an epoxy mounting method has advantages of constant exposure area, ease of surface preparation without touching the specimen surface during polishing or cleaning, use of small amount of material and ease of specimen reuse by polishing or etching. However, in order to eliminate unexpected errors resulting from preferable reaction at the specimen/epoxy interface and contact resistance between the specimen and copper conducting line for electrical connection, it is recommended to cover the wall side of the specimen with porous anodic oxide films and to remain the contact resistance lower than 1 ohm. The increased contact resistance between the specimen and Cu conducting line appeared to result in increases of anodizing voltage and solution temperature during anodizing by which thickness and hardness of anodizing film on Al2024 alloy were drastically decreased and color of the films became more brightened.

Effects of Hydroxide and Silicate ions on the Plasma Electrolytic Oxidation of AZ31 Mg Alloy

Sungmo Moon(문성모),Cheolnam Yang(양철남),Sangjo Na(나상조) 한국표면공학회 2014 한국표면공학회지 Vol.47 No.4

Formation behavior of PEO (Plasma Electrolytic Oxidation) films on AZ31 Mg alloy was studied in aqueous solutions containing various concentrations of hydroxide ion (OH<SUP>?</SUP>) and silicate ion (SiO3<SUP>2?</SUP>) by voltage-time curves, and corrosion resistance of the PEO film-covered specimen was investigated by immersion test in 0.5 M NaCl solution. From the analyses of the voltage-time curves, it is suggested that two different types of anions are essentially needed for the formation of PEO films on AZ31 Mg alloy: film formation agent and local film breakdown agent. SiO3 <SUP>2?</SUP> ion acts only as a film formation agent but OH<SUP>-</SUP> ion acts not only as a film formation agent but also film breakdown agent. The PEO films prepared on AZ31 Mg alloy in alkaline silicate solution showed very good corrosion resistance without any pitting or filiform corrosions up to 480 h of immersion in 0.5 M NaCl.

주조용 Al-Si-Cu 알루미늄 합금의 기계가공 및 주조된 표면에서의 양극산화피막 형성

문성모(Sungmo Moon),남윤경(Yoonkyung Nam),양철남(Cheolnam Yang),정용수(Yongsoo Jeong) 한국표면공학회 2009 한국표면공학회지 Vol.42 No.6

The anodic oxidation behaviour of a cast component of AC2A Al alloy with machined surface and ascast surface was investigated in sulfuric acid solution. The anodized specimen showed relatively uniform and thick anodic oxide films on the as-cast surface, while non-uniform and very thin oxide films were formed on the machined surface. Non-anodized as-cast surface was observed to be covered with thick oxide scales and showed a number of second-phase particles containing Si, while non-anodized machined surface showed no oxide scales and relatively very small number of Si particles. Thus, the very limited growth of anodic oxide films on the as-cast surface was attributed to the presence of thick oxide scales and Si-containing second-phase particles on its surface.