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ISSN : 1225-0562(Print)
ISSN : 2287-7258(Online)
Korean Journal of Materials Research Vol.28 No.10 pp.544-550
DOI : https://doi.org/10.3740/MRSK.2018.28.10.544

Effect of Power Mode of Plasma Anodization on the Properties of formed Oxide Films on AZ91D Magnesium Alloy

Sung-Hyung Lee1,2†, Hitoshi Yashiro2, Song-Zhu Kure-Chu3
1GEO Nation Research institute, Tokyo 102-0093, Japan
2Department of Chemistry and Biological Science, Iwate University, Morioka, Iwate 020-8550, Japan
3Materials Function and Design, Nagoya Institute of Technology, Nagoya, Aichi 466-855, Japan
Corresponding author
E-Mail :shlee@geo-nation.co.jp (S.-H. Lee, Iwate Univ.)

Abstract

The passivation of AZ91D Mg alloys by plasma anodization requires deliberate choice of process parameters due to the presence of large amounts of structural defects. We study the dependence of pore formation, surface roughness and corrosion resistance on voltage by comparing the direct current (DC) mode and the pulse wave (pulse) mode in which anodization is performed. In the DC plasma anodization mode, the thickness of the electrolytic oxide film of the AZ91D alloy is uneven. In the pulse mode, the thickness is relatively uniform and the formed thin film has a three-layer structure. The pulse mode creates less roughness, uniform thickness and improved corrosion resistance. Thus, the change of power mode from DC to pulse at 150 V decreases the surface roughness (Ra) from 0.9 μm to 0.1 μm and increases the corrosion resistance in rating number (RN) from 5 to 9.5. Our study shows that an optimal oxide film can be obtained with a pulse voltage of 150 V, which produces an excellent coating on the AZ91D casting alloy.

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