Effect of Negative Current on the Microstructure of Oxide Coatings Prepared by Hybrid Pulse Anodization

The oxide coatings were prepared on 6061 Al alloy at different negative current densities in oxalic acid using the hybrid pulse anodization (HPA) method at room temperature. The variation curves of positive and negative voltages with anodization time were recorded. The nanopore diameters and distrib...

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Bibliographic Details
Published in:Metals (Basel ) 2019-01, Vol.9 (1), p.22
Main Authors: Huang, Shuo, Jiang, Bailing, Liu, Cancan, Shao, Qingying, Li, Hongtao
Format: Article
Language:English
Subjects:
aluminum alloy
Aluminum base alloys
Anodizing
Current density
Diameters
Electrolytes
Emission analysis
Heat
hybrid pulse anodization
Membrane reactors
Microstructure
negative current
Oxalic acid
Oxide coatings
Room temperature
Trends
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Summary:The oxide coatings were prepared on 6061 Al alloy at different negative current densities in oxalic acid using the hybrid pulse anodization (HPA) method at room temperature. The variation curves of positive and negative voltages with anodization time were recorded. The nanopore diameters and distribution regularities in HPA coatings were analyzed with the Image-Pro Plus software based on field-emission scanning electron microscope (FE-SEM) images. The results showed that the negative current could reduce the growth rate of HPA coatings, and thus led to a small thickness of the coatings within the same anodization time. Besides, appropriate negative current densities resulted in the better distribution uniformity of nanopores, but the excessive negative current densities tended to cause inferior nanopore arrangement. These were attributed to the existence of the negative current, causing H+ and O2− to move in opposite directions, so that a large number of H+ concentrated on the surface of the HPA coatings, resulting in the accelerated dissolution of the coatings.
ISSN:2075-4701
2075-4701
DOI:10.3390/met9010022