Optimization of Pickling Solution for Improving the Phosphatability of Advanced High-Strength Steels
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Department of Materials Science and Engineering, Sungkyunkwan University, Suwon-Si 16419, Korea
2
Steel Solution Marketing Dept., POSCO Global R&D Center, Incheon 21985, Korea
*
Author to whom correspondence should be addressed.
Materials 2021, 14(1), 233; https://doi.org/10.3390/ma14010233
Received: 2 December 2020
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Revised: 30 December 2020
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Accepted: 30 December 2020
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Published: 5 January 2021
(This article belongs to the Special Issue Surface Engineering & Coating Technologies for Corrosion and Tribocorrosion Resistance)
This study investigated the optimum pickling conditions for improving the phosphatability of advanced high-strength steel (AHSS) using surface analysis and electrochemical measurements. To remove the SiO2 that forms on the surface of AHSS, 30 wt.% NH4HF2 was added to the pickling solution, resulting in a significant reduction in the amount of SiO2 remaining on the surface of the AHSS. The phosphatability was improved remarkably using HNO3 concentrations higher than 13% in the pickling solution. Furthermore, phosphate crystals became finer after pickling with a HNO3-based solution rather than a HCl-based solution. Electrochemical impedance spectroscopy (EIS) data indicated that the corrosion resistance of AHSS subjected to HNO3-based pickling was higher than that of AHSS subjected to HCl-based pickling. Fluorine compounds, which were involved in the phosphate treatment process, were only formed on the surface of steel in HNO3-based solutions. The F compounds reacted with the phosphate solution to increase the pH of the bulk solution, which greatly improved the phosphatability. The phosphatability was better under HNO3-based conditions than a HCl-based condition due to the fineness of the phosphate structure and the increased surface roughness.
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Keywords:
advanced high-strength steel; phosphate coating; acid cleaning; electrochemical impedance spectroscopy
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MDPI and ACS Style
Cho, S.; Ko, S.-J.; Yoo, J.-S.; Park, J.-C.; Yoo, Y.-H.; Kim, J.-G. Optimization of Pickling Solution for Improving the Phosphatability of Advanced High-Strength Steels. Materials 2021, 14, 233. https://doi.org/10.3390/ma14010233
AMA Style
Cho S, Ko S-J, Yoo J-S, Park J-C, Yoo Y-H, Kim J-G. Optimization of Pickling Solution for Improving the Phosphatability of Advanced High-Strength Steels. Materials. 2021; 14(1):233. https://doi.org/10.3390/ma14010233
Chicago/Turabian StyleCho, Sangwon, Sang-Jin Ko, Jin-Seok Yoo, Joong-Chul Park, Yun-Ha Yoo, and Jung-Gu Kim. 2021. "Optimization of Pickling Solution for Improving the Phosphatability of Advanced High-Strength Steels" Materials 14, no. 1: 233. https://doi.org/10.3390/ma14010233
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