Autocatalytic duplex Ni-P/Ni-W-P coatings on AZ 31B magnesium alloy

Ezhil Selvi, V and Balaraju, JN (2013) Autocatalytic duplex Ni-P/Ni-W-P coatings on AZ 31B magnesium alloy. Surface and Coatings Technology, 240. pp. 103-109. ISSN 0257-8972

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Autocatalytic duplex Ni-P/Ni-W-P coatings were deposited on AZ31B magnesium alloy using stabilizer free nickel carbonate bath. Some of the coated specimens were passivated in chromate solution with and without heat treatment. Plain Ni-P coatings were also prepared for comparison. Coatings were characterized for their surface morphology, composition and corrosion resistance. Energy dispersive analysis of X-ray (EDX) showed that the duplex coating contained about 3 wt.% P and 2 wt.% W with balance Ni. Marginal increase in P and W contents were observed on passivated coupons along with Cr (0.18 wt.%) and O (2.8 wt.%) contents. Field emission scanning electron microscopy (FESEM) examination of these coatings surfaces exhibited the nodular morphology. Chromate passivated surfaces showed the presence of uniformly distributed bright Ni particles along with nodules. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies were carried out in deaerated 0.15 M NaCl solution to find out the corrosion resistance of the coatings. Among the coatings developed, duplex-heat treated-passivated (duplex-HTP) coatings showed lower corrosion current density (icorr) and higher polarization resistance (Rp) indicating the improved corrosion resistance. The charge transfer resistance (Rct) value obtained for the duplex-HTP was about 170 times higher compared to Ni-P coating.

Item Type: Article
Uncontrolled Keywords: Magnesium alloy; Duplex Ni-P/Ni-W-P; Corrosion; EIS
Subjects: CHEMISTRY AND MATERIALS > Chemistry and Materials (General)
Depositing User: Mr. BS Shivaram
Date Deposited: 02 Dec 2014 08:03
Last Modified: 02 Dec 2014 08:03

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