钼酸钠含量对无铬锌铝涂层性能的影响

doi:10.11896/cldb.19010102

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Abstract In this study, we sought to find out the alterations in morphology, composition, porosity, adhesion and corrosion resistance of chromium-free zinc-aluminum coatings caused by variation of sodium molybdate (inhibitor) content. Specifically, SEM and EDS was adopted to characterize the morphology, porosity and composition of the coatings. The adhesion of the coatings was evaluated by adhesion tester. The corrosion resis-tance of the coatings were analyzed based on polarization curves and electrochemical impedance spectroscopy. When 1.3wt%~2.6wt% sodium molybdate was contained, the coatings were glossy and smooth with silver-gray metallic luster in appearance. Meanwhile, the coatings were complete and compact with low porosity according to the microscopic observation, and the sheet-like zinc-aluminum powders stacked layer by la-yer, forming an effective physical shielding. When the content of sodium molybdate ranged from 1.3wt% to 2.2wt%, the adhesion of coatings leveled ISO-1. While higher sodium molybdate content would do harm to the adhesion of the coatings. As the sodium molybdate content increased, the self-corrosion potential of the coatings first dropped and then went up. When the content of sodium molybdate exceeded 2.6wt%, the coating held a self-corrosion potential higher than Q235 steel matrix, and failed to provide cathodic protection for the matrix. Furthermore, the self-corrosion current of the coatings varied in the range of 9.141×10^-6—1.176×10^-4 A/cm², and the R_f value (the resistance of zinc-aluminum powders surface film layer) varied in the range of 212.1—649.5 Ω·cm². The coatings achieved the best comprehensive performance under the sodium molybdate content of 1.8wt%. In this case, the coating exhibited the minimum self-corrosion current density of only 9.141×10^-6 A/cm², and the highest R_f value of 649.5 Ω·cm². As a result, the corrosion product film on the surface of zinc-aluminum powders was the most compact, with strong adhesion and optimal corrosion resistance.

Key words： sodium molybdate chromium-free zinc-aluminum coating adhesion polarization curves electrochemical impedance spectroscopy corrosion resistance

Published: 03 January 2020

CLC number:

TG178

About author:: Huiying Li,master degree student, her esearch focus is materials corrosion and protection;Junwen Zhao, doctor, associate professor, research focus is processing and service performance of metal materials for rail transportation.

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	LI Huiying
	ZHAO Junwen
	DAI Guangze
	HAN Jing
	LI Xujia

Cite this article:

LI Huiying,ZHAO Junwen,DAI Guangze, et al. Impact of Sodium Molybdate Content on Properties of Chromium-free Zinc-Aluminum Coatings[J]. Materials Reports, 2020, 34(2): 2105-2109.

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http://www.mater-rep.com/EN/10.11896/cldb.19010102 OR http://www.mater-rep.com/EN/Y2020/V34/I2/2105

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