Abstract
The electrochemical deposition by pulse current of Zn-Co alloy coatings on steel was examined, with the aim to find out whether pulse plating could produce alloys that could offer a better corrosion protection. The influence of on-time and the average current density on the cathodic current efficiency, coating morphology, surface roughness and corrosion stability in 3% NaCl was examined. At the same Ton/Toff ratio the current efficiency was insignificantly smaller for deposition at higher average current density. It was shown that, depending on the on-time, pulse plating could produce more homogenous alloy coatings with finer morphology, as compared to deposits obtained by direct current. The surface roughness was the greatest for Zn-Co alloy coatings deposited with direct current, as compared with alloy coatings deposited with pulse current, for both examined average current densities. It was also shown that Zn-Co alloy coatings deposited by pulse current could increase the corrosion stability of Zn-Co alloy coatings on steel. Namely, alloy coatings deposited with pulse current showed higher corrosion stability, as compared with alloy coatings deposited with direct current, for almost all examined cathodic times, Ton. Alloy coatings deposited at higher average current density showed greater corrosion stability as compared with coatings deposited by pulse current at smaller average current density. It was shown that deposits obtained with pulse current and cathodic time of 10 ms had the poorest corrosion stability, for both investigated average deposition current density. Among all investigated alloy coatings the highest corrosion stability was obtained for Zn-Co alloy coatings deposited with pulsed current at higher average current density (jav = 4 A dm-2).
Highlights
U prethodnim istraživanjima je pokazano [14,15,16,17] da su prevlake najveće korozione stabilnosti dobijene taloženjem iz hloridnog rastvora sa velikim odnosom koncentracija jona kobalta i cinka, gustinom struje od 4 A dm–2, pa su ovi parametri izabrani za analizu uticaja pulsirajućeg režima taloženja, sa ciljem da se ispitaju parametri taloženja prevlaka Zn–Co legura pulsirajućom strujom, kojima bi se dalje poboljšala koroziona stabilnost
Brzine korozije u aerisanom rastvoru 3% NaCl su određivane ekstrapolacijom Tafelovih pravih na potencijal otvorenog kola
Among all investigated alloy coatings the highest corrosion stability was obtained for Zn–Co alloy coatings deposited with pulsed current at higher average current density (jav = 4 A dm–2)
Summary
Kao široko korišćene prevlake na čeliku, mogu se znatno poboljšati njegovim legiranjem [1,2,3]. Legiranjem se dobijaju prevlake znatno boljih mehaničkih, fizičkih i elektrohemijskih svojstava, a koroziona stabilnost legura zavisi od sastava rastvora za taloženje i parametara taloženja. U prethodnim istraživanjima je pokazano [14,15,16,17] da su prevlake najveće korozione stabilnosti dobijene taloženjem iz hloridnog rastvora sa velikim odnosom koncentracija jona kobalta i cinka, gustinom struje od 4 A dm–2, pa su ovi parametri izabrani za analizu uticaja pulsirajućeg režima taloženja, sa ciljem da se ispitaju parametri taloženja prevlaka Zn–Co legura pulsirajućom strujom, kojima bi se dalje poboljšala koroziona stabilnost. Pošto je u uslovima taloženja metala pulsirajućom strujom moguće znatno povećati katodnu gustinu struje, a da se dobije ravnomernija prevlaka u odnosu na taloženje konstantnom strujom [10,18], prevlake su taložene i manjom srednjom gustinom struje (2 A dm–2). Praćen je uticaj katodnog vremena i srednje gustine struje taloženja na iskorišćenje struje, hrapavost i izgled prevlaka, kao i korozione osobine prevlaka legura
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