Surface Modification by Compositionally Modulated Multilayered Zn‐Fe Alloy Coatings

Abstract

Compositionally modulated multilayered alloy (CMMA) coatings of Zn-Fe were developed from acid chloride baths by single bath technique. The production and properties of CMMA Zn-Fe coatings were tailored as a function of switching cathode current densities (SCCD's) and thickness of individual layers. Corrosion rates (CR) were measured by electrochemical methods. Corrosion resistances were found to vary with SCCD's and the number of sub layers in the deposit. SCCD's were optimized for production of Zn-Fe CMMA electroplates showing peak performance against corrosion. The formation of discrete Zn-Fe alloy layers having different compositions in the deposits were demonstrated by scanning electron microscopy (SEM). Improvements in the corrosion resistance of multilayered alloys are due to the inherent barrier properties of CMMA coatings as evidenced by electrochemical impedance spectroscopy (EIS). Corrosion resistance afforded by Zn-Fe CMMA coatings are explained in terms of the n-type semiconductor films at the interface, supported by Mott-Schottky's plot. It was observed that the alloy with high w(Fe) on the top showed better corrosion resistance compared to that with the less w(Fe) on top. At optimum SCCD's of 3.0-5.5 A•dm -2 , a Zn-Fe CMMA coatings with 600 sub layers showed ca. 45 times better corrosion resistance than conventional Zn-Fe alloy of the same thickness. The deposit showed no red rust even up to 1130 h in salt spray test.

The continued development of multilayered and compositionally modulated electrodeposits

“…In 2008, Thangaraj et al reported the preparation of similar coatings with a comparable total thickness in 2008 in which the coatings were made up from <600 layers, using a layer thicknesses as low as 10 nm. These nanoscale zinc rich (Zn-Fe)/iron rich (Zn-Fe) multilayers were reported to have mean corrosion rates as low as 0.025 mm y −1 ) in 5% NaCl at 25 o C [53].…”

Electrolytic preparation of cyclic multilayer Zn–Ni alloy coating using switching cathode current densities

“…Kirilova et al [18][19][20] reported CMA coatings of Zn-Co from SBT. Recently, Thangaraj et al [21] optimized a chloride bath for the production of Zn-Fe CMA coatings over mild steel, and showed that coating were found to have *45 times better corrosion stability than monolithic Zn-Fe coatings of same thickness. Though improvement in corrosion resistance of Zn-Ni CMA electrodeposits, were widely reported, very little was done with regard to optimization of the deposition condition, using SBT to achieve the peak performance against corrosion.…”

Optimization of deposition conditions for development of high corrosion resistant Zn–Fe multilayer coatings

“…In this direction, Thangaraj et al (2008) have recently studied the corrosion behavior CMMA Zn-Fe alloy through SBT, using glycine as additive. The corrosion rates were calculated from Tafel's extrapolation method, supported by EIS study.…”