Abstract

Zn–Ni plating is indispensable in various industries because of its high corrosion resistance. However, Ni has been reported to trigger allergies; thus, an alternative Ni-free plating is desired. Zn–Fe plating is considered to be a promising candidate, albeit its corrosion resistance still needs to be improved. The corrosion resistance of Zn–Fe plating is expected to increase by the addition of Mo as the third alloying element as it is more noble than Zn and Fe. In this study, Zn–Fe–Mo plating with a corrosion resistance nearly equivalent to that of the Zn–Ni plating was fabricated. Zn–Fe–Mo plating was electrically deposited from continuously-agitated plating baths prepared by mixing ZnSO4, FeSO4, Na2MoO4, Na3C6H5O7, and Na2SO4 using Fe or Ni plates as the substrate. The surface morphology, composition, crystal phase, and electronic state of Mo of the platings were investigated by scanning electron microscopy equipped with energy-dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The anti-corrosion performance was evaluated by Tafel extrapolation method. Formation of plating comprising a Mo containing alloy phase was found to be crucial for improving corrosion resistance. The Zn–Fe–Mo plating demonstrates promise for replacing anti-corrosion Zn–Ni platings.

Highlights

  • Metals, such as steel and cast iron, are typically used as the major components of architecture and machines in daily life [1]

  • Protective coatings with a high corrosion resistance are desired to extend the life of industrial products for realizing a sustainable society and for withstanding a more severe environment to meet industrial demands

  • Zn–Fe–Mo plating was electrically deposited at various pH values

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Summary

Introduction

Metals, such as steel and cast iron, are typically used as the major components of architecture and machines in daily life [1] In several cases, these metals are exposed to harsh environments, and protection against corrosion is a critical issue, where high reliability is required. The application of corrosion-resistant alloys, including stainless steels, is an effective solution; the high cost hinders its applications for daily use [2]. Another promising method to improve corrosion resistance is protection by Zn plating or so-called galvanization [3]. Alloying with iron-group elements, such as Fe and Ni, is well known in Coatings 2017, 7, 235; doi:10.3390/coatings7120235 www.mdpi.com/journal/coatings

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