Controlled compositions in Zn-Ni coatings by anode material selection for replacing cadmium

Abstract

Cadmium-based sacrificial coatings have long been used in the aerospace industry for anodic protection of high-strength steel components. However, due to the carcinogenic and toxic nature of cadmium, its use is increasingly restricted. Zinc-nickel (Zn-Ni) coatings, with their superior corrosion resistance and mechanical properties, have emerged as a viable alternative. The anodic corrosion protection offered by Zn-Ni alloys makes them an excellent candidate to replace cadmium coatings in aerospace and other industries. It has been reported that Zn-Ni coatings with Ni content in the range of 10- 14 wt% exhibit corrosion resistance five times greater than that of pure zinc. However, maintaining consistent nickel concentration and phase composition within the coatings remains a significant challenge, leading to inconsistent properties, as shown in previous studies which used different kinds of anode material. This study explores the influence of different anode materials (zinc, nickel, mild steel, and stainless steel) on the electrodeposition and performance of Zn-Ni alloy coatings on AISI 1020 steel substrates. The work shows significant differences in voltage during electrodeposition when varying anode materials. X-ray diffraction (XRD) analysis was employed to determine the influence on the phase composition and average crystallite size induced by using different anode materials. Electrochemical tests, including polarization curves and electrochemical impedance spectroscopy, were conducted to evaluate the corrosion resistance of the coatings. The results demonstrated that the choice of anode material significantly affects the nickel content and crystalline phases in the Zn-Ni coatings. The results revealed that zinc and nickel anodes produce higher-quality coatings with better uniformity, density, and corrosion resistance, while mild steel and 316L stainless steel anodes result in coatings with significant defects and lower performance. These findings highlight the critical role of anode material selection in optimising the performance of Zn-Ni coatings for industrial applications.
Cadmium-based sacrificial coatings, widely used in the aerospace industry for anodic protection, are increasingly restricted due to their carcinogenic and toxic nature. Zinc-nickel (Zn-Ni) coatings, with superior corrosion resistance and mechanical properties, have emerged as viable alternatives. Zn-Ni coatings with 10-14 wt% Ni exhibit corrosion resistance five times greater than pure zinc, but maintaining consistent nickel concentration and phase composition is challenging.

This study examines the impact of different anode materials (zinc, nickel, mild steel, stainless steel) on the electrodeposition and performance of Zn-Ni alloy coatings on AISI 1020 steel substrates. Zn and Ni anodes produced superior coatings with better uniformity and corrosion resistance, whereas mild steel and stainless steel anodes resulted in coatings with significant defects. Zn anodes led to coatings with the highest Ni content and 15.5 µm thickness, while Ni anodes produced 14.8 µm coatings. Coatings from 1020 steel and stainless steel anodes were thicker (20-30 µm) but had lower Ni content and higher defect density. Crystallite sizes varied, with Zn anode coatings having the largest grains (>9.0 nm) and 316L stainless steel the smallest (<8.0 nm). Zn anodes yielded the highest microhardness (210 Hv) and lowest corrosion potential (-0.977 V) and current density (30 µA/cm²), indicating superior corrosion resistance.

These findings underscore the critical role of anode material in optimizing Zn-Ni coatings, highlighting Zn anodes for achieving high-quality, corrosion-resistant coatings suitable for industrial applications.

More information

Identifiers

ORCID for Robert J.K. Wood: orcid.org/0000-0003-0681-9239

Catalogue record

Export record

Altmetrics