Corrosion behaviour of hot-dip Zn-Al-Mg coatings with different Al content

Abstract

Purpose

The purpose of the present study is to simulate the industrial hot-dip process of Zn-2.5Wt.%Mg-3 Wt.%Al and Zn-2.5 Wt.%Mg-9 Wt.%Al-0.15 Wt.%Si coatings and to study the effect of low and high Al variation on their microstructure, microhardness, adhesion and corrosion behaviour.

Design/methodology/approach

The hot-dip Zn-2.5 Mg-xAl coating simulation on steel substrate was carried out using a hot-dip process simulator. The microstructure of the coatings was characterized using a scanning electron microscope, energy dispersive spectroscopy and X-ray diffraction. The corrosion behaviour of the coatings was studied using a salt spray test in 5% NaCl solution as well as dynamic polarization in 3.5% NaCl solution.

Findings

Microhardness of the developed Zn-2.5 Mg-xAl coatings has been found to be approximately two times higher than that of the conventional galvanized coating. Zn-2.5 Mg-3Al coating has exhibited two times higher corrosion resistance as compared to that of Zn-2.5 Mg-9Al-0.15Si coating because of formation of more homogeneous and defect-free microstructure of the former. The MgZn₂ phase has undergone preferential dissolution and provided Mg²⁺ ions to form a protective film.

Originality/value

The relative corrosion resistance of the two Zn–Al–Mg coatings with different Al content has been studied. The defect formed because of higher Al addition in the coating has been detected, and its effect on corrosion behaviour has been analysed.

Citation

Rai, P.K., Rout, D., Kumar, D.S., Sharma, S. and Balachandran, G. (2022), "Corrosion behaviour of hot-dip Zn-Al-Mg coatings with different Al content", Anti-Corrosion Methods and Materials, Vol. 69 No. 1, pp. 29-37. https://doi.org/10.1108/ACMM-05-2021-2487