Effect of Magnesium on Corrosion Behavior of Hot-Dip Zn-Al-Mg Coating

Rout

et al. 2021

ACMM

Self Cite

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.

Section: Resultsmentioning

confidence: 77%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Rout

et al. 2021

ACMM

Self Cite

Section: Introductionmentioning

confidence: 99%

“…Recent studies show that Zn-Al alloys have promising applications as metallic coatings, mainly with additions of Mg [29][30][31]. Rai et al [29] show that the improvement in the corrosion resistance of steel coated with a Zn-Al-Mg alloy is due to preferential dissolution of MgZn 2 present in the interdendritic regions of Zn-rich phases, promoting better sacrificial protection. However, the available literature does not address the influence of the manufacturing parameters on the resulting microstructure, which are related in the present work to the solidification cooling rate.…”

Section: Introductionmentioning

confidence: 99%

Hypereutectic Zn–Al Alloys: Microstructural Development under Unsteady-State Solidification Conditions, Eutectic Coupled Zone and Hardness

Septimio

Silva

Costa

et al. 2022

Metals

The present study investigates the effects of Al content and solidification thermal parameters on the microstructural development under transient heat flow conditions for two hypereutectic Zn–Al alloys: Zn-6wt.%Al and Zn-11wt.%Al. The alloys were directionally solidified and had experimental cooling profiles monitored permitting cooling rates and growth rates to be determined along the length of the directionally solidified (DS) castings. The microstructure of the Zn-6wt.%Al alloy is shown to be formed by eutectic colonies, constituted by a eutectic mixture of (Zn) and (Al′) phases in the form of lamellae and the Zn-11wt.% Al alloy by the pro-eutectic (Al′) dendrites and the eutectic mixture in the interdendritic regions. Growth laws are experimentally determined relating eutectic and dendritic spacings to the growth rate and cooling rate. A diagram exhibiting the coupled zone of Zn–Al alloys as a function of cooling rate is proposed, which shows different microstructural morphologies influenced by composition and thermal parameters, that is, growth rate and the temperature gradient, synthesized by the cooling rate (Ṫ = G.V). The microhardness of both Zn-6wt.%Al and Zn-11wt.%Al alloys were shown not to depend on the length scale of the resulting microstructure.

Role of Al and Mg alloying elements on corrosion behavior of zinc alloy‐coated steel substrates in 0.1 M NaCl solution

Pham

Nguyen

et al. 2023

Materials & Corrosion

The corrosion behavior and corrosion products of three zinc alloy-coated steel substrates with different Al and Mg contents such as hot-dip galvanized steel (HDG), Zn-Al-coated steel (ZA), and Zn-Al-Mg-coated steel (ZM) substrates were investigated during 168 h of immersion in 0.1 M NaCl solution. The characteristics and morphology of corrosion products on all the substrates formed during exposure to electrolyte solution were observed by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy/energy-dispersive X-ray spectroscopy. Their electrochemical behavior was investigated by open-circuit potential, polarization curves, and electrochemical impedance spectroscopy. The addition of Al and Mg alloying elements affected the corrosion mechanism as well as the anticorrosion properties. The main crystalline corrosion products on the HDG surface were simonkolleite and zincite, while the ZnAl hydrotalcite was identified as the main corrosion product on ZA and ZM surfaces. The corrosion resistance of ZA and ZM substrates was improved compared to the HDG substrate due to the enhanced adhesion of the corrosion product layer.