Effect of Native Oxide Film on Commercial Magnesium Alloys Substrates and Carbonate Conversion Coating Growth and Corrosion Resistance.

Sebastián Feliu, Jr.,Elkin Bermudez,Amir El-Hadad,Irene Llorente,Alejandro Samaniego,Juan Galván

doi:10.3390/ma7042534

Sebastián Feliu, Jr., Elkin Bermudez + Show 4 more

Open Access

https://doi.org/10.3390/ma7042534

Copy DOI

Abstract

Possible relations between the native oxide film formed spontaneously on the AZ31 and AZ61 magnesium alloy substrates with different surface finish, the chemistry of the outer surface of the conversion coatings that grows after their subsequent immersion on saturated aqueous NaHCO3 solution treatment and the enhancement of corrosion resistance have been studied. The significant increase in the amount of aluminum and carbonate compounds on the surface of the conversion coating formed on the AZ61 substrate in polished condition seems to improve the corrosion resistance in low chloride ion concentration solutions. In contrast, the conversion coatings formed on the AZ31 substrates in polished condition has little effect on their protective properties compared to the respective as-received surface.

Highlights

Materials chosen for the study are Mg alloys which have aroused a great deal of scientific and technological interest over the past two decades
The findings revealed the presence of a significant fraction of the as-received alloy surface covered by islands of spinel (
AZ31 and AZ61 alloys treated with saturated aqueous NaHCO3 solution induced by the protective properties of the oxide film that forms spontaneously on the surface of magnesium alloys

Summary

Introduction

Materials chosen for the study are Mg alloys which have aroused a great deal of scientific and technological interest over the past two decades. The objectives of this research are as follows: 1) To study the possible changes on the surface chemistry of the conversion coating formed on the AZ31 and AZ61 alloys treated with saturated aqueous NaHCO3 solution induced by the protective properties of the oxide film that forms spontaneously on the surface of magnesium alloys. In this sense, the research compares the behavior of substrates of the above alloys in the following two surface conditions: (a) specimens in as-received condition and (b) freshly polished specimens. The corrosion resistance of the treated surfaces is evaluated by means of EIS and hydrogen evolution measurement

Results and Discussion

Protective Properties of NaHCO3 Treatment

Electrochemical Impedance Measurements as a Function of Immersion Time in

Experimental Section

Conclusions