Corrosion and Surface Engineering of Magnesium: An Overview

Abstract

Fueled by demands for reductions of carbon emissions and improving the recyclability of automobiles and other transport vehicles, manufacturers have looked to magnesium (Mg) alloys as a possible replacement for heavier metallic counterparts and non-recyclable materials. Use of alternative energy sources such as hybrid and battery or fuel cell powered cars alleviates some of the environmental impact of fossil fuels. However, these technologies continue to require lighter materials in order for vehicles to remain energy efficient. The reduction of CO2 emissions due to use of Mg alloys in automotive applications is significant. 1 The advantages of Mg are counterbalanced by its high electrochemical activity, 2 creating a large driving force and propensity for corrosion. It is known that MgO and Mg(OH)2 scales formed during corrosion or oxidation of Mg are porous and easily dissolved in water, 3 thus becoming nonprotective. Gaining a fundamental understanding of the active corrosion mechanisms and their resultant effect on the surface condition and overall behavior of the alloy will lead to improved alloy designs and surface coatings for structural applications. In addition, recent Mg alloys have been considered to be viable as a temporary biomaterial. In this case, controlled corrosion of Mg alloys is preferred. Inevitably, understanding of corrosion behavior would lead to appropriate alloy and surface coating designs for optimized performance in aqueous environments. Corrosion prevention and mitigation is a complicating and determining factor in further acceptance of Mg alloys in structural applications. The development of new alloys for use in high-performance applications where service conditions are deemed to be chemically aggressive greatly amplifies the need and importance of understanding fundamental mechanisms within a microstructural context. The effect of crystallographic orientation, defects, and microstructural texture is central to this knowledge. Furthermore, accurate measurement of corrosion rates and the effect of surface chemistry on the overall corrosion behavior are also vital to the development of future alloys. The four papers presented in this special issue of JOM address the various aspects associated with understanding the underlying science and design considerations when engineering the surface properties of these alloys. They each provide up-to-date, unique insight and working knowledge into the processing–structure– property relationships that drive corrosion behavior in Mg and its alloys. The contribution from Chen et al. provides an