The high strength to weight ratio of magnesium alloys makes them extremely attractive for applications in transport or aerospace technology. However, their corrosion behavior is a major issue and one reason why they are still not as popular as aluminum alloys. This papers reviews the corrosion mechanisms of magnesium and provides the basis for the design of new alloys with improved corrosion properties.

An isotopic tracer study of the film growth mechanism for pure magnesium, AZ31B, and ZE10A (Elektron 717, E717) magnesium alloys in water at room temperature was performed. A series of individual and sequential exposures were conducted in both H 2 18 O and D 2 16 O, with isotopic tracer profiles obtained using secondary ion mass spectrometry (SIMS). The water-formed films consisted primarily of partially hydrated MgO. The SIMS sputter depth profiles indicate that H and D penetrated throughout the film and into the underlying metal, particularly for the Zr-and Nd-containing E717 alloy. Film growth for the UHP Mg involved aspects of both metal outward diffusion and oxygen/hydrogen inward diffusion. In contrast, the film on the Al-containing AZ31B alloy grew primarily by inward oxygen and inward hydrogen diffusion. The 18 O and D profiles for the film formed on E717 were the most complex, with the 18 O data most consistent with inward lattice oxygen diffusion, but the D data suggests inward, short-circuit diffusion through the film. It is speculated that preferential inward short circuit hydrogen transport may have been aided by the presence of nano Zn 2 Zr 3 particles throughout the E717 film. Such hydrogen penetration may have implications from both a corrosion resistance and hydrogen storage perspective. Magnesium alloys are of great interest because they can be used to manufacture lightweight automotive and aircraft structural materials that reduce vehicle weight and improve fuel efficiency.1-3 However, the poor corrosion resistance of Mg is a major challenge.4-6 A key contributor to the poor corrosion resistance of Mg is the inability to establish and/or maintain protective surfaces films. Surface films formed on Mg under ambient air and water conditions typically consist of mixtures of Mg(OH) 2 and MgO, with small amounts of MgCO 3 often also reported.7-12 They provide adequate protection under some circumstances, but are particularly vulnerable to disruption by salt species.The ambient corrosion of Mg differs from many corrosion-resistant structural alloy classes in that the protective surface films can become quite thick, on the order of tens to hundreds of nanometers, rather than the few nanometers typically encountered for protective films on stainless steels, for example. As such, corrosion resistance is influenced not only by classical thin film electrochemical passivity considerations, but also thermodynamic and kinetic considerations typically encountered in thick-film (> 0.5 micron range), high-temperature alloy oxidation phenomena.Isotopic tracer studies have been widely applied to studies of the high-temperature oxidation of alloys (Al, Fe, Ni, and Zr base; SiC), with significant new insights gained regarding the growth mechanism of the oxide films. [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] Such insights have proven particularly useful for understanding the influence of various alloying additions on film growth, and provide a basis for improved alloy design. For examp...

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There is growing interest in magnesium alloys as structural materials for the automotive, aerospace and electronic industries. However, the corrosion performance of most magnesium alloys is not good enough for the increasingly diverse practical applications. The Cooperative Research Centre for Cast Metals Manufacturing (CAST) is an Australian research organisation established to cope with the problems associated with development and application of light metals. Corrosion and prevention of magnesium and its alloys has been an important part of CAST’s research program since 1995. The research effort in this area is focused on solving corrosion problems relative to the application of magnesium alloys in the automotive industries. Nevertheless, encompassed by the requirements of the applied research, some fundamental studies have also been conducted. This paper presents a brief summary of some of the research achievements in this area recently made by CAST. They include studies of corrosion behaviour, alloying effects, corrosion inhibition and surface treatment of magnesium alloys.

Magnesium alloys are potential biodegradable implant materials. However, magnesium alloys normally corrode rapidly in the in-vivo fluid, resulting in subcutaneous gas bubbles and alkalisation of the in-vivo solution. The paper presents a new approach to control the degradation rate of magnesium in a simulated body fluid (SBF) through employing a recently developed anodising technique. It was found that the ceramic like anodised coating formed on the surface of magnesium can effectively slow down the biodegradation process and hence result in slow hydrogen evolution and solution alkalisation processes. The results imply that an anodised magnesium alloy may be successfully used as a biodegradable implant material.