Understanding Magnesium Corrosion—A Framework for Improved Alloy Performance

Abstract

The purpose of this paper is to provide a succinct but nevertheless complete mechanistic overview of the various types of magnesium corrosion. The understanding of the corrosion processes of magnesium alloys builds upon our understanding of the corrosion of pure magnesium. This provides an understanding of the types of corrosion exhibited by magnesium alloys, and also of the environmental factors of most importance. This deep understanding is required as a foundation if we are to produce magnesium alloys much more resistant to corrosion than the present alloys. Much has already been achieved, but there is vast scope for improvement. This present analysis can provide a foundation and a theoretical framework for further, much needed research. There is still vast scope both for better fundamental understanding of corrosion processes, engineering usage of magnesium, and also on the corrosion protection of magnesium alloys in service.

Seawater-driven magnesium based Janus micromotors for environmental remediation

“…In fact, the intrinsic galvanic cell (macrogalvanic and microgalvanic effects from the gold coating and impurities of the Mg particles, respectively) serves to further increase the anodic dissolution of Mg, assisting in the pitting corrosion. 27 Thus, the rapidly evolving hydrogen bubbles at the Mg surface provide the thrust essential for the directional propulsion of the Janus micromotors.…”

“…Even faster Mg dissolutions and propulsions were observed in strongly acidic environments (pH < 2), while strongly alkaline media (pH > 12) resulted in nearly complete hindrance of the Mg-water reaction. 27 Adding 0.1 mM EDTA to the natural seawater resulted in a decreased speed (to 40 mm s À1 ), possibly due to chelation of Mg + ions, and hence hindrance of the hydrogen evolution reaction (eqn (2)). …”

The use of a multiscale approach in electrochemistry to study the corrosion behaviour of as-cast AZ91 magnesium alloy

“…A similar occurrence was observed for η-Al 8 Mn 5 particles in 1 M NaOH; this was followed by the formation of pits around these particles [36]. It has been shown that β-Mg 17 Al 12 plays a dual role in the corrosion resistance of AZ91 alloy [24][25][26]32]. Indeed, it can act as either a barrier or a galvanic cathode: as mentioned above, the corrosion potential of β-Mg 17 Al 12 has been found to be more positive than that of the α-magnesium phase (matrix), which may therefore accelerate the galvanic corrosion of α-magnesium [21].…”

Building towards a standardised approach to biocorrosion studies: a review of factors influencing Mg corrosion in vitro pertinent to in vivo corrosion

“…Corrosion of Mg alloys is typically faster than the corrosion of high-purity Mg in simple chloride solutions, because the second phase in the Mg alloy causes microgalvanic acceleration of the corrosion of the alpha-Mg matrix [22,[54][55][56]. This micro-galvanic corrosion acceleration typically occurs preferentially next to the second phase, and is often wrongly characterised as pitting corrosion.…”

“…Chen [20] proposed a mesh made from a Mg alloy for cranial repair, as the Mg enhances bone regrowth, and the H 2 that diffuses into the brain tissue may reduce the extent of tissue damage. However, despite the potential benefits of Mg alloys in medical applications, the key factor that must be addressed is the apparent, relatively-high corrosion rates of Mg alloys [21,22]. The tendency to corrode in the body allows Mg alloys to be used in temporary medical implants or devices.…”