Improvement of corrosion resistance of magnesium alloys for biomedical applications

Abstract

In recent years, magnesium (Mg) alloys have attracted great attention due to superior biocompatibility, biodegradability, and other characteristics important for use in biodegradable implants. However, the development of Mg alloys for clinical application continues to be hindered by high corrosion rates and localized corrosion modes, both of which are detrimental to the mechanical integrity of a load-bearing temporary implant. To overcome these challenges, technologies have been developed to improve the corrosion resistance of Mg alloys, among which surface treatment is the most common way to enhance not only the corrosion resistance, but also the bioactivity of biodegradable Mg alloys. Nevertheless, surface treatments are unable to fundamentally solve the problems of fast corrosion rate and localized corrosion. Therefore, it is of great importance to alter and improve the intrinsic corrosion behavior of Mg alloys for biomedical applications. To show the significance of the intrinsic corrosion resistance of biodegradable Mg alloys and attract much attention on this issue, this article presents a review of the improvements made to enhance intrinsic corrosion resistance of Mg alloys in recent years through the design and preparation of the Mg alloys, including purifying, alloying, grain refinement, and heat treatment techniques. The influence of long-period stacking-ordered structure on corrosion behavior of the biodegradable Mg alloys is also discussed.

Mg and Its Alloys for Biomedical Applications: Exploring Corrosion and Its Interplay with Mechanical Failure

“…Mg and its alloys are reactive metals and they corrode in aqueous environments according to the reactions given below [64,65]:…”

“…According to Ghali et al [72], two different corrosion modes are possible, uniform and localized. Mg alloys with slow and constant degradation rate (lower than 0.5 mm/year [65]) are required to facilitate sufficient time to heal for the bone. Further, a uniform degradation mode is key as localized corrosion can lead to toxicity and early failure of the implant.…”

“…The most common impurities are Fe, Ni and Cu. They are most harmful in terms of corrosion resistance due to their very negative corrosion potential [65,[74][75][76]. They are cathodic with respect to the Mg matrix, resulting in a faster corrosion rate and determining a higher and more severe susceptibility to pitting that quickly destroys the Mg(OH) 2 protective film [60].…”

“…Once this film is removed, the surrounding corrosive fluid will have contact with the Mg matrix, causing further corrosion according to the just mentioned mechanism. If the inhomogeneities are not uniformly distributed [65] or above a tolerance limit [77], the material will corrode in a localized manner, acting as precursor for stress corrosion cracking (SCC) and corrosion fatigue (CF). These mechanisms highly affect the corrosion resistance of Mg and its alloys, hampering their application for biomedical implants and they will be described in detail in the next section.…”

Effect of Solution Treatment on Microstructure and Corrosion Properties of Mg–4Gd–1Y–1Zn–0.5Ca–1Zr Alloy

“…To overcome these drawbacks, extensive studies have been carried out to enhance the mechanical properties and corrosion resistance of the Mg alloys [10][11][12][13][14][15]. For instance, Mg-Al-Zn series alloys were a category of widely used commercial Mg alloys, and the mechanical properties of these Mg alloys were enhanced by the methods of hot extrusion, severe plastic deformation and so on [16][17][18][19][20].…”