Corrosion Of Mg Alloys Research Articles

Enhanced corrosion resistance and cytocompatibility of biomimetic hyaluronic acid functionalised silane coating on AZ31 Mg alloy for orthopaedic applications.

This paper reports the corrosion resistant and cytocompatible properties of the hyaluronic acid-silane coating on AZ31 Mg alloy. In this study, the osteoinductive properties of high molecular weight hyaluronic acid (HA, 1-4 MDa) and the corrosion protection of silane coatings were incorporated as a composite coating on biodegradable AZ31 Mg alloy for orthopaedic applications. The multi-step fabrication of coatings first involved dip coating of a passivated AZ31 Mg alloy with a methyltriethoxysilane-tetraethoxysilane sol-gel to deposit a dense, cross-linked and corrosion resistant silane coating (AZ31-MT). The second step was to create an amine-functionalised surface by treating coated alloy with 3-aminopropyl-triethoxy silane (AZ31-MT-A) which facilitated the immobilisation of HA via EDC-NHS coupling reactions at two different concentrations i.e 1 mg.ml-1 (AZ31-MT-A-HA1) and 2 mg.ml-1 (AZ31-MT-A-HA2). These coatings were characterised by Fourier transform infrared spectroscopy, atomic force microscopy and static contact angle measurements which confirmed the successful assembly of the full coatings onto AZ31 Mg alloy. The influence of HA-silane coating on the corrosion of Mg alloy was investigated by electrical impedance spectroscopy and long-term immersion studies measurements in HEPES buffered DMEM. The results showed an enhanced corrosion resistance of HA functionalised silane coated AZ31 substrate over the uncoated equivalent alloy. Furthermore, the cytocompatibility of MC3T3-E1 osteoblasts was evaluated on HA-coated AZ31-MT-A substrates by live-dead staining, quantification of total cellular DNA content, scanning electron microscope and alkaline phosphatase activity. The results showed HA concentration-dependent improvement of osteoblast cellular response in terms of enhanced cell adhesion, proliferation and differentiation. These findings hold great promise in employing such biomimetic multifunctional coatings to improve the corrosion resistance and cytocompatibility of biodegradable Mg-based alloy for orthopaedic applications.

Effect of anodic T phase on surface micro-galvanic corrosion of biodegradable Mg-Zn-Zr-Nd alloys

A complete understanding of the role of Mg-Zn-Nd (T) phase in surface micro-galvanic corrosion of Mg alloys has not been fully developed. Therefore, the microstructure evolution and corrosion behavior in simulated body fluid (SBF) of Mg-2Zn-0.6Zr-xNd alloys (x = 0, 0.2, 0.6 and 1 wt%) were investigated. It was found that the MgZn phase in Mg-2Zn-0.6Zr alloy changed to Mg60Zn32Nd8 (T2) and Mg35Zn40Nd25 (T3) phases after adding 0.2–1 wt% Nd. With the formation of T phases, the grain size increased first and then decreased. By using scanning kelvin probe force microscopy (SKPFM), the Volta potentials of second phases relative to Mg matrix were measured. T2 and T3 phases with a relative Volta potential of about −400 mV acted as micro-anodes, so that they were corroded preferentially during the corrosion process. Because of the appropriate amount of anodic T phases and their discontinuous distribution, the alloy with 0.2 wt% Nd addition showed a uniform surface corrosion characteristic and exhibit the best corrosion resistance.

The Reduction of Dissolved Oxygen During Magnesium Corrosion.

The consumption of dissolved oxygen (DO) during the corrosion of commercially pure magnesium specimens was investigated by localized corrosion techniques. The concentration of oxygen and the local current density on the near‐surface of magnesium were measured simultaneously by a micro‐optode DO sensor and the scanning vibrating electrode technique (SVET), respectively. Diamond microelectrodes were also used for DO mapping. Significant DO depletion was found since the initial immersion time of Mg in NaCl 0.5 m, and a correlation could be established between DO consumption and areas of anodic and cathodic activity. These findings assume particular relevance for the corrosion of Mg alloys or magnesium components with impurity levels higher than the tolerance limit. Moreover, this study points out the significance of the partial oxygen pressure as an influential parameter during magnesium corrosion.

Initial Corrosion Study of Magnesium Alloys in Simulated Body Fluid By SECM

Magnesium alloys have been proposed as suitable biomaterials for resorbable implant applications. Although a substantial amount of research has been performed on the use of Mg alloys for biomedical applications, there are few studies employing micro-electrochemical techniques for characterizing these materials in physiological environments. The unique capabilities of the scanning electrochemical microscope (SECM) make this a powerful tool for in situ study of the localized corrosion of Mg alloys in physiological fluids. The work presented will assess the initial stages of electrochemical corrosion attack of AZ31 and AZ91D Mg alloys, and compare their performance in simulated body fluid (SBF). SECM measurements in amperometric operation modes were carried out in order to characterize the alloys surface during corrosion. Substrate Generation/Tip Collection (SG/TC) mode was used to spatially resolve regions of hydrogen flux related to cathodic sites while Feedback mode was used to distinguish between conductive/insulating regions on the passive layer. These results show intensive electrochemical activity on substrate surfaces at short exposure times of up to one hour, demonstrating rapid pit nucleation and formation of nearby, surrounding corrosion products. These results provide useful information on the localized hydrogen evolution process at Mg alloy surfaces under physiologically relevant conditions.

Magnesium alloys and graphite wastes encapsulated in cementitious materials: reduction of galvanic corrosion using alkali hydroxide activated blast furnace slag

ABSTRACTMagnesium alloys (Mg-0.5%Zr and Mg-1.2%Mn) and graphite from spent nuclear fuel that has been used in the former French gas cooled reactors, have been stored together in AREVA La Hague plant. The recovery and packaging of these wastes is currently studied and several solutions are under consideration. One of the developed solutions would be to mix these wastes in a grout composed of industrially available cement, e.g. OPC, OPC blended with blast furnace slag or aluminous cement. Within the alkaline pore solution of these matrixes, magnesium alloys are imperfectly protected by a layer of magnesium hydroxide (Mg(OH)2, Brucite) resulting in a slow process of corrosion releasing hydrogen. As the production of this gas must be considered for the storage safety, and the quality of wasteform, it is important to select a cement matrix capable of lowering the corrosion kinetics of magnesium alloys. This is especially true when magnesium alloys are conditioned together with graphite wastes. Indeed, galvanic coupling phenomena may increase early age corrosion of the mixed wastes, as magnesium and graphite will be found in electrical contact in the same electrolyte. Many types of cements have been tested and most of them have caused strong hydrogen production when magnesium alloys and graphite are conditioned together into such cement pastes. Exceptions are geopolymer binder which is already known for that and another binder based on alkali hydroxide activated ground granulated blast furnace slag (AHABFS) which is presented in the present article. First are presented hydrogen production experiments that demonstrate the efficiency of AHABFS towards reduction of corrosion of Mg alloys embedded. In a second part, a formulation of fluid mortar based on this binder is proposed.

Feasibility of physicochemical recovery of nutrients from swine wastewater: Evaluation of three kinds of magnesium sources

Abstract In this study, two physicochemical methods (struvite precipitation and ammonia stripping) were coupled for the recovery of nutrients from swine wastewater. Recovering phosphate (PO4-P) as struvite was first performed using three different types of magnesium (Mg) sources: Mg alloy, low-grade magnesium oxide (LG-MgO), and Mg-containing supernatant, followed by the removal of total ammonia nitrogen (TAN) by ammonia stripping using LG-MgO as the pH adjustor. The results indicated that the PO4-P in swine wastewater can be recovered as struvite with high purity through chemical corrosion of Mg alloy, whereas a very low-purity struvite was obtained using LG-MgO as the Mg source for struvite precipitation. Approximately >94% of TAN could be removed from the effluent generated from the phosphate-recovery stage by ammonia stripping at an aeration rate of 5 L air/l wastewater · min, LG-MgO dosage of 8 g/l, and a temperature of 25 °C for 180 min. Recycling the supernatant after ammonia stripping as the Mg source of struvite precipitation could recover PO4-P as struvite with a purity of 85.8% at pH 9.5 and Mg:P molar ratio of 1.2:1. The comparison analysis indicated that the optimal Mg source for the recovery of phosphate was Mg-containing supernatant.

Corrosion Behavior of Calcium Phosphate-Coated Biomedical Magnesium Alloy Under in Vitro and In Vivo Environments

Magnesium alloys attract attention as a biodegradable/bioabsorbable medical device because of the biodegradability and good mechanical integrity. Corrosion rate of the magnesium alloys should be controlled depending on the implantation part of body as well as the biocompatibility should be improved. Hydroxyapatite (HAp) and octacalcium phosphate (OCP) coatings were developed to control the corrosion rate and to improve the hard tissue compatibility. Corrosion behavior of HAp- and OCP-coated Mg-3mass% Al-1mass% Zn (AZ31) was examined in cell culture medium (in vitro) or in subcutaneous tissue of mouse (in vivo). Effect of medium-replacement and addition of gelatin in medium on the corrosion behavior was also examined. Chemically polished AZ31 was used as a reference. Concentration of Mg ions in medium was quantified. Apparent corrosion initiation of substrate AZ31 was delayed for ca. 1 week with HAp and OCP coatings in medium while Mg ion release from as-polished AZ31 initiated from the beginning. Filiform corrosion took place, but visible growth of filiform corrosion stopped within several days. Afterwards, Mg ion release continued for 1 year with almost a constant corrosion rate. The corrosion rate of AZ31 alloy in medium was reduced by more than 50% with HAp and OCP coatings. HAp coating showed superior corrosion protection effect than OCP coating. After 1 year of immersion, cross section of the immersed specimens showed that uniform corrosion took place underneath the coatings. The wall of filiform corrosion pits was covered with thick corrosion products layer. These results indicate that corrosion continued for long time under the coating and corrosion products layer in medium. The periodical medium replacement during immersion test did not significantly change the initial corrosion rate for 4 weeks. However, the medium-replacement rather reduced the corrosion rate of HAp-coated AZ31 comparing to the result without medium-replacement. Deposition of calcium phosphate from medium was enhanced with the medium-replacement, leading to the improvement of corrosion protection effect of HAp coating. As-polished AZ31 caused the formation of gas cavity in subcutaneous tissue of mouse due to H2 gas generated in corrosion reaction. Such a gas cavity formation was not observed around the implanted HAp- and OCP-coated specimens, indicating that corrosion of substrate AZ31 was also reduced by HAp and OCP coating in subcutaneous tissue. After 16 weeks of implantation, the specimens were retrieved from the mouse and surface and cross section was observed using SEM. Macro- and micro-pits were observed on the surface and underneath the coatings. Unlike in medium, corrosion pits appeared to grow in depth direction rather than in lateral direction in subcutaneous tissue. Because body fluid circulation in the subcutaneous tissue is limited, to simulate the soft tissue environment, gelatin was added in medium and HAp-coated AZ31 was immersed for 4 weeks. Then, the similar corrosion morphology with macro- and micro-pits was obtained in the gelatin-added medium. These results indicate that corrosion of HAp- and OCP-coated AZ31 is localized in diffusion limited environment. The developed HAp and OCP coatings reduced the corrosion rate of Mg alloy in medium and in soft tissue. The corrosion morphology, especially shape of local corrosion, depended on the corrosion environment. The decrease of mass transfer in the environment caused the localization of corrosion of Mg alloy.

Enhanced in Vitro and in Vivo Performance of Mg-Zn-Y-Nd Alloy Achieved with APTES Pretreatment for Drug-Eluting Vascular Stent Application.

Bioabsorbable magnesium alloys are becoming prominent as temporary functional implants, as they avoid the risks generated by permanent metallic implants such as persistent inflammation and late restenosis. Nevertheless, the overfast corrosion of Mg alloys under physiological conditions hinders their wider application as medical implant materials. Here we investigate a simple one-step process to introduce a cross-linked 3-amino-propyltrimethoxysilane (APTES) silane physical barrier layer on the surface of Mg-Zn-Y-Nd alloys prior to electrostatic spraying with rapamycin-eluting poly(lactic-co-glycolic acid) (PLGA) layer. Surface microstructure was characterized by scanning electron microscope and Fourier transform infrared spectroscopy. Nanoscratch test verified the superior adhesion strength of PLGA coating in the group pretreated with APTES. Electrochemical tests combined with long-term immersion results suggested that the preferable in vitro anticorrosion behavior could be achieved by dense APTES barrier. Cell morphology and proliferation data demonstrated that APTES pretreated group resulted in remarkably preferable compatibility for both human umbilical vein endothelial cells and vascular smooth muscle cells. On the basis of excellent in vitro mechenical property, the animal study on the APTES pretreated Mg-Zn-Y-Nd stent implanted into porcine coronary arteries confirmed benign tissue compatibility as well as re-endothelialization without thrombogenesis or in-stent restenosis at six-month followup.

Enhanced corrosion resistance and biocompatibility of Mg-Zn-Y-Nd alloy achieved with APTES pre-treatment for drug-eluting vascular stent application

Event Abstract Back to Event Enhanced corrosion resistance and biocompatibility of Mg−Zn−Y−Nd alloy achieved with APTES pre-treatment for drug-eluting vascular stent application Jing Liu1, Tingfei Xi1 and Ming Chen2 1 Peking University, Academy for Advanced Interdisciplinary Studies, China 2 Peking University First Hospital, Cardiovascular Internal Medicine Department, China Bioabsorbable magnesium alloys (Mg) are advantageous in temporary functional implant applications, as they avoid the risks posed by permanent metallic implants. Nevertheless, the over-fast corrosion of Mg alloys under physiological conditions hinders its wider use as medical implants. Here we introduce a convenient one-step process to introduce a cross-linked 3-amino-propyltrimethoxysilane (APTES) silane physical barrier layer on the surface of Mg-Zn-Y-Nd alloys before coating with drug-eluting poly (glycolide-co-lactide) (PLGA) layer loaded with rapamycin. Surface microstructure was characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS). Nano-scratch test verifies the adhesion strength of the PLGA pre-treated with APTES is superior to direct PLGA coating. Electrochemical testing combined with long-term immersion results indicate that the APTES coating results in preferable in vitro anti-corrosion behaviour. Cell morphology and proliferation tests demonstrate that APTES pre-treated Mg-Zn-Y-Nd substrate shows markedly preferable effects for both human umbilical vein endothelial cells (EA. hy926) and vascular smooth muscle cells (VSMC). Furthermore, the in vivo test via implanting APTES pre-treated Mg-Zn-Y-Nd stent to porcine coronary arteries for 6 months confirms benign tissue compatibility with the well re-endothelialized vessel with no sign of obvious thrombogenesis and restenosis. National Basic Research Program of China (Grant No. 2012CB619102); Shenzhen Science and Technology Funding Projects (CXZZ20140730091722497); Shenzhen Special Funds for Development of Strategic Emerging Industries(Project No. JCYJ20130402172)

Corrosion of Mg alloy in the presence of ammonium ion. Evidence of hydride sub-products

Corrosion of AZ31 Mg alloy was systematically investigated by different experimental approaches in the presence and in the absence of NH4+. Remarkable reactivity of Mg/NH4+ system was manifested by copious evolution of hydrogen over a dark corrosion film, associated to active deprotonation of complex Mg hydrides, more likely bridged {Mg2+(AlH4−)2Mg2+(H−)2} complexes covered by a skin of MgO. Metastability of hydride phases is favored in the presence of species that alter the equilibrium dissociation of water, such as NH4+ and SO42−. Chemical recombination of hydrogen atoms of oxidic Mg hydrides is proposed as the kinetically determinant process.

A study on atomic diffusion behaviours in an Al-Mg compound casting process

Al and Mg alloys are main lightweight alloys of research interest and they both have superb material properties, i.e., low density and high specific strength, etc. Being different from Al alloys, the corrosion of Mg alloys is much more difficult to control. Therefore to combine merits of these two lightweight alloys as a composite-like structure is an ideal solution through using Al alloys as a protective layer for Mg alloys. Compound casting is a realistic technique to manufacture such a bi-metal structure. In this study, a compound casting technique is employed to fabricate bi-layered samples using Al and Mg and then the samples are analysed using electron probe micro-analyzer (EPMA) to determine diffusion behaviours between Al and Mg. The diffusion mechanism and behaviours between Al and Mg are studied numerically at atomic scale using molecular dynamics (MD) and parametric studies are conducted to find out influences of ambient temperature and pressure on the diffusion behaviours between Al and Mg. The results obtained clearly show the effectiveness of the compound casting process to increase the diffusion between Al and Mg and thus create the Al-base protection layer for Mg.

The stability of aluminum‐manganese intermetallic phases under the microgalvanic coupling conditions anticipated in magnesium alloys

The electrochemical behaviour of two Al‐Mn materials (Al‐ 5.5 at % Mn and Al‐ 13.5 at % Mn) has been studied in 0.275 M NaCl and 0.138 M MgCl2 solutions to simulate the cathodic environment of Al‐Mn particles during the corrosion of a Mg alloy. Upon polarization in NaCl solution to a potential in the range expected on a corroding Mg alloy, the Al‐5.5 at % Mn alloy proved unstable undergoing de‐alloying (loss of Al) and delamination of layers of the Al(OH)3 formed. This leads to a steady increase H2O reduction current. When polarized in MgCl2 solution the surface was partially protected from de‐alloying and the current for H2O reduction suppressed by the deposition of Mg(OH)2. The Al‐13.5 at % Mn alloy was considerably more stable when cathodically polarized. This increased stability was attributed to the higher density of Mn‐enriched areas in the alloy surface. This simulation of the microgalvanic cathodic behaviour of Al‐Mn intermetallic particles confirms that the appearance of corrosion product domes on the Al‐Mn intermetallic particles during the corrosion of Mg alloys as an indication of their cathodic behaviour and that Al‐Mn intermetallic particles are efficient, yet unstable cathodes.

Corrosion of magnesium alloys: the role of alloying

The demand for light-weighting in transport and consumer electronics has seen rapid growth in the commercial usage of magnesium (Mg). The major use of Mg is now in cast Mg products, as opposed to the use of Mg as an alloying element in other alloy systems and there is an emerging market of wrought Mg products and biomedical Mg components – such that the past two decades have seen a significant number of new Mg-alloys reported. None-the-less, the corrosion of Mg alloys continues to be a challenge facing engineers seeking weight reductions by deployment of Mg. Herein, authors review the influence of alloying on the corrosion of Mg-alloys, with particular emphasis on the underlying electrochemical kinetics that dictate the ultimate corrosion rate. Such a review focusing on the chemistry–corrosion link, both in depth and in a holistic approach, is lacking. As such the authors do not describe aspects such as high-temperature oxidation or cracking, but focus on delivering the state-of-the-art with regards to alloying influences on corrosion kinetics. It has been demonstrated that Mg itself will not be thermodynamically passive in environments of pH<11, regardless of the extent and type of alloying and hence corrosion kinetics require unique attention. Authors consolidate the presentation to include essentially all commercially available alloys and in excess of 350 custom alloys with wide variations in composition; in addition to reviewing the range of intermetallic compounds and impurities that form in such alloys systems. An update is also given regarding mechanistic advances and the role of grain size on corrosion of Mg. A wider understanding of the role of chemical effects upon corrosion of Mg is both timely and serves to highlight metallurgical approaches towards kinetically retarding the corrosion problem. The latter is of key relevance to next generation lightweight alloys and rational design of wrought Mg and bio-Mg.

Effect of hydrogen on the corrosion behavior of the Mg–xZn alloys

Abstract Hydrogen evolution reaction is inevitable during the corrosion of Mg alloys. The effect of hydrogen on the corrosion behavior of the Mg–2Zn and Mg–5Zn alloys is investigated by charging hydrogen treatment. The surface morphologies of the samples after charging hydrogen were observed using a scanning electron microscopy (SEM) and the corrosion resistance was evaluated by polarization curves. It is found that there are oxide films formed on the surface of the charged hydrogen samples. The low hydrogen evolution rate is helpful to improve the corrosion resistance of Mg alloys, while the high hydrogen evolution rate can increases the defects in the films and further deteriorates their protection ability. Also, the charging hydrogen effect is greatly associated with the microstructure of Mg substrate.

Development of a Novel, Environmentally Compliant Magnesium Coating System for Corrosion Protection of Magnesium Alloys

Due to its low density and good mechanical properties, Mg and its alloys are very attractive materials for aerospace applications. However since Mg is the most electrochemically active structural metal, protecting it from environmental degradation presents a real challenge. Corrosion of Mg alloys depends on their chemical composition and microstructure. The intermetallic phases formed during production processes are more noble than the Mg matrix and result in the establishment of microgalvanic cells within the Mg alloy; thus, accelerating the overall corrosion of the Mg. To shield Mg and its alloys from corrosive environments, their surfaces are usually protected by chemical and conversion inorganic coatings, sol-gel coatings, anodization, or thermal spraying. But one has to be aware that defects present in the coating or developed during operation often result in the formation of galvanic cells leading to accelerated corrosion of Mg component. An ideal, effective coating should be able to simultaneously provide corrosion protection through: sacrificial anode-based cathodic protection, active corrosion protection to minimize corrosion at defects (for example by releasing active inhibitors), and formation of a protective barrier layer on the substrate surface. Producing a protective coating which could fulfill the above requirements is extremely challenging. For example, creation of sacrificial coatings for Mg substrate is not an easy task, because there are not many engineering materials more active than Mg alloys. However physical vapor deposition technology can be employed to produce anodic coatings capable of sacrificially protecting Mg alloy components.Our preliminary results show that physical vapor deposition process indeed can produce thin films of Mg alloys with sacrificial properties. These thin films were tested in artificial sea water in ambient conditions: Alloy Form OCP (V vs. SCE) Corrosion rate, mpy Pure Mgbulk-1.6131.3Thin film-1.927.6AZ31bulk-1.634.3Thin film-1.83.6AZ91bulk-1.69.5Thin film-1.86.3 The electrochemical parameters show that thin films not only exhibit lower corrosion potential (on average lower by 200 mV) but also have lower corrosion rate. Obviously, the corrosion performance of the thin film is a function of the microstructure of the deposits and this in turn depends on deposition parameters. The key factors in deposition process which enable production of films with tailored properties will be discussed.

High extracellular magnesium inhibits mineralized matrix deposition and modulates intracellular calcium signaling in human bone marrow-derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) have the potential to differentiate into several cell types and provide an attractive source of autologous cells for regenerative medicine. However, their cellular biology is not fully understood. Similar to Ca2+, extracellular Mg2+ plays an important role in the functions of the skeletal system. Here, we examined the effects of extracellular Mg2+ on the deposition of calcium phosphate matrix and Ca2+ signaling with or without ATP stimulation in human bone marrow-derived mesenchymal stem cells (hBMSCs). We found that high extracellular Mg2+ concentration ([Mg2+]e) inhibited extracellular matrix mineralization in hBMSCs in vitro. hBMSCs also produced a dose-dependent decrease in the frequency of calcium oscillations during [Mg2+]e elevation with a slight suppression on oscillation amplitude. In addition, spontaneous ATP release was inhibited under high [Mg2+]e levels and exogenous ATP addition stimulated oscillation reappear. Taken together, our results indicate that high [Mg2+]e modulates calcium oscillations via suppression of spontaneous ATP release and inactivates purinergic receptors, resulting in decreased extracellular mineralized matrix deposition in hBMSCs. Therefore, the high magnesium environment created by the rapid corrosion of Mg alloys may result in the dysfunction of calcium-dependent physiology processes and be disadvantageous to hBMSCs physiology.

Finite Element Analysis of Residual Stresses in Metallic Coatings through a Compound Casting

Al and Mg alloys are widely used in industry as main lightweight alloys. They have excellent properties, such as low density, high ductility, and high specific strength, and so on. Generally speaking, Mg alloys are better than Al alloys. However the corrosion of Mg alloys is much more difficult to control compared Al alloys. Therefore to combine these two lightweight alloys, a composite-like structure is an ideal solution since Al alloys can be used as protective coatings for Mg alloys. Compound casting is a realistic technique to get this coating system. In the current study, we numerically study the compound casting using finite element method (FEM) to make these two alloys, a composite-like structure, satisfy requirements to resist corrosion required from industry, in which the aluminum layer is acting as a protective coating for the magnesium substrate. Several finite element models have been developed by using the birth and death element technique and we focus on compound casting-induced residual stresses in the compounded structure. The numerical results obtained from the proposed finite element models show the distribution profiles of thermal residual stresses. We found the major factors influencing the residual stresses are the temperature to pre-heating the Al substrate and the thickness of Mg deposits.

Corrosion mechanism and evaluation of anodized magnesium alloys

The corrosion of anodized Mg alloys is investigated by means of immersion, salt spray, polarization curve, AC electrochemical impedance spectroscopy (EIS), SEM and optical microscopy analyses. Based on the blocking, retarding and passivating effects of an anodized coating on corrosion of Mg alloys, a corrosion model is proposed to illustrate the corrosion reaction at the coating/substrate interface in coating through-pores. It is found that EIS can sensitively respond to the occurrence of corrosion in anodized Mg alloys and reflect the protection performance of anodized coatings, which may be used as an in situ method of monitoring corrosion for anodized Mg alloys.

The in vitro and in vivo evaluation of the biocompatibility of Mg alloys

Magnesium (Mg) and its alloys are being widely investigated for their potential use as resorbable biomaterials for orthopaedic applications. However, the natural corrosion of the metals results in potentially harmful perturbations to the physiological environment, which requires a comprehensive understanding of their biocompatibility. Currently, most investigations proceed directly from in vitro biocompatibility studies to intraosseous implantation. However, this can result in the unnecessary elimination of appropriate materials due to over sensitive in vitro methods or the implantation of potentially harmful materials. This study involved the development of a relevant in vitro cell culture method, and an in vivo soft tissue implantation technique to provide an intermediate step between basic cell culture methods and large animal intraosseous investigations. A Live/Dead fluorescent assay was used to investigate the viability of both L929 and SaOS-2 cells exposed to Mg alloys, with the results compared to those seen with the intramuscular implantation of the same materials in Lewis rats. These methods were able to successfully provide data on the corrosion of Mg alloys, allowing the identification of slowly and safely corroding materials that may be used in future intraosseous investigations.

A Cumulative Approach to Tracking the Corrosion of Mg Alloys on the Microscale

not Available.