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Coatings on the surface of Mg alloys are inevitably damaged during their practical applications, and corrosion can easily initiate from the damaged areas to accelerate the failure of Mg parts. A dual self-healing coating has already been developed to solve this problem in our previous work. Considering the practical application of this coating, it is necessary to investigate its service behavior in atmospheric environment. Thus, the corrosion behavior of AM60 Mg substrate with and without the self-healing coating was compared in Shenyang industrial atmospheric environment. The results show that the enrichment of sediments and rainwater on the scratch areas can accelerate the corrosion of the exposed Mg substrate. The inhibitors can be released from the damaged coating to inhibit corrosion. The dual self-healing coating shows better inhibition ability to narrow scratches due to the higher inhibitor concentration and less resumption. Also, the coating with wide scratches displays enough inhibition ability as well. The dual self-healing coating is a good alternative for Mg alloy parts in the practical applications.

Purpose The formation and corrosion processes of a conversion film on the AZ80 Mg alloy with different second phases were compared to clarify the effect of microstructure on the quality of protective coatings. Design/methodology/approach The size and distribution of second phases in the edge and central regions of the AZ80 cast ingot exhibit a great difference. The film growth processes and their corrosion resistance on the edge and central regions of the AZ80 cast ingot were investigated by scanning electron microscope observations, immersion tests and electrochemical measurements. Findings The results indicate that second phases act as micro-cathodes and hydrogen evolution reaction occurs on their surface, which is not beneficial for the deposition of the conversion film. Originality/value The conversion film formed on the central regions of AZ80 cast ingot with a low volume fraction of second phases exhibits a more uniform surface and higher corrosion resistance than that formed on the edge regions of the sample with a higher volume fraction of second phases.

Deformation treatment is an efficient method to improve the mechanical properties of Mg alloys. However, twins inevitably arise during the deformation treatment due to the hexagonal closed–packed crystal structure of Mg. The role of twins in the corrosion behavior of Mg–5Y–7Gd–1Nd–0.5Zr (EW75) Mg alloy was studied by scanning electron microscopy (SEM) observations, scanning Kelvin probe force microscopy (SKPFM), zero–resistance ammeter (ZRA) measurements, scanning vibrating electrode technique (SVET), electrochemical tests and weight loss measurements. It is found that the micro–galvanic corrosion between twins and matrix plays the dual roles: accelerate the dissolution reaction of Mg substrate and promote the formation of surface film. The formation of compact surface film dominates the reactions in the EW75 alloy with twins. As a result, the twins in EW75 alloy can improve the corrosion resistance.

In this study, the synergistic effects of NH4HF2, sodium phytate (Na12Phy), K2ZrF6, and treatment time on corrosion resistance of a micro-arc oxidation (MAO) treated magnesium alloy and the entrance mechanism of P, F, and Zr into anodic coatings were investigated using an orthogonal method. In addition, the roles of NH4HF2, Na12Phy, and K2ZrF6 on coating development were separately studied. The results show that NH4HF2 and Na12Phy, the corrosion inhibitors of magnesium alloys, are beneficial but K2ZrF6 is harmful to developing anodic coatings. The corrosion resistance of MAO coatings is synergistically determined by coating characteristics, though the coating thickness plays a main role. Na12Phy significantly improves but NH4HF2 decreases the corrosion resistance of MAO coatings, while excess high K2ZrF6 is harmful to the coating corrosion resistance. Treatment time can increase the coating thickness but is the least important factor in corrosion resistance. During MAO, NH4HF2, Na12Phy, and K2ZrF6 take part in coating formation, causing P, F, and Zr to compete with each other to enter into anodic coatings.

The deterioration process of a self-sealing pore micro-arc oxidation (MAO) film was investigated. The surface and cross-section corrosion morphologies were observed by scanning electron microscopy (SEM). Chemical composition was detected by EDS elemental mapping and XRD. The corrosion process was analyzed by electrochemical impedance spectroscopy (EIS). The surface of the film in dark and light regions exhibits different corrosion behavior. In the dark regions, the corrosion process mainly concentrates on the migration of corrosion media through the pores inward. In the light regions, the transverse expansion of cracks plays a key role, accompanying the exfoliation of film constituents.

The influence of potassium fluoride (KF) on the in-situ sealing pores of plasma electrolytic oxidation (PEO) film on AM50 Mg alloy has been investigated using a stereo–zoom optical microscope, scanning electron microscope (SEM) and energy dispersive X–ray spectroscope (EDS). The films formed in the solutions with and without KF were compared. The sketch map for the formation process of in-situ sealing pores was established. The in-situ sealing pore PEO film can be obtained in the solution with KF, while the PEO film with open pores is obtained in the solution without KF. It indicates that the addition of KF plays a key role in the formation of in-situ sealing pores. Moreover, KF can change the initial film and promote the film growth rate.

A novel manasseite/carbonates composite conversion film on Mg2Zn alloy has been developed by a two-step in situ growth method. A precursor film with cracks is first formed and then it is transformed into a compact, uniform and well adherent manasseite/carbonates composite film. The corrosion tests show that the film can provide an excellent protection to the Mg2Zn alloy. From the comparison between the manasseite and its isomeride hydrotalcite, it can be found that the platelets of the manasseite film stack a little more densely, and the manasseite/carbonates composite film delays the initial corrosion of the Mg substrate more effectively than the hydrotalcite film.

The influence of alloying elements and microstructure of Mg substrates on the formation of hydrotalcite film has been investigated. It is found that the two-step process is also available for the pure Mg and other alloys after modification. A small amount of Zn does not impact the composition of the hydrotalcite film much; whereas the highly active rare earth (RE) affects the constituents of the precursor film as well as the final film on WE54 alloy significantly. The microstructure impacts the initial nucleation and the film morphology depending on the size and chemical activity of the intermetallic particles.

Ceramic films are formed on AM60 magnesium alloy by micro-arc oxidation (MAO) using a new fluorotitanate electrolyte system. Compared to the films obtained with traditional electrolytes, the film has the characteristics of self-sealing pores and different chemical compositions. To investigate the film's growth mechanism, X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) were used to characterize the phase structure and chemical composition. Mott–Schottky (M–S) curve measurements were used to study the electrical properties of the passive layer and the influence of the fluorine during initial film deposition. The NaF content in the new electrolyte plays an important role in improving the compactness of the initial film. By increasing oxidation voltages in the MAO process, an increase of titanium oxides in the film is produced. Different melting points of film constituents and high titanium oxide content in the MAO film are key factors for forming self-sealing pores.

The corrosion product films formed on the surface of Mg–2Zn and Mg–5Zn alloys in NaCl solution were investigated by electrochemical measurement, scanning electron microscopy (SEM) observation and X-ray photoelectron spectroscopy (XPS) analysis. It is found that a compact corrosion product film is formed in the initial stage of immersion, and then the film gradually degrades due to dissolution reaction. The product film formed on Mg–2Zn alloy presents better protection property than that on Mg–5Zn alloy, which can be attributed to the different chemical composition and microstructure of the both alloys.

A novel micro arc oxidation (MAO) film is developed to protect Mg alloys from corrosion. This film contains plenty of titanium oxides, which exhibits higher chemical stability than traditional MAO films. Especially, the micropores on the surface of the film are in situ sealed during the film formation process instead of the sealing pores post treatment. The film formation process is investigated by the observation of surface and cross-section morphologies and analysis of chemical composition. It is found that the sizes of micropores increase but the quantities decrease with increasing oxidation voltages. The micropores are open in the initial stage of oxidation and then they are sealed gradually. The growth direction of the film takes place change at different oxidation voltages. The elements of F and Ti play a significant role in the film growth process.

Respiratory syncytial virus (RSV) is an important viral pathogen that causes life-threatening respiratory infections in both infants and the elderly; no vaccines are at present available. In this report, we examined the use of influenza virus as a vehicle for production of an experimental RSV vaccine. We used reverse genetics to generate a recombinant influenza A virus with epitopes from the RSV fusion (F) and attachment (G) proteins (rFlu/RSV/F+G) in the influenza virus nonstructural (NS1) protein gene. Expression of RSV F+G epitope proteins was confirmed by Western blotting, and no changes in viral morphology were evident following examination by electron microscopy. BALB/c mice immunized intranasally with rFlu/RSV/F+G showed viral-specific antibody responses against both influenza and RSV. Total IgG, IgG1, IgG2a and IgA were measured in mice immunized with rFlu/RSV/F+G, revealing robust cellular and mucosal immune responses. Furthermore, we found that rFlu/RSV/F+G conferred protection against subsequent influenza and RSV challenges, showing significant decreases in viral replication and obvious attenuation of histopathological changes associated with viral infections. These findings suggest that rFlu/RSV/F+G is a promising vaccine candidate, which should be further assessed using cotton rat and primate models.

The hydrotalcite (HT) film is a promising bioactive coating for magnesium alloys. In the present study, we investigate the corrosion behavior of HT film in the simulated body fluid (SBF), and compare with which in NaCl solution. The HT film can provide a very plummy initial protection to the AZ31 alloy in SBF. The corrosion behavior of the HT film in the two solutions is quite different. When in 0.1 mol·L−1 NaCl solution, the film is dissolved gradually, and filiform corrosion is predominant after 3 days immersion. While in Hank’s solution, the thickness and composition of the film are changed. A corrosion products layer mainly consisted of Mg/Ca⁻PO43−/HPO42−, and minor of CaCO3 is deposited on the top of HT film, which enhances the barrier effect of the HT film. As a result, except for local pit corrosion at several active places, most of the area of the coated sample still remains integral even after immersion for 15 days. It is demonstrated that the HT film has better corrosion protection effect in SBF than in NaCl solution.

The austenite reversion process and the distribution of carbon and other alloying elements during tempering in 0Cr13Ni4Mo martensitic stainless steel have been investigated by in-situ high temperature X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM). The microstructure of the reversed austenite was characterized using transmission electron microscopy (TEM). The results revealed that the amount of the reversed austenite formed at high temperature increased with the holding time. Direct experimental evidence supported carbon partitioning to carbides and Ni to the reversed austenite. The reversed austenite almost always nucleated in contact with lath boundary M23C6 carbides during tempering and the diffusion of Ni promoted its growth. The Ni enrichment and the ultrafine size of the reversed austenite were considered to be the main factors that accounted for the stability of the reversed austenite.

An environmentally friendly corrosion inhibitor phytic acid (PA) has been successfully added to modify the hydrotalcite (HT) film by adsorption and ion exchange approaches. In alkali PA solution, PO 4 3 - cannot substitute CO 3 2 - in the HT, but adsorb to the external surface; H 2 PO 4 - / HPO 4 2 - can insert into the HT after decarbonation under acidic condition. Partial decomposition occurs under both conditions. The PA/pH 11-HT film shows superior stability and lasting protective efficiency, and also can provide self-healing effect associated with the P adsorption in the filament. The worse resistance of the PA/pH 6.5-HT film may be related to the micro-cracks.

The naturally formed oxide films on Mg–2Zn and Mg–5Zn alloys were investigated by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and electrochemical measurements. The oxide films on the both alloys present a similar chemical composition, consisting of surface layer of basic magnesium carbonate and MgO following with MgO and ZnO, but the oxide film on Mg–5Zn is thicker and contains more defects. The protection performance of the oxide film on Mg–5Zn is worse under open circuit potential but better in a suitable anodic potential scope compared with that on Mg–2Zn alloy.

The effect of Zn concentration on the corrosion behavior of Mg-xZn alloys is investigated. The microstructure is observed by scanning electron microscopy (SEM). The corrosion resistance is evaluated by electrochemical and immersion tests. The initiation and propagation of corrosion are analyzed based on the electrochemical measurements and corrosion morphologies observation. It is found that the MgxZny second phases are precipitated on the boundaries and their volume fractions rise with increasing Zn concentration. As a result, the corrosion resistance of Mg-xZn alloys reduces with increasing Zn concentration, which is greatly associated with the micro-cathodic effect of the MgxZny second phases. (C) 2012 Elsevier Ltd. All rights reserved.

The corrosion mechanism of Mg-Al-CO32- hydrotalcite film is discussed based on its corrosion behavior and the anion-exchange or adsorption effect of Cl-. The results demonstrate that the film is very compact and acts as a barrier against Cl- attack in the early stage. Then the surface of the film is dissolved gradually due to its instability in aqueous solutions. Only after eliminating CO32-, Cl- can insert into the hydrotalcite interlayer to balance charges. Cl- cannot substitute CO32- just in NaCl solution, but can adsorb on active spots of the film to accelerate the decomposition. (C) 2012 Elsevier Ltd. All rights reserved.

By means of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), open circuit potential (OCP) measurement and scanning electronic microscope (SEM), the in situ growth mechanism of the Mg-Al hydrotalcite film has been proposed. The composition and morphology of the films undergo a series of variations during the growth processes. The added Al compounds are a vital contribution to the formation of hydrotalcite. The film formation involves the dissolution of the AZ31 substrate, adsorption of the ions from solution, nucleation of the precursor, followed by the dissolution of Al3+, exchanging of OH- by CO32- and growth of the hydrotalcite film. (C) 2012 Elsevier Ltd. All rights reserved.

The MgxZny second phases in Mg-5Zn alloy were adjusted by T4 and T6 treatment, and then the role of second phases in the corrosion behavior of Mg-5Zn alloy was investigated. The dimension of the MgxZny second phases is only some hundred nanometers. They present discrete distribution on the boundaries of the as-received sample and continuous distribution in the T6 sample. The T4 sample in absence of second phases exhibits the best corrosion resistance while the T6 sample with the largest volume fraction of second phases exhibits the worst one, which can be attributed to the micro-cathodic effect of second phases. (c) 2012 Elsevier Ltd. All rights reserved.

The deterioration process of a plasma electrolytic oxidation (PEO) coating containing zirconium oxides on AM30 magnesium alloy in 3.5 wt.% NaCl solution have been investigated. The coating consists of an outer porous layer and an inner dense layer. The content of MgF(2) is high in the pores and an MgO-rich layer is evident in the inner layer. The corrosion resistance of the outer layer gradually decreases in the initial immersion stage (96 h) due to the decomposition of MgO. and the deterioration of the inner layer is delayed by the blocking effect of the outer layer. (C) 2011 Elsevier Ltd. All rights reserved.

In situ growth of Mg–Al hydrotalcite conversion film on AZ31 alloy has been developed by a two-step method. The characteristics of the films were investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electronic microscope (SEM) observation, electrochemical and immersion tests. The film formation process was proposed based on the open circuit potential (OCP) measurements and surface analysis. A precursor film with network cracks is first formed and then this film is transformed into a compact and uniform hydrotalcite (Mg6Al2(OH)16CO3·4H2O) film after the post treatment. This dense Mg–Al hydrotalcite film can provide effective protection to the AZ31 alloy.

Product/metal ratio (PMR) was introduced as a novel criterion for the evaluation of electrolytes on micro-arc oxidation (MAO) of Mg and its alloys. The criterion initially sprang from Pilling-Bedworth ratio (PBR), focused on the roles of electrolytes for the compactness of the fabricated coatings, and took attention on properties of reactants/products during MAO. Meanwhile, based on our experiments as well as the results from literatures, the effects of electrolyte additives on morphologies and compositions of the fabricated MAO coatings of Mg alloys were exploited for verification and supplement of the initial criterion. In combination of the initial PMR criterion and experimental verification, PMR could be represented by special mode (PMR s=V oxide products/V alloy substrates) and general mode (PMR g= PMR s+ PMR d). The ideal PMR s should be between 1 and 2, while PMR d is related to the coating deposition during MAO. PMR d is a supplement to PMR s when the effect of the overlaying property (O) of the coatings and the effective deposition (D) of electrolyte composites are considered (PMR d=f(O, D). O is related to the melting point (MP) and boiling point (BP) of the MAO products. D is related to the effective reactions between alloy substrates and electrolytes during MAO.

The influence of the quantity of the Mg(2)Sn phase on the corrosion behavior of different solution temperature treated Mg-7Sn magnesium alloy has been investigated by electrochemical measurements, scanning electron microscope (SEM) observation, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis. With the increase of solution temperature, the quantity of Mg(2)Sn phase decreased and the tin concentration of matrix increased. The dissolved tin in Mg matrix took part in the film formation and the constituent of film was magnesium oxide and stannic oxide. The corrosion mode and corrosion rate were associated with the quantity of Mg(2)Sn phases and tin concentration of the matrix. If most of tin was present as Mg(2)Sn, the corrosion mode was pitting corrosion and it accelerated the corrosion rate. If most of tin was dissolved in matrix, the corrosion mode was filiform corrosion and it decreased the corrosion rate. The experiment evidences demonstrated that the corrosion resistance can be improved by increasing the tin concentration of matrix and the lowest corrosion rate was observed for sample solution treated at 540 degrees C. (C) 2010 Elsevier Ltd. All rights reserved.

An environmentally friendly molybdate/phosphate black film for light absorption application was developed as an alternative to the chromate system on Mg-Zn-Y-Zr alloy. The microstructure, surface morphology, chemical composition, light absorbance and protection property of the black film were investigated. The initiation and growth mechanisms of the black film were also discussed. The black film consists of MoO(2) and a fraction of Mg(3)(PO(4))(2). The MoO(2) contributes to the black color and the Mg(3)(PO(4))(2) aims to improve the protection property. The experimental results indicate that the black film can provide not only high light absorbance but also corrosion protection to the Mg-Zn-Y-Zr substrate. The formation mechanism of the black film is associated with the electrochemical heterogeneity of the Mg-Zn-Y-Zr substrate. At the cathodic sites, MoO(4)(2-) is reduced to MoO(2) accompanying with the hydrogen evolution reaction. At the anodic sites, the dissolution of Mg(2+) bonds with PO(4)(3-) to form Mg(3)(PO(4))(2). (C) 2010 Elsevier B.V. All rights reserved.

The corrosion mechanism of Mg-8Li alloy in NaCl solution was investigated by electrochemical testing and SEM observation. The electrochemical results indicated that the corrosion resistance of Mg-8Li alloy in 0.1 M NaCl solution gradually deteriorated with increasing of immersion time expect for 2 h immersion, which was consistent with the SEM observation of corrosion morphology. Mg-8Li alloy exhibited filiform type of attack under significant anodic control of magnesium solution reaction. The cathodic reaction was driven by hydrogen evolution reaction. The presence of filiform corrosion also proved a resistant oxide film naturally formed on the surface of Mg-8Li alloy. (C) 2009 Elsevier Ltd. All rights reserved.

Magnesium alloys have unique advantages to act as biodegradable implants for clinical application. The biodegradable behaviors of AZ31 in simulated body fluid (SBF) for various immersion time intervals were investigated by electrochemical impedance spectroscopy (EIS) tests and scanning electron microscope (SEM) observation, and then the biodegradable mechanisms were discussed. It was found that a protective film layer was formed on the surface of AZ31 in SBF. With increasing of immersion time. the film layer became more compact. If the immersion time was more than 24 h, the film layer began to degenerate and emerge corrosion pits. in the meantime, there was hydroxyapatite particles deposited on the film layer. The hydroxyapatite is the essential component of human bone, which indicates the perfect biocompatibility of AZ31 magnesium alloy. (C) 2008 Elsevier B.V. All rights reserved.

[Song, Yingwei; Shan, Dayong; Chen, Rongshi; Zhang, Fan; Han, En-Hou] Chinese Acad Sci, State Key Lab Corros & Protect, Inst Met Res, Shenyang 110016, Peoples R China.;Song, YW (reprint author), Chinese Acad Sci, State Key Lab Corros & Protect, Inst Met Res, 62 Wencui Rd, Shenyang 110016, Peoples R China;ywsong@imr.ac.cn

A novel phosphate conversion film was obtained on Mg–8.8Li alloy. The film formation mechanism was studied by electrochemical measurements, scanning electron microscopy (SEM) observation and X-ray photoelectron spectroscopy (XPS) analysis. The deposition of conversion film contained three stages. Stage I: loose surface film consisting of oxides and hydroxides was dissolved to expose the bare substrate. Stage II: β phase was preferentially dissolved, accompanying with the deposition of conversion film, and then α phase was deposited with conversion film. Stage III: conversion film was gradually improved until the dynamic balance of film dissolution and formation was established.