Corrosion studies of modified organosilane coated magnesium–yttrium alloy in different environments

Magnesium (Mg) and its alloys have numerous potential applications as biodegradable implants, but the fast degradation rate of Mg alloys at the initial implanted stage could be a problem. This paper describes the modification of the water-based bis-[triethoxysilyl] ethane (BTSE) silane applied to the surface of magnesium–yttrium (Mg–4Y) to increase its corrosion resistance. Surface characterization by SEM, FTIR, and EDX showed that the hydrolysis and condensation of the silane resulted in a covalent bonding to the Mg–4Y surface. Corrosion behavior of the uncoated and coated Mg–4Y alloy was evaluated in different environments by using a novel self-developed corrosion probe. Based on the electrochemical results of DC polarization and electrochemical impedance spectroscopy (EIS), we conclude that the epoxy-modified BTSE silane coating successfully increases the corrosion resistance at the initial stage of implantation. The corrosion rates in the flesh of dead mice environments such as body cavity and subcutaneous tissue of the mice were lower than the corrosion rates in in vitro environments.     

Bio-corrosion characterization of Mg–Zn–X (X = Ca, Mn, Si) alloys for biomedical applications

The successful applications of magnesium-based alloys as biodegradable orthopedic implants are mainly inhibited due to their high degradation rates in physiological environment. This study examines the bio-corrosion behaviour of Mg–2Zn–0.2X (X = Ca, Mn, Si) alloys in Ringer’s physiological solution that simulates bodily fluids, and compares it with that of AZ91 magnesium alloy. Potentiodynamic polarization and electrochemical impedance spectroscopy results showed a better corrosion behaviour of AZ91 alloy with respect to Mg–2Zn–0.2Ca and Mg–2Zn–0.2Si alloys. On the contrary, enhanced corrosion resistance was observed for Mg–2Zn–0.2Mn alloy compared to the AZ91 one: Mg–2Zn–0.2Mn alloy exhibited a four-fold increase in the polarization resistance than AZ91 alloy after 168 h exposure to the Ringer’s physiological solution. The improved corrosion behaviour of the Mg–2Zn–0.2Mn alloy with respect to the AZ91 one can be ascribed to enhanced protective properties of the Mg(OH)₂ surface layer. The present study suggests the Mg–2Zn–0.2Mn alloy as a promising candidate for its applications in degradable orthopedic implants, and is worthwhile to further investigate the in vivo corrosion behaviour as well as assessed the mechanical properties of this alloy.     

Anticorrosion and cytocompatibility behavior of MAO/PLLA modified magnesium alloy WE42

Recently, biodegradable magnesium alloys have been introduced in the field of cardiovascular stents to avoid the specific drawbacks of permanent metallic implants. However, the major obstacle of the clinical use of magnesium-based materials is their rapid corrosion rate. In this paper, a composite micro-arc oxidation/poly-l-lactic acid (MAO/PLLA) coating was fabricated on the surface of the magnesium alloy WE42 to improve its corrosion resistance and the cytocompatibility of the modified materials was also investigated for safety aim. In our study, the morphology of materials was analyzed by Scanning electron microscopy. Potentiodynamic polarization was used to evaluate the corrosion behavior of the samples and corrosion weight loss was used to demonstrate their degradation rate. Furthermore, we applied cytotoxicity test in testing the cytocompatibility of the modified samples. The results showed that the PLLA coating effectively sealed the microcracks and micropores on the surface of the MAO coating by physical interlocking to interfere the corrosion ions. The corrosion rate was decreased and the cyototoxicity test showed that the MAO/PLLA composite coating WE42 had good cytocompatibility.     

镁合金表面耐磨涂层研究进展

镁及其合金具有优异的物理及机械性能,从而在许多领域得到应用.但其不耐磨性限制了镁合金在汽车和航空工业中的应用.最简单且有效的解决办法是在镁合金表面施加耐磨涂层.综述了几种新的表面耐磨涂层技术,即激光表面改性涂层(激光表面重熔/激光表面合金化/激光表面熔敷)、表面纳米陶瓷涂层和微弧氧化陶瓷基涂层,并分析了它们的研究和应用前景.     

Chrome-free neodymium-based protective coatings for magnesium alloys

The microstructure of chrome-free neodymium-based conversion coating on magnesium alloy was investigated and the corrosion resistance was evaluated as well. The micro-morphology, transverse section, crystal structure and composition of the coating were observed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS), respectively. The corrosion resistance was evaluated by potentiodynamic polarization curve and electrochemical impedance spectroscopy (EIS).The results revealed that the morphology of neodymium conversion coating is of crack-mud structure. Tiny cracks distribute in the compact coating deposited by neodymium oxides. EDS results characterize that the coating is made of neodymium oxides. The potentiodynamic polarization curve, EIS and OCP indicate that the neodymium conversion coating can improve the corrosion resistance of magnesium alloys.     

Corrosion and drug release properties of EN-plating/PLGA composite coating on MAO film

The electroless nickel plating/poly(dl-lactide-co-glycolide) composite coating (EN-plating/PLGA composite coating) was fabricated on the surface of the micro-arc oxidation (MAO) film of the magnesium alloy AZ81 to double control the corrosion and drug release in the hanks' solution. The EN-plating was fabricated on the MAO coating to improve the corrosion resistance by overlaying most pores and micro-cracks on the surface of the MAO film. Meanwhile, a double layered organic poly(dl-lactide-co-glycolide)/paclitaxel (PLGA/PTX) drug releasing coating with a top layered PLGA drug controlled releasing coating on EN plating was prepared to control the drug release rate by adjusting the different lactide: glycolide (LA:GA) ratio of PLGA. Scanning electron microscopy (SEM) and the X-ray powder diffraction (XRD) were used to analyze the morphology and the composition of the EN-plating. The corrosion behavior of the magnesium alloy substrate and the status of the drug in the PLGA matrix were respectively evaluated by Potentiodynamic polarization and Differential scanning calorimetry (DSC). The drug release was determined by ultraviolet–visible (UV–visible) spectrophotometer. EN-plating coating which was composed of compact cauliflower nodules was uniform in size and defect free with no pores or cracks. EN-plating could seal the microcracks and microholes on the outer layer of the MAO coating effectively. The corrosion resistance was improved by preventing the corrosive ions from diffusing to the magnesium alloy substrate. The drug release rate of PTX exhibited a nearly linear sustained-release profile with no significant burst releases.     

Bond strength and corrosion resistance of bioglass coated magnesium alloy fabricated by uniaxial pressing and microwave hybrid heating

Bioactive ceramics coated magnesium alloys with a combination of suitable mechanical strength and adjustable corrosion resistance are desired for biodegradable implants. In this study, a dense bioglass coated magnesium alloy was fabricated by uniaxial pressing and microwave hybrid heating technique. The microstructure, bond strength and corrosion behavior of the samples were evaluated by means of scanning electron microscopy, X-ray diffraction, tensile bond test, electrochemical and immersion test. It was shown that uniaxial pressing conducted at the glass transition temperature significantly densified the sol–gel derived bioglass coating, which was free of pores and micro-cracks. The compact coating structure combined with mild interfacial stress not only improved the cohesion/adhesion strength (25.8 ± 2.6 MPa) but also enhanced corrosion resistance by retarding the penetration of corrosive solution. Furthermore, the formed CaP precipitates on the surface of the coating would provide another protection for the magnesium alloy to some extent.     

Preparation and characterization of a new biomedical magnesium–calcium alloy

Magnesium alloys are currently used in many structural applications. It is believed that magnesium and its alloys may also find applications in biomedical fields. In this study, a new biomedical magnesium-based alloy, i.e., magnesium–calcium (Mg–Ca) has been designed from biological and metallurgical viewpoints. The microstructure, mechanical and corrosion behaviors of Mg–Ca alloys with varying calcium content were investigated. The results show that a magnesium alloy with 0.6 wt.% calcium content (denoted as Mg–0.6Ca) shows good corrosion and mechanical properties. Our preliminary results demonstrate a good potential of this Mg–0.6Ca alloy as a new biomedical material.     

The surface chemistry of 3-mercaptopropyltrimethoxysilane films deposited on magnesium alloy AZ91

Magnesium and its alloys have desirable physical and mechanical properties for a number of applications. Unfortunately, these materials are highly susceptible to corrosion, particularly in the presence of aqueous solutions. The purpose of this study is to develop a uniform, non-toxic surface treatment to enhance the corrosion resistance of magnesium alloys. This paper reports the influence of the coating bath parameters and alloy microstructure on the deposition of 3-mercaptopropyltrimethoxysilane (MPTS) coatings on magnesium alloy AZ91. The surface chemistry at the magnesium/MPTS interface has also been explored. The results indicate that the deposition of MPTS onto AZ91 was influenced by both the pH and MPTS concentration in the coating bath. Furthermore, scanning electron microscopy results showed that the MPTS film deposited uniformly on all phases of the magnesium alloy surface. X-ray photoelectron spectroscopy studies revealed that at the magnesium/MPTS interface, the molecules bond to the surface through the thiol group in an acid-base interaction with the Mg(OH)₂ layer, whereas in the bulk of the film, the molecules are randomly oriented.     

In vivo behavior of biodegradable Mg-Nd-Y-Zr-Ca alloy

The aim of the this study is to evaluate the in vivo behavior of Mg–1.5%Nd–0.5%Y–0.5%Zr implants with and without 0.4%Ca in comparison with inert Ti-6Al-4V reference implants. This was carried out by implanting cylindrical disks at the back midline of Wister male rats within the subcutaneous layer of the skin for up to 12 weeks. The degradation of magnesium-based implants in terms of hydrogen gas bubble formation was evaluated by radiography assessment; corrosion rate was analyzed by visual examination and weight loss measurements. The physiological response of the rats post-implantation was obtained by evaluating their wellbeing behavior and blood biochemical analysis including serum Mg, blood urea nitrogen, and serum creatinine. In addition, histological analyses of the soft tissue around the implants were carried out to assess local lesions relating to the implants such as inflammation, tissue necrosis, granulation, mineralization, and tumor development. The results obtained clearly indicate that apart from the normal degradation characteristics and subsequent formation of hydrogen gas bubbles, the in vivo behavior of Mg implants was adequate and comparable to that of Ti-6Al-4V reference alloy. In addition, it was evident that the corrosion degradation of the magnesium alloys was strongly related to the location of the implant within the animal’s body. The addition of 0.4%Ca improves the biodegradation corrosion resistance of the tested magnesium implants.     

物理气相沉积在镁合金表面防护领域的研究现状

镁合金表面耐腐蚀性能、耐磨性能较差,物理气相沉积(PVD)镀膜技术是一种提高镁合金表面性能的有效方法。总结了PVD镀膜防腐蚀层和耐磨层的特性,分析了涂层耐腐蚀耐磨的机理和存在的不足。综述了镁合金表面PVD膜层的研究进展,阐述了物理气相沉积技术对镁合金的表面改性的应用现状,并对该技术在镁合金上的发展进行了概括,指出了目前PVD技术在镁合金表面防护领域的新前景,为今后PVD技术对镁合金表面防护的研究与发展提供了相关参考。     

Corrosion behavior of friction stir welded AZ31B magnesium alloy with plasma electrolytic oxidation coating formed in silicate electrolyte

A protective ceramic coating of about 50 μm thick on a friction stir welded (FSW) joint of AZ31B magnesium alloy was prepared by plasma electrolytic oxidation (PEO) in silicate electrolyte. Electrochemical corrosion behavior of uncoated and coated FSW joints was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The equivalent circuits of EIS plots for uncoated and coated FSW magnesium alloy were suggested. The corrosion resistance of FSW magnesium alloy depended on microstructure of the FSW joint. The heat-affected zone with severe grain growth was more susceptible to corrosion than the stir zone and base metal. The PEO coating consisted of a porous outer layer and a dense inner layer. The inner layer of PEO coating played a key role on corrosion protection of the FSW joint of magnesium alloy. Meanwhile, corrosion potential, corrosion current density and impedance at different zones of coated FSW joint were almost the same. The PEO surface treatment significantly improved the corrosion resistance of FSW joints of AZ31B magnesium alloy.     

汽车用镁合金铈盐改性硅烷复合膜的耐蚀性

目前镁合金表面稀土-硅烷化改性多采用复合工艺,简单硅烷化处理研究较为少见。将不同含量的硝酸铈直接添加到KH-550硅烷溶液中,应用简单化学浸渍法在AZ91D压铸镁合金表面制备了铈盐改性硅烷复合膜;通过点滴腐蚀试验、全浸腐蚀试验和电化学交流阻抗谱评价了铈盐改性复合膜的耐蚀性能,利用扫描电子显微镜和椭偏仪分析了铈盐改性复合膜的表面微观形貌和厚度。结果表明:与硅烷膜相比,铈盐改性硅烷复合膜较均匀、致密、平整,厚度明显增加;随着硝酸铈含量的增加,铈盐改性硅烷复合膜的耐蚀性能先上升后下降,当硝酸铈掺杂量达到0.50 g/L时,复合膜的耐蚀性能最佳;随盐水浸泡时间的延长,复合膜的低频阻抗值先增大后减小,表明其具有一定的"自修复"能力。     

Fabrication of anticorrosive multilayer onto magnesium alloy substrates via spin-assisted layer-by-layer technique

To improve the corrosion resistance of magnesium alloy, we reported a novel approach for the fabrication of anticorrosive multilayers onto AZ91D substrates. The multilayers were composed of poly(ethylene imine) (PEI), poly(styrene sulfonate) (PSS) and 8-hydroxyquinoline (8HQ). They were deposited onto AZ91D substrates via a spin-assisted layer-by-layer (LbL) technique. The multilayered structure was stabilized with glutaraldehyde (GA) as crossing linker. It was confirmed by Fourier transform infrared spectroscopy (FT-IR). Surface morphologies and elemental compositions of the formed anticorrosive multilayers were characterized with scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), respectively. The corrosion performance of the multilayer coated AZ91D substrates was characterized by hydrogen evolution. The results of electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements suggested that the multilayered coating improved the corrosion resistance of AZ91D substrates. In vitro study revealed that the multilayered coating was cytocompatible. The study provides a potential alternative for the fabrication of corrosion resistant magnesium alloy-based implants.     

Hydrophobic epoxy resin coating with ionic liquid conversion pretreatment on magnesium alloy for promoting corrosion resistance

A hydrophobic epoxy resin coating with an environmental-friendly deep eutectic solvent(DES)-based conversion pretreatment was proposed to enhance the corrosion resistance of magnesium alloys. The hydrophobic epoxy resin coatings on the AZ31B magnesium alloy with and without the DES-based conversion pretreatment were thoroughly compared. It is found that the DES-based conversion film on the AZ31B magnesium alloy is mainly composed of MgH_2, MgO and MgCO_3. Furthermore, the conversion film possesses porous structure, which provides more anchor points for the following epoxy resin coating.However, without the DES-conversion pretreatment, the epoxy resin is difficult to be attached on the substrate during the dip-coating process. The double layered hybrid coating system promotes the corrosion resistance of the magnesium alloys significantly, which can be ascribed to the unique architecture and component including the hydrophobicity of the surface layer, the dense and interlocked epoxy resin,and the corrosion resistant DES-based conversion pretreatment.     

铝及铝合金零件镀银前化学浸锌的工艺研究

对铝及铝合金电镀工艺的难点进行了分析,通过化学浸锌前处理工艺的试验研究,确定了二次浸锌的较优工艺配方及条件为:400～500 g/L NaOH,50～80 g/L ZnO,适量添加剂,室温,第一次浸锌0.5～1.0 min,第二次浸锌0.5～1.0 min.通过外观、结合力、耐蚀性、电器焊接性能测试表明,经该工艺处理后能获得性能优良的银镀层,满足了生产需求.     

Mechanical and corrosion properties of Al/Ti film on magnesium alloy AZ31B

Preparation of titanium film on magnesium substrate faces a challenge due to non-Fickian inter-diffusion between titanium and magnesium. Aluminum can build a bridge between titanium and magnesium. Al/Ti duplex coatings were deposited on magnesium alloy AZ31B using magnetron sputtering (MS). The low temperature diffusion bonding behavior of the Mg/Al/Ti coating was investigated through SEM and its affiliated EDS. The phase structure and critical load of the coatings were examined by means of XRD and scratch tests, respectively. The results demonstrated that the bonding strength was significantly improved after a post heat treatment (HT) at a temperature of 210°C. The diffusion mechanism of the interfaces of Mg/Al and Al/Ti in the coating was discussed based on the analysis of formation energy of vacancies and diffusion rates. The Al/Ti dual layer enhanced the corrosion resistance of the alloy. And the HT process further increased the corrosion resistance of the coated alloy. This result implies that a post HT at a lower temperature after MS is an effective approach to enhance the bonding strength and corrosion resistance of the Al/Ti film on Mg alloys.     

Laser cladding of Mg-Al alloys

Among rapid solidification processing methods, laser cladding is a unique and promising technique which can be used to increase the corrosion resistance of materials. This paper describes the improvement of the laser-cladding process for magnesium-based alloys and an investigation of the effect of the laser-cladding technique upon the microstructure and the corrosion resistance of magnesium-based alloys. The cladding apparatus and techniques have been adapted for magnesium cladding to overcome the oxidation and high vapour pressurerelated problems. Laser-clad Mg₂₇Al₇₃, Mg₅₃Al₄₇, and Mg₇₂Al₂₈ have been obtained. Eutectic phases were observed in the two magnesium-rich alloys and in the interface of the aluminiumrich alloy. Polycrystalline structure was formed in Mg₂₇Al₇₃. Laser-clad Mg₂₇Al₇₃ was found to be superior to laser-clad Mg-5 wt% Zr, Mg-2 wt% Zr, cast AZ91 B and cast magnesium in corrosion properties.     

Fluoride treatment and in vitro corrosion behavior of an AZ31B magnesium alloy

As a new class of biodegradable material, magnesium alloys have attracted much attention in recent years. In order to improve the corrosion resistance, a fluoride coating was prepared on the surface of AZ31B magnesium alloy. The surface characterization analysis showed a dense coating with some irregular pores was formed. The TF-XRD analysis indicated that the coating was mainly composed of MgO and MgF₂. Electrochemical and immersion tests proved that the fluoride conversion coating significantly improved the corrosion resistance of AZ31B. Three-point bending test revealed that the degradation behavior of the fluoride treated AZ31B could meet the requirement as a biodegradable material.     

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.

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