Corrosion Rate Of Magnesium Alloy Research Articles

Preparation and characterization of dopamine-induced biomimetic hydroxyapatite coatings on the AZ31 magnesium alloy

Mg alloys have great potential in biodegradable orthopedic implant applications owing to their rapid degradation in physiological environments and mechanical properties similar to those of bone. However, the extremely high corrosion rate of magnesium alloys has also restricted their medical applications. In this work, a hydroxyapatite (HA) coating was prepared by polydopamine (PDA) induced biomimetic mineralization in a CaP solution to improve the in vitro corrosion resistance and biocompatibility of the AZ31 Mg alloy. The evolution of the phase structure, chemical composition, and surface morphology of the modified AZ31 Mg alloy substrate was evaluated by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy. Potentiodynamic polarization and hydrogen evolution tests demonstrated that the corrosion resistance of the modified AZ31 Mg alloy significantly increased compared with that of the pristine sample. Cytotoxicity testing and cell morphology analysis showed that the as-modified alloy did not induce toxic effects, and promoted the proliferation of L-929 cells. The results suggest that the dopamine-induced biomimetic apatite coating approach is of significant value in the development of biodegradable Mg alloy implants.

Preparation and Characterization of Polylactic Acid Coating on the Surface of Magnesium Alloy

Magnesium is one of the elements necessary for the body, is the man behind the body’s content of potassium ions within the cell are involved in a series of metabolic processes in vivo, including the formation of bone cells , acceleration of bone healing ability. Resulting from the good mechanical properties and biocompatibility, magnesium alloy is used in medical intervention material, but the high corrosion rate of magnesium alloys is the main drawback to their widespread use, especially in biomedical applications. There is a need for developing new coatings that provide simultaneously corrosion resistance and enhanced biocompatibility. In this work the medical magnesium alloy surface are dipped and coated with polylactic acid, so that obtain a dense uniform polylactic acid coating. And the corrosion resistance of the coating is studied in order to obtain controlled degradable and corrosion resisted magnesium alloy biological material. This paper mainly studies the influence of different concentrations of polylactic acid coating on AZ91D magnesium alloy corrosion resistance. The coated samples were immersed in Hank’s solution and the coating performance was studied by electrochemical impedance spectroscopy and scanning electron microscopy. This research is about the influence of the coating on the corrosion resistance of magnesium alloy through the open circuit potential, polarization curves, electrochemical impedance spectroscopy and Mott-Schottky. The results confirmed that the polylactic acid slow down the corrosion rate of AZ91D magnesium alloys in Hank’s solution. And along with the increase of poly lactic acid concentration, the corrosion resistance of magnesium alloys is improved. There is a wide variation of the corrosion morphology magnesium alloy AZ91D specimens after the surface modification using polylactic acid coating, compared with the unmodified.

Reducing the corrosion rate of magnesium alloys using ethylene glycol for advanced electrochemical imaging

The corrosion of an AM50 Mg alloy was studied in ethylene glycol using electrochemical and electron microscopy techniques. Switching from H2O to ethylene glycol, it was shown that the corrosion of the AM50 alloy was significantly suppressed thereby slowing H2 evolution. The corrosion of the AM50 alloy was mapped using scanning electrochemical microscopy in the feedback mode. Ferrocenemethanol can be used to expose the reactive anodic areas on the Mg alloy. These studies confirmed that studies in ethylene glycol can be used to elucidate reaction features obscured by rapid corrosion in H2O without significantly altering the mechanism and damage morphology.

Determination of the local corrosion rate of magnesium alloys using a shear force mounted scanning microcapillary method.

The successful development of scanning probe techniques to characterize corrosion in situ using multifunctional probes is intrinsically tied to surface topography signal decoupling from the measured electrochemical fluxes. One viable strategy is the shear force controlled scanning microcapillary method. Using this method, pulled quartz micropipettes with an aperture of 500 nm diameter were used to resolve small and large variations in topography in order to quantify the local corrosion rate of microgalvanically and galvanically corroded Mg alloys. To achieve topography monitoring of corroded surfaces, shear force feedback was employed to position the micropipette at a reproducible working height above the substrate. We present proof of concept measurements over a galvanic couple of a magnesium alloy (AE44) and mild steel along with a microgalvanically corroded ZEK100 Mg alloy, which illustrates the ability of shear force to track small (1.4 μm) and large (700 μm) topographic variations from high aspect ratio features. Furthermore, we demonstrate the robustness of the technique by acquiring topographic data for 4 mm along the magnesium-steel galvanic couple sample and a 250 × 30 μm topography map over the ZEK100 Mg alloy. All topography results were benchmarked using standard optical microscopies (profilometry and confocal laser scanning microscopy).

The effects of pulse electrodeposition parameters on morphology and formation of dual-layer Si-doped calcium phosphate coating on AZ31 alloy

Controlling the corrosion rate of magnesium alloys in vivo to match the bone repair is crucially important for application as biodegradable orthopedic implants. To solve this challenge, a Si-doped Ca–P coating with a novel dual-layer structure was deposited on AZ31 alloy substrate by pulse electrodeposition. The morphology, composition and formation of dual-layer coating were believed to be determined by pulse electrodeposition parameters, thus the deposition time, temperature, duty cycle, pH value of the electrolyte and the standing duration of mixed electrolyte were regulated to seek possible influences and mechanism on the coating formation. Weight gain and pH monitoring tests were also used to evaluate the performance of coating under the varied parameters. The results indicated that deposition temperature and time remarkably influenced the morphology, homogeneity and crystallinity of Ca–P coating. A uniform and compact coating with better degradation performance was obtained at 60°C with deposition time of 40min. The shorter standing duration of the electrolyte lead to an incomplete coating and uneven distribution of Si contents. The two coupled deposition models contributed to this dual-layer structure of Si-doped Ca–P coating and possible formation mechanism was proposed.

Influence of proteins and cells on in vitro corrosion of Mg–Nd–Zn–Zr alloy

The influence of proteins and primary human umbilical vein endothelial cells (HUVECs) coculture on in vitro corrosion of Mg–Nd–Zn–Zr alloy is investigated in this study. Protein supplemented in cell culture medium slows down the corrosion rate of magnesium alloy, while cell coculture accelerates it. Corrosion surface composition is studied using XPS. The Mg–Nd–Zn–Zr alloy shows no adverse effects on cell viability and apoptosis. The mechanisms how proteins and cells affect magnesium alloy corrosion are also discussed.

Formation of bioactive anticorrosion coatings on resorbable implants by plasma electrolytic oxidation

Calcium phosphate coatings (Ca/P = 1.61) containing magnesium oxide MgO and hydroxyapatite Ca10(PO4)6(OH)2 accelerating the growth of bone tissue have been prepared by the method of plasma electrolytic oxidation (PEO) on MA8 magnesium alloy. The phase and element compositions, morphology, and anticorrosion properties of coatings were investigated. Such PEO layers were found to essentially reduce the corrosion rate of magnesium alloy (polarization resistance being increased by two orders). This makes it possible to consider the formed PEO coatings as likely anticorrosion layers for medical bioresorbable implants.

In vitro degradation of AZ31 magnesium alloy coated with hydroxyapatite by sol–gel method

In recent years, magnesium and its alloys have been proposed as a new class of metallic bioabsorbable implant material. Unfortunately, the rapid corrosion rate of magnesium alloys could result in the accumulation of the hydrogen gas and the reduction in the mechanical properties before the healing of bone tissue. It is necessary to develop biocompatible coatings to delay the degradation rate. In the present research, hydroxyapatite coatings are successfully deposited on AZ31 magnesium alloy by sol–gel technique to slow down the degradation and improve the bioactivity. The structure, composition and chemical states of the sol–gel coatings are characterised by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The bonding strength, corrosion behaviours and hydrogen evolution rate of the samples are also studied. The results show that improving the heat treatment temperature can improve the corrosion resistance and the bonding strength between the coating and the substrate. The degradation rate of the samples reduces with improving heat treatment temperature. However, the lowest hydrogen evolution rate is still much higher than the tolerated level of human body. Because of the low melting point of magnesium alloy, it is difficult to reduce the hydrogen evolution rate to the tolerated level of human body only by improving the heat treatment temperature.

Combined anodizing and picosecond laser treatment to control the corrosion rate of biodegradable magnesium alloy AZ31

The corrosion rate of magnesium alloys is generally too high for biodegradable implant applications. This work explored combinations of anodizing and picosecond laser surface treatments to modify the corrosion response of magnesium alloy AZ31. Anodizing of the AZ31 in NaOH solutions produced porous oxide layer structures. Shallow laser treatment of these anodized surfaces, using low pulse powers, resulted mainly in oxide ablation and impaired corrosion resistance. Higher pulse power, resulting in rapid melting and resolidification into the substrate, provided an improved corrosion response. The refined grain structure produced is approximately only 5 µm deep and therefore has minimal influence on bulk mechanical properties. It is therefore a suitable process for surface modifications on small medical device structures. Controlling the initial point of degradation has been demonstrated by the use of selective laser treatment of the AZ31 surface.

Corrosion resistance of a composite polymeric coating applied on biodegradable AZ31 magnesium alloy

The high corrosion rate of magnesium alloys is the main drawback to their widespread use, especially in biomedical applications. There is a need for developing new coatings that provide simultaneously corrosion resistance and enhanced biocompatibility. In this work, a composite coating containing polyether imide, with several diethylene triamine and hydroxyapatite contents, was applied on AZ31 magnesium alloys pre-treated with hydrofluoric acid by dip coating. The coated samples were immersed in Hank’s solution and the coating performance was studied by electrochemical impedance spectroscopy and scanning electron microscopy. In addition, the behavior of MG63 osteoblastic cells on coated samples was investigated. The results confirmed that the new coatings not only slow down the corrosion rate of AZ31 magnesium alloys in Hank’s solution, but also enhance the adhesion and proliferation of MG63 osteoblastic cells, especially when hydroxyapatite nanoparticles were introduced in the coating formulation.

Influence of Edge Effects on Local Corrosion Rate of Magnesium Alloy/Mild Steel Galvanic Couple

The effect of the insulator-mixed-material edge on the galvanic corrosion rate of magnesium alloy (AE44)-mild steel (MS) couple is experimentally studied using scanning vibrating electrode technique (SVET), profilometry, and classical electrochemistry. The local and average corrosion rates estimated from the experimental depth of anodic attack profile of AE44-MS couple are validated by 2D and 3D corrosion numerical models. Our study demonstrates experimentally and theoretically that the presence of the insulator edge increases the local current density, which enhances the corrosion rate. The extent of the local corrosion rate enhancement and its effect on the overall corrosion rate of the mixed material is discussed and depends on the mixed material's geometry and the edge type.

Anti-corrosion performance of a new silane coating for corrosion protection of AZ31 magnesium alloy in Hank's solution

Mg alloys can be used as bioresorsable metallic implants. However, the high corrosion rate of magnesium alloys has limited their biomedical applications. Although Mg ions are essential to the human body, an excess may cause undesirable health effects. Therefore, surface treatments are required to enhance the corrosion resistance of magnesium parts, decreasing its rate to biocompatible levels and allowing its safe application as bioresorbable metallic implants. The application of biocompatible silane coatings is envisaged as a suitable strategy for retarding the corrosion process of magnesium alloys. In the current work, a new glycidoxypropyltrimethoxysilane (GPTMS) based coating was tested on AZ31 magnesium substrates subjected to different surface conditioning procedures before coating deposition. The surface conditioning included a short etching with hydrofluoric acid (HF) or a dc polarisation in alkaline electrolyte. The silane coated samples were immersed in Hank's solution and the protective performance of the coating was studied through electrochemical impedance spectroscopy (EIS). The EIS data was treated by new equivalent circuit models and the results revealed that the surface conditioning process plays a key role in the effectiveness of the silane coating. The HF treated samples led to the highest impedance values and delayed the coating degradation, compared to the mechanically polished samples or to those submitted to dc polarisation.

Comparison of biodegradable behaviors of AZ31 and Mg–Nd–Zn–Zr alloys in Hank's physiological solution

The main challenge for the application of magnesium and its alloy as degradable biomaterials lies in their high degradation rates in physiological environment. In the present work, the biodegradable behavior of a patent magnesium alloy Mg–Nd–Zn–Zr (JDBM) and a reference alloy AZ31 was systematically investigated in Hank's physiological solution. The corrosion rate of JDBM (0.28 mm/year) was much slower than that of AZ31 (1.02 mm/year) in Hank's solution for 240 h. After corrosion products were removed, smooth surface of the JDBM was observed by SEM observation compared to many deep pits on the surface of AZ31. Open-circuit potential and potentiodynamic polarization results manifested that pitting corrosion did not occurred on the surface of JDBM at the early period of immersion time due to the formation of a more protective and compact film layer suggested by electrochemical impedance spectroscopy study. The corrosion rate of magnesium alloys was found to slow down in dynamic corrosion in comparison with that in the static corrosion. This provided the basis for scientific evaluation of in vitro and in vivo corrosion behavior for degradable biomagnesium alloy. The present results suggest that the new patent magnesium alloy JDBM is a promising candidate as degradable biomaterials and is worthwhile for further investigation in vivo corrosive environment.

Evaluation of corrosion resistance of magnesium alloys in radiator coolants

Coolant corrosion is a major drawback for the use of magnesium alloys in engine and cooling system, but the coolant is not normally intended to prevent corrosion of magnesium alloys. This research assessed the corrosion performance of two magnesium alloys, AZ91D and AM50A, in two newly formulated radiator coolants using immersion test, potentiodynamic polarisation test, and corroded surface analysis. Two coolants were named as Irgacool Plus L and Irgacool Plus S. C7, C8-organic acids and polycarboxylic acid were the main inhibitor species in Irgacool Plus L while Irgacool Plus S was formulated with C7, C8-organic acids and sebacic acid inhibitors. Corrosion rates of magnesium alloys decreased twice in Irgacool Plus L compared with Irgacool Plus S. AZ91D alloy had better corrosion resistance than AM50A alloy in both radiator coolants. Both alloys suffered corrosion due to microgalvanic coupling between cathodic β-Mg17Al12 intermetallic and anodic α-Mg matrix, and the presence of Al8Mn5 and Al11Mn4 intermetallics in AM50A led to further microgalvanic corrosion. A continuous network of β-Mg17Al12 phase and higher Al content α-Mg matrix accounted for better corrosion resistance of AZ91D alloy.

The History, Challenges and the Future of Biodegradable Metal Implants

New interest in magnesium alloys as temporary biomaterials was reborn in the recent years. Especially metals based on physiological trace elements seem to be promising as an alternative to current biodegradable implant materials in cardiovascular and musculoskeletal applications. First clinical reports can be dated back before 1900. Magnesium alloys were used by surgeons of different clinical background in cardiovascular, neural, skin, general and musculoskeletal surgery. All patients have benefited from the treatment with magnesium alloys, although rapid corrosion caused sometimes painless subcutaneous gas cavities. These reports encouraged researchers to study and invent new magnesium alloys which aim to provide more uniform and slow corrosion rates. The most challenging part was to analyze the corrosion of implanted magnesium alloys in-vivo, since the magnesium alloys interlock with the surrounding tissue during corrosion. Therefore, the implanted samples could not be retrieved without damaging the fragile implant-tissue interface. Synchrotron-radiation based microtomography (SRµCT) was introduced as a solution to this challenge. SRµCT enables to measure non-destructively the in-vivo corrosion rates of magnesium alloys as well as their corrosion morphology. Based on these data, it was concluded that suitable magnesium implants should provide small grains, which are distributed very homogenously and should be produced with highest purity. The future of biodegradable magnesium alloys might be directed towards implant areas where high ductility, maximal tensile strength as well as high compression strength is needed and the properties of current biodegradable implant-materials are exceeded by the properties of magnesium alloys.

Biocorrosion behavior of magnesium alloy in different simulated fluids for biomedical application

The biocorrosion behavior of a magnesium alloy in two simulated body solutions, Hank's solution and simulated blood plasma (SBP) solution was investigated by electrochemical and weight loss testing for biomedical application. The solution volume/surface area (SV/SA) ratio was changed to reveal the effect of immersion condition on the biocorrosion behavior. A same tendency was observed in the corrosion rate of magnesium alloy in all testing conditions: a high corrosion rate at the initial stage, and rapid decrease in the first 2–3 days followed by a stable corrosion rate in the following stage. A higher corrosion rate was observed in Hank's solution than in SBP solution due to high Cl −, low Ca 2+ and PO 4 3− concentration in Hank's solution. However, no difference in the surface reaction product was observed between the samples immersed in Hank's solution and in SBP solution. It was found that the SV/SA ratio significantly affected the corrosion rate of magnesium alloy. Low ratio resulted in a high pH, which resisted the corrosion. But when the ratio was high enough, 6.7 for example, the influence was negligible. By changing the ratio, the biocorrosion behavior of magnesium implant in different implantation sites can be simulated, for example, low ratio for the case of in muscle and high ratio for the case of in marrow cavity. It is suggested that selection of the simulated solution and the SV/SA ratio would be very necessary to simulate different the in-vivo biodegradation behavior of magnesium in different implantation environment.

In vitro and in vivo corrosion measurements of magnesium alloys

The in vivo corrosion of magnesium alloys might provide a new mechanism which would allow degradable metal implants to be applied in musculo-skeletal surgery. This would particularly be true if magnesium alloys with controlled in vivo corrosion rates could be developed. Since the magnesium corrosion process depends on its corrosive environment, the corrosion rates of magnesium alloys under standard in vitro environmental conditions were compared to corrosion rates in an in vivo animal model. Two gravity-cast magnesium alloys (AZ91D, LAE442) were used in these investigations. Standardized immersion and electrochemical tests according to ASTM norms were performed. The in vivo corrosion tests were carried out by intramedullar implantation of sample rods of the magnesium alloys in guinea pig femura. The reduction in implant volume was determined by synchrotron-radiation-based microtomography. We found that in vivo corrosion was about four orders of magnitude lower than in vitro corrosion of the tested alloys. Furthermore, the tendency of the corrosion rates obtained from in vitro corrosion tests were in the opposite direction as those obtained from the in vivo study. The results of this study suggest, that the conclusions drawn from current ASTM standard in vitro corrosion tests cannot be used to predict in vivo corrosion rates of magnesium alloys.

Effect of LaCl3 on the Structure and Properties of Magnesium Alloys

By use of the Zwick electronic universal material testing machine, X-ray diffractometer, SEM, EDX, image analyzer and corrosion test, the effects of LaCl3 on the mechanical properties, structure, fractography and corrosion behavior of magnesium alloy have been studied. The results show that minute nodular Al10La2Mn7 phases can be formed in Mg melts after fluxes containing LaCl3 are added to Mg melt. The Al10La2Mn7 phases can act as the nucleating site of γ phases, and the γ phases can be refined. With the flux containing 5% LaCl3, the σb and δ of the Mg alloy can be improved from 161MPa and 2.1% to 203MPa and 4.0% by 26% and 100%, respectively. The corrosion rate of magnesium alloys can decrease from 1.10 mg/(cm2.d) to 0.17 mg/(cm2.d) by 84% with the use of flux containing 5% LaCl3. Rare earth (RE) elements are often added to the magnesium alloy to improve the alloy structure and the room or elevated temperature mechanical properties. But up to present, the RE elements added to Mg melt is often in the form of pure RE alloy or RE master alloy [1]. Because RE is the oxidizable material, this kind of adding process often leads to low RE utilization ratio and high use-cost. Besides, this process can easily induce segregation of RE and the appeared coarse RE phases will lower the Mg alloy mechanical properties. By far, there is few research reports about RE contained compound added to Mg alloy melt. In this paper, the effects of Lanthanum chloride (LaCl3) on the structure and mechanical properties of Mg alloy are studied for the first time. The aim is to explore a new way to improve the Mg alloy properties.

ＡＺ９１Ｄマグネシウム合金の腐食速度に及ぼす塩素の影響

Chlorine is considered influential in the corrosion of magnesium alloys, however, there are few reports which describe the effects of chlorine quantitatively. In this report the relationship between chlorine content and corrosion rate of magnesium alloys was made clear. Firstly, the discussion was made how to obtain HPDC magnesium samples containing chlorine. The samples were obtained by adding powder flux containing MgCl2 in a ladle before injection. Corrosion rate was measured by means of Salt Spray Test. The relationship is formulated in the following equation: Corrosion rate (mg•dm-2•h-1)=1.04+1.92× chlorine content (%) Humid Box Test showed similar results.

冷却池中におけるマグネシウム合金被覆の腐食

To study the corrosion of magnesium alloy cladding in spent fuel cooling pond, the effect of pH, the temperature of the water and also of the contact with dissimilar metals were investigated. The results show that the general corrosion of magnox A-12 alloy in tap water and the occurrence of pitting corrosion can be suppressed by keeping the pH of the water higher than 12 by the addition of caustic soda, and that the contact corrosion of magnox with zirconium or stainless steel can be inhibited by increasing the pH of the water. This inhibitive action of alkali addition to the water is not affected by the dissolution of small amount of carbon dioxide from air or of chloride salt from sea water.Though the corrosion rate of magnesium alloy increased appreciably by elevating the temperature from 20° to 70°C, the penetration rate even at the temperature of 70°C was only 0.040.06 mm/6 months and pitting corrosion was not observed.