Corrosion Behavior Of Mg Alloy Research Articles

Comparing the Corrosion Behavior and Microstructure of a WE43 Mg Alloy in Simulated Body Fluids Under Different CO2 Conditions

With the low density and high specific strength, magnesium (Mg) alloys are lightweight alloys with various applications. In addition, combined with biocompatibility, similar mechanical properties to human bones, and unique biodegradability, Mg alloys are promising biodegradable implant materials for orthopedic surgeries. However, the degradation rates of Mg alloys are too fast in physiological environments, which limits the clinical applications of Mg implants. Therefore, understanding the corrosion behavior in physiological environments is crucial for developing biodegradable Mg alloys.During Mg alloy degradation, hydroxide (OH-) ions are generated, and the pH near the alloy surface increases. Since carbonate-bicarbonate (CO3 2--HCO3 -) is a vital pH buffer system in the human body, the corrosion behavior of Mg alloys would be affected by the CO2 concentrations of the test environments. In this study, we performed electrochemical and corrosion tests of a solution heat-treated WE43 (Mg-4 wt%Y-3 wt%Nd) alloy in Hanks’ balanced salt solutions (HBSS) at 37°C. By performing the tests in air and in an incubator maintained at 5% CO2, the effect of carbonate-bicarbonate pH buffering on the corrosion behavior and corrosion microstructure of the WE43 Mg alloy was investigated.When testing the WE43 Mg alloy in air, a general corrosion morphology was observed during the 24-hour immersion. In contrast, WE43 Mg alloy tested in the incubator shows a more active surface potential and localized corrosion initiates on the alloy surface in the early stages of immersion. Electrochemical impedance spectroscopy (EIS) analysis shows that WE43 Mg alloy tested in air has better corrosion resistance than in the incubator. Furthermore, the corrosion resistance of the alloy tested in air increases with immersion time but decreases when tested in the incubator. Potentiodynamic polarization curves after 24-hour immersion confirm that the corrosion current density (i corr) of the WE43 Mg alloy tested in the incubator is higher than that when tested in air. The difference in corrosion behavior is owing to the carbonate-bicarbonate pH buffering effect and will be discussed based on corrosion microstructure characterizations. Figure 1

The uniform corrosion of biodegradable Mg alloy induced by protein addition in Hanks’ balanced salt solution

The localized corrosion caused by the interphase potential differences and incompleteness of the corrosion product layer results in the premature failure of Mg alloys. In biomedical applications, understanding about the corrosion behavior of Mg alloys in complex environment is still insufficient. In this work, mechanical tests after corrosion were employed to indirectly but generally reflect the localized corrosion of Mg alloy in the protein-containing electrolytes. The results reveal that protein alters the Mg corrosion mode to uniform corrosion and an appropriate amount of protein is beneficial for maintaining its mechanical bearing capacity. This work is helpful for understanding the corrosion behavior of Mg alloys and consummating degradation evaluation systems for Mg alloys.

CORROSION PREDICTION OFMAGNESIUM IMPLANT USING MULTISCALE MODELING BASED ON MACHINE LEARNING ALGORITHMS

Significant thoughtful research is really necessary to improve the patient outcomes and reduce the social and financial burdens associated with implant failure. The primary focus of the researchers is to minimize the major implant failure due to corrosion attributed to making orthopedic surgery safer and more effective. Hence, a critical review has been done in this present article on the various multiscale modelings based on machine learning algorithms (MLAs) to predict the corrosion behavior of magnesium (Mg) alloy implants. According to the best of the authors' knowledge, all the available multiscale modelings tools, such as artificial neural network (ANN), least absolute shrinkage and selection operator (LASSO) regression model, multiple linear regression and random forest regression (RFR) models, etc., are methodically presented and discussed in detailed here for the prediction of corrosion mechanism. Subsequently, various multiscale model tools and assessment metrics for models have been thoroughly compared and criticized for better understanding and optimizing of the corrosion behavior of implants. The comparison indicates that the RFR model may be the best option, whereas the LASSO regression model and ANNs show inefficient performance for the prediction of corrosion behavior. Apart from the multiscale modeling approach, the authors have also explored the physiology and properties of alloys, bone implant, immune and tissue system, and the corrosion control mechanisms of Mg alloy. Finally, the present review on multiscale modeling approach and assessment metrics models will enhance the knowledge and understanding of the corrosion behavior of Mg alloy for implant application.

Prediction of electrochemical corrosion behavior of magnesium alloy using machine learning methods

The corrosion of magnesium (Mg) alloys is a major challenge in many industrial applications because of their extreme reactivity, this greatly limits their applicability. The traditional methods in the prediction of corrosion rate depend on experimental or empirical models that can be time-consuming and expensive. Besides how to integrate experiments with faster machine-learning approaches is still a challenge of research. In recent years machine learning (ML) algorithms have proved and promised better magnesium corrosion predictability. In this study, different training algorithms such as linear regression (LR), decision tree (DT), extra tree (ET), random forest (RF), K-nearest neighbor (KNN), extreme gradient boosting (XGBoost), and Artificial Neural Network (ANN) were used to develop and predict corrosion rate of magnesium alloys based on magnesium chemical alloy composition as independent input variables. The data used for model preparation and validation were obtained from literature and experimental studies respectively. The feature selection methods were used to identify the most important and influential input parameters for magnesium alloy thus Shapley Additive Explanations (SHAP) interpretation was employed in this manuscript to facilitate feature visualization of the model. The results of the study show that the random forest (RF) algorithm has the greatest prediction impact than other machine learning algorithms. The magnesium alloy corrosion prediction model provides a better ability for the prediction of magnesium corrosion alloys. The study demonstrates the potential of ML models in the prediction of the corrosion behavior of Mg alloys and these models can be used to optimize an alloy composition for designing improved corrosion resistance of new Mg alloys.

Understanding the Effect of Electrochemical Properties and Microstructure on the Microgalvanic Corrosion of Mg Alloys via Phase-Field Simulations

In this work, we apply a phase-field model to gain insights into the corrosion behavior of Mg alloys. Specifically, we study the effect of electrochemical properties of the materials and their environment and the spatial distribution of second phases in a magnesium alloy. To this end, we perform sensitivity analyses in which we separately vary the exchange current density and corrosion potential of the second phase, as well as the electrolyte conductivity. We describe the effects of these parameters on the corrosion current and the resulting corrosion-front morphology. We also confirm that the ratio between the Wagner length, calculated for the anodic phase, and the initial width of the anodic domain is a good predictor of the morphological characteristic of the corroding surface. In addition, we examine the effect of the microstructure on the corrosion behavior in both 2D and 3D systems by varying the shape, size, and distribution of the second-phase regions. Our findings provide insights into the influence of the two-phase microstructure on the corrosion behavior in a magnesium alloy.

Effect of the microstructure parameters on the mechanical properties and corrosion behavior of Mg alloys with high Zn or Ca content

Effect of the microstructure parameters on the mechanical properties and corrosion behavior of Mg alloys with high Zn or Ca content

The inhibition effect of etidronate on degradation behavior of Mg–Zn–Y-Nd-Zr alloy

The control of corrosion behavior of Mg alloys for biomedical applications is a research hotspot in the field of biodegradable metallic implant materials. In recent years, the employment of corrosion inhibitors for regulating the corrosion behavior of Mg alloys has attracted attention. In this work, a promising corrosion inhibitor for Mg alloys, Etidronate (ETN), was selected from the drugs for the treatment of osteoporosis, and its effect on the corrosion behavior of Mg–Zn–Y-Nd-Zr (ZE21C Mg alloy) in simulated body fluids was systematically studied. The results show that ETN not only reduces the corrosion rate of the alloy, but also significantly weakens its tendency of localized corrosion, which is beneficial for improving the service reliability of Mg alloy for orthopedic application. This study provides an idea for corrosion control of biodegradable Mg alloys and is of great significance for promoting their development and applications.

Insight of the role of cooling method and soil environment on the corrosion behavior of Mg–2Nd alloys

Understanding the corrosion behavior of Mg alloys in the soil environments is crucial to preventing catastrophic accidents in their facilities due to the soil corrosion. The Mg–2Nd alloys were exposed to the soil after cooling in different ways under the same heat treatment conditions. The corrosion mechanisms of Mg–2Nd alloy in the soil are mainly affected by corrosion micro-batteries and macro-batteries. The more precipitates, the more severe micro-galvanic corrosion are formed. Meanwhile, the corrosion product films are damaged by micro-galvanic corrosion, which have a serious impact on the differential concentration of oxygen and differential infiltration of rainwater corrosion. The Mg–2Nd alloy buried in the soil with high water content and low oxygen permeability in corrosive macro-batteries will be corroded into anodes, thereby accelerating the corrosion rate of Mg–2Nd alloy in this part. Furthermore, the formation of corrosion product MgCO3 reduces the electrochemical activity of the sample surface, thereby reducing the corrosion rate of Mg–2Nd alloy in the soil. Therefore, the Mg–2Nd alloy after water-cooling has the best corrosion behavior in the soil environment.

First-principles calculation and experimental study on the effect of rare earth Ce and Nd on the corrosion behavior of Mg alloys

In this study, the influence mechanism of rare earth elements Ce and Nd on the corrosion behavior of Mg alloy was studied by combining experimental characterization with the first-principles calculation. The changes of work function and surface energy of the rare Earth phase and matrix phase in binary rare Earth Mg alloys Mg-0.3%Ce and Mg-0.3%Nd. In addition, the electronic properties of the second rare Earth phase and matrix phase, and the correlation between the interface energy of the second rare Earth phase and matrix and the corrosion behavior of Mg alloys were investigated. The experimental results show that Mg12Ce and Mg12Nd as the second phases of Mg-0.3%Ce and Mg-0.3%Nd, respectively, have not obvious roles in the galvanic corrosion of the alloys. The corrosion morphology of the two alloys is similar, the matrix undergoes filamentary corrosion through the grain to a large area. The results of the first-principles calculation show that the binding energy of the rare Earth phase is higher than that of the matrix phase, this implied the addition of light rare Earth elements Ce and Nd can improve the stability of the second phase. The work function of different surfaces of the second phase is similar to that of the matrix phase, so limited effect of the rare Earth phase on corrosion behavior has been found. In addition, the addition of rare Earth Ce and Nd will decrease the surface stability of Mg matrix, this result reaffirms the higher corrosion rates of Mg-0.3%Ce and Mg-0.3%Nd over that of the pure Mg.

Effect of galvanostatic anodic polarization on hydrogen evolution rate and residual fatigue strength of Mg alloys for implant use

For surgery, biodegradable magnesium alloys are considered promising candidates. The low corrosion resistance is advantageous since the implant is degraded in the presence of aqueous body fluids, supporting the human bone for a defined time and be fully degraded after this functional phase, making a second surgery for implant removal unnecessary. To design this phase and prevent early implant failure, precise knowledge of the degradation behavior over months and the correlating mechanical stability is essential. In vitro tests of the required duration are associated with enormous time and cost efforts. Therefore, a short-time method is developed to accelerate the degradation progress by anodic polarization without affecting the corrosion mechanism. The method is based on the corrosion behavior of Mg alloys under polarization, accompanied by increasing hydrogen evolution for increasing current densities, allowing conclusions to be drawn about the corrosion rate. Three-week immersion tests of the alloy WE43 with and without plasma electrolytic oxidation are the starting point. The time-dependent corrosion rates are to be reproduced by applying anodic polarization within three days. An experimentally determined relationship between current density and corrosion rate is used to design the polarization. The corrosion morphology of both testing strategies is analyzed by µCT. To evaluate the influence of the morphology on the mechanical stability, ex situ multiple amplitude tests are performed, allowing an estimation of the residual fatigue strength. The results show that a qualitative simulation of the hydrogen evolution rate is possible by applying polarization, achieving an enormous time saving. Due to a changed corrosion morphology with increased pitting tendency and the associated reduced residual fatigue strength, the method has to be considered as a worst-case evaluation allowing to exclude unsuitable Mg-based biomaterials right from the beginning, in particular before further preclinical studies.

Dual-functional coatings on magnesium alloys: Enhancing corrosion behavior under stress and osteogenic effect in osteoporotic rats

Magnesium-based implants are subjected to complicated stresses during implantation in the human body. In this case, they undergo stress-induced corrosion and usually lead to early breakage or disintegration of implants. Calcium phosphate compounds have been used as coatings, bone cement and drug carrier in orthopedic application. Their success has been expanded to Mg alloys. Calcium phosphate-based coatings succeeded in corrosion control and osteointegration of Mg alloys in a big extent. However, their protective effect under stress condition is questionable considering the brittle nature. With the assistance of high pH microenvironment near Mg alloy surface, calcium phosphate coatings have the self-repair potential via the dissolution-precipitation mechanism. Inspired by this phenomenon, strontium doped hydroxyapatite (Sr-HA) coatings with higher solubility have been prepared on the surface of Mg alloys. Sr-HA coatings served as not only a physical barrier effect to postpone pitting formation, but also provide ion supplement to seal the cracks initiated during tensile deformation. The results obtained in slow strain rate tensile test (SSRT) demonstrated improved corrosion and mechanical behaviors of Sr-HA coated Mg alloys. Specifically, the elongation of Sr-HA coated alloy increased by 56.7 and 35.2% as compared to the bare and HA coated one in DMEM. In ovariectomized rats, the implants exhibited only 2.7–5.6% reduction of implant volume after 12 weeks implantation. Sr-HA coating further increased early new bone formation than HA coated implants. 12 weeks post-implantation, a large amount of bony tissue with higher trabecular thickness and hardness was formed adjacent to the Sr-HA coated implants. This study demonstrated the efficiency of a rapid dissolved Sr-HA coating on the corrosion behavior of Mg alloys under mechanical loading and the osteogenesis in ovariectomized rats. It therefore holds a promising practical significance for the future coating design strategy for Mg alloys when trying to expand their application range to locations with higher loading conditions.

Effect of stray current on corrosion behavior of Mg alloy sacrificial anode in buried pipeline

In this work, a self-designed stray current simulated system was employed in corrosion evaluation test, and the effect of stray current on corrosion behavior of Mg alloy was investigated. The anti-corrosion performance of Mg alloy directly related to its corrosion film. The corrosion film covered on Mg surface was incomplete, which was a mixture of porous MgO + Mg(OH)2, and the corrosion happened on the bare Mg substrate at the rupture of corrosion film. The pitting corrosion randomly occurred on α-Mg, and the anodic hydrogen evolution (AHE) further damaged the corrosion film. With the extension of time, the pits developed into severe localized corrosion and the corrosion rate was accelerated. The stray current was composed of direct current (DC) and low-frequency alternating current (AC), which promoted the rupture of corrosion film, hence the stray current significantly accelerated the corrosion rate of Mg alloy.

Roles of the heat treatment on the Mg-Nd phases and corrosion mechanisms of Mg-4Nd alloy under sulfuric acid type acid rain

Mg alloys are widely used in the fields of aerospace, automotive, and electronic communication equipment. Understanding the corrosion behavior of Mg alloys is critical to prevent their catastrophic failures from the acid rain corrosion. The influences of heat treatment on corrosion behaviors of Mg-4Nd alloy in acid rains were investigated. The corrosion mechanisms of Mg-4Nd alloy are dominated by electrochemical and chemical corrosion, and the corrosion behaviors of Mg-4Nd alloy are affected by the concentrations of acid rain and heat-treated temperatures. Furthermore, Nd2O3 are derived from the oxidation of exposed Nd atoms at the edge of precipitates and solid-solution atoms.

Effect of crystallographic texture and twinning on the corrosion behavior of Mg alloys: A review

Magnesium and its alloys have gained significant popularity due to their light weight and their potential for use as bioresorbable materials. However, their application is limited in practice due to their relatively poor corrosion resistance. Several methods are available for improving the corrosion resistance of Mg alloys for bio-applications such as using different coatings, alloying, and modifying the microstructural parameters such as the grain size and the crystallographic texture. This review provides a comprehensive summary of the effects of crystallographic texture and twinning, as one of the most important deformation mechanisms of Mg and Mg alloys, on the corrosion behavior. Regarding the crystallographic texture, it is shown that theoretically the basal planes should exhibit a lower corrosion rate but in some cases, such as when there is a galvanic effect or when corrosion films control the overall corrosion behavior, different results may take place. Also, there are contradictory results concerning the effect of twinning on the corrosion behavior. Thus, in some cases twinning may provide preferential sites for corrosion due to the higher energies of atoms located in the twin region by comparison with normal atomic positions in the crystalline lattice whereas there are also other examples where experiments show that twins produce more protective films than in the surrounding matrix.

Influence of tensile twinning on electrochemical and corrosion behavior of Mg alloy

Influence of tensile twinning on electrochemical and corrosion behavior of Mg alloy

Quantitative analysis on surface potentials of impurities and intermetallic compounds dispersed in Mg alloys using scanning Kelvin probe force microscopy and ultraviolet photoelectron spectroscopy

It is well known that metallic impurities such as Fe, Cu, and Ni cause galvanic corrosion of Mg alloys because of the local cells formed at the interface between these impurities and the Mg matrix. The alloying elements of Mg alloys, such as Al, Mn, Si, and Ca, exist as intermetallic compounds (IMCs) to enhance their mechanical properties. On the other hand, some of these metallic impurities and IMCs influence the galvanic corrosion. In this study, the effects of secondary phases such as impurities and IMCs on the galvanic corrosion behavior of Mg alloys were quantitatively evaluated using the surface potential difference at the interface measured through scanning Kelvin probe force microscopy and ultraviolet photoelectron spectroscopy. Bulk IMC samples were successfully fabricated from the elemental mixture powder by solid-state sintering method based on powder metallurgy process. The correlation between the work functions and surface potentials of the impurities and IMCs was experimentally and theoretically investigated.

Microstructural, Thermal and Corrosion Characterization of Friction Stir Welded Magnesium Alloys

The requirement for structural materials with demanding properties is always a major concern among automotive researchers. Magnesium alloys possess the required properties. In this work magnesium alloys, AZ31B and AZ91B were joined by friction stir welding. The influence of process parameters on the weld properties has been studied. The process parameters were tool rotational speed, welding speed, tilt angle. Three different combinations AZ31B-AZ91B, AZ31B-AZ31B and AZ91B-AZ91B were friction stir welded. Non-destructive tests have been performed on the welded joints as the primary analysis. After mechanical testing, optical microscopic examination comprising of macrostructure analysis, microstructure analysis and SEM analysis were carried out on selected specimens and the results are formulated. The corrosion behavior of Mg alloys has been tested using a salt spray test. The thermal behavior was studied using thermogravimetric and differential thermal analysis. The joints were friction stir welded with maximum efficiency where grain refinement was observed in the weld microstructure of dissimilar alloys and the elongated grains was recrystallized. This paper primarily focuses on the microstructural aspects, corrosion performances and TG/DTA analysis.

Biodegradable Mg alloys for orthopedic implants – A review

The last decade has seen a significant growth in the market for alloys used for implants, especially for those intended for orthopedic implants. Research into biodegradable magnesium-based alloys has made great strides in this period, so huge progress has been made in their use in the medical industry. The important factors that led to the intensification of research in this regard, were social but also economic, wanting to improve the quality of life, by reducing the use of conventionally permanent metallic implants (stainless steel, cobalt-based alloys, and titanium alloys) which involve the second implant removal surgery and other undesirable effects (stress shielding and metal ion releases), with a negative impact on the emotional and physical condition of patients, and by significantly reducing the costs for both the patient and the health system in the field of orthopedics. This paper refers to the impact and importance of biodegradable Mg alloys, reviewing the beginning of their development, the significant characteristics that make them so desirable for such applications (orthopedic implants) but also the characteristics that must be modulated (corrosion rate and mechanical properties) to arrive at the ideal product for the targeted application. It highlights, in detail, the mechanism and aspects related to the corrosion behaviour of Mg alloys, electrochemical characterization techniques / methods, as well as strategies to improve the corrosion behaviour and mechanical properties of these types of biodegradable alloys. The means of optimization, the category and the effect of the alloying elements, the design criteria, the requirements that the implants of biodegradable alloys Mg-based must meet and the aspects related to their efficiency are also presented. Finally, the potential applications in the specialized clinics, as well as the final products currently used and made by important prestigious companies in the world are approached.

Elucidation of the Growth of Filiform Corrosion of AZ91D Mg Alloy in NaCl Solution

Magnesium (Mg) is the lightest structural metallic material with high specific strength. Mg alloys are highly expected to be applied in electronic, automotive vehicles and aerospace, etc. The most severe drawback of Mg and its alloys is corrosion susceptibility. When Mg alloys are used in chloride solutions, filiform corrosion sometimes occur. Being a common practice in the research of Mg corrosion, galvanostatic tests allow for easy comparison of the rate of hydrogen evolution with the applied current. But there are scarce studies reported about the in situ observation of filiform corrosion behavior of Mg alloys under galvanostatic polarization. The purpose of this study is to elucidate the growth of filiform corrosion of AZ91D Mg alloy in NaCl solutions by in situ observation.An ingot of AZ91D die-cast was cut into 25 mm × 30 mm × 5 mm sheets. The specimen surface was polished to 2000 grit with SiC paper and finished with a 0.25 µm diamond paste, followed by ultrasonically cleaning in ethanol. To confirm the metallographic structures, the sample was etched with a mixed reagent of 3 mL HNO3 and 80 mL of ethanol for 3 s. Galvanostatic polarization was performed using a micro electrochemical system with an in situ observation function. The electrolytes used were naturally aerated 0.1 M and 0.01 M NaCl (pH 8.0, adjusted with NaOH). The area of the electrode was about 0.01 mm2 or larger, the surfaces of the sample was covered with a silicone sealant except for the working electrode area. To start the experiments, an objective lens was put down to be immersed in the solution and clear view of the electrode area was attempted to obtain. After polarization, the specimen surface was assessed using OM, AES, FE-SEM and STEM.The AZ91D die-cast Mg alloys mainly consist of an α phase matrix (Mg solid solution) and β phases (Mg17Al12 intermetallic compounds). Lamellar (α + β) structures are also observed in the adjacent of β phases. Among these lamellar structures, some black dots are Mg-Al-Mn compounds. In the video of corrosion process, pits were observed in the boundaries of lamellar (α + β) structures and β phases. After polarization, EDS maps were taken. It was confirmed that filiform corrosion propagated in lamellar (α + β) structures and α phase matrix.

Optimization of the Experimental Parameters Affecting the Corrosion Behavior for Mg–Y–Zn–Mn Alloy via Response Surface Methodology

This paper optimizes experimental parameters on controlling corrosion performance of the Mg-rare-earth alloys with long period stacking ordered structure using response surface methodology. Different NaCl concentrations, temperatures, and varying pH values are selected as input parameters. The corrosion current density (icorr) and open circuit potential (OCP) are used as the multiple responses to evaluate the corrosion performances. The corrosion surface morphology and corrosion mechanism of the Mg alloys are also investigated by scanning electron microscopy for the optimization. Analysis of variance (ANOVA) has given the impact of individual factors and interactions on the corrosion rate. The results indicated that the three test parameters had significant impacts in controlling the corrosion behavior of Mg alloy. Moreover, the increased NaCl concentration decreased the pitting potential (Epit) of the target materials. Filiform corrosion can be detected in high pH solutions, whereas the matrix suffered from severe dissolution phenomenon in low pH solutions. High temperature aggravated the local destruction and dissolution of the protective film. The interaction of the experimental parameters showed a sizable influence on corrosion performance.