Corrosion Behavior Of Pure Magnesium Research Articles

Using high pressure torsion to process magnesium alloys for biological applications

The effect of high pressure torsion processing on mechanical properties and corrosion behavior of pure magnesium and Mg-Zn, Mg-Zn-Ca, Mg-Li-Y and Mg-Y-RE alloys is investigated. Micro-tomography and SEM characterization are used to estimate corrosion rate and evaluate non-uniform corrosion features. The results show that severe plastic deformation processing improves the strength of all magnesium alloys, but deformation localization can take place in the Mg-Zn-Ca and Mg-Y-RE alloys. The occurrence of deformation localization is associated with low strain rate sensitivity in these alloys and with severe corrosion localization. Pure magnesium and Mg-Zn and Mg-Li-Y alloys display good corrosion resistance with a low corrosion rate and maintain integrity after 28 days of immersion in Hank's solution.

Microstructure and Corrosion Behavior of Extruded Mg-Sn-Y Alloys

Magnesium and its alloys, with their unique properties such as high strength/density ratio, good castability, and machinability, have found several applications in the aerospace and automotive industries. One of the reasons that restrict their widespread applicability is their poor corrosion resistance since Mg is readily oxidized in the presence of oxygen and humidity. The oxide layer is pseudo-passive and non-protective. The present effort tried to improve the passivity of this layer with the addition of alloying elements such as Tin (Sn) and Yttrium (Y) to create phases that interact differently with the oxidizing environment, thereby improving the corrosion resistance. In this work, the corrosion behavior of pure magnesium and Mg-5Sn-xY (x = 0.5, 1, 2 wt.%) were evaluated using immersion and potentiodynamic polarization tests. XRD, SEM-EDS, and EBSD have investigated the microstructure and elemental composition of the alloys. The present study is focused on elucidating the microstructure-corrosion relationship in Mg-Sn-Y alloys.

Corrosion behavior of pure magnesium processed by accumulative roll bonding for biomaterial application

Magnesium is one of the materials that can be used as an implant for the human body. It is because the daily intake ofmagnesium for an adult is 240-420 mg/day. Also, the elastic modulus (41 – 45 GPa) and density (1.74 g/cm3) of magnesiumis closer to that of natural bone. However, pure magnesium in the as-cast condition has a very fast corrosion rate,2,89mmPY in 0.9% NaCl solution. Accumulative roll bonding (ARB) is done in this recent study to improve the corrosionrate of pure magnesium. ARB is one of the severe plastic deformations (SPD) method, which provides the possibility toobtain high strained materials without a macroscopic change after a cyclic roll-bonding process (stacking, preheating androlling). Magnesium is annealed at 250°C and 350°C for 25 minutes, and then the ARB process is done with variation; one,two, three and four cycles. The composition was tested using SEM-EDS, showing that the content of a pure magnesiumplate (as annealed) is 99.77%. The grain size is observed using the optic microscope and measured by ImageJ, while thecorrosion rate was measured with an electrochemical and immersion test. The result showed the smallest grain size achievedis 7.204 ± 1,185 μm and that the lowest corrosion rate is 0,0012mmPY. The polarization resistance determined the thicknessand the ability of passivation area obtained with the increasing number of ARB cycles. The higher plastic deformation isrecommended for improve the corrosion resistance of the metallic material for future works.

Effect of corrosion inhibiting compounds on the corrosion behaviour of pure magnesium and the magnesium alloys EV31A, WE43B and ZE41A

This paper studied corrosion of pure Mg and the Mg alloys EV31A, WE43B, ZE41A, coated with commercial corrosion inhibiting compounds (CICs) (LPS 3, LPS2, AMLGuard, Ardrox 3961) immersed in 3.5 wt% (0.6 M) NaCl solution saturated with Mg(OH)2. All four CICs reduced corrosion rates. LPS 3 resulted in zero corrosion rates and 100% inhibition in most cases. LPS 2 and AMLGuard had comparable inhibition efficiencies, whilst Ardrox 3961 had the lowest inhibition efficiency. Reduction in corrosion rates was tentatively attributed to barrier films formed by chemical adsorption for LPS 3 and AMLGuard, and by physical adsorption for LPS2 and Ardrox 3961.

Corrosivity of haze constituents to pure Mg

Abstract The corrosion behavior of pure Magnesium (Mg) in a Mg(OH)2-saturated solution containing different individual constituents of PM2.5 in haze were studied by hydrogen evolution, weight loss and electrochemical experiments. The results indicated that the corrosivity of these constituents to pure Mg decreased in the following order: (NH4)2SO4>Haze-contaminated-solution>NH4NO3>NH4Cl>NaCl ≈ KCl ≈ Na2SO4 ≈ MgCl2 ≈ CaSO4>Mg(OH)2 (basic solution) >Ca(NO3)2. Possible mechanisms behind the different corrosion behaviors of Mg in response to these constituents were also briefly discussed in this paper.

Experimental comparison of corrosion behavior of pure magnesium, iron coated magnesium and hydroxyapatite coated magnesium in Hanks Basic salt solution for cardiovascular application

Biomaterials (BM) research is one of the emerging fields, and much research has been carried out towards the development of new and improved BMs. The latest development in the field of biomaterials is to develop biodegradable BMs for different applications. Many attempts have been carried out with alloys of Magnesium (Mg) and Iron (Fe), and even though Mg and Fe are found to be suitable materials, each has its limitations. Problem with Mg is its high rate of degradation while Fe has a very slow degradation rate. Hydroxyapatite (HaP) is one of the naturally occurring materials found in human bones, and many research publications have discussed the utilization of HaP. In the present study, Mg has been considered as the base material, and the effect of coating Fe and HaP on Mg substrate has been studied via immersion test in Hanks Basic salt solution (HBSS). Fe and HaP were coated on pure Mg substrate using physical vapor deposition technique (PVD). Pure Mg was used as control while Fe coated and HaP coated Mg were compared against it for mass loss and corrosion rate in HBSS for 20 days. Electrochemical corrosion test was carried on a three-electrode test rig. Fe coated Mg showed very high degradation as compared to pure Mg samples due to the formation of galvanic cells. Corrosion rate for Fe coated Mg was observed as high as (42.88 ± 1.39) mm yr−1, and it was verified with the electrochemical test, while pure Mg specimen had a maximum corrosion rate of (5.8 ± 0.35)mm yr−1. HaP coated samples showed low corrosion rate as compared to pure Mg and Fe coated Mg. The maximum corrosion rate in Hap coated specimen was observed to be (5.55 ± 0.95) mm yr−1. PVD is a very good method for coating HaP and Fe on Mg substrate, but galvanic cell formation in case of Fe coating inhibits its usage while nonreactive passive layer of HaP proved to very effective in reducing the corrosion rate of Mg.

The Inhibitive Effect of Artificial Seawater on Magnesium Corrosion

The corrosion behavior of pure magnesium (Mg) immersed in 3.5 wt% NaCl and artificial seawater is evaluated by immersion test, electrochemical impedance spectroscopy (EIS), polarization curve, scanning electrochemical microscopy (SECM), and corrosion morphology analysis. The results show that the corrosion rate of the pure Mg in the artificial seawater is nearly a half of that in the 3.5 wt% NaCl, and the serious localized corrosion of Mg in the NaCl is inhibited in the artificial seawater. The main constituents MgCl2 and Na2SO4 in artificial seawater are found to be inhibitive for the corrosion of Mg. The presence of Mg2+ ions could facilitate the formation of Mg(OH)2 film and thus to some extent retard the dissolution of Mg. The SO42– ions in the artificial seawater might be absorbed competitively against Cl− on the Mg surface to retard the corrosion of Mg. The corrosive and inhibitive effects of other anions and cations on Mg dissolution in the artificial seawater were also briefly analyzed.

Comparative Study of Pure Mg and AZ91D as Sacrificial Anodes for Reinforced Cement Concrete Structures in Chloride Atmosphere

Comparative study of the corrosion behavior of pure Magnesium and AZ91D anodes in reinforced cement concrete was undertaken in the present work. The steel reinforcements were kept in contact with these anodes electrochemically in chloride atmosphere and the half-cell potential drop was observed. Bare steel reinforcements were tied to the anodes and were also kept in high chloride atmosphere to test the mechanical properties. The yield stress and ultimate tensile stress were found to decrease by approximately 50MPa while the reduction in percentage elongation is approximately 25% for reinforcements tied to AZ91D and pure Mg at the end of 80 days compared to fresh steel reinforcement. The rate of corrosion of pure Mg was reportedly slightly higher compared to AZ91D due to the presence of inter-metallics as inferred through micro-graphs.

Corrosion behavior of pure Mg and AZ31 magnesium alloy

Purpose of this article is to study corrosion behavior of pure magnesium and AZ31 magnesium alloy in electrolyte containing different concentrations of sodium chloride and pH. For this aim, different concentrations (3.5, 0.3 and 0.03 wt %) of NaCl salt has been utilized in immersion and potentiodynamic polarization tests. pH of electrolytes were fixed at 3, 6 and 11 in order to determine combined effects of acidity and chloride ion concentration on corrosion behavior. It was found out that in the case of AZ31 alloy similar to magnesium, corrosion rate is higher and open-circuit potential was more negative at higher chloride ion concentration in each pH, and also same trend is observed at lower pH for each chloride ion concentration in corrosion rate and open circuit potential. Indeed, solution pH value will have inverse relationship with alloy’s corrosion rate in that solution and by increasing pH, corrosion rate will be decreased. The impact of variations in chloride ion concentration is greater than the change in the solution pH. Corrosion behavior of the magnesium alloy is controlled through a slightly superficial protective layer. It is also expected that the corrosion rate obtained from immersion test to be higher than the one derived from polarization test.

Corrosion Behavior of Pure Magnesium with Low Iron Content in 3.5 wt% NaCl Solution

The microstructure and corrosion behavior of pure magnesium, with 25 ppm Fe but a high corrosion rate, have been studied in this work. It was found that Fe-rich particles, containing also Si, distribute non-uniformly in the Mg matrix and they are spaced at a distance of 100–1000 μm. Before the initiation of localized corrosion, Fe-rich particles play a key role in determining the overall corrosion behavior by supporting hydrogen evolution. During corrosion propagation, Fe-rich particles could be oxidized once they were detached from the Mg matrix and, consequently, lose their cathodic activation. Once the corrosion has taken place over majority of the surface, the effects of crystallographic orientation of the underlying metal dominate the last stage of corrosion, which propagates parallel to the (0001) planes.

Corrosion behavior of magnesium powder fabricated by high-energy ball milling and spark plasma sintering

Microstructural changes and corrosion behavior of pure magnesium for different milling times were investigated. The samples with a finer grain size showed poor corrosion resistance because of unstable or metastable protective film formation after immersion in 0.8 wt% NaCl solution. The corrosion resistance did not improve despite the strong (0002) texture of the sample prepared by spark plasma sintering at 500 °C for 0.3 Ks and milling for 2 h. By studying the microstructural changes and texture development, we concluded that the deformation-dependent grain size is the dominant factor controlling the corrosion properties of mechanically milled magnesium. Increased grain boundary densities lead to an enhancement of the overall surface reactivity and, consequently, the corrosion rate.

Galvanic Corrosion between Magnesium Alloys and Steel

The corrosion behaviour of pure magnesium, cast Elektron 21-T6, and extruded Elektron 43-T5, galvanically coupled to mild steel, has been investigated. The coupling current and potential were measured in selected concentrations of sodium chloride solutions in order to establish the effects of the environment and the alloy type on the galvanic corrosion behaviour. The time evolution of the galvanic currents was related to the results of potentiodynamic polarisation and to the corrosion morphologies revealed on specimens comprising a steel bolt and washer after salt spray testing. During the galvanic coupling, the measured current for pure magnesium was less than that for Elektron 21; the highest current was measured for Elektron 43, suggesting the highest corrosion rate. These results were in agreement with the behaviour expected from the individual potentiodynamic polarisation curves. Concerning the corrosion morphology of the galvanic couple, for Elektron 43, the corrosion close to the washer was relatively deep but extended only about 10 mm. For Elektron 21, the corrosion was shallower but advanced further (up to 15 mm). For pure magnesium, a relatively deep and laterally spread attack (approximately 20 mm around the bolt) was developed. These results suggest differences between observed corrosion in galvanically coupled assemblies and corrosion rates expected based on coupling currents alone.

Degradation behaviour of pure magnesium in simulated body fluids with different concentrations of [formula omitted

Corrosion behaviour of pure magnesium in simulated body fluids (SBF) with HCO 3 − concentrations of 4, 15 and 27 m mol/L is studied. Magnesium is not sensitive to pitting corrosion in all the SBFs. Higher HCO 3 − concentration effectively slow down the corrosion rates. Uniform and compact corrosion product layer preferentially forms in SBF with HCO 3 − of 27 m mol/L. Potentiodynamic polarization test indicates that HCO 3 − of 27 m mol/L dramatically enhance corrosion potential and induce passivation. EIS results further confirm that higher concentration of HCO 3 − induce more effective protection layer, especially in SBF with HCO 3 − of 27 m mol/L.

Functionalization of Metallic Magnesium with Protein Layers via Linker Molecules

We present an innovative method to cover pure magnesium with protein monolayers by utilizing the OH termination of the oxide surface and silane coupling chemistry. The protein of interest was albumin. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) were used to monitor the success of the treatment. The attachment of proteins via linker groups yielded smoother and more homogeneous surfaces than coatings produced by steeping magnesium in protein solution. A positive effect on the corrosion behavior of pure magnesium was also observed.

Effect of Magnesium Hydride on the Corrosion Behavior of Pure Magnesium in 0.1 M NaCl Solution

The effect of magnesium hydride on the corrosion behavior of pure magnesium in 0.1 M NaCl solution was investigated using the gas collection method, potentiostatic current decay test, and in situ Raman spectrum. The formation of magnesium hydride (MgH2,Mg2H4) was observed at the cathodic region. Applying anodic potential leads to decomposition of magnesium hydride. Magnesium hydride plays an important role on the negative difference effect (NDE) in both the cathodic and anodic regions.

Effects of impurities on the biodegradation behavior of pure magnesium

The corrosion behavior of pure magnesium that has different content ratio of impurities (such as Fe/Mn ratio) in Hanks’ solution was investigated in order to tailor the lifetime of biodegradable implant made of pure magnesium. Two distinct stages of corrosion were observed: a slow corrosion rate stage and a subsequent fast corrosion rate stage. The first stage was characterized by uniform corrosion that produced magnesium hydroxide and calcium phosphate film on a magnesium surface, resulting in a slow corrosion rate. The second stage with an abrupt increase in the corrosion rate was induced by Fe precipitates and was stimulated by an increase in the Fe/Mn ratio. This corrosion was developed to a preferred crystallographic pitting corrosion where the pits propagated along the preferred crystallographic plane and several layers of Mg planes with narrow interplanar space remained uncorroded. From this study, it is expected that the lifetime of the biodegradable implant made of pure Mg can be tailored by controlling the amount and ratio of the impurities.

Corrosion behaviour of Mg–Cu and Mg–Mo composites in 3.5% NaCl

The corrosion behaviour of pure magnesium, Mg–Cu (0.3, 0.6, and 1 vol.%) and Mg–Mo (0.1, 0.3, and 0.6 vol.%) composites has been studied in 3.5% NaCl solution by weight loss and polarisation methods. Corrosion rates determined by weight loss method were considerably higher than that determined by polarisation method. The corrosion rate increased with increasing volume fraction of reinforcement in Mg–Cu and Mg–Mo composites. At the same volume fraction of reinforcement, molybdenum reinforced composite corroded faster than copper reinforced composite. The galvanic current density between Mg–Cu and Mg–Mo couples has been experimentally measured using zero resistance ammeter technique. The experimentally observed galvanic current densities were in close agreement with those obtained using mixed potential theory analysis. SEM observation of corroded samples confirmed microgalvanic activity at the matrix/reinforcement interfaces. The poor corrosion resistance of composites has been attributed to microgalvanic effects between the matrix and reinforcements and inferior quality of surface films.

Corrosion of pure magnesium under thin electrolyte layers

The corrosion behavior of pure magnesium was investigated by means of cathodic polarization curve, electrochemical impedance spectroscopy (EIS) and electrochemical noise (EN) under aerated and deaerated thin electrolyte layers (TEL) with various thicknesses. Based on shot noise theory and stochastic theory, the EN results were quantitatively analyzed by using the Weibull and Gumbel distribution function, respectively. The results show that the cathodic process of pure magnesium under thin electrolyte layer was dominated by hydrogen reduction. With the decreasing of thin electrolyte layer thickness, cathodic process was retarded slightly while the anodic process was inhibited significantly, which indicated that both the cathodic and anodic process were inhibited in the presence of oxygen. The absence of oxygen decreased the corrosion resistance of pure magnesium in case of thin electrolyte layer. The corrosion was more localized under thin electrolyte layer than that in bulk solution. The results also demonstrate that there exist two kinds of effects for thin electrolyte layer on the corrosion behavior of pure magnesium: (1) the rate of pit initiation was evidently retarded compared to that in bulk solution; (2) the probability of pit growth oppositely increased. The corrosion model of pure magnesium under thin electrolyte layer was suggested in the paper.

An Impedance Investigation of the Mechanism of Pure Magnesium Corrosion in Sodium Sulfate Solutions

The corrosion behavior of pure magnesium in sodium sulfate solutions was investigated using voltammetry and electrochemical impedance spectroscopy with a rotating disk electrode. The analysis of impedance data obtained at the corrosion potential was consistent with the hypothesis that Mg corrosion is controlled by the presence of a very thin oxide film, probably MgO, and that the dissolution occurs at film-free spots only. This hypothesis was substantiated both by the superposition of the EIS diagrams, obtained for different immersion times and for two concentrations once normalized, and by use of scanning electrochemical microscopy in the ac mode to sense the local conductivity of the material. On the basis of the electrochemical results, a model was proposed to describe magnesium corrosion at the open-circuit potential. Simulation of the impedance diagrams was in good agreement with the experimental results.

Corrosion Behaviour of Pure Magnesium in a Simulated Body Fluid

The corrosion behaviour of pure magnesium in Hank's simulated body fluid (SBF) was investigated. It was found that the polarization of Mg in the SBF solution was similar to that in a NaCl aqueous solution. However, AC impedance analysis suggested that the detailed dissolution steps involved in the corrosion of Mg in the SBF could be different in terms of their rates or contributions to corrosion damage of Mg. Moreover, the corrosion rate of Mg in the SBF solution was found to be increasing with time and significant hydrogen evolution and alkalization of the SBF solution resulting from corrosion of Mg were measured in the study. The results suggested that after some proper measures are taken to retard corrosion reaction, Mg can be successfully employed as a degradable and absorbable implant material.