Corrosion Resistance Of Mg Alloy Research Articles

Improved protective properties of Mg alloy AZ31 using bis-[triethoxysilylpropyl] tetrasulfide silane films modified with nano TiO2 by electrochemically assisted deposition

Magnesium (Mg) and its alloys were favored by biomedical practitioners thanks to availability of bioactivity and degradability. However, the mismatch between the degradation properties of Mg alloys and the rate of osteogenesis often led to implant failure and bacterial infections within the desired period. The goal of this study was to improve the corrosion resistance of Mg alloys, providing theoretical guidance for solving the problems of implantable Mg-based materials. In this experiment, we prepared a dense and uniform BTESPT/TiO2 film layer on the surface of Mg substrate by electrochemically assisted deposition. The BTESPT/TiO2 film layer provided a physical barrier to avoid direct contact between AZ31 and the corrosive medium. When the addition amount was 2 g/L TiO2, the coating had the best corrosion resistance behavior, its corrosion current density could be up to 9.973×10−8 A/cm2. The BTESPT/TiO2 revealed good cell viability as well as osteogenic differentiation potential on MC3T3-E1 cells.

Surface microstructure and corrosion characterization of AZ31 magnesium alloys fabricated by laser surface-modification

This study aimed to improve the corrosion resistance of Mg alloys, and to this end, AZ31 Mg alloy was subjected to laser surface re-melting using a fiber laser. Subsequently, a comparative analysis was conducted on the microstructures of the re-melted surfaces under various laser power settings, and the influence of laser surface re-melting on corrosion characteristics was investigated through a potentiodynamic polarization test. The test results show that laser surface re-melting produced a distinct reduction in the crystallite size of magnesium, ranging from 11.23–15.80 μm within the laser-melted layers. The maximum melted layer thickness of 820 μm was achieved with a laser power of 2100 W. The process of laser surface re-melting notably heightened the hardness, particularly as the power increased, which was attributed to swift solidification. The most noteworthy hardness measurement of 92.1 HV0.02 was recorded at 2100 W. Thus, the study shows that laser surface re-melting significantly enhances the corrosion resistance of Mg alloys, primarily owing to the formation of a corrosion product. The smaller grain size on the surface contributes to the formation of a dense product film.

A Review of Corrosion-Resistant PEO Coating on Mg Alloy

The corrosion problem of Mg alloy limits its application in many engineering fields. Plasma electrolytic oxidation (PEO) is an economical and eco-friendly technology that can create a dense oxide layer on Mg alloy, offering a solution to the corrosion issue. This research summarizes the use of PEO technology in developing corrosion-resistant coatings for Mg alloys and examines the growth mode and corrosion process of PEO coatings. It is concluded that current efforts to enhance the corrosion resistance of PEO coatings on Mg alloys can be categorized into two approaches: improving the internal structure of the coating and enhancing the phase composition. This includes optimizing coating thickness, roughness, and density; repairing micropores and cracks; and introducing corrosion-resistant compounds by doping. Micropores and cracks are identified as vulnerable points for corrosion, and sealing is an effective strategy to address this. By modifying the phase composition of the coating, corrosion occurrence can be minimized, significantly boosting the corrosion resistance of Mg alloys. Finally, future challenges and potential advancements in corrosion-resistant PEO coatings for Mg alloys are discussed.

Corrosion resistance study of ZIF-67/Co-Fe LDHs composite coating on the surface of AZ31 magnesium alloy micro-arc oxidation film

Magnesium (Mg) alloys can be applied in many fields, but their poor corrosion resistance limits their widespread applications. This study prepared a zeolitic imidazolate framework (ZIF-67)/Co-Fe layered double hydroxides (LDHs) composite coating on micro-arc oxidation (MAO) coated Mg alloy AZ31. The surface, interface, and corrosion resistance of the composite coating were studied. The results demonstrate that the ZIF-67/LDHs composite coating showed lower corrosion current density icorr (1.31×10−8 A∙cm–2) than AZ31 (5.20×10−5 A∙cm–2), MAO (1.16×10−7 A∙cm–2) or LDHs (7.78×10−8 A∙cm–2). After immersing in a 3.5 wt% NaCl solution for 14 days, its icorr still remained the lowest, exhibiting excellent corrosion resistance to AZ31. It was of great significance in improving the corrosion resistance of Mg alloys, and this compositely growth technology was expected to be applied to other metals.

In situ electrochemical deposition enables dense polypyrrole grown on AZ31 surface for improving corrosion resistance

This study addresses the poor corrosion resistance of Mg alloy. Based on an in-situ electrochemical strategy, poly(pyrrole) coatings were selectively prepared on the surface of Mg alloys with controlled thickness using constant current and cyclic voltammetry techniques. The results indicate that PPy-CV coatings possess greater thickness and a denser structure. Combining studies on corrosion behaviors such as electrochemical analysis, and immersion, it was found that the coatings effectively prevent solution intrusion, thereby enhancing the alloy's resistance to corrosion. And also provides a new avenue for designing corrosion-resistant coatings, particularly for conductive materials such as polyaniline, poly(3,4-ethylenedioxythiophene), etc.

Low-temperature induced enhancement of corrosion/wear resistance in inverse nacre-like graphene-based waterborne coatings

The poor corrosion resistance of Mg alloys severely limits their industrial application. In this work, an inverse nacre-like waterborne coating composed of polyvinyl alcohol/glutaraldehyde (PVA/GA) and graphene oxide/glutaraldehyde (GO/GA) was prepared on Mg alloys. The in-situ heat treatment was applied to reduce hydrophilic transport channels within the bonding network and multilayer GO. The hydrophobicity of RGO sheets was increased owing to the thermal removal of oxygen-containing functional groups. Meanwhile, the heat-treated PVA/GA enriched with acetal linkage network performs “interlock effect” between the reduced graphene oxide/glutaraldehyde (RGO/GA) layers, inhibiting the interface delamination. Therefore, the thermally reduced graphene-based waterborne coating exhibited stable maze effect with extended hydrophobic barrier path. Besides, the low shear coordination of PVA/GA and RGO/GA weakened the contradictory relationship between the relative slipping and bonding strength of GO/RGO sheets, which effectively decreased the wear rate of samples, forming mechanical durability protection for the substrate. Therefore, the coating exhibits integrated corrosion/wear protection performance.

Improved Corrosion Properties of Mg-Gd-Zn-Zr Alloy by Micro-Arc Oxidation

In order to improve the corrosion resistance of Mg-3Gd-1Zn-0.4Zr (GZ31K) alloys for biomedical application, the alloy was micro-arc oxidation (MAO)-treated using silicate electrolyte system under various voltages (400 V, 425 V, 450 V, 475 V). The effects of voltage on the microstructure and corrosion properties of MAO coating were investigated via X-ray diffraction (XRD) and a scanning electron microscope (SEM) combined with an energy-dispersive spectrometer (EDS), X-ray photoelectron spectroscope (XPS), and electrochemical experiments. The results showed that, with the increase in voltage, the MAO coatings became thicker and the micropores on the MAO coating increased in diameter. The main phase compositions of the MAO coatings were MgO and Mg2SiO4. Potentiodynamic polarization curve results showed that MAO coatings could enhance corrosion resistances, where the corrosion current density decreased by six orders of magnitude and the corrosion potential of the specimens increased by 300 mV for the voltage of 450 V in the MAO treatment; nevertheless, the corrosion resistance rapidly deteriorated due to the creation of large micropores in the MAO coating, which provide a pathway for corrosive media when the voltage is 475 V. The electrochemical impedance spectroscopy results showed that MAO treatments could increase low-frequency modulus resistance and increase the corrosion resistance of Mg alloys. In addition, MAO-treated GZ31K alloys still exhibited uniform corrosion, which is desirable for biomedical applications.

Effect of bath temperature on the growth kinetics and characteristics of permanganate conversion coating on LZ91 magnesium alloy

Permanganate conversion coating is one of the possible alternatives to chromate conversion coating for magnesium (Mg) alloys. Permanganate conversion coating enhances the corrosion resistance of Mg alloys, which is closely related to the thickness and defects of the coating. In this study, the growth kinetics of the permanganate conversion on the LZ91, a dual-phase magnesium alloy, as affected by the bath temperature ranging from 15 to 60 °C, was detailed. The permanganate conversion coating was mainly composed of MnO2/MnOOH and MgO/Mg(OH)2. Increasing the bath temperature reduced the growth rate and thickness of the coating although the bath temperature hardly influenced the composition and crystallinity of the coating. The permanganate conversion coating formed at 15 °C for 10 s was nonuniform with a thickness ranging from 100 to 300 nm, which was prone to cracking after post-coating drying at room temperature. The presence of cracks on the permanganate conversion coating was detrimental to the corrosion resistance. On the other hand, the permanganate conversion coating formed at 40 and 60 °C for 10 s was more uniform with a thickness of less than 100 nm, yet exhibited better corrosion resistance than the counterpart formed at low temperatures (15 and 25 °C).

Anodization and Plasma Electrolytic Oxidation Treatments of AZ91D Mg Alloy in Alkaline Aqueous Solutions

Mg alloys, such as AZ91 (Mg-9mass%Al-1mass%Zn), are lightweight materials with excellent mechanical properties. The applications of Mg alloys in automobiles could significantly contribute to reducing carbon dioxide emissions. Mg alloys are fully recyclable and abundantly available, which increases their desirability in light of rising environmental consciousness. However, the low corrosion resistance of Mg alloys is one of the major limitations to further applications.In Mg alloys, corrosion behavior is known to be related to the microstructure. During the real-time in situ observation of the corrosion process under galvanostatic polarization, filiform corrosion proceeded along the outside of the β phase (in lamellar α + β microstructure and along the α-mother phase 1. Furthermore, the β phase exhibited a higher potential in the OCPs of each phase and a small area with the boundary in 0.1 M NaCl at pH 8.0 2. Thus, the surface films of β phases was thought to suppress the corrosion of Mg alloys. Mg alloys can be treated by anodic oxidation or plasma electrolytic oxidation to obtain excellent corrosion resistance. The latter is similar to anodic oxidation but applies a higher voltage, which causes a discharge on the electrode surface and the resulting plasma modifies the oxide film significantly.In this study, anodic oxidation and plasma electrolytic oxidation were performed on AZ91D Mg alloy in alkaline solutions such as sodium phosphate. This study aims to compare the two methods in the same solution and to produce an Al-rich surface film with excellent corrosion resistance.In anodic oxidation, the size of the electrode area was approximately 1 cm2. The surface of the specimen was coated with epoxy resin, followed by paraffin. The reference electrode was Ag / AgCl (3.33 M KCl). The experiments were performed at 25 ℃. The scan rate of potentiodynamic polarization was set at 23 mV min-1. The starting potential was set at 20 mV lower than the open-circuit potential. The anodic oxidation treatments were terminated at 0 V, 3 V, and 5 V. Plasma electrolytic oxidation was performed with a liquid volume of 500 mL. The sample was mounted on a resin holder. The electrode surface was approximately 50 mm2. A Pt plate was used as the counter electrode. The sample and the counter electrode were fixed at a distance of 0.5 cm. A plasma-generating power supply was used. The solution was cooled down to 20 ℃ while the voltage was applied. The frequency and the pulse interval were adjusted. The voltage and type of solution were changed to produce the film. Z. Shao, M. Nishimoto, I. Muto, and Y. Sugawara, Corrosion Science, 192, 109834 (2021).Z. Shao, M. Nishimoto, I. Muto, and Y. Sugawara, Journal of Magnesium and Alloys, 11, 137-153 (2023).

Enhanced corrosion resistance of Mg alloy embedded in Cl--containing Portland cement with the formation of CaCO3-coated Mg(Al)O passive film via one-step pulse electrodeposition

In this study, a novel CaCO3/Mg(Al)O coating system was successfully synthesized via one-step pulse electrodeposition. The thickness of inner passivation layer and outer CaCO3 layer was tailored by modulating the pulse voltage. Anticorrosion performance of the coated Mg alloy was assessed by both electrochemical methods and embedment tests. The coated Mg alloy demonstrated improved corrosion resistance, attributed to the synergistic impact of a compact outer CaCO3 layer and an Al-assisted inner passivation layer. Both layers' quality primarily governed the alloy's anticorrosion performance. Remarkably, embedment tests revealed a re-passivation phenomenon instead of corrosion, with its mechanism discussed comprehensively.

Effect of Mn and Ca on mechanical, corrosion and surface roughness of Mg-5Sn alloy

Magnesium and its alloys have an extensive application prospect in the aerospace, automotive industry, sports equipment, biomedical and energy storage due to their high specific strength and low density compared with iron and Aluminum alloys. However, the strength and the corrosion resistance of Mg alloys is still the major drawback that hampers their application. Alloying is generally used to improve mechanical and corrosion properties. The mg-Sn alloy system was extensively studied and the Mg-5Sn alloy was chosen as the base composition owing to the addition of 5 wt% Sn improves the strength and corrosion resistance of pure Mg. The present work aims to investigate the effect of Mn and Ca addition on mechanical, corrosion and roughness properties of as-cast Mg-5Sn-Mn-Ca alloy. The addition of Mn and Ca elements significantly refined α-Mg grains. Mn-rich phase precipitated alongside intermetallic eutectic Mg2Snphases and CaMgSn eutectics observed on the grain boundaries. The strength, hardness, roughness, and corrosion resistance of Mg-5Sn alloy are observed to be improved by the addition of Mn and Ca.

Insights into the design of oxidation-resistant Mg alloy by alloying with rare-earth elements

The strategy of rare-earth elements addition into Mg alloys has been successfully developed and applied to enhance the mechanical performance and corrosion resistance of Mg alloys. Although this strategy has also been applied to enhance their high-temperature oxidation resistance, the mechanistic understanding of the beneficial effects remains elusive. Here, the oxidation of Mg–4Nd and Mg-4Nd–1Y alloys in Ar–20%O2 at 500 °C was studied and compared. It was found that even though a continuous layer of Nd2O3 did not form, the Nd addition could still enhance the oxidation tolerance of Mg–4Nd alloy by facilitating the generation of a more continuous and intact oxide scale and working as oxygen sinks to delay the violent oxidation of Mg. The formation of a continuous Y2O3 layer on Mg-4Nd–1Y alloy suggests that Y was more capable of facilitating the external oxidation due to its much faster diffusion rate in Mg matrix than that of Nd. However, the Nd addition could decrease the critical content of Y necessary for the oxidation transition from internal to external because of the synergistic effect of the Nd and Y addition. The dissolution of the thermal unstable Mg12Nd precipitates resulted in a localized increase of Nd content, accelerating the oxidation by increasing the preferential oxidation of Nd. Hence, in the design of oxidation-resistant Mg alloys, the addition of RE elements with faster diffusion rate and the addition of multiple alloy elements are preferred. In addition, the number of thermal unstable precipitates needs to be strictly controlled.

Designing organic-inorganic hybrid coating from composite and structures for the tribological property and corrosion resistance of Mg alloys

Magnesium alloys are promising materials for the regeneration of bioabsorbable implants, but restricted by its poor tribological property and the rapid corrosion. In this work, a robust organic–inorganic hybrid coating was fabricated on the surface of Mg-Nd-Zn-Zr alloys through a combination of chemical assembly technique of hydroxylated boron nitride (BNO) and plasma-enhanced chemical vapour deposition of vinyltriethoxysilane. The obtained hybrid coating simultaneously enhanced anti-wear and anti-corrosion properties in both the dry friction and simulated body fluid (SBF)-condition friction. The wear rates of the Mg alloy modified by BNO/siloxane hybrid coating were significantly reduced by 97.3% and 96.4% under dry and SBF conditions, respectively. This step-by-step coating modification method is applicable to various shapes of magnesium alloys and hence displays great potential in implant application.

Influence of Alloying Materials Al, Cu, and Ca on Microstructures, Mechanical Properties, And Corrosion Resistance of Mg Alloys for Industrial Applications: A Review.

Magnesium is renowned for its favorable low-density attributes, rendering it a viable choice for commercial engineering applications in which weight has substantial design implications. Magnesium (Mg) stands as a readily obtainable metallic element, exhibiting robustness, efficient heat dissipation, and excellent damping properties. The utilization of pure magnesium remains infrequent due to its susceptibility to instability under high temperatures and pronounced vulnerability to corrosion within humid environments. Hence, the incorporation of magnesium alloys into the design process of aircraft, automotive, and biomedical applications assumes paramount importance. This Review presents a comprehensive review of research endeavors and their resultant achievements concerning the advancement of magnesium alloys. Specifically focusing on aerospace, automotive, and biomedical applications, the Review underscores the pivotal role played by alloying constituents, namely aluminum (Al), copper (Cu), calcium (Ca), and PEO coatings, in influencing the microstructural attributes, mechanical potency, and resistance to corrosion.

Influence of texture on the corrosion behavior of an as-extruded Mg–8Al-0.5In alloy sheet

This work aims to clarify the influence of texture on the corrosion behavior of an as-extruded Mg–8Al-0.5In alloy sheet. The weight loss, hydrogen evolution and electrochemical results show that the sample with strong basal texture has the best corrosion resistance. The morphology examinations show the corrosion product film is thinner and more uniform with less cracks for the sample with (0001) plane. The inhomogeneity of corrosion product in samples with (10-10) and (-12-10) planes is the main cause of poor corrosion performance. The findings of this study confirm the corrosion resistance of Mg alloy could be regulated by controlling texture.

Improving Corrosion and Stress Corrosion Cracking Performance of Machined Biodegradable Alloy ZX20 by HF-Treatment

The treatment with hydrofluoric acid (HF-treatment) was suggested to be an effective way of improving the corrosion resistance of Mg alloys, including Mg-Zn-Ca (ZX) ones used for biodegradable implants. However, the effect of the HF-treatment on the stress corrosion cracking (SCC) susceptibility of ZX alloys has not been reported yet, although this phenomenon can induce premature brittle failures of the metallic medical devices, and thus, it is critical for their in-service structural integrity. In the present study, the effect of the HF-treatment on the microstructure, cytotoxicity, corrosion rate, mechanical properties, and fracture and side surface characteristics of the as-cast ZX20 alloy were investigated with the use of scanning electron microscopy, immersion, and slow-strain rate tensile testing in Hanks’ solution and indirect cell viability tests. It is found that the HF-treatment exerts no cytotoxic effect and results in a significant reduction in corrosion rate (up to 6 times of magnitude) and SCC susceptibility indexes (up to 1.5 times of magnitude). The observed improvement of corrosion and SCC performance of the alloy by the HF-treatment is found to be attributed to three effects, including (i) formation of the protective surface film of MgF2, (ii) removal of surficial contaminations originating from sample preparation procedures, and (iii) dissolution of surficial secondary phase particles. The mechanism of corrosion and SCC in the specimens before and after the HF-treatment are discussed.

Corrosion and Protection of Magnesium Alloys: Recent Advances and Future Perspectives

Magnesium alloys are of significant importance for lightweight manufacturing and weight-saving applications due to their high weight-to-strength ratio and good mechanical properties. However, the poor corrosion resistance of Mg alloys limits their large-scale practical application. An essential theoretical foundation for the development of corrosion-resistant magnesium alloys and their surface protection technologies can be elucidated via the investigation of the corrosion mechanism of the magnesium surface and the alteration of the corrosion rate after surface conversion and coating. This paper discusses some typical corrosion behaviors by originally describing the corrosion mechanism of magnesium alloys with and without different coatings and surface treatments. In order to predict the future theoretical investigation and research directions for the surface protection of magnesium alloys, some techniques and preventative measures to enhance the corrosion resistance of magnesium alloys are reviewed, and these protection techniques are intercompared for better understanding.

Enhanced corrosion resistance, antibacterial properties and osteogenesis by Cu ion optimized MgAl-layered double hydroxide on Mg alloy

Magnesium (Mg) and its alloys have similar densities and elastic moduli to natural bone, making them an excellent choice for orthopedic implants. However, Mg alloys are prone to electrochemical corrosion, which often leads to implant failure and hinders the further development of Mg alloys due to bacterial infection around the implant. This work aims to enhance the corrosion resistance of Mg alloys, and provide theoretical guidance for solving the problem that Mg-based orthopedic implants are susceptible to bacterial infection and, thus, implant failure. In order to solve the corrosion problem, the Mg alloy AZ91D was used as the substrate, and a compact and uniform MgAlCu-layered double hydroxide (Mg(Cu)-LDH) was prepared on its surface using a hydrothermal method. The Mg(Cu)-LDH provides a barrier between the AZ91D and corrosive liquid, which effectively protects the Mg substrate from being corroded. The Mg(Cu)-LDH shows great cell viability for MC3T3-E1 cells. The Cu2+ and Mg2+ in the coating also endow the Mg(Cu)-LDH/AZ91D with antibacterial properties, showing strong antibacterial effects on both E. coli and S. aureus with antibacterial rates over 85%. Finally, in vivo results indicated that a LDH-coated implant had no systemic effects on the hearts, livers, spleens, lungs or kidneys. It was shown that 4 weeks after surgery the ratio of bone volume to tissue volume (BV/TV) of the LDH implant was 24%, which was 1.7 times that observed for AZ91D.

Synthesis of ZIF-67 film in micro-arc oxidation anticorrosion coating on AZ31 magnesium alloy

In order to improve the corrosion resistance of AZ31 magnesium (Mg) alloy and the adhesion of metal-organic frameworks (MOFs) coating, a MAO/ZIF-67 (Co-based MOFs) (micro arc oxide/ZIF-67) composite coating was fabricated by in-situ growth on AZ31 MAO coating. The results showed that ZIF-67 with rhombic dodecahedron uniformly grew on the surface of MAO coating, and exhibited good adhesion to the substrate, which made MAO/ZIF-67 composite coating have good corrosion resistance. It was proved that ZIF-67 could effectively seal the pores of MAO coating, increase the tortuosity of the invasion path of corrosion medium, and significantly improve the corrosion resistance of Mg alloy. In addition, MAO pretreatment gave the coating strong adhesion, which was more conducive to ZIF-67 sealing micro-pores. This study is of great significance to reduce the limitation of MOF coating applied to all metal substrates.

Femtosecond laser surface processing combined with thermal oxidation for enhancing corrosion resistance of AZ31B magnesium alloy in chloride solutions

A novel method of ultrafast femtosecond laser surface processing (FLSP) combined with the post thermal oxidation (TO) treatment was employed to improve the corrosion resistance of AZ31B magnesium (Mg) alloys. FLSP with laser powers (< 100 mW) mainly creates the nanostructures on AZ31B alloy surfaces, while the higher laser powers (> 200 mW) induce the hierarchical micro/nanostructures. According to the electrochemical results, the corrosion resistance of AZ31B alloys in Cl− solutions is weakened after the FLSP. However, an obvious enhancement in corrosion resistance is found when the femtosecond (fs) laser-processed samples subjected to the TO treatment in the temperature range from 100 °C to 280 °C. TO treatment actually supports the oxidation and growth of the nanostructure to form a dense film, considerably improving its protective ability and enhancing the corrosion resistance of Mg alloys in Cl− solutions. The uniform corrosion is evidently inhibited and localized corrosion emerges on laser-processed samples after the TO treatment.