Corrosion Resistance Of AZ31 Alloy Research Articles

Improved corrosion resistance of hydroxyapatite-reinforced plasma electrolytic oxide coatings on AZ31 alloy from one-step and two-step fabrications

The improved corrosion resistance of AZ31 alloy by plasma electrolytic oxidation (PEO) counteracts its apatite-forming ability. To overcome the issue, apatite-containing coatings were fabricated. One-step and two-step fabrications were compared to incorporate the nanoparticle hydroxyapatite (HA) in the coating and to evaluate their effect on the corrosion resistance. The corrosion resistance was evaluated by polarization test and EIS measurement in 0.9% NaCl solution. The electron microscopy and chemical analysis revealed that the HA particles were dispersed in the one-step coatings, while an interspersed HA distribution was observed in the two-step coatings. The dispersed particles enhanced the coating’s hardness from 490 to 554 HV. In the two-step coatings, the HA particles mainly accumulated inside the pores, reducing the coating porosity down to 3.9%. The one-step coatings were more stable in the corrosive solution, offering a remarkably higher corrosion resistance, than the two-step coatings. Moreover, the one-step coating required a shorter (half) processing time (10 min) than the two-step process (20 min) to achieve a similar order of corrosion current density of 10−7 A cm−2. The results demonstrated that the arrangement of reinforcement in the PEO coatings and its effect on the corrosion resistance can be adjusted.

Improving mechanical properties and corrosion resistance of AZ31 alloy by micro-arc oxidization and post supercritical CO2-assisted electroless plating

Anti-corrosion and wear resistance of AZ31 alloy were enhanced through a three-stage surface treatment, which comprised surface micro-arc oxidation (MAO), sputtering and post supercritical CO2-assisted electroless plating (PSC–CO2-EP). In the MAO treatment, attempts were made to vary the F ion content in the electrolyte to investigate its impact on the morphology and composition of the oxide film. Subsequently, the MAO-treated AZ31 alloy underwent Ag sputtering, followed by the preparation of the Ni coating using the PSC-CO2-EP method (PSC–CO2–Ni). The SEM micrographs indicate that the addition of F ions to the electrolyte effectively improved the uniformity, thickness and compactness of the MAO-generated oxide film. Further modification with the sputtered Ag layer could enhance the adhesion between the Ni coating and the as-prepared oxide film. Additionally, the application of SC-CO2, with high diffusivity and low surface tension, significantly improved the anti-corrosion and wear resistance of the AZ31 alloy surface even after pressure release. The results demonstrate that the multilayer design proposed in this study addresses the vulnerability of the AZ31 alloy surface to corrosion. Furthermore, compared to the SC–CO2–assisted plating method, the PSC-CO2-EP technique offers greater process flexibility and exhibits high potential for practical applications.

Design and characterization of β-tricalcium phosphate-based self-passivating coatings on magnesium alloys.

Background: Magnesium alloys degrade rapidly in salt solutions, which limits their use without passivating treatments. AZ31 alloy is particularly promising for implant applications owing to its biodegradability and mechanical properties, necessitating effective corrosion-resistant coatings. Aim: In this study, a self-passivating reactive coating was designed and evaluated for AZ31 magnesium alloy plates using β-tricalcium phosphate (TCP) to enhance corrosion resistance and biocompatibility. Methods: Solutions of TCP, trisodium citrate, magnesium nitrate, hydroxyethyl cellulose (HEC), and sodium chloride were used to dip-coat AZ31 plates. The coated samples were immersed in 3.5 wt% NaCl solution. Phase evolution was analysed using gravimetry, X-ray diffraction (XRD), energy-dispersive X-ray (EDX) spectroscopy, and scanning electron microscopy (SEM). The biological response of the coated samples was evaluated through MTT and resazurin assays. Results: The coating formed a stable TCP/HEC layer that gradually dissolved over two weeks, converting the surface to magnesium hydroxide, magnesium oxychloride, and magnesium phosphate phases. The formation of brucite, responsible for passivation in the long term, was observed. The coating effectively prevented excessive magnesium oxychloride formation and stabilised magnesium hydroxide after one week. Biological characterization indicated that the coating on AZ31 is safe on the Saos-2 and L929 cell lines. Conclusion: The TCP-based coating enhances the corrosion resistance of AZ31 alloy in salt solutions, promoting passivating phases and limiting corrosive products, thereby ameliorating biocompatibility issues. This coating demonstrates substantial potential for extending the longevity and functionality of magnesium alloy implants.

Improvement of corrosion resistance of AZ31 magnesium alloy by laser remelting/microarc oxidation/LDH composite layer

Laser remelting (LR) pretreatment, micro-arc oxidation (MAO) treatment and layer double hydroxides (LDH) sealing post-treatment are conducted on AZ31 alloy surface in sequence. The results show that the corrosion resistance of prepared LR/MAO/LDH composite layer is significantly improved. Compared with the solution-aged AZ31 alloy and LR/MAO layer, the corrosion current densities of AZ31-LR/MAO/LDH were reduced by 4 and 2 orders of magnitude, respectively, and the self-corrosion potentials were increased by 1.23 V and 0.25 V, respectively. Laser remelting pre-treatment increased the average thickness of the MAO layer by 5–10 μm. LR/MAO/LDH composite layers can effectively improve the corrosion resistance of AZ31 alloy, and have the potential for application.

Enhanced corrosion resistance of AZ31 alloy by laser remelting pre-treatment and Mg/Al-LDH layer

After laser remelting (LR) of magnesium alloys by different processes, a simple hydrothermal method was applied to prepare Mg/Al-layered double hydroxide films (LDHs) on them to improve their corrosion resistance. The results show that LR/LDH can effectively improve the corrosion resistance of magnesium alloys. Comparing to that of the bare AZ31 Mg alloy, the corrosion current density of the AZ31-LR/LDH was decreased by 4 orders of magnitude. LR makes the distribution of LDH more uniform and dense, the physical protection of LR layer and adsorption of Cl− by LDHs inhibit the corrosion of AZ31 alloy.

Elevating the mechanical properties and corrosion resistance of AZ91 alloy by adding CaO and Al element

Elevating the mechanical properties and corrosion resistance of AZ91 alloy by adding CaO and Al element

Anti-Corrosive and Anti-Bacterial Polymeric Coatings Consisting of PCL and Lawsone

The clinical application of magnesium (Mg)-based alloys as biodegradable orthopedic implants is highly restricted because of their rapid corrosion rate in the physiological environment [1]. Polymeric coatings have been recognized as one of the most effective methods to tailor the corrosion rate of Mg alloys without changing their bulk properties, while providing them with other functionalities such as enhanced biocompatibility and antibacterial properties [2]. In this study, a bi-layered anti-corrosive polymeric coating based on polycaprolactone (PCL) and lawsone, a natural corrosion inhibitor extracted from the leaves of Lawsonia inermis plant, was fabricated on AZ31 Mg alloy to improve its corrosion resistance. The result of electrochemical and in vitro immersion studies clearly demonstrated the corrosion inhibitory effect of lawsone and the enhanced corrosion resistance of AZ31 alloy by almost two orders of magnitude (inhibition efficiency of 98.3%) after being coated with PCL-lawsone. Moreover, coated AZ31 substrates exhibited significantly hampered local alkalization and excessive H2 generation. Apart from the corrosion inhibition properties, incorporation of lawsone imparted a strong antibacterial activity to the coating, which is helpful in the prevention of microbial infection and early implant failure. While most of the commonly used corrosion inhibitors are known to be toxic and have limited biomedical applications, no cytotoxic effect was observed for lawsone-containing coating toward human fetal osteoblast cells (viability of > 85%). The findings of this work highlighted the great potential of lawsone as a natural corrosion inhibitor for fabrication of corrosion protective, antibacterial, and biocompatible coatings on Mg-based biodegradable implants. References Wang, Jia‐Li, et al. "Biodegradable magnesium‐based implants in orthopedics—a general review and perspectives." Advanced science 7.8 (2020): 1902443. Asadi, Hamid, et al. "A multifunctional polymeric coating incorporating lawsone with corrosion resistance and antibacterial activity for biomedical Mg alloys." Progress in Organic Coatings 153 (2021): 106157.

Characterization of Prepared Superhydrophobic Surfaces on AZ31 and AZ91 Alloys Etched with ZnCl2 and SnCl2

Superhydrophobic surfaces were prepared using a two-step method that involved the etching of AZ31 and AZ91 magnesium alloys and then modifying the etched alloys with stearic acid. Magnesium alloys etched with ZnCl2 and SnCl2 exhibited surfaces roughened with micro- and nanoscale hierarchical structures consisting of two chemically distinct regions (Zn/Zn(OH)2 or Sn/SnO2 and Mg(OH)2). An optimum etching time of ten minutes was chosen for both etchants. Superhydrophobic surfaces with the highest contact angle were prepared when stearic acid reacted with the etched alloys at 50 °C for 4 h. Stearic acid was bound as zinc stearate and magnesium stearate on Mg alloys etched with ZnCl2 and SnCl2 solutions, respectively. The superhydrophobic process on AZ31 alloys etched with ZnCl2 and SnCl2 improved the corrosion resistance in phosphate buffered saline (PBS) solution compared to bare AZ31 alloy, with the use of ZnCl2 etchant leading to better results. An improvement in the corrosion resistance of AZ91 alloy was observed when the stearic-acid-modified AZ91 alloy was etched with SnCl2. In contrast, the use of ZnCl2 etchant to pretreat AZ91 alloy resulted in a significant deterioration in corrosion properties compared to bare AZ91 alloy. The microstructure of the Mg alloy had an impact on the etching and modification process. On the basis of the findings, a characterization of the chemistry of etching magnesium alloys and the formation of superhydrophobic surfaces was proposed. Magnesium alloys were prepared with superhydrophobic surfaces, incorporating antibacterial metals, features which may increase their potential for use in medical applications.

Corrosion resistance of AZ31 alloy after treatment with high current density impulse or/and laser irradiation in Hank’s solution

In this article, we have introduced a new method that can improve the corrosion resistance of AZ31 alloy. We compared the biodegradation of AZ31 alloy foil treated with a high current density impulse (HCDI), laser irradiation (LI) and HCDI-LI with that of the untreated one. The rate of the biodegradation of AZ31 alloy treated with HCDI-LI was lower than those of the untreated one, the alloy treated with HCDI or LI. Thus, the improved corrosion resistance of the AZ31 alloy treated with HCDI-LI allows its use for medical purposes.

Traditional Chinese medicine extracts as novel corrosion inhibitors for AZ91 magnesium alloy in saline environment.

Zingiber officinale Roscoe extract, Raphanus sativus L. extract, Rheum palmatum extract, Coptis chinensis extract, Glycyrrhiza uralensis extract (GUE), Potentilla discolor extract (PDE) and Taraxacum officinale extract (TOE) were screened for the green corrosion inhibitors of AZ91 alloy in saline environment. The experiment results demonstrated that GUE, PDE and TOE can significantly enhance the corrosion resistance of AZ91 alloy by 73.4, 87.6 and 84.6%, respectively. Surface characterization using FTIR, UV–Vis and XPS revealed that the organic compounds of GUE, PDE and TOE can interact with the alloy surface to form a protective physisorbed film, effectively mitigating the corrosion process of AZ91 alloy. The present results may be helpful to discover the new green inhibitors with high inhibition efficiency for AZ91 alloy.

Effect of ZrSiO4 Concentration on the Microstructure and Corrosion Resistance of MAO Coatings Formed on AZ91 Magnesium Alloy

As a metallic material with lightweight and high specific strength, magnesium alloy has excellent application prospects. However, the rapid corrosion rate and localized corrosion behavior of magnesium alloys limit the practical application in the automobile industry. In this study, to improve the corrosion resistance of AZ91 alloy, the film of different concentrations containing zirconium (AZR0, AZR5, AZR10, AZR15) was prepared on the surface of AZ91 alloy by micro-arc oxidation technology in the Na2SiO3-Na3PO4 system. Furthermore, the influence of electrolyte composition on the corrosion resistance of the MAO film was systematically investigated. The experimental results revealed that the ZrSiO4 particles added in the electrolyte could enter into the MAO film and ZrSiO4 particles were also decomposed into ZrO2 and Mg2Zr5O11 in the process of micro-arc oxidation. More importantly, the formation of micro-cracks and other defects in the film could be reduced after this process. The addition of 15 g l−1 ZrSiO4 in the electrolyte was contributed to the best comprehensive properties of MAO-processed AZ91 specimens, including improved Vickers hardness of 167.16 Hv, Young’s modulus of 652 MPa, and enhanced corrosion resistance (RP = 9.82 × 105 Ω cm2). This approach could provide the approach for developing Mg-based materials with high anticorrosion in industrial fields.

A self-healing corrosion protection coating with graphene oxide carrying 8-hydroxyquinoline doped in layered double hydroxide on a micro-arc oxidation coating

The fabrication of remarkable self-healing coatings is the key to achieving excellent anti-corrosion of magnesium (Mg) alloys. In this research, 8-hydroxyquinoline@graphene oxide (8-HQ@GO) composite was successfully synthesized through ring-opening reaction and a micro-arc oxidation (MAO) coating was grown on AZ31 beforehand. Afterwards, the 8-HQ@GO composite was doped into the layered double hydroxides (LDHs) sheet by hydrothermal chemical transformation based on the MAO coating without introducing any kind of salts. The incorporation of 8-HQ@GO composite and Mg-Al LDHs sheets can distinctly boost the corrosion resistance of AZ31 alloy. The self-healing performance and the anti-corrosion mechanism of MAO-LDHs/HG coating are discussed.

Corrosion and wear resistance of AZ31 Mg alloy treated by duplex process of magnetron sputtering and plasma electrolytic oxidation

In order to improve the wear and corrosion resistance of AZ31 magnesium alloy, a magnetron-sputtered Al layer with a thickness of 11 μm was firstly applied on the alloy, and then treated by plasma electrolytic oxidation (PEO) in an aluminate and silicate electrolytes, respectively. The performance of PEO coatings was investigated by dry sliding wear and electrochemical corrosion tests. The aluminate coating exhibits excellent wear resistance under both 10 and 20 N loads. The silicate coating only shows low wear rate under 10 N, but it was destroyed under 20 N. Corrosion tests show that the Al layer after magnetron sputtering treatment alone cannot afford good protection to the Mg substrate. However, the duplex layer of PEO/Al can significantly improve the corrosion resistance of AZ31 alloy. Electrochemical tests show that the aluminate and silicate coatings have corrosion current densities of ∼1.6×10−6 and ∼1.1×10−6 A/cm2, respectively, which are two orders lower than that of the un-coated AZ31 alloy. However, immersion tests and electrochemical impedance spectroscopy (EIS) show that the aluminate coating exhibits better long-term corrosion protection than silicate coating.

In Situ Observation of the Degradation Behavior and the Systematic Investigation of Corrosion Mechanism in AZ31 Alloy

The degradation behaviors of as‐received and as‐solutionized AZ31 alloys in Hanks’ solution are in situ studied by a 3D digital optical microscope. The initiation and extension processes of corrosion are investigated. Long‐time immersion and electrochemical tests are applied to investigate the corrosion mechanism systematically. The corrosion attacks of as‐received and as‐solutionized AZ31 alloy both start from the grain boundaries (with and without the Al8Mn5 phase) while show no preferential propagation, and the scratches also can act as the corrosion starting positions. The Al8Mn5 phase does not show an obvious accelerated effect on the Mg matrix's corrosion, and it also suffers corrosion. Solid solution treatment can enhance the corrosion resistance of AZ31 alloy is primarily due to the reduced dislocation density. Degradation products on as‐received AZ31 alloy are studied, the Al, Zn, and Mn elements degrade as Al2O3, ZnO, and MnO, respectively.

Influence of graphene particles on the wear and corrosion performance of MAO produced AZ31 alloy

In this study, graphene was incorporated into a micro-arc oxidation coating to improve the wear and corrosion resistance of AZ31 alloy. For this purpose, the different concentration of graphene particles was used as 0 g/l, 0.5, 1, and 2 g/l. The wear tests were performed under loads of 2, 4, and 8 N. The composition and morphology of the coatings were investigated by scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The coating thickness increased with increasing graphene concentration. To evaluate the corrosion performance of the coatings, potentiodynamic polarization, and electrochemical impedance spectroscopy tests were performed after immersed samples for 0.5, 16, and 32 h. The wear test results show that wear rates significantly decreases with increasing graphene concentration. Corrosion tests showed that polarization resistance increased and corrosion current density decreased for the coatings with the graphene addition compared to substrate material.

Quantitative relation of discontinuous and continuous Mg17Al12 precipitates with corrosion rate of AZ91D magnesium alloy

Although qualitative investigations have been performed on the effects of discontinuous and continuous Mg17Al12 precipitates (DP and CP, respectively) on the corrosion resistance of AZ91 alloy, it is not clear whether the change in the corrosion resistance (i.e., an improvement or deterioration) is due to the DP, CP, or the different corrosion experimental conditions used. Herein, the effects of the DP and CP produced by an aging-treatment on the corrosion resistance of the AZ91D Mg alloy were systemically investigated in the same corrosion test condition (i.e. 3.5 wt% NaCl). The morphologies of the DP and CP were controlled by changing the aging-treatment conditions. The area fraction of the DP, the number of CPs per unit area, and the average length of the CPs were quantified as microstructural factors. A quantitative correlation analysis between the corrosion rate and the quantified microstructural factors revealed that the corrosion resistance of the aging-treated AZ91D Mg alloy depended on the DP and CP connectivities. DP with low connectivity accelerated the corrosion by acting as a galvanic source, while DP with high connectivity along the grain boundary functioned as a corrosion barrier, resulting in a reduced corrosion rate. Finely precipitated CPs inside the alloy grains always functioned as a corrosion barrier regardless of their amount and distribution. As the CP connectivity increased, the corrosion rate decreased, and the macroscopic corrosion morphology changed from local to uniform.

Corrosion behavior of electron beam processed AZ91 magnesium alloy

The increasing use of light alloys owing to their high performance makes magnesium alloys very attractive for the use in automotive and biomedical applications. However, it is well known that magnesium and its alloys have poor corrosion resistance in different atmospheric and aqueous environments. As a means of improving corrosion resistance through the microstructure modification, electron beam processing (EBP) was applied on the as-cast AZ91 magnesium alloy. To evaluate the microstructure influence on the corrosion-resistant, the EB processed samples underwent a solution heat treatment and an artificial aging heat treatment. Four different obtained microstructures were investigated by standard microscopy and electrochemical corrosion tests to evaluate the microstructure and its effects on the corrosion resistance of AZ91 alloy. The EBPed specimens show a significant microstructure refinement and homogenous distribution of β-phase at the grain boundaries surrounded by supersaturated α-Mg which acts as a barrier against corrosion. The electrochemical corrosion test of the samples immersed in 3.5 wt% NaCl after 4 weeks indicates that the EBP improves the corrosion resistance of the alloy due to the nobler corrosion potential of supersaturated α-Mg and more stable protective hydroxide films compared to the heat-treated and as-cast conditions.

Effect of friction stir processing and heat treatment on the corrosion properties of AZ31 alloy

ABSTRACT Magnesium alloys are widely used to lightweight the components in the automobile, aerospace, and electronics industries because of their low density and high specific strength. However, factors like low ductility, low mechanical strength, and high corrosion rate restrict the extensive use of the material. To utilise the alloy with improved mechanical and corrosion properties, friction stir processing followed by heat treatment was performed. The study explored the effect of ageing temperature and ageing time on the microstructure, mechanical and corrosion properties of friction stir processed AZ31 alloy. The results indicate that friction stir processing at TRS of 1200 rpm and TTS of 60 mm/min, followed by heat treatment augments the corrosion resistance of AZ31 alloy.

Influence of trace As content on the microstructure and corrosion behavior of the AZ91 alloy in different metallurgical conditions

Abstract The influence of trace As content (0.04, 0.05, 0.06 wt%) on the microstructure and corrosion behavior of AZ91 alloy in different metallurgical conditions (as-cast, as-quenched, peak-aged) was firstly investigated. It is found that the corrosion resistance of AZ91 alloy in all conditions is significantly enhanced by As addition, mainly due to cathodic toxication, melt purification and incidence reduction of local corrosion. As alloying leads to the formation of Mg3As2 and makes the β-Mg17Al12 phase less continuous in the as-cast alloys. The alloy containing 0.06 wt% As obtains a higher corrosion rate than those of the alloy containing 0.05 wt% As owing to a more discontinuity of β phase. The β phase is dissolved into the matrix in the as-quenched alloys and reprecipitates along the grain boundaries after aging. The more continuous β phase distribution in the peak-aged alloys contributes to corrosion resistance. The corrosion rates are in the order of as-quenched>as-cast>peak-aged. The lowest corrosion rate (0.67 mm/y) in 3.5 wt% NaCl solution is obtained in the peak-aged AZ91-0.05As alloy, which is over 70% lower than that of as-cast AZ91 alloy (2.22 mm/y).

Evaluation of corrosion resistance of multipass friction stir processed AZ31 magnesium alloy

AbstractMultipass friction stir processing (FSP) is an effective method to produce a homogeneous microstructure and enhance the mechanical properties of magnesium (Mg) alloys. However, few studies have concentrated on the variation of corrosion resistance of Mg alloys during multipass FSP. Electrochemical alternating current (AC) impedance, polarization behavior, hydrogen evolution, and corrosion morphology were used to investigate the effects of subsequent passes on the corrosion resistance of FSP AZ31 plates. A quasi‐in‐situ observation of the growth of corrosion products was carried out to further study the corrosion behaviors of FSP AZ31 alloy. It is found that subsequent passes could further reduce the grain size of FSP AZ31 alloy and result in an increase in the hardness compared with the first pass. Moreover, subsequent passes are beneficial to the improvement in the corrosion resistance of AZ31 alloy. Pitting corrosion occurs in FSP AZ31 plates, which has not changed after subsequent passes.