Corrosion Resistance Of Magnesium Alloy Research Articles

Investigations of microstructure and corrosion resistance of WC-Co and WC-Cr3C2-Ni coatings deposited by HVOF on magnesium alloy substrates

Magnesium alloys have found widespread application in various industries, mainly due to the combination of low density, the best structural material known today, and high strength to weight ratio. However, the use of magnesium alloys is limited due to their poor wear and corrosion behavior. In this study, two commercial powders, agglomerated and sintered WC-Co and WC-Cr3C2-Ni were thermally sprayed to deposit coatings onto two magnesium alloy substrates (AZ31 and AZ91) with a combination of two different spraying distances (320 and 400 mm). The main aim of this work was to investigate the microstructure and corrosion resistance of the coatings deposited by High Velocity Oxy Fuel (HVOF) spraying. The morphology and microstructure of the sprayed coatings were analyzed by Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD). Additionally, porosity, microhardness and surface roughness were examined. Furthermore, potentiodynamic polarization was used to characterize the corrosion behavior of the deposited coatings. The experimental results showed that manufactured coatings are characterized by a dense microstructure with porosity typical for coatings sprayed with the HVOF method. Moreover small cracks and unmelted carbide particles embedded in the metal matrix were found in the as-sprayed coatings. Based on the results of the potentiodynamic studies it was found that the corrosion resistance of AZ31 and AZ91 magnesium alloys is not very high in a sodium chloride solution. The polarization resistance of AZ31 is very low (241.3 Ω∙cm2) and the corrosion current density is high (57.4 μA∙cm−2), whereas for AZ91 these values are 17.8 Ω∙cm2 and 1612.1 μA∙cm−2, respectively. The corrosion potential of the AZ31 and AZ91 alloy equal −1.56 V which is characteristic for magnesium alloys in a NaCl solution. For both type of substrates, better corrosion resistance has been obtained for the WC-Co coating. The Rp value was nearly 150 times higher than the one for uncoated AZ91 alloy, whereas for AZ31 the polarization resistance was about 17 times higher (Rp = 4.2 kΩ∙cm2) in comparison to non-covered alloy. In summary, all deposited coatings improved the corrosion resistance of the magnesium alloy. However, the WC-Co one protects the magnesium substrate against corrosion more effectively than the WC-Cr3C2-Ni.

Preparation and performance study of corrosion-resistant surfaces of magnesium alloys

Magnesium alloy has good application prospects in high-precision industries such as electronics and aerospace due to its low density, high stiffness, and excellent properties. However, the poor corrosion resistance of magnesium alloy limits its wide application. In this study, a corrosion-resistant protective coating of magnesium hydroxide doped with nano-silica was grown in situ on a magnesium alloy substrate by the hydrothermal method. The morphology, composition, structure, and corrosion resistance of the coating were investigated by scanning electron microscopy, FTIR, XRD, and electrochemical processes, respectively. The results showed that the prepared coating had good corrosion resistance, as the corrosion current of the magnesium alloy was reduced by about four orders of magnitude for the bare magnesium alloy substrate.

Corrosion resistance of AlN monolayer and Al/AlN multilayer deposited by filtered cathodic vacuum arc

The AlN monolayer and (Al/AlN)5 multilayer coatings were deposited on AZ31 magnesium alloys by filtered cathodic vacuum arc technology. The AlN monolayer showed a dense structure, but there were some holes at the coating/substrate interface. The (Al/AlN)5 multilayer showed a compact layered structure and the holes were interrupted by the Al/AlN interface. Both AlN monolayer and (Al/AlN)5 multilayer provided excellent corrosion resistance for magnesium alloys, with low corrosion current density of 1.91 × 10−6 and 1.11 × 10−6 A/cm2, respectively. Better corrosion resistance of the (Al/AlN)5 multilayer is attributed to its denser layered structure, better adhesion strength, better crack propagation resistance, and deformation coordination between coating and substrate during corrosion.

Corrosion behavior and protective performance of robustness mineralized layer formed on AZ80-0.38Nd (wt%) alloy

In our previous work, a novel robustness mineralized layer was prepared on surface of AZ80–0.38Nd (wt%) alloy, which mainly consisted of rod-like structure MgCO3•3 H2O and flake structure 4MgCO3•Mg(OH)2•4 H2O. The mineralized layer exhibited outstanding robustness structure. While its corrosion protection for magnesium alloy has not been explored. In this paper, the corrosion behavior and protective performance of the robustness mineralized layer were investigated via hydrogen evolution and electrochemical measurements, systematically. The results show that the mineralized layer exhibited excellent anti-corrosion property in the NaCl solution compared with the oxide layer, due to the outstanding impermeability. And the mineralized layer presented better corrosion passivation and micro-galvanic corrosion inhibition effects due to the characteristics of slight defects and good adhesion to matrix. Besides, the mineralized layer could launch CO32− during degradation of corrosion, which slowed down the penetration of Cl− across the layer and inhibited the attack of Cl− on magnesium substrate. The fabrication of robustness mineralized layer on magnesium alloys surface provides a novel effective strategy for improving the corrosion resistance of magnesium alloys.

Enhancing corrosion resistance of magnesium alloys via combining green chicory extracts and metal cations as organic-inorganic composite inhibitor

Organic inhibitors provide advantages for corrosion protection through formation of chelation layers. However, individual inhibitors have weak inhibition efficiency when they are exposed to neutral media containing chloride ions. In this study, corrosion resistance of Mg alloy AZ91D is synergistically enhanced by combining green chicory (CA) extracts with metal cations (Ca2+, Fe3+, Fe2+, and Ni2+). The Mg(OH)2 and MgO corrosion products are porous in the early stages of immersion. The main organic compounds in CA including caffeic acid (Caf) and chicoric acid (Chi), which combine with inorganic cations via chelation reaction, are adsorbed on the corroded area. The large Bader charge and adsorption energies of Chi-Calcium-Chi (CaChi) complexes determined through density functional theory calculations suggest that CaChi interacts strongly with inorganic cations. The combined organic–inorganic inhibitors can therefore be absorbed firmly on the Mg substrate to form an active inhibitory layer. Among the various investigated CA-cation mixtures, CA-Ca2+ exhibited the highest anti-corrosion effect after immersion for 120 h and a corrosion current density (icorr), corrosion potential (Ecorr), and inhibition efficiency (η) of 0.09 ± 0.03 μA·cm−2, –0.87 ± 0.03 V (vs. SCE), and 92%, respectively. This work provides an effective approach for corrosion protection through combination of organic and inorganic inhibitors.

The effects of chemical conversion parameters on morphology and corrosion performance of calcium phosphate coating on AZ31 alloy

To improve the corrosion resistance of magnesium alloy, Ca–Ph coatings were prepared on AZ31 alloy substrates by chemical conversion. The treatment time and temperature have been adjusted to prepare the coatings with various morphologies, compositions, and properties. The surface morphologies and chemical compositions were investigated using a scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS), and the phase structure was investigated using X-ray diffraction (XRD). The corrosion performance of the coatings was investigated by an electrochemical test and immersion test. All the coatings showed significant corrosion protection to the substrate in the simulated body fluid (SBF) solution. The coating prepared at 5 h duration was thicker than other coatings but with the lowest corrosion current density in the electrochemical test and weight loss studies after being immersed in the SBF solution for 7 days had the slightest loss. The results showed that higher temperatures favored the presence of hydroxyapatite and that the coating thickness had an enhanced influence on the corrosion performance.

Wettability and Salt Spray Corrosion Resistance of Magnesium Alloys Treated with Laser Surface Texturing

Wettability and Salt Spray Corrosion Resistance of Magnesium Alloys Treated with Laser Surface Texturing

Improving the Corrosion Resistance of Magnesium Alloy by Magnesium Phosphate/Glass Composite Coatings Using Sol–Gel Method

Coating of Mg alloys with Mg-phosphate is usually performed by complex and costly methods. This work was mainly aimed at using Mg-phosphate ceramic for Mg metal implants by simple and cost-effective spin coating combined with a sol–gel approach. Where, Mg-phosphate ceramic particles were dispersed with different percentages (0, 10, and 30 wt. %) in the glass sol (85 SiO2 – 10 CaO – 5 P2O5 system) as a coating solution. The coated substrates were characterized by TGA, XRD, FTIR, contact angle, and SEM/EDX analyses, and the in vitro bioactivity test was performed in revised simulated body fluid (rSBF). The results showed the coating thickness was 8.8 ± 0.8, 5.4 ± 0.6, and 5 ± 0.7 μm for MP0, MP10, and MP30, respectively. Moreover, the coatings increased the hydrophilicity of the metal surface. All coatings enhanced the formation of an apatite-bone like layer on the Mg metal surface, and they were viable with oral epithelial cells at a concentration ≤ 125 μg/ml. Moreover, MP0 and MP10 coatings significantly enhanced the corrosion resistance of the metal, while; MP30 coating did not show a significant effect on it. Thus, the percentage of Mg-phosphate in the coating was valuable for corrosion resistance when it was ≤ 10 wt. %. As a result, the composite coatings showed promising coatings for Mg metal substrate to enhance its corrosion resistance at low percentages of Mg-phosphate ceramic.

Effect of magnesium-to-phosphate ratio on the corrosion resistance of magnesium alloy embedded in magnesium potassium phosphate cement

Effect of magnesium-to-phosphate (M/P) ratio on the corrosion resistance of magnesium alloys embedded in magnesium phosphate cement pastes was studied via electrochemical methods and surface characterizations in this study. Results show that corrosion resistance of magnesium alloy increased with the increased M/P ratio. pH played a dominant role in protective capability of oxide film formed on magnesium alloy. M/Ps 7 and 12 leads to formation of oxide film mainly consisting of magnesium phosphates. In contrast, an oxide film composed of magnesium and aluminium oxide/hydroxide formed in M/P 17, possibly with adsorption of phosphate ions which further enhances the corrosion resistance.

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.

Effects of Severe Plastic Deformation and Ultrasonic Treatment on the Structure, Strength, and Corrosion Resistance of Mg-Al-Zn Alloy.

Nowadays, there is a great demand for increasing the strength and corrosion resistance of magnesium alloys for their wider use in machine engineering, oil industry, and medicine. This paper is devoted to a study on the effects of the combined process of reduction and equal channel angular pressing, as well as the subsequent ultrasonic irradiation on the structure, strength, and corrosion properties of the Mg-Al-Zn alloy. Deformation processing results in an increase of the strength up to 280 ± 10 MPa. A fine-grained structure is formed with a grain size of 10–20 µm and small recrystallized grains 1–2 µm in size. The corrosion resistance in the HCl medium falls down significantly. Action of ultrasound on the deformed specimen leads to an increased fraction of high-angle boundaries, in particular, the fractions of special, fully overlapping Σ13a boundaries and twin boundaries of Σ15b and Σ17a systems. Due to the ultrasonic treatment, the strength of the Mg-Al-Zn alloy increases up to 310 ± 5 MPa, while the corrosion resistance in HCl almost doubles.

Microstructure and Corrosion Resistance of Two-Dimensional TiO2/MoS2 Hydrophobic Coating on AZ31B Magnesium Alloy

The corrosion resistance of magnesium alloys can be effectively improved by surface treatment. In this study, a hydrophobic two-dimensional (2D) TiO2/MoS2 nanocomposite coating was fabricated on AZ31B magnesium alloy by an electrophoretic deposition method. The corrosion resistance of the coating was evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy analyses. After being modified by a silane coupling agent (KH570), the TiO2/MoS2 coating changed from hydrophilic to hydrophobic, and the static water contact angle increased to 131.53°. The corrosion experiment results indicated that the hydrophobic 2D TiO2/MoS2 coating had excellent anticorrosion performance (corrosion potential: Ecorr = −0.85 VAg/AgCl, and corrosion current density: Icorr = 6.73 × 10−8 A·cm−2). TiO2/MoS2 films have promising applications in magnesium alloy corrosion protection.

Effect of extrusion parameters on degradation of magnesium alloys for bioimplant applications: A review

Magnesium alloys, as a new generation temporary biomaterial, deserve the desirable biocompatibility and biodegradability, and also contribute to the repair of the damaged bone tissues. However, they do not possess the required corrosion resistance in human body fluid. Hot mechanical workings, such as extrusion, influence both the mechanical properties and bio-corrosion behavior of magnesium alloys. This review aims to gather information on how the extrusion parameters (extrusion ratio and temperature) influence the bio-corrosion performances of magnesium alloys. Their effects are mainly ascribed to the alteration of extruded alloy microstructure, including final grain size and uniformity of grains, texture, and the size, distribution and volume fraction of the second phases. Dynamic recrystallization and grain refinement during extrusion provide a more homogeneous microstructure and cause the formation of basal texture, resulting in improved strength and corrosion resistance of magnesium alloy. Extrusion temperature and extrusion ratio are reported as the influential factors in the degradation. The reports reveal that the increase in extrusion ratio and/or the reduction in extrusion temperature cause a decrease in the final grain size, leading to intensification of basal texture, in parallel side of the samples with extrusion line, and to lower volume fraction and size of precipitates in magnesium alloys. These all lead to improving the bio-corrosion resistance of the magnesium alloy implants.

Enhanced corrosion resistance and biocompatibility of an elastic poly (butyleneadipate-co-terephthalate) composite coating for AZ31 magnesium alloy vascular stents

Surface modification has been considered to provide an effective solution to the poor corrosion resistance of magnesium alloys. A large number of relevant studies have demonstrated that various protective coatings can reduce the degradation rate of magnesium alloys, but most of them are for magnesium alloy materials and devices without deformation. For biodegradable magnesium alloy stents, the selection of protective coating is vitally important due to the residual stress during implantation and cyclic loading after implantation. Therefore, compared with commonly used poly-D,l-lactide (PDLLA), a reliable protection was proposed on HF-treated Mg alloy via application of poly(butyleneadipate-co-terephthalate) (PBAT) with high elongation at break in this paper. In the long term, the corrosion resistance of PBAT-F coating of both flake samples and stents was decisively superior to PDLLA, which could be attributed to its outstanding barrier performance and mechanical properties. Simultaneously, PBAT composite coating exhibited better hemocompatibility and higher cell proliferation rates. The above results show that PBAT is an excellent coating material for vascular stents whereas PBAT composite coating could be a promising candidate as a protective coating for Mg stents.

Preparation and characterization of Y-doped microarc oxidation coating on AZ31 magnesium alloys.

The rapid degradation characteristics of magnesium alloys limit its application in the field of orthopedic fracture fixation and cardiovascular stents. This study aimed to improve the corrosion resistance and biocompatibility of AZ31 magnesium alloys and prepare degradable implant materials. Micro-arc oxidation (MAO) was used to change the concentration of yttrium acetate in the electrolyte to prepare coatings with different yttrium content on the surface of AZ31 magnesium alloy. Through characterization, it is proved that the yttrium in the coating mainly exists in the form of Y3+. The polarization potential experiment shows that the micro-arc oxidation coating significantly improves the corrosion resistance of magnesium alloys. With the increase of yttrium acetate concentration in the electrolyte, the corrosion resistance of the coating first increases and then weakens. When the concentration is 0.0035mol/L, the coating has the highest corrosion resistance. The results of CCK-8 cytotoxicity experiment and cell morphology observation also proved that the cell viability in each group was greater than 140%, and the yttrium-doped coating on the surface of AZ31 magnesium alloy has no cytotoxicity, can promote cell growth, and has good biocompatibility.

Hybrid coating of polydimethylsiloxane with nano-ZrO2 on magnesium alloy for superior corrosion resistance

To enhance the corrosion resistance of magnesium alloys, an organic-inorganic coating of polydimethylsiloxane (PDMS) hybridized with ZrO2 nanoparticles is developed, where the PDMS is selected as the polymeric matrix for superhydrophobic surface, and nano-ZrO2 particles as a physical barrier to strengthen and densify the polymeric matrix. The nanocomposite materials were characterized by field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectrophotometry (FT-IR), and X-ray diffraction (XRD). Electrochemical, dropping corrosion, and salt spray tests were carried out to evaluate the effect of the amount of ZrO2 on the corrosion property of the PDMS-ZrO2 coatings. Thermal stability, hydrophobicity, and corrosion resistance of the composite coatings are substantially improved by the introducing ZrO2 modifier into PDMS matrix. Depending on the ZrO2 content, the PDMS-ZrO2 hybrids exhibit superior corrosion resistance, where the corrosion current density of PDMS-ZrO2 coatings containing 10% (wt.%) ZrO2 decreases about five orders of magnitude compared with Mg alloy substrate. Furthermore, it is noteworthy that ZrO2 nanoparticles are filled in the PDMS matrix to provide a long-term protection in the salt spray test up to 210 h. The PDMS-ZrO2 coatings demonstrate an excellent shielding ability for the Mg alloy, which is attributed to the strong hydrophobic surface of PDMS and compact network structure separated by the physical barrier of ZrO2 nanoparticles in the PDMS chains. The proposed mixed matrix membrane guides a design direction for highly water-repellent coating with a long-term corrosion protection performance.

Liquid-Infused Surfaces with Anti-Corrosion on Magnesium Alloy

The poor corrosion resistance of magnesium alloy has become the main reason restricting its application. In this paper, the layered double hydroxide (LDH) with good compactness was prepared on the surface of magnesium alloy by one-step hydrothermal method. The film thickness was 13 μm. The surface was injected with silicone oil to prepare the Liquid-infused surfaces (LIS). Electrochemical test studies show that the LIS has good corrosion resistance, and the lubricant and LDH on the surface can provide a double lasting physical barrier for magnesium alloy materials, effectively isolating chloride ions from corrosion to magnesium alloy substrates. In addition, the LIS is hydrophobic, which can reduce the contact area (CA) between the NaCl solution and the surface, and further improve the corrosion resistance of the magnesium alloy surface.

Hydroxyapatite/chitosan-metformin composite coating enhances the biocompatibility and osteogenic activity of AZ31 magnesium alloy

The rapid degradation rate of degradable magnesium alloys limits their application as orthopaedic implants. To improve the osteogenic activity and corrosion resistance of magnesium alloys, a hydroxyapatite/chitosan-metformin (HA/CS-MF) composite coating was prepared on AZ31 magnesium alloy by hydrothermal treatment. The structure and morphology of the composite coating were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), energy dispersive spectroscopy (EDS), and scanning electron microscopy (SEM). Electrochemical tests and hydrogen evolution experiments were carried out to evaluate the corrosion resistance of the HA/CS-MF composite coating. At the same time, the cytocompatibility, osseointegration ability and anti-inflammatory activity of the HA/CS-MF composite coating were studied. The findings revealed that the HA/CS-MF composite coating exhibits excellent corrosion resistance, biocompatibility and osteogenic activity; can upregulate the expression level of bone-related genes; and is conducive to the polarization of M2 macrophages.

Effect of grain size on the mechanical properties and bio-corrosion resistance of pure magnesium

In addition to grain size, the mechanical properties and corrosion resistance of magnesium alloys depend on other factors such as texture, distribution of alloying elements, and homogeneity of the microstructure. These attributes might change during grain refining processes, making the situation more complex and masking the real effect of grain size. Accordingly, in the present work, the grain size of commercially pure (CP) Mg was adjusted by grain growth annealing after casting and deformation by hot rolling (for grain refinement via dynamic recrystallization during thermomechanical processing) to investigate the effect of grain size on tensile properties, hardness, and bio-corrosion resistance in simulated body fluid (SBF) for biomedical implant applications. The grain growth kinetics of commercially pure Mg was studied, where the grain growth activation energy (Q) was found to be consistent with that of the grain boundary diffusion in Mg. Based on the Hall–Petch plots, it was revealed that the yield stress (YS), ultimate tensile strength (UTS), and hardness of pure Mg are highly sensitive to average grain size in comparison to common Mg alloys. Moreover, based on the polarization curves and Nyquist plots obtained from electrochemical impedance spectroscopy (EIS) analysis, grain coarsening led to the enhanced corrosion resistance due to the decreased grain boundary regions, where a simple linear formula was obtained for correlating corrosion current density to average grain size.

Effect of Rolling Treatment on Microstructure, Mechanical Properties, and Corrosion Properties of WE43 Alloy.

Magnesium alloys show broad application prospects as biodegradable implanting materials due to their good biocompatibility, mechanical compatibility, and degradability. However, the influence mechanism of microstructure evolution during forming on the mechanical properties and corrosion resistance of the magnesium alloy process is not clear. Here, the effects of rolling deformation, such as cold rolling, warm rolling, and hot rolling, on the microstructure, mechanical properties, and corrosion resistance of the WE43 magnesium alloy were systematically studied. After rolling treatment, the grains of the alloy were significantly refined. Moreover, the crystal plane texture strength and basal plane density decreased first and then increased with the increase in rolling temperature. Compared with the as-cast alloy, the strength of the alloy after rolling was significantly improved. Among them, the warm-rolled alloy exhibited the best mechanical properties, with a tensile strength of 346.7 MPa and an elongation of 8.9%. The electrochemical experiments and immersion test showed that the hot working process can greatly improve the corrosion resistance of the WE43 alloy. The hot-rolled alloy had the best corrosion resistance, and its corrosion resistance rate was 0.1556 ± 0.18 mm/year.