Corrosion Resistance Of Magnesium Alloy Research Articles

Microstructure, mechanical and corrosion properties of magnesium alloy bone plate treated by high-energy shot peening

Abstract To enhance the mechanical properties and corrosion resistance of magnesium alloys, high-energy shot peening (HESP) was used. According to the results, the in-situ surface nanocrystallization (ISNC) microstructure was fabricated on the magnesium alloy surface, and its formation mechanism was the coordination among twins, dislocations, subgrain boundary formation and dynamic recrystallization. Under the released surface stress of sample, the residual compressive stress and microhardness rose, thus enhancing compactness of the surface passivation film Mg(OH)2. Besides, the corrosion rate dropped by 29.2% in maximum. In the polarization curve, the maximum positive shift of the corrosion potential of sample was 203 mV, and the corrosion current density decreased by 31.25% in maximum. Moreover, the compression resistance and bending resistance of the bone plate were enhanced, and the maximum improvement rates were 18.2% and 23.1%, respectively. Accordingly, HESP significantly enhanced mechanical properties and corrosion resistance of magnesium alloys.

Effect of extrusion treatment on mechanical, thermal conductivity and corrosion resistance of magnesium alloys

The effect of extrusion treatment on the mechanical, thermal and corrosion resistance of Mg–La–Zn–Zr alloys were presented. It is suggested that the amount of recrystallized grains played a major role in both mechanical properties and thermal properties. It should be noted the as-cast alloy shows the best thermal conductivity reached the value about 137.507 W/(m · K), however, the mechanical performance of magnesium alloys does not reach the expected results. The thermal properties of extruded alloys have slightly decreased and then increased with the increase of extrusion temperature. Then the tensile properties of Mg–La–Zn–Zr were significantly improved after extrusion treatment. Furthermore, with the increase of extrusion temperature, the elongation-to-fracture increased substantially. After extrusion treatment, the corrosion driving force of the alloy decreases, which reduces the corrosion tendency of the magnesium alloy. The alloy presented in this paper is expected to be applied in industry.

Ultrasonic aqueous synthesis of corrosion resistant hydroxyapatite coating on magnesium alloys for the application of long-term implant.

For the orthopedic application, the promising biodegradable magnesium alloys gained increasing attention. In order to improve the interface bonding strength and corrosion resistance of magnesium alloys, a novel ultrasonic aqueous synthesis approach was performed to produce hydroxyapatite coating on biodegradable magnesium alloys. The effect of ultrasonic time on the composition, microstructure, interface bonding strength and corrosion resistance of HA coated magnesium alloys were investigated. A dense and crack-free HA coating was synthesized by only ultrasonic cavitation for 1 h in the aqueous solution containing Ca2+ and PO43- ions and the coating was constituted of bamboo leaf-like HA staggered irregularly, which endowed magnesium alloy with a sufficient interface bonding strength of 18.1 ± 2.2 MPa. The electrochemical performance and mineralization ability of the coated magnesium alloys were carried out in the simulated body fluids. Compared with bare magnesium samples, the coated samples presented excellent corrosion resistance and could rapidly induce apatite formation after only three days of immersion in the simulated body fluid (SBF). Moreover, in the immersion test of 90 days, HA coatings could provide a long-term protection for magnesium alloy substrate, indicating that ultrasonic aqueous synthesized HA coating could be acted as a promising modified biomaterial on magnesium alloys for the orthopedic application.

Fabrication of chitosan/heparinized graphene oxide multilayer coating to improve corrosion resistance and biocompatibility of magnesium alloys.

Due to its good biodegradability and mechanical properties, magnesium alloys are considered as the ideal candidate for the cardiovascular stents. However, the rapid degradation in human physiological environment and the poor biocompatibility seriously limit its application for biomaterials. In the present study, a chitosan/heparinized graphene oxide (Chi/HGO) multilayer coating was constructed on the AZ31B magnesium alloy surface using layer-by-layer (LBL) method to improve the corrosion resistance and biocompatibility. The results of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), Raman spectrum (RAMAN), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) showed that a dense and compact Chi/HGO multilayer coating was fabricated on the magnesium alloy surface. The results of potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), pH value changes and magnesium ion release suggested that the multilayer coating can significantly enhance the corrosion resistance of the magnesium alloy. Moreover, the Chi/HGO multilayer coating could not only significantly reduce the hemolysis rate and platelet adhesion, but also promote the adhesion and proliferation of endothelial cells. Therefore, the Chi/HGO multilayer coating can simultaneously improve the corrosion resistance and biocompatibility of the magnesium alloys.

The study on corrosion resistance of superhydrophobic magnesium hydroxide coating on AZ31B magnesium alloy

Superhydrophobic technology is very practical for anti-corrosion, anti-rust, and anti-fouling in the construction industry, automobile industry and metal industry. Herein, a facile approach was developed to fabricate superhydrophobic and anti-corrosive (SAC) coatings on the surface of magnesium alloy. The magnesium alloy was hydrothermally treated to form a layer of magnesium hydroxide, on which stearic acid (STA) were grafted. The micro-nano structure fabricated by intersected lamellar magnesium hydroxide and low surface energy provided by STA created a superhydrophobic surface with a water contact angle (WCA) of 159°, improving the corrosion resistance of magnesium alloy. The self-growing superhydrophobic coating is of strong adhesion. With the X-cut on the surface of magnesium alloy, the corrosion appeared just along the X-cut without any spread even after 10-day immersion in 3.5 wt.% NaCl aqueous solution, indicating good corrosion resistance and durability. This approach for fabricating SAC magnesium alloys is simple, cost-effective and eco-friendly, demonstrating significant advantages in practical application.

In Vitro and in Vivo Degradation Behavior and Biocompatibility Evaluation of Microarc Oxidation-Fluoridated Hydroxyapatite-Coated Mg-Zn-Zr-Sr Alloy for Bone Application.

Magnesium and its alloys are biodegradable materials with great potential for biomedical development; however, their high rate of degradation in biological environments limits the widespread application of these materials. In order to improve the corrosion resistance of magnesium alloy, a functional calcium phosphate coating was prepared on Mg-3Zn-0.5Zr-0.5Sr alloy by microarc oxidation (MAO) combined with chemical deposition of fluoridated hydroxyapatite (FHA). A dense calcium-phosphorus coating 6 μm thick composed of needle-shaped fluoridated hydroxyapatite formed on the surface of the MAO layer. The MAO-FHA coating exhibited good mineralization ability to induce hydroxyapatite deposition on its surface during degradation testing in simulated bodily fluids.

Newly-Developed Molybdate-Based Protective Coatings for AZ31D Magnesium Alloys

Molybdate-based eco-friendly protective coatings were developed for AZ31D magnesium alloy. Mg AZ31D substrates treated first in boiling molybdate for oxide thickening pretreatment followed by molybdate chemical conversion coating. Highly protective and uniformly distributed molybdate coatings were deposited over Mg AZ31D substrates. The corrosion resistance enhanced from ~ 2 KΩ.cm2 for the as-polished samples to ~ 8 KΩ.cm2 for the samples treated under the boiling molybdate conditions. The high performance of molybdate-based coatings can be attributed to molybdenum oxide role in rejecting chloride ions. It also stimulates blocking the pits and cracks initiated at the surface under the effect of corrosive medium attack. The designed coating treatment is characterized by its simplicity in which it can be deposited over the Mg AZ31D surface at room temperature via a free immersion technique. The eco-friendly coatings seems very promising and effective for improving the corrosion resistance of magnesium alloys in chloride containing solutions. Subsequent organic top coats are needed for adequate corrosion protection performance. The newly-developed approach can be extended to include other boiling solutions for oxide thickening as well as other metal substrates to explore its universal application.

A Zinc-Rich Coating Fabricated on a Magnesium Alloy by Oxide Reduction

The corrosion resistance of magnesium alloys could be enhanced by covering metallic coatings on the surface. The zinc-rich coating is one of these metallic coatings. To fabricate a zinc-rich coating on magnesium alloys, the substrate should be pretreated carefully, and a protective atmosphere is usually required. In this research, a zinc-rich coating was successfully fabricated on the AZ91D magnesium alloy in air by a diffusion alloying method, with zinc oxide as the zinc source. At the same time, the pretreatment of the magnesium alloy matrix was greatly simplified. The as-diffusion-alloyed zinc-rich intermetallic layer was investigated, utilizing SEM, EDS, and XRD, respectively. It is inferred that zinc oxide was reduced into Zn atoms by the active Mg atoms, and the Mg atoms were coming from the magnesium alloy matrix. Then the Zn atoms passed through the oxide film and formed an intermetallic layer on the magnesium alloy surface. Thus, taking advantage of the activity of Mg atoms, magnesium alloys could be surface alloyed with oxides.

Silk fibroin film-coated MgZnCa alloy with enhanced in vitro and in vivo performance prepared using surface activation

Magnesium and its alloys have generated considerable interest as one of the most promising biodegradable metals for biomedical bone implants. However, the enormous challenges are to improve their rapid corrosion excessively as well as to endow them with biocompatibility and biosafety. Herein, we introduce a natural silk fibroin protein coating to control the corrosion resistance and enhance the biocompatibility of MgZnCa alloy. To obtain a robust and reliable coated structure, different surface-activation processes are employed to increase the available functional groups on MgZnCa surfaces before coating. Compared to oxygen plasma activation, our unique vacuum ultraviolet-ozone (VUV/O3) activation method is effective in realizing uniform silk fibroin films as a protective barrier on MgZnCa alloy surfaces, and the nanoscratch test verified the superior adhesion strength of the silk fibroin-coated magnesium alloy structure. Long-term immersion results combined with electrochemical tests showed the preferable in vitro anticorrosion behavior and a low degradation rate of coated Mg alloy (1/8 times that of uncoated Mg alloy). Cell adhesion and cytotoxicity tests demonstrated that silk fibroin-coated MgZnCa presented improved biocompatibility with bone marrow mesenchymal stem cells. An animal study involving silk fibroin-coated MgZnCa implanted on one side of a rabbit spine for 180 days showed remarkably improved in vivo corrosion resistance, with 1/18 times the degradation rate of uncoated MgZnCa. These results not only comprehensively confirmed the validity of the VUV/O3-activation method as a coating strategy but also implied the tremendous potential of the modified Mg alloy for application as a degradable biomedical implant material. Statement of SignificanceMgZnCa alloy is a promising material in clinical implantation. Silk fibroin (SF) is a natural organic material with biocompatibility and biodegradability. To date, the combination of SF and MgZnCa alloy has exhibited considerable prospects for orthopedic applications. The realization of a direct coating is an enormous challenge because strong chemical bonds cannot be easily formed between organic and inorganic materials. To solve this bottleneck, we proposed a unique vacuum ultraviolet-ozone (VUV/O3) surface-activation method for the first time to modify the Mg alloy surface before SF coating, which significantly enhanced both in vitro and in vivo performance, such as superior biocompatibility and remarkably improved corrosion resistance of magnesium alloys (∼1/18 the in vivo degradation rate of uncoated MgZnCa).

An approach to fabricating protective coatings on a magnesium alloy utilising alumina

There are various methods available to enhance the corrosion resistance of magnesium alloys. Here, through utilising microstructure observations and phase identification, we show that, even with stable alumina, magnesium alloys can have their surface strengthened. Active magnesium atoms can be utilised to reduce the alumina and produce aluminum atoms. Aggregation of aluminum atoms on the magnesium alloy surface leads to an Al-rich intermetallic layer, which could enhance the corrosion resistance of the magnesium alloy. This is a new approach to protect magnesium alloys which takes advantage of the activity of magnesium atoms to fabricate protective coatings.

Study on the preparation and corrosion resistance of hydroxyapatite/stearic acid superhydrophobic composite coating on magnesium alloy surface

Magnesium alloys have been widely used as a new medical metal implant material because of their good physicochemical properties, biodegradability and biocompatibility. But magnesium alloys are very chemically active and easily corroded after being implanted in the human body. In this paper, a hydroxyapatite/fatty acid salt superhydrophobic composite film was prepared on the surface of magnesium alloys by hydrothermal method. By testing, the water contact angle of the prepared composite film layer reaches 154.5°, and the corrosion current density is reduced by two orders of magnitude, which effectively improves the corrosion resistance of magnesium alloys. The hydrophobic properties of the prepared superhydrophobic composite membrane show good chemical stability. This preparation method can have good application prospects in industry and medical materials because of its simplicity and efficiency.

Effects of Extrusion on Mechanical and Corrosion Resistance Properties of Biomedical Mg-Zn-Nd-xCa Alloys.

Magnesium alloys act as ideal biomedical materials with good biocompatibility. In this paper, the extruded biomedical Mg-6Zn-0.5Nd-0.5/0.8Ca alloys were prepared and their microstructure, mechanical properties and corrosion properties were investigated. The results showed that the surfaces of Mg-6Zn-0.5Nd-0.5/0.8Ca alloys extruded at medium temperature were smooth and compact without cracks. The tensile strength and elongation of Mg-6Zn-0.5Nd-0.5/0.8Ca alloys were 222.5 MPa and 20.2%, and 287.2 MPa and 18.4%, respectively. A large number of dislocations were generated in the grains and on grain boundaries after the extrusion. The alloy was immersed in simulating body fluid (SBF) for the weightlessness corrosion, and the corrosion products were analyzed by FTIR, SEM equipped with EDS. It was found that the corrosion rate of Mg-6Zn-0.5Nd-0.5Ca and Mg-6Zn-0.5Nd-0.8Ca alloy were 0.82 and 2.98 mm/a, respectively. Furthermore, the compact layer was formed on the surface of the alloy, which can effectively hinder the permeation of Cl− and significantly improve the corrosion resistance of magnesium alloys.

Degradable magnesium-based alloys for biomedical applications: The role of critical alloying elements.

Magnesium-based alloys exhibit biodegradable, biocompatible and excellent mechanical properties which enable them to serve as ideal candidate biomedical materials. In particular, their biodegradable ability helps patients to avoid a second surgery. The corrosion rate, however, is too rapid to sustain the healing process. Alloying is an effective method to slow down the corrosion rate. However, currently magnesium alloys used as biomaterials are mostly commercial alloys without considering cytotoxicity from the perspective of biosafety. This article comprehensively reviews the status of various existing and newly developed degradable magnesium-based alloys specially designed for biomedical application. The effects of critical alloying elements, compositions, heat treatment and processing technology on the microstructure, mechanical properties and corrosion resistance of magnesium alloys are discussed in detail. This article covers Mg-Ca based, Mg-Zn based, Mg-Sr based, Mg-RE based and Mg-Cu-based alloy systems. The novel methods of fabricating Mg-based biomaterials and surface treatment on Mg based alloys for potential biomedical applications are summarized.

Improvement of corrosion resistance of magnesium alloy by high-temperature high-pressure cavitation treatment

In this study, basic research on the formation of a film for improving the corrosion resistance of a Mg alloy (AZ31) surface was carried out by the addition of dilute phosphoric acid during water jet peening (WJP) and multifunction cavitation (MFC). These mechanochemical (MC) processes are referred to as MC-WJP and MC-MFC, respectively. MC-WJP and MC-MFC processing formed a film on the AZ31 alloy surface that contained phosphate compounds, including oxides, hydroxides, and carbides. Because MFC or WJP processing forms fine cracks on the alloy surface, we concluded that a thick film was formed on the “MC” surfaces because phosphoric acid adhered to these cracks. The film formed on the surface processed by MC-MFC was thicker than that formed on the MC-WJP processed surface because the former process produces higher-temperature cavitation bubbles.

Ratio of total acidity to pH value of coating bath: A new strategy towards phosphate conversion coatings with optimized corrosion resistance for magnesium alloys

In this work, with the aid of thermodynamic equilibrium calculations, a crucial contributor, i.e. total acidity/pH value (TA/pH), was proposed for the first time to guide the design of the chemical formulation of metal-phosphate-based conversion coatings having excellent corrosion resistance for Mg alloys. The present study and published works were compared to validate the proposed theory and correlation between the TA/pH and corrosion resistance of the resulting coatings. A significant contribution of this work was the elucidation of the kinetic role of the buffering nature of chemical bath in regulating the formation of corrosion resistant phosphate conversion coatings.

The Effect of High‐Pressure Torsion on Microstructure, Hardness and Corrosion Behavior for Pure Magnesium and Different Magnesium Alloys

Severe plastic deformation by high pressure torsion (HPT) is used to process and refine the grain structure of commercial purity magnesium and AZ31, AZ91, and ZK60 magnesium alloys. Transmission electron microscopy shows that the microstructure of pure magnesium is characterized by a bi‐modal grain size distribution with grains in the range of a few microns and ultrafine grains after HPT, whereas the magnesium alloys display a homogeneous ultrafine grain structure after processing. X ray diffraction analysis reveals that the AZ91 alloy displays the largest lattice microstrain and this alloy also exhibits the highest hardness after processing. The processed AZ31 and the ZK60 alloys show similar microstructures and maximum values of hardness. Contrary to earlier reports of significant improvements in the corrosion resistance of magnesium alloys in biological environments, the present results show that processing by HPT has no significant effect on the corrosion behavior of magnesium alloys in a 3.5% NaCl solution. By contrast, pure magnesium exhibits an increased corrosion resistance after HPT.

Interfacial characteristics of Zn/AZ31/Zn clad sheets fabricated by hot roll-bonding and annealing

ABSTRACTThe Zn/AZ31/Zn tri-layer clad sheets are prepared by hot roll-bonding technology and post-roll annealing in this study and the interfacial microstructure, mechanical and corrosion properties are investigated. The annealing temperature can influence the interfacial bonding behaviour. Upon annealing at 200°C, a good metallurgical bonding interface composed of Mg4Zn7 and MgZn2 phases is obtained. A higher temperature (300°C) can induce the precipitation of the brittle Mg2Zn11 phase at the interface. The clad sheets annealed at 200°C can attain the maximum bonding strength among all the clad sheets investigated. Importantly, the corrosion rate can be obviously reduced by cladding pure Zn layer on both sides of AZ31 alloys, which provides another effective method to improve the corrosion resistance of magnesium alloys.

Synergistic effect of hydrophobic film and porous MAO membrane containing alkynol inhibitor for enhanced corrosion resistance of magnesium alloy

Magnesium and magnesium alloys have important applications in aviation, electronic devices, medical equipment, and automotive industries, while the corrosion is a common and real problem that must be solved for these applications. In this paper, a novel and effective anti-corrosive composite coating on AZ31 Mg alloys was prepared by the combination of micro-arc oxidation (MAO) layer, corrosion inhibitor and hydrophobic wax film technologies. And among these, the MAO treated micro- and nanopores as the container of corrosion inhibitor and the solid hydrophobic wax as the multifunctional sealing isolating agent. The morphology and phase composition of the resulting composite coatings were investigated by field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD), respectively, indicating the successful synthesis of the organic-inorganic composite coating. The potentiodynamic polarization and electrochemical impedance spectroscopy measurements showed that compared with the MAO membrane covered Mg alloys, the organic-inorganic composite coating has superior corrosion resistance with the a lower corrosion current (5.764 × 10−9 A/cm2) and a higher protection efficiency (99.7%) after immersion in 3.5 wt% NaCl solution, attributing to the synergistic effect of effective inhibition of inhibitor and the physical barrier ability of hydrophobic film and MAO membrane. This simple and low cost strategy to fabricate organic-inorganic composite anticorrosion coatings would have promising applications in the corrosion protection of the light metals and their alloys.

Corrosion resistant coatings based on synergistic effects of alkaline etching and molybdate treatment for AZ31D magnesium alloy

ABSTRACTEco-friendly, non-toxic protective coatings deposited from molybdate–based solutions have been developed as undercoat thin-films (for subsequent organic top coats) for AZ31D magnesium alloy. Direct treatment of Mg AZ31D substrates with molybdate–based solutions has no significant effect on the overall surface resistance (charge transfer resistance). Alkaline etching of Mg AZ31D surfaces using KOH solution prior to molybdate conversion coating showed significant enhancement in the corrosion resistances The optimum conditions of alkaline etching and molybdate treatment steps have been determined. The total surface resistance was improved from 2.1 × 103 Ω.cm2 (for as-polished AZ31D) to be 3.2 × 103 Ω.cm2 for the alkaline etched samples followed by 10 g L−1 molybdate treatment. The resistance to localised corrosion (pitting and crevice) improved significantly after applying the alkaline etching step. Molybdate–based coatings formed on Mg AZ31D exhibited a network of flower-like and needle-like protective molybdenum oxide structures which are belived to be responsible for the improvement in the pitting and crevice corrosion resistance. They impede the corrosive media from reaching the bare metal and hence improve the pitting and crevice corrosion resistances. This simple eco-friendly, low-toxicity pretreatment approach seems very promising and effective for improving the corrosion resistance of magnesium alloys in chloride containing solutions.

Anticorrosion Performance of LDH Coating Prepared by CO2 Pressurization Method

Many surface treatment methods are used to improve the corrosion resistance of magnesium alloys. LDH (layered double hydroxides) conversion coatings are currently found in the most environmentally friendly and pollution-free coatings of magnesium alloy. In this study, the CO2 pressurization method was applied to the preparation of LDH coating on magnesium alloy for the first time. The effect of CO2 pressurization on the formation and corrosion resistance of LDH coating on AZ91D alloy was investigated. The hardness and adhesion were significantly higher on LDH coating in the case of CO2 pressurization than it is in atmospheric pressure. The surface and cross-sectional morphologies show that LDH coating is more compact in the case of CO2 pressurization than with atmospheric pressure. The results of the polarization curve, hydrogen evolution, and immersion tests indicate that the corrosion resistance of the LDH coating prepared by the CO2 pressurization method was significantly improved.