Corrosion Of AZ91D Magnesium Alloy Research Articles

Synthesis of a green inhibitor and its inhibition behavior on AZ91D magnesium alloy in distilled water

In this paper, a green inhibitor (pheophorbide) was synthesized, and its inhibition mechanism on AZ91D magnesium alloy in distilled water was studied by electrochemical methods, surface analysis technologies, quantum chemical calculation and molecular dynamics simulation. The effect of chloride ions on the inhibition behavior of pheophorbide was also discussed. The results showed that pheophorbide alleviated the corrosion of AZ91D magnesium alloy, and it still had good inhibition effect with the prolongation of immersion time.The addition of 0.5 mg/L chloride ion improved its inhibition efficiency, but reduced its long-term effectiveness. The adsorption of pheophorbide on the surface of AZ91D magnesium alloy conformed to Langmuir adsorption model. The pheophorbide molecules were adsorbed on the surface of AZ91D magnesium alloy in parallel.

Galvanic corrosion behavior between AZ91D magnesium alloy and copper in distilled water

The galvanic corrosion behavior between AZ91D magnesium alloy and copper in distilled water was studied by electrochemical methods and surface characterization. These results showed that the potential difference between coupled metals under coupling condition can be more suitable for the calculation of galvanic current density in galvanic corrosion, and the galvanic effect between them enhances the corrosion of AZ91D magnesium alloy and reduces the protection of corrosion product film. The galvanic current density increases with the rising of temperature and soaking time, and this may be ascribed to the destruction of cathodic hydrogen evolution on the corrosion product film.

Corrosion behavior of AZ91D magnesium alloy in distilled water

The corrosion of AZ91D magnesium alloy has received extensive attention due to the continuous expansion of its application field in recent years. However, the corrosion of AZ91D magnesium alloy in distilled water is relatively few. In this paper, the corrosion behavior of AZ91D magnesium alloy was studied in distilled water by electrochemical tests in combination with weight loss and surface analysis methods. The results indicated that the corrosion rate of AZ91D magnesium alloy increased with the increase of temperature and immersion time. The increase of the corrosion rate of AZ91D magnesium alloy with the increase of immersion time might be attributed to the damage of the structure of corrosion product film by hydrogen evolution, significantly accelerating the anodic process of AZ91D magnesium alloy. It was interesting that, in distilled water, the EIS of AZ91D magnesium alloy excluded an inductive arc in the low frequency region, which indicated that there was no the adsorption and desorption of aggressive ions or the damage and repair of film. The corrosion product film of AZ91D magnesium alloy in distilled water was composed of a compact inner corrosion product film and a loose outer corrosion product film.

Influences of NH4+ ions and thin electrolyte layers (TEL) thickness on the corrosion behavior of AZ91D magnesium alloy

In this study, the influences of NH4 + ions and the thin electrolyte layer (TEL) thickness on the corrosion behavior of the AZ9D magnesium alloy in NH4+‐containing environments were investigated by electrochemical measurements and surface characterization. The experimental results indicate that NH4+ greatly accelerates the corrosion of AZ91D magnesium alloy whether in a bulk solution or in a TEL. As the TEL thickness decreasing, the corrosion resistance of the AZ91D magnesium alloy is strengthened. According to the corrosion morphology, electrochemical analysis, and characterization analysis of corrosion products, the corrosion mechanism of AZ91D under TELs with different thicknesses is divided into three stages: (a) uniformly distributed corrosion pits with deep depth and large size when TEL thickness is higher than or equal to 500 μm; (b) slightly corrosion with randomly distributed corrosion pits and the accumulation of small amount of corrosion product when TEL thickness is between 100 μm and 200 μm; (c) no corrosion pit with only deposition of corrosion product when TEL thickness is lower than or equal to 100 μm. Among which, the roles of NH4+, TEL thickness, and corrosion product are emphasized and discussed in the corrosion process of AZ91D magnesium alloy under TEL with different thicknesses.

Effect of flow velocity on corrosion behavior of AZ91D magnesium alloy at elbow of loop system

A loop system was used to investigate the effect of flow velocity on corrosion behavior of AZ91D magnesium alloy at an elbow of loop system based on array electrode technology by polarization, computational fluid dynamics (CFD) simulation and surface analysis. The experimental results showed that the corrosion rate increased with increasing flow velocity, and a critical flow velocity could exist in the corrosion of AZ91D magnesium alloy. When flow velocity exceeded the critical flow velocity, fluid hydrodynamics was dominant in the corrosion of AZ91D magnesium alloy. On the contrary, the electrochemical factors were dominant.

Galvanic corrosion of magnesium alloy and aluminum alloy by kelvin probe

Galvanic corrosion on samples of AZ91D magnesium alloy coupled with 2A12 aluminum alloy during neutral salt spray test was investigated. The variations of the surface potential were measured using scanning kelvin probe (SKP). The results showed that galvanic effect on the corrosion of AZ91D magnesium alloy is closely related to the potential difference between the anodic and cathodic materials. In the initial period, corrosion only occurred in a narrow area at the coupling interface because of the limited distance galvanic current. Then, the corrosion rate of 2A12 aluminum alloy was accelerated due to its poor stability in strong alkali environment, which was attributed to the strong alkalization caused by the corrosion of AZ91D magnesium alloy. With the increase of the potential of 2A12 aluminum alloy as a result of the continuous covering of corrosion products, the potential difference between the two materials was enlarged, which enhanced the galvanic corrosion.

Study of Flow-Assisted Corrosion of AZ91D Magnesium Alloy in Loop System Based on Array Electrode Technology

A loop system was used to investigate flow-assisted corrosion (FAC) of AZ91D magnesium alloy at an elbow based on array electrode technology by potentiodynamic polarization, computational fluid dynamics, simulation and surface analysis. The experimental results demonstrate the fluid hydrodynamics plays a significant role in the FAC of AZ91D magnesium alloy. The corrosion rate increases from the outer wall to the inner wall of the elbow, with the higher corrosion rate corresponding to the higher flow velocity and larger shear stress at the elbow. The maximum corrosion rate appears at the innermost wall of the elbow, the location with the maximum flow velocity and shear stress.

Improvement of polypyrrole films for corrosion protection of zinc-coated AZ91D alloy

Abstract To improve the protection against the corrosion of AZ91D magnesium alloy provided by conducting polypyrrole (PPy) films, optimization of the electrochemical synthesis of the PPy film was investigated. The bi-layered PPy film was prepared under constant current control, first in a sodium tartrate solution containing molybdate and second in a sodium dodecylsulfate (DS) solution (after the AZ91D alloy was covered by zinc electroplating). Corrosion testing of the zinc-coated AZ91D alloy covered with the PPy film was performed in 3.5% NaCl solution. The more protective PPy film doped with tartrate ions (PPy-Tart film) was formed by the lower current density (CD). Doping of molybdate ions (MoO42−) into the PPy-Tart film significantly improved its corrosion protection properties. When the PPy-Tart-MoO4 layer was covered by an outer PPy layer doped with DS ions, the corrosion protection was further improved. The imposition of ultrasonic waves during the electropolymerization of the inner PPy-Tart-MoO4 layer was effective in the improvement of corrosion protection. The bi-layered PPy-Tart-MoO4/PPy-DS film prepared under ultrasonic irradiation maintained the zinc-coated AZ91D alloy in the passive state during the corrosion test in NaCl solution for 221 h, during which no corrosion products appeared.

A study of environment-friendly synergistic inhibitors for AZ91D magnesium alloy

The synergistic inhibition effect of sodium silicate (SS) and sodium alginate (SA) on the corrosion of AZ91D magnesium alloy was studied by electrochemical impedance spectroscopy and potentiodynamic polarization tests in 3.5 wt% NaCl corrosive solution. Results indicate that the mixed SS and SA inhibitors have the best inhibition efficiency. Infrared and fluorescence spectroscopies were performed to examine the surface. It was found that SA was adsorbed on the surface of AZ91D magnesium alloy. Finally, the synergistic inhibition mechanism of SS and SA was proposed.

Corrosion and self‐healing behaviour of AZ91D magnesium alloy in ethylene glycol/water solutions

AbstractCorrosion behaviour of magnesium alloy‐based engine parts in cooling system is an urgent fundamental issue in automotive field where magnesium alloys are increasingly used. In the present work, the corrosion behaviour of AZ91D magnesium alloys in various ethylene glycol/water solutions was studied by electrochemical measurements and immersion tests at room temperature. The surfaces of the samples after immersion tests were examined using scanning electron microscope (SEM) and X‐ray diffraction (XRD). The results showed that the corrosion rates of AZ91D magnesium alloys decreased with the increase of ethylene glycol concentration in ethylene glycol/water solutions and the corrosion process was dominated by pitting corrosion. A continuous protective film transferred from corrosion products was formed on the corroded surface after sufficient immersion duration in ethylene glycol/water solutions, which is able to heal the corrosion pits. The self‐healing behaviour inhibited the further corrosion of AZ91D magnesium alloy.

High efficiency corrosion inhibitor 8-hydroxyquinoline and its synergistic effect with sodium dodecylbenzenesulphonate on AZ91D magnesium alloy

The inhibition effects of sodium dodecylbenzenesulphonate (SDBS) and 8-hydroxyquinoline (8HQ) on the corrosion of AZ91D magnesium alloy in ASTM D1384-87 corrosive solution were investigated by the electrochemical impedance spectroscopy and potentiodynamic polarization tests. For SDBS, the inhibition effect was not significant. For 8HQ, a monotonic increase in inhibition efficiency was observed as a function of the immersion time, and the component of the film was Mg(8HQ) 2, which was characterized by three spectra methods. Upon mixing 8HQ and SDBS inhibitors, a synergistic inhibition behavior was observed, and a proper synergistic inhibition mechanism was proposed.

Electrochemical noise analysis of the corrosion of AZ91D magnesium alloy in alkaline chloride solution

The corrosion behavior of AZ91D magnesium alloy in alkaline chloride solution was investigated by electrochemical noise (EN). The wavelet transform, as well as noise resistance ( R n) and power spectral density (PSD), had been employed to analyze the EN data. It was revealed that there exist three different stages of corrosion for AZ91D magnesium alloy in alkaline chloride solution, including an anodic dissolution process companying with the growth, absorption and desorption of hydrogen bubbles, a development of pitting corrosion, an inhibition process by protective MgH 2 film. The results demonstrated that energy distribution plot (EDP) was a powerful tool to provide useful information about the dominant process for the different corrosion stages.

Corrosion of AZ91D magnesium alloy with a chemical conversion coating and electroless nickel layer

A chemical conversion treatment and an electroless nickel plating were applied to AZ91D alloy to improve its corrosion resistance. By conversion treatment in alkaline stannate solution, the corrosion resistance of the alloy was improved to some extent as verified by immersion test and potentiodynamic polarization test in 3.5 wt.% NaCl solution at pH 7.0. X-ray diffraction patterns of the stannate treated AZ91D alloy showed the presence of MgSnO 3 · H 2O, and SEM images indicated a porous structure, which provided advantage for the adsorption during sensitisation treatment prior to electroless nickel plating. A nickel coating with high phosphorus content was successfully deposited on the chemical conversion coating pre-applied to AZ91D alloy. The presence of the conversion coating between the nickel coating and the substrate reduced the potential difference between them and enhanced the corrosion resistance of the alloy. An obvious passivation occurred for the nickel coating during anodic polarization in 3.5 wt.% NaCl solution.