Anodization of Mg-alloy AZ91 in NaOH solutions

Barbosa, D. Peixoto; Knörnschild, Gerhard Hans

doi:10.1016/j.surfcoat.2008.12.018

Cited by 31 publications

(9 citation statements)

References 20 publications

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“…Characteristics of PEO coating.-Figure 1 shows the voltage transient (instantaneous value) at a constant applied current density of 5 A=dm 2 during PEO. Consistent with previous reports, 43,44 the voltage transient was divided into two stages. At the first stage corresponding to the conventional anodizing, the cell voltage increased linearly and reached a plateau ($250 V), accompanied by a gaseous evolution without a sparking.…”

Section: Resultssupporting

confidence: 61%

Microstructure Evolution During Plasma Electrolytic Oxidation and Its Effects on the Electrochemical Properties of AZ91D Mg Alloy

Ryu

Mun

Lim

et al. 2011

J. Electrochem. Soc.

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The microstructure development during plasma electrolytic oxidation (PEO) and its influence on the electrochemical corrosion properties of AZ91D Mg alloy were investigated. PEO was conducted in a KF-NaAlO2 electrolyte, and the corrosion properties of PEO coatings were evaluated by potentiodynamic and potentiostatic tests and electrochemical impedance spectroscopy (EIS). At the breakdown voltage, a non-porous, fluoride-containing barrier-type layer with less-crystalline MgAl2O4 and MgF2 was formed. With the intense sparking, a porous layer appeared at the surface. The outer porous layer was a nearly amorphous oxide. The inner dense layer was composed of nano-crystalline MgAl2O4 and MgF2, and its fluoride content and crystallinity increased with PEO time. The existence of MgF2 phase in the innermost layer was clearly demonstrated by high resolution transmission electron microscopy (HRTEM). The potentiodynamic tests indicated that the corrosion potential (E corr) remained relatively constant, but the corrosion current density (i corr) significantly decreased with PEO time. The EIS results revealed that ∼2 orders of magnitude higher resistance of inner dense layer mainly contributed to the improved corrosion resistance of AZ91D Mg alloy. The enhanced corrosion resistance with the progress of PEO was discussed in terms of thickness, fluoride content, and crystallinity of inner dense layer.

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Section: Resultssupporting

confidence: 61%

Microstructure Evolution During Plasma Electrolytic Oxidation and Its Effects on the Electrochemical Properties of AZ91D Mg Alloy

Ryu

Mun

Lim

et al. 2011

J. Electrochem. Soc.

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“…The orthogonal tests were designed to include four-factor and three-level to optimize the PEO electrolyte compositions, as shown Table 1. The levels of these three factors were determined by experience and with reference to the literature [3,[37][38][39]. In the orthogonal experimental study, the electrical parameters are as follows: oxidation time 15 min, current density 1 A/dm 2 , pulse frequency 100 Hz, duty cycle 10%.…”

Section: Coating Prepacyclenmentioning

confidence: 99%

“…This alloy is known as "green engineering material in the 21st century" owing to its various applications such as in the automotive, aerospace and communication industries. However, poor corrosion resistance has become a key issue limiting the widespread use of magnesium alloys [3]. Surface treatment of magnesium alloy is currently the most effective anti-corrosion method by covering the surface of the magnesium alloy with a protective coating to isolate the substrate from the external environment.…”

Section: Introductionmentioning

confidence: 99%

Optimization of AZ31B Magnesium Alloy Anodizing Process in NaOH-Na2SiO3-Na2B4O7 Environmental-Friendly Electrolyte

et al. 2022

Coatings

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The optimization of NaOH-Na2SiO3-Na2B4O7 electrolyte for the plasma electrolytic oxidation of AZ31B magnesium alloy was investigated through orthogonal tests. The properties of the anodized films were evaluated by film thickness, roughness measurements, salt spray tests, scanning electron microscopy (SEM), X-ray diffraction (XRD) and potentiodynamic polarization tests, respectively. The orthogonal tests revealed that the optimal formulation of the electrolyte comprised NaOH 45 g/L, Na2SiO3 50 g/L, and Na2B4O7 90 g/L. NaOH exhibited the most significant effect on film thickness, while Na2SiO3 had the greatest effect on corrosion resistance. Moreover, the optimal electrical parameters were also obtained with the values of current density 1 A /dm2, oxidation time 15 min, pulse frequency 200 Hz and duty cycle of 10%. The surface morphology of the anodized coating formed under optimal conditions was uniform and compact. Furthermore, the phase compositions of all samples were mainly composed of MgO and Mg2SiO4. The corrosion potential, corrosion current density and polarization resistance of the prepared coating by plasma electrolytic oxidation improved remarkably compared with that of the substrate.

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“…However, they have high electrochemical reactivity that limits their applications during service. The surface treatment techniques to improve corrosion resistance of magnesium alloys have been attracted a great amount of researchers in recent years, such as chemical conversion , microarc oxidation , anodization , electroless plating , electroplating , plasma‐chemical oxidation , and so on. But some surface technologies advance corrosion resistance of materials without protecting environment pollution.…”

Section: Introductionmentioning

confidence: 99%

The preparation and corrosion resistance of Al-Ni-Y-Co amorphous and nanocrystalline composite coating

Zhang

Liang²,

Chen³

et al. 2013

Materials and Corrosion

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High velocity arc spraying (HVAS) process was used to deposit Al-Ni-Y-Co amorphous and nanocrystalline composite coating on AZ91 magnesium alloy substrate. The microstructure of the coating was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive spectrometer (EDS) and transmission electron microscopy (TEM). The results show that the coating with thickness of 500 mm presents a dense layered structure with low porosity (1.8%). The coating consists of amorphous, nanocrystalline, and crystalline phases. The microhardness was measured by a microhardness tester. The average values of Vickers hardness for the Al-Ni-Y-Co coating, pure Al coating and AZ91 alloys are about HV 0.1 310, HV 0.1 70, and HV 0.1 60, respectively. The electrochemical corrosion resistance of the coating in 5 wt% NaCl aqueous solution was also investigated, and the results showed that the Al-Ni-Y-Co coating exhibits better corrosion resistance than pure Al coating and AZ91 magnesium alloy.

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Anodization of Mg-alloy AZ91 in NaOH solutions

Cited by 31 publications

References 20 publications

Microstructure Evolution During Plasma Electrolytic Oxidation and Its Effects on the Electrochemical Properties of AZ91D Mg Alloy

Microstructure Evolution During Plasma Electrolytic Oxidation and Its Effects on the Electrochemical Properties of AZ91D Mg Alloy

Optimization of AZ31B Magnesium Alloy Anodizing Process in NaOH-Na2SiO3-Na2B4O7 Environmental-Friendly Electrolyte

The preparation and corrosion resistance of Al-Ni-Y-Co amorphous and nanocrystalline composite coating

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