Study on the Formation Mechanism of Micro-Arc Oxidation Coatings on Magnesium Alloys

2010 ◽  
Vol 650 ◽  
pp. 228-233 ◽  
Author(s):  
Xian Ming Chen ◽  
Cheng Ping Luo ◽  
Jiang Wen Liu
Keyword(s):  
Magnesium Alloys ◽  
Formation Mechanism ◽  
Cellular Structure ◽  
Az91 Magnesium Alloy ◽  
Transmission Electron ◽  
Micro Arc Oxidation ◽  
Az91 Magnesium ◽  
Ac Current ◽  
Means Of Transmission ◽  
Nano Grains

This article concerned with the formation mechanism of the micro-arc oxidization(MAO) coating on magnesium alloys. The micro-arc oxidation ceramic coating on AZ91 magnesium alloy was prepared in a silicate alkaline solution (Na2SiO3:5-30g/l, NaOH: 1-5g/l, KF: 5-8g/l, Na3C6H5O7: 0.5-2g/l, EDTA: 0.5-2g/l). The experiments were carried out in AC current galvanostatic mode with a current density of 20-50A/dm2. The microstructure of the MAO coating was characterized by means of transmission electron microscopy(TEM). Microcrystallite and/or nanocrystallite were found in the MAO coatings, the size of the former was about 50-200nm and the latter was about 20-50nm. Cellular structure was observed in the coatings, which was composed of a lot of micro/nano grains. The grains grew preferentially in some directions during the MAO process, and the cellular structure is formed by the grains growing in a laminar way. The cellular structures also grew and aggregated by laminar way to form the whole MAO coatings.

Influence of 8-hydroxyquinoline on properties of anodic coatings obtained by micro arc oxidation on AZ91 magnesium alloys

2012 ◽  
Vol 539 ◽  
pp. 249-255 ◽  
Author(s):  
R.F. Zhang ◽  
S.F. Zhang ◽  
N. Yang ◽  
L.J. Yao ◽  
F.X. He ◽  
...  
Keyword(s):  
Magnesium Alloys ◽  
Micro Arc Oxidation ◽  
Az91 Magnesium

scholarly journals Synthesis of Nanocrystalline AZ91 Magnesium Alloy Dispersed with 15 vol.% Submicron SiC Particles by Mechanical Milling

Materials ◽  
2019 ◽  
Vol 12 (6) ◽  
pp. 901
Author(s):  
Shitian Su ◽  
Jixue Zhou ◽  
Shouqiu Tang ◽  
Huan Yu ◽  
Qian Su ◽  
...  
Keyword(s):  
Mechanical Milling ◽  
Sem Analysis ◽  
Submicron Particles ◽  
X Ray Diffraction ◽  
Az91 Magnesium Alloy ◽  
Magnesium Matrix ◽  
Pinning Effect ◽  
Sic Particles ◽  
Transmission Electron ◽  
Az91 Magnesium

The development of a magnesium matrix composite with a high content of dispersions using conventional liquid-phase process is a great challenge, especially for nanometer/submicron particles. In this work, mechanical milling was employed to prepare nanocrystalline AZ91 dispersed with 15 vol.% submicron SiC particles (SiCp/AZ91). AZ91 with no SiCp was applied as a comparative study with the same mechanical milling. In order to investigate the mechanism of dispersing, the morphology evolution of powders and the corresponding SiCp distribution were observed. As the scanning electron microscope (SEM) analysis exhibited, the addition of SiCp accelerated the smashing of AZ91 particles, which promoted the dispersion of SiCp in AZ91. Thus, after mechanical milling, 15 vol.% SiCp, which was smashed from 800 to 255 nm, got uniformly distributed in the Mg matrix. Based on X-ray diffraction (XRD) results, part of the Mg17Al12 precipitate got dissolved, and an Al-supersaturated Mg solid solution was formed. The transmission electron microscopy (TEM) results showed that the ultimate Mg grain (32 nm) of milled SiCp/AZ91 was much smaller than that of milled AZ91 (64 nm), which can be attributed to a pinning effect of submicron SiCp. After mechanical milling, the hardness of SiCp/AZ91 reached 185 HV, which was 185% higher than the original AZ91 and 33% higher than milled AZ91, due to fine Mg grain and submicron dispersions.

Effects of Erbium Addition on the Corrosion Resistance and Microstructure of AZ91 Magnesium Alloy

2011 ◽  
Vol 194-196 ◽  
pp. 1221-1224 ◽  
Author(s):  
Zhong Jun Wang ◽  
Yang Xu ◽  
Jing Zhu
Keyword(s):  
Corrosion Resistance ◽  
Magnesium Alloy ◽  
Magnesium Alloys ◽  
Discontinuous Precipitation ◽  
Az91 Magnesium Alloy ◽  
Continuous Precipitation ◽  
Az91 Magnesium ◽  
Precipitation Phase

The microstructures and corrosion resistance of AZ91 and AZ91+0.5 wt.% erbium (Er) magnesium alloys were studied, respectively. The results show that the Er addition in scrap AZ91 magnesium alloy can improve the corrosion resistance, markedly. The discontinuous precipitation phase (DPP) for Mg17Al12was retarded and the amount of DPP was decreased by 41% due to the formation of Al8ErMn4phase during solidification. The amount of continuous precipitation phase (CPP) in grains was decreased by 8% because of the formation of Al7ErMn5phase during solidification.

Corrosion and Protection of Magnesium Alloys

2015 ◽  
Vol 1120-1121 ◽  
pp. 1078-1082 ◽  
Author(s):  
Yang Yang Lv ◽  
Ling Feng Zhang
Keyword(s):  
Corrosion Resistance ◽  
Magnesium Alloy ◽  
Magnesium Alloys ◽  
Automotive Industry ◽  
Physical And Mechanical Properties ◽  
Current Status ◽  
Strain Rates ◽  
Metallic Materials ◽  
Az91 Magnesium Alloy ◽  
Az91 Magnesium

Magnesium alloy as a green material in the 21st century, because of its excellent physical and mechanical properties of metallic materials as an ideal in the automotive industry, electronic industry and aviation, aerospace and other industries[1]. However, poor corrosion resistance of magnesium alloys become an important issue hinder application of magnesium alloys[2]. So magnesium alloy corrosion problems and the current status of research paper reviews several magnesium alloy protection methods at home and abroad, and also highlighted with our latest laser shock (LSP) study of AZ91 magnesium alloy at high strain rates of corrosion resistance results.

Magnesium Alloys as Biodegradable Implants

2009 ◽  
Vol 618-619 ◽  
pp. 83-86
Author(s):  
M. Bobby Kannan ◽  
R.K. Singh Raman
Keyword(s):  
Magnesium Alloy ◽  
Magnesium Alloys ◽  
Electrochemical Impedance ◽  
Alkali Treatment ◽  
Test Sample ◽  
Az91 Magnesium Alloy ◽  
Biodegradable Implant ◽  
Degradation Behaviour ◽  
Az91 Magnesium

In this study, an attempt was made to enhance the degradation resistance of magnesium alloys for potential biodegradable implant applications through surface treatment. AZ91 magnesium alloy was taken as the test sample and was alkali-treated for two different periods of time and then the in vitro degradation behaviour of the alloy was studied using electrochemical impedance spectroscopy and polarization techniques in simulated body fluid. The study suggests that alkali-treatment reduces the degradation rate in AZ91 magnesium alloy.

scholarly journals Plasma electrolytic oxidation of AZ31 and AZ91 magnesium alloys: Comparison of coatings formation mechanism

2020 ◽  
Vol 8 (3) ◽  
pp. 587-600 ◽  
Author(s):  
A.G. Rakoch ◽  
E.P. Monakhova ◽  
Z.V. Khabibullina ◽  
M. Serdechnova ◽  
C. Blawert ◽  
...  
Keyword(s):  
Magnesium Alloys ◽  
Formation Mechanism ◽  
Plasma Electrolytic Oxidation ◽  
Electrolytic Oxidation ◽  
Az91 Magnesium ◽  
Plasma Electrolytic

Micro Arc Oxidation of AZ91 Magnesium Alloy – Effect of Organic Compounds in the Electrolyte

2014 ◽  
Vol 353 ◽  
pp. 217-222 ◽  
Author(s):  
Namik Kemal Gozuacik ◽  
Mert Altay ◽  
Murat Baydogan
Keyword(s):  
Corrosion Resistance ◽  
Coating Thickness ◽  
Electrochemical Corrosion ◽  
Organic Chemicals ◽  
X Ray Diffraction ◽  
Az91 Magnesium Alloy ◽  
Micro Arc Oxidation ◽  
Az91 Magnesium ◽  
Alloy Effect ◽  
Thickness Measurements

AZ91 Mg alloy was micro arc oxidized under constant electrical parameters in silicate based and phosphate based electrolytes with and without addition of organic chemicals, namely Hexamethylenetetramine (HMTA), TRIS (hydroxymethyl) aminomethane (THAM) and Glycerol in two different concentrations. Following oxidation, samples were characterized by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), coating thickness measurements, hardness measurements and electrochemical corrosion tests. Results showed that coating layers mainly consisted of MgO, Mg2SiO4 and MgF2 for silicate based electrolytes, and MgO for phosphate based electrolytes. Incorporation of organic chemicals into electrolyte composition did not change the type of the phases in the coating. However, when they are added in silicate based electrolytes, pore density and coating thickness are reduced and pore size is increased. On the other hand, there is no significant change in surface morphology when organic chemicals are added in phosphate based electrolyte. In the view point of corrosion resistance, organic chemicals did not enhance corrosion resistance of the samples oxidized in silicate based electrolytes, but exhibited some increment in corrosion resistance of the samples oxidized in phosphate based electrolytes.

Study on Micro-Arc Oxidation Behavior of AZ91 Magnesium Alloy in Aluminate Environmentally Friendly Electrolyte

2020 ◽  
Vol 1003 ◽  
pp. 67-75
Author(s):  
Xian Ming Chen ◽  
Ying Ying Fan
Keyword(s):  
Corrosion Resistance ◽  
Electron Microscope ◽  
Magnesium Alloy ◽  
Oxide Film ◽  
Oxidation Behavior ◽  
Salt Spray ◽  
Alkaline Electrolyte ◽  
Az91 Magnesium Alloy ◽  
Micro Arc Oxidation ◽  
Az91 Magnesium

In aluminate alkaline electrolyte the effect of aluminate on the microstructure and properties and the MAO(micro-arc oxidation) behavior of micro-arc oxide film of AZ91 magnesium alloy was studied. Transmission electron microscope(TEM), energy dispersive spectrum (EDS), X-ray diffraction(XRD), salt spray test and scanning electron microscope(SEM)were used to analyze and characterize the structure and properties of the film. The results show that the concentration of aluminate has an important effect on the tank voltage, corrosion resistance, surface morphology and phase structure of micro-arc oxidation film. The corrosion resistance and film quality of the film were increased first and then decreased, but the surface roughness decreased first and then increased with the increase of aluminate concentration from 5g/L to 30g/L. At our work, the concentration of 10g/L aluminate electrolyte is most favorable to the formation of micro-arc oxide film.

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