scholarly journals The mechanism for tuning the corrosion resistance and pore density of plasma electrolytic oxidation (PEO) coatings on Mg alloy with fluoride addition

2021 ◽  
Author(s):  
Zhu Lujun ◽  
Li Hongzhan ◽  
Ma Qingmei ◽  
Lu Jiangbo ◽  
Li Zhengxian
Keyword(s):  
Corrosion Resistance ◽  
Plasma Electrolytic Oxidation ◽  
Mg Alloy ◽  
Pore Density ◽  
Electrolytic Oxidation ◽  
Plasma Electrolytic ◽  
Peo Coatings ◽  
Fluoride Addition

scholarly journals Effects of a Carbon Nanotube Additive on the Corrosion-Resistance and Heat-Dissipation Properties of Plasma Electrolytic Oxidation on AZ31 Magnesium Alloy

Materials ◽  
2018 ◽  
Vol 11 (12) ◽  
pp. 2438 ◽  
Author(s):  
Myungwon Hwang ◽  
Wonsub Chung
Keyword(s):  
Corrosion Resistance ◽  
Carbon Nanotube ◽  
Plasma Electrolytic Oxidation ◽  
Heat Dissipation ◽  
X Ray ◽  
Steady State Method ◽  
Electrolytic Oxidation ◽  
Plasma Electrolytic ◽  
Dissipation Property ◽  
Peo Coatings

Plasma electrolytic oxidation (PEO) coating was obtained on AZ31 Mg alloy using a direct current in a sodium silicate-based electrolyte with and without a carbon nanotube (CNT) additive. The surface morphology and phase composition of the PEO coatings were investigated through field emission scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The corrosion-resistance properties of the PEO coatings were evaluated using potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS) in a 3.5 wt.% NaCl solution. Furthermore, the heat-dissipation property was evaluated by a heat-flux measurement setup using a modified steady-state method and Fourier transform infrared spectroscopy (FT-IR). The results demonstrate that, by increasing the concentration of CNT additive in the electrolyte, the micropores and cracks of the PEO coatings are greatly decreased. In addition, the anticorrosion performance of the PEO coatings that incorporated CNT for the protection of the Mg substrate was improved. Finally, the coating’s heat-dissipation property was improved by the incorporation of CNT with high thermal conductivity and high thermal emissivity.

scholarly journals Influence of Electrolyte Temperature on the Color Values of Black Plasma Electrolytic Oxidation Coatings on AZ31B Mg Alloy

Coatings ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 890
Author(s):  
Aihua Yi ◽  
Zhongmiao Liao ◽  
Wen Zhu ◽  
Zhisheng Zhu ◽  
Wenfang Li ◽  
...  
Keyword(s):  
Plasma Electrolytic Oxidation ◽  
Mg Alloy ◽  
Electrolyte Temperature ◽  
Electrolytic Oxidation ◽  
Key Factor ◽  
Different Temperatures ◽  
Color Value ◽  
Coating Color ◽  
Plasma Electrolytic ◽  
Peo Coatings

A coating was prepared on an AZ31B Mg alloy substrate via black plasma electrolytic oxidation (PEO). The colorant NH4VO3 was added to Na2SiO3–(NaPO3)6 electrolyte at different temperatures (5, 15, 25, and 35 °C). The influences of electrolyte temperature on the structures, compositions, and color values of black PEO coatings were studied by UV–Visible, XRD, XPS, Raman, and SEM techniques. The results showed that the relative content of V2O3 and V2O5 was the key factor affecting the coating color value. At higher temperatures, more NH3 escaped from the electrolyte and the NH3 quantity participating in the reaction decreased, resulting in a decrease of V2O3 content, an increase in color value, and a darker coating. In the PEO process, VO3− mainly reacted to form V2O5, and then, the generated V2O5 reacted with NH3 to form V2O3.

scholarly journals Improving Corrosion Resistance of MRI 230D Mg Alloy by Hybrid Coating of Laser Surface Alloying and Plasma Electrolytic Oxidation

2012 ◽  
Vol 706-709 ◽  
pp. 1209-1214 ◽  
Author(s):  
G. Rapheal ◽  
Subodh Kumar ◽  
Carsten Blawert ◽  
Narendra B. Dahotre
Keyword(s):  
Corrosion Resistance ◽  
Plasma Electrolytic Oxidation ◽  
Laser Surface ◽  
Mg Alloy ◽  
Hybrid Coatings ◽  
Corrosion Tests ◽  
Micro Cracks ◽  
Electrolytic Oxidation ◽  
Plasma Electrolytic ◽  
Scanning Electron

A permanent mould cast creep resistant MRI 230D Mg alloy was laser surface alloyed (LSA) with Al and Al2O3 in order to improve its wear and corrosion resistance. However, this treatment was successful only in improving wear resistance but not corrosion resistance due to the presence of micro−cracks in the coated layer, which has been discussed in an earlier paper. The LSA coated Mg alloy has been further subjected to plasma electrolytic oxidation (PEO) treatment in alkaline silicate electrolyte in order to cover those micro−cracks and improve corrosion resistance, which is discussed in the present manuscript. For comparison, the PEO coating has also been applied on the as−cast MRI 230D Mg alloy. The microstructural characterization of coatings and corroded surfaces was carried out by scanning electron microscope and X−ray diffraction. Electrochemical corrosion tests were conducted in 3.5 wt% NaCl solution having neutral pH to investigate the corrosion behavior. The LSA coatings consisted mainly of β (Mg17Al12) phase, the coatings produced by PEO treatment on MRI 230D Mg alloy consisted mainly of Mg2SiO4 phase, and hybrid coatings of PEO on LSA consisted of Mg2SiO4 and MgAl2O4 phases in the PEO layer. Scanning electron micrographs of the cross−section revealed that the PEO treatment covered the micro−cracks present in the LSA and corrosion tests revealed that it improved the corrosion resistance, though not to the extent of the corrosion resistance of the PEO coated MRI 230D Mg alloy. All the samples exhibited localized form of corrosion.

scholarly journals Effect of Pulse Current Mode on Microstructure, Composition and Corrosion Performance of the Coatings Produced by Plasma Electrolytic Oxidation on AZ31 Mg Alloy

Coatings ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 688 ◽  
Author(s):  
Maryam Rahmati ◽  
Keyvan Raeissi ◽  
Mohammad Reza Toroghinejad ◽  
Amin Hakimizad ◽  
Monica Santamaria
Keyword(s):  
Plasma Electrolytic Oxidation ◽  
Low Frequency ◽  
Current Mode ◽  
Mg Alloy ◽  
Corrosion Performance ◽  
Micro Cracks ◽  
Az31 Mg Alloy ◽  
Electrolytic Oxidation ◽  
Plasma Electrolytic ◽  
Peo Coatings

Plasma electrolytic oxidation (PEO) coatings were grown on AZ31 Mg alloy in a silicate-based electrolyte containing KF using unipolar and bipolar (usual and soft-sparking) waveforms. The coatings were dual-layered consisting of MgO, MgF2 and Mg2SiO4 phases. Surface morphology of the coatings was a net-like (scaffold) containing a micro-pores network, micro-cracks and granules of oxide compounds. Deep pores were observed in the coating produced by unipolar and usual bipolar waveforms. The soft-sparking eliminated the deep pores and produced the lowest porosity in the coatings. It was found that the corrosion performance of the coatings evaluated using EIS in 3.5 wt. % NaCl solution is mostly determined by the inner layer resistance, because of its higher compactness. After 4 days of immersion, the inner layer resistances were almost the same for all coatings. However, the coatings produced by unipolar and usual bipolar waveforms showed sharp decays in inner layer resistances after 1 week and even the barrier effect of outer layer was lost for the unipolar-produced coating after 3 weeks. The low-frequency inductive loops appeared after a 3-week immersion for all coatings indicated that the substrate was under local corrosion attack. However, both coatings produced by soft-sparking waveforms provided the highest corrosion performance.

scholarly journals Wear and Corrosion Resistance of Plasma Electrolytic Oxidation Coatings on 6061 Al Alloy in Electrolytes with Aluminate and Phosphate

Materials ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4037
Author(s):  
Zhenjun Peng ◽  
Hui Xu ◽  
Siqin Liu ◽  
Yuming Qi ◽  
Jun Liang
Keyword(s):  
Corrosion Resistance ◽  
Plasma Electrolytic Oxidation ◽  
Salt Spray ◽  
P Element ◽  
Alumina Coating ◽  
Al Alloy ◽  
Wear Properties ◽  
Electrolytic Oxidation ◽  
Plasma Electrolytic ◽  
Peo Coatings

Phosphate and aluminate electrolytes were used to prepare plasma electrolytic oxidation (PEO) coatings on 6061 aluminum alloy. The surface and cross-section microstructure, element distribution, and phase composition of the PEO coatings were characterized by SEM, EDS, XPS, and XRD. The friction and wear properties were evaluated by pin-on-disk sliding tests under dry conditions. The corrosion resistance of PEO coatings was investigated by electrochemical corrosion and salt spray tests in acidic environments. It was found that the PEO coatings prepared from both phosphate and aluminate electrolytes were mainly composed of α-Al2O3 and γ-Al2O3. The results demonstrate that a bi-layer coating is formed in the phosphate electrolyte, and a single-layered dense alumina coating with a hardness of 1300 HV is realizable in the aluminate electrolyte. The aluminate PEO coating had a lower wear rate than the phosphate PEO coating. However, the phosphate PEO coating showed a better corrosion resistance in acidic environment, which is mainly attributed to the presence of an amorphous P element at the substrate/coating interface.

Sign in / Sign up

Export Citation Format

Share Document