Effects of Pulse Current Mode on Plasma Electrolytic Oxidation of 7075 Al in KMnO4Containing Solution

Plasma electrolytic oxidation (PEO) has earned much attention due to its powerful and easy formation of hard and corrosion-resistant oxide layers on valve metals, such as Al alloys. Here we report the effects of current density (CD) on microstructure and properties of coatings on 6061 Al alloy by PEO using direct current mode. The electrolyte contains the chemicals of Na2SiO3, Na2WO4´2H2O, and NaH2PO2´H2O. The CDs adopted 5.0, 7.5, 10.0, and 12.5 A/dm2, respectively, for a fixed PEO time of 30 min. The thickness, surface morphology, phase composition, hardness, and corrosion resistance of PEO coatings as the function of the applied CD have been studied and discussed. Studied results show the coating thickness is proportional to the applied CD. When the applied CD increases 2.5 times from 5.0 to 12.5 A/dm2, the growth rate of oxide layers increased by more than 3.5 times, from 0.423 to 1.493 μm/min, respectively. SEM images are characterized by a reduction in the ratio of agglomerate-bumps-region/flatten-region as applied CD increases. However, cracks and larger pores appear when the applied CD is higher than 10.0 A/dm2. X-ray diffraction pattern shows that the main phases of Al, g-Al2O3, α-Al2O3, and W are contained in all coatings. PEO coated sample has the highest hardness of 1290 HV and highest polarization resistance of 8.80 ´ 106 Wcm2 obtained at applied CD 10 A/dm2 which shows the best performance of the coating. The variation in coating performance is explained by microstructure details, specifically phases, compositions of oxide-layers, and micro-pores and cracks.

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Synergistic effect of W incorporation and pulsed current mode on wear and tribocorrosion resistance of coatings grown by plasma electrolytic oxidation on 7075 Al alloy

Materials Research Express ◽

10.1088/2053-1591/ab3630 ◽

2019 ◽

Vol 6 (10) ◽

pp. 106502 ◽

Cited By ~ 3

Author(s):

Amirhossein Toulabifard ◽

Amin Hakimizad ◽

Francesco Di Franco ◽

Keyvan Raeissi ◽

Monica Santamaria

Keyword(s):

Synergistic Effect ◽

Plasma Electrolytic Oxidation ◽

Current Mode ◽

Al Alloy ◽

Pulsed Current ◽

7075 Al Alloy ◽

Electrolytic Oxidation ◽

Plasma Electrolytic

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Corrosion Properties of Plasma Electrolytic Oxidation Ceramic Coatings on an A356 Alloy Tested in an Ethanol-Gasoline Fuel (E85) Medium

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.282-283.774 ◽

2011 ◽

Vol 282-283 ◽

pp. 774-778

Author(s):

Zhi Jing Peng ◽

Ying Chen ◽

Xue Yuan Nie

Keyword(s):

Corrosion Resistance ◽

Plasma Electrolytic Oxidation ◽

A356 Alloy ◽

Current Mode ◽

Ceramic Coatings ◽

Corrosion Properties ◽

Cross Sectional ◽

Electrolytic Oxidation ◽

Zero Resistance ◽

Plasma Electrolytic

Ceramic oxide coatings were prepared on an aluminum A356 alloy by a plasma electrolytic oxidation (PEO) technique under unipolar, bipolar and duplex unipolar/bipolar current modes. Cross-sectional morphologies of the coatings were studied using a scanning electron microscope (SEM). The corrosion behavior of the coated and uncoated samples was evaluated in ethanol-gasoline E85 fuels through potentiodynamic polarization and zero resistance ammeter (ZRA) testing methods. The results indicated that all the coatings had a better corrosion resistance compared to the uncoated substrate. The unipolar current mode created the PEO coating with a thicker coating microstructure and thus a better corrosion resistance, compared to a bipolar current mode. The duplex treatments of unipolar/bipolar or bipolar/unipolar current modes produced the best performance of the coatings against galvanic corrosions caused by a steel/Al coupling in the E85 fuel medium.

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Microstructural and Corrosion Properties of Hydroxyapatite Containing PEO Coating Produced on AZ31 Mg Alloy

Materials ◽

10.3390/ma14061531 ◽

2021 ◽

Vol 14 (6) ◽

pp. 1531

Author(s):

Luca Pezzato ◽

Katya Brunelli ◽

Stefano Diodati ◽

Mirko Pigato ◽

Massimiliano Bonesso ◽

...

Keyword(s):

Plasma Electrolytic Oxidation ◽

Silicon Oxide ◽

Current Mode ◽

Xrd Analysis ◽

Az31 Alloy ◽

Corrosion Properties ◽

Short Treatment ◽

Treated Sample ◽

Electrolytic Oxidation ◽

Plasma Electrolytic

In this work, the composition of an electrolyte was selected and optimized to induce the formation of hydroxyapatite during Plasma electrolytic oxidation (PEO) treatment on an AZ31 alloy for application in bioabsorbable implants. In detail, the PEO process, called PEO-BIO (Plasma Electrolytic Oxidation-Biocompatible), was performed using a silicate-phosphate-based electrolyte with the addition of calcium oxide in direct-current mode using high current densities and short treatment times. For comparison, a known PEO process for producing anticorrosive coatings, called standard, was applied on the same alloy. The coatings were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and XPS analyses. The corrosion performance was evaluated in simulated body fluid (SBF) at 37 °C. The coating produced on the PEO-BIO sample was porous and thicker than the standard PEO one, with zones enriched in Ca and P. The XRD analysis showed the formation of hydroxyapatite and calcium oxides in addition to magnesium-silicon oxide and magnesium oxide in the PEO-BIO sample. The corrosion resistance of PEO-BIO sample was comparable with that of a traditional PEO treated sample, and higher than that of the untreated alloy.

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

Coatings ◽

10.3390/coatings9100688 ◽

2019 ◽

Vol 9 (10) ◽

pp. 688 ◽

Cited By ~ 12

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.

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