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.

Corrosion behaviour of plasma electrolytic oxidation coated AZ91 Mg alloy: influence of laser surface melting pretreatment

RSC Advances ◽  
2016 ◽  
Vol 6 (74) ◽  
pp. 70343-70351 ◽  
Author(s):  
Cancan Liu ◽  
Jun Liang ◽  
Jiansong Zhou ◽  
Qingbiao Li ◽  
Zhenjun Peng ◽  
...  
Keyword(s):  
Plasma Electrolytic Oxidation ◽  
Corrosion Behaviour ◽  
Surface Melting ◽  
Laser Surface ◽  
Laser Surface Melting ◽  
Mg Alloy ◽  
Electrolytic Oxidation ◽  
Plasma Electrolytic

Plasma electrolytic oxidation (PEO) was performed on a laser surface melting (LSM) modified AZ91 Mg alloy.

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.

Enhancement of Corrosion Resistance of PEO Coating on AZ91 Biomedical Magnesium Alloy by Surface Laser Treating

2013 ◽  
Vol 365-366 ◽  
pp. 1110-1113 ◽  
Author(s):  
Miao Wang ◽  
Yun Long Wang ◽  
Zhong De Liu ◽  
Hua Ding
Keyword(s):  
Corrosion Resistance ◽  
Magnesium Alloy ◽  
Plasma Electrolytic Oxidation ◽  
Ceramic Coating ◽  
Alloy Sample ◽  
Corrosion Tests ◽  
Coating Surface ◽  
Electrolytic Oxidation ◽  
Surface Laser ◽  
Plasma Electrolytic

Ceramic coating was fabricated on AZ91 biomedical magnesium alloy by plasma electrolytic oxidation. The coating was then subjected to surface laser treating, and the influence of laser treating on the morphologies and corrosion resistance of the coating were investigated. The results showed that PEO coating without laser treating showed coarse and porous surface and the pores on coating surface were big. When subjected to laser treating, the pores on coating surface became little and few. The corrosion tests in SBF indicated that corrosion resistance of PEO coating on magnesium alloy sample could improve the corrosion resistance of the substrate, and surface laser treating could further increase the corrosion resistance.

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