Abstract
The plasma electrolyte oxidation (PEO) process has been considered an environmentally friendly surface engineering method for improving the corrosion resistance of light weight metals. In this work, the corrosion resistance of commercially pure Al and PEO treated Al substrates were studied. The PEO layers were grown on commercially pure aluminum substrates using two different alkaline electrolytes with different addition concentrations of Si3N4 nanoparticles (0, 0.5 and 1.5 gL−1) and different duty cycles (25%, 50%, and 80%) at a fixed frequency. The corrosion properties of PEO coatings were investigated by the potentiodynamic polarization and electrochemical impedance spectroscopy test in 3.5 wt.% NaCl solutions. It showed that the weight gains, layer thickness and surface roughness of the PEO grown oxide layer increased with increasing concentrations of Si3N4 nanoparticles. The layer thickness, surface roughness, pore size, and porosity of the PEO oxide layer decreased with decreasing duty cycle. The layer thickness and weight gain of PEO coating followed a linear relationship. The PEO layer grown using the Na2B4O7∙10H2O contained electrolyte showed an excellent corrosion resistance and low surface roughness than other PEO coatings with Si3N4 nanoparticle additives. It is noticed that the corrosion performance of PEO coatings were not improved by the addition of Si3N4 nanoparticle in the electrolytic solutions, possibly due to its detrimental effect to the formation of a dense microstructure.
Highlights
IntroductionAluminum and its alloys have been extensively used in different industrial applications (shipbuilding, marine, automotive, aerospace, and in innumerable other areas) due to their high quality of properties, i.e., high strength to weight ratio, low density, light weight, noble ductility, and non-magnetic properties
Aluminum and its alloys have been extensively used in different industrial applications due to their high quality of properties, i.e., high strength to weight ratio, low density, light weight, noble ductility, and non-magnetic properties
We suggest that the fabrication of APA coating without the addition of Si3 N4 nanoparticle and borax in electrolyte makes the relationship between weight gain and layer thickness differ from other five plasma electrolytic oxidation (PEO) coatings, which were grown with the addition of Si3 N4 nanoparticle or borax in electrolyte
Summary
Aluminum and its alloys have been extensively used in different industrial applications (shipbuilding, marine, automotive, aerospace, and in innumerable other areas) due to their high quality of properties, i.e., high strength to weight ratio, low density, light weight, noble ductility, and non-magnetic properties. PEO is a relatively new surface modification technique which can significantly improve the hardness, corrosion and wear resistance, adhesion strength, thermal and other desirable properties of Al alloys by efficiently growing thick alumina rich ceramic coatings [7,8,9,10]. During this process, plasma discharge can cause the formation of a highly adhesive and dense oxide layer on the substrate [11,12]. The influences of Si3 N4 nanoparticle additives, electrolytes, and duty cycles on the corrosion resistance of PEO grown oxide layers on pure aluminum were studied
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