An Investigation Of The Phase Composition And Corrosion Resistance Of Plasma Electroletic Oxidation Coatings On Aluminium

Plasma electrolytic oxidation?PEO?treatment was performed on AA1060 pure aluminium and 6061 aluminium alloy using the self-designed WH-1A PEO power supply.The PEO coatings were detached from the pure aluminium by a self-developed electrochemical method.Two main aspects were investigated as follows:?1?An investigation on the phase composition of the PEO coating on AA1060 pure aluminium and the element composition of the amorphous phase in the coating;?2?An investigation of the ultrasonic effect on the corrosion resistance of the PEO coatings on 6061 aluminium alloy.The results show that: there is a compact thin layer at the coating/substrate interfacial region of the PEO treated specimens which is composed of spherical particles,and the thickness of this layer maintains at ¹ ?m,which does not increase with treating time.Through the analysis of XRD,we can know that the PEO coatings are composed of mullite,amorphous phase,?-Al₂O₃ and ?-Al₂O₃,and Al,Si,O compose the amorphous phase.The content of each element in the amorphous phase are compared with the element content of different location of the coatings,and it can be deduced that most of the amorphous phase distribute on the outer layer of the coating.We introduce the ultrasonic during PEO process in order to improve the non-uniform discharge.We hope the ultrasound can provide more micro defects during the discharge process so that the discharges occur in more locations.The surface,cross-section and interface are analyzed by SEM,XRD and electrochemical testing in order to explore how the frequency and power of the ultrasound influence the properties of the coatings.The results show that: the introduction of ultrasonic does increase the amount of the discharge location,and the coatings are more uniform,the size of the hole becomes smaller,the roughness of the surface relatively reduces.Also,the ultrasonic has a great influence on the phases of the coatings,it promotes ?-Al₂O₃ into ?-Al₂O₃.When the frequency of the ultrasonic is 53 kHz,?-Al₂O₃ is transformed into ?-Al₂O₃ completely no matter what the power of the ultrasonic is.Through the electrochemical test we can know that the corrosion resistance of the coatings increases with the increase of the ultrasonic power when the ultrasonic frequency is 35 kHz.And when the ultrasonic frequency is 53 kHz and ultrasonic power is 144 W,the corrosion resistance of the coatings is best.When the ultrasonic power is further increased,the corrosion resistance of the coatings is worse instead.