Abstract
AbstractThis study aims to investigate the effect of the processing parameters in plasma electrolytic oxidation (PEO) on the corrosion resistance of magnesium alloy type AZ91. The PEO coatings were prepared on the samples using alkaline‐based electrolyte. Both unipolar and bipolar, different frequencies and duty cycles were applied. Corrosion tests, using potentiodynamic polarization, linear and cyclic, and electrochemical impedance spectroscopy techniques, were applied on the as‐received and PEO coated samples. Scanning electron microscopy was used to investigate the surface morphology, for example, micropores, as well as to measure the thickness of the coated layer by changing the processing parameters. The results show that the size of micropores is interrelated to the duty cycle percentage and current polarities, as the higher frequency causes thinner coating layers, with fewer micropores, consequently higher corrosion resistance. In addition, increasing the duty cycle, a denser and more compact coating was obtained. The XRD results showed a missing peak of the α‐Mg phase in a PEO coated sample using bipolar, the highest frequency (1666 Hz), and the highest duty cycle (66.6%). The mils per year calculations showed that the PEO coated has a lower corrosion rate by at least 8 times than the as‐received alloy.
Highlights
INTRODUCTIONThe features such as high strength/weight ratio, good machinability, thermal conductivity, and electromagnetic shielding make the magnesium alloys highly used in different industries such as automobile, aerospace, and electronics industries.[1,2,3,4,5] Magnesium alloys, are used in clinical applications such as biodegradable implants for
Anodizing, where aluminium is coated on magnesium, is among the traditional methods, which has been used for a while, to improve the corrosion resistance, because the mechanical properties of aluminium are relatively low, for example, yield strength, other attempts have been conducted, such as adding nanoparticles and forming a hybrid coating, using plasma electrolyte oxidation (PEO).[9,10,11,12,13,14,15,16,17,18]
The results showed that the PEO coating which was composed of only MgO suffered from localized corrosion, whereas the PEO coating with ZrO2 compounds showed higher stability and provided efficient corrosion protection
Summary
The features such as high strength/weight ratio, good machinability, thermal conductivity, and electromagnetic shielding make the magnesium alloys highly used in different industries such as automobile, aerospace, and electronics industries.[1,2,3,4,5] Magnesium alloys, are used in clinical applications such as biodegradable implants for. Hussein et al.[24] studied the PEO mechanism by investigating the formation of a coating layer, up to 110 μm thickness on AJ62 Mg alloy They found that during the PEO process some of the metal cations are transferred outwards from the substrate and react with anions to form ceramic coatings. It was found that the uptake of particles was accompanied by the coating growth at the initial stage, while the particle content remained unchanged at the final stage, which is dissimilar to the evolution of the coating thickness They found that the corrosion performance of the coating mainly depends on the barrier property of the inner layer, while wear resistance primarily relies on the coating thickness.[25,26]. Pezzato et al.[27] used nanoindentation, potentiodynamic polarization (PDP), EIS and scanning vibrating electrode tests to evaluate the mechanical properties and the corrosion resistance of PEO-coated AZ80 magnesium alloy before and after a sealing treatment in boiling water. This research has examined the impact of using unipolar and bipolar currents on PEO coating of AZ91 alloy
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
