Preparation and Characterization of Plasma Electrolytic Oxidation Coating on 5005 Aluminum Alloy with Red Mud as an Elec
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Preparation and Characterization of Plasma Electrolytic Oxidation Coating on 5005 Aluminum Alloy with Red Mud as an Electrolyte Additive SHIFENG LIU, JIANMIN ZENG, and YOUBIN WANG A coating with red mud as an electrolyte additive was applied to 5005 aluminum alloy using plasma electrolytic oxidation (PEO). The phase composition of the coating was investigated using X-ray diffraction. Scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDS) was used to determine the microstructure and composition profiles of the coating. The coating/substrate adhesion was determined by scratch testing. The corrosion behaviors of the substrate and coating were evaluated using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS). The results indicated that the PEO coating with red mud consisted mainly of a-Al2O3 and c-Al2O3, with small amounts of Fe2O3, CaCO3, and CaTiO3. The surface of the coating was the color of the red mud. The coating had a uniform thickness of about 80 lm and consisted of two main layers: a 6-lm porous outer layer and a 74-lm dense inner layer, which showed typical metallurgical adhesion (coating/substrate adhesion strength of 59 N). The coating hardness was about 1142 HV, much higher than that of the substrate (60 HV). The corrosion potential Ecorr and corrosion current density icorr of the coating were estimated to be 0.743 V and 3.85 9 106 A cm2 from the PDP curve in 3.5 wt pct NaCl solution, and the maximum impedance and phase angle of the coating were 11 000 X and 67 deg, respectively, based on EIS. PEO coating with red mud improved the surface properties and corrosion resistance of 5005 aluminum alloy. This study also shows a potential method for reusing red mud. DOI: 10.1007/s11663-017-1013-x Ó The Minerals, Metals & Materials Society and ASM International 2017
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INTRODUCTION
ALUMINIUM alloys are commonly used in a wide range of industrial areas such as the aerospace, automotive, construction, and electronics industries because of their excellent properties, such as small thermal expansion coefficient and density, light weight, and good formability, which satisfy the increasing demand for light, economical, recyclable, and durable materials.[1,2] However, low hardness and poor corrosion resistance have limited their use, especially for components that require good wear resistance. Plasma electrolytic oxidation (PEO) is a surface modification technique that can be used for in situ formation of ceramic coatings on the surfaces of nonferrous metals.[3,4] PEO occurs above the electric breakdown voltage. The instantaneous plasma
SHIFENG LIU, JIANMIN ZENG, and YOUBIN WANG are with the State Key Laboratory of Solidification Processing, Department of Materials Science and Engineering, Northwestern Polytechnical University, 127 Youyixi Road, Xi’an, Shaanxi 710072 P.R.China. Contact e-mail: [email protected] Manuscript submitted December 03, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS B
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