Corrosion resistance of cold sprayed aluminum/micro-arc oxidation composite coating on AZ80 magnesium alloy

Abstract

A layer of pure aluminum coating was prepared on AZ80 magnesium alloy by cold spray, and then a pure aluminum/aluminum oxide composite coating was successfully fabricated on the surface of pure aluminum coating by micro-arc oxidation. The surface and cross-section morphology, composition and phase structure of the coatings were analyzed by scanning electron microscope (SEM), energy spectrometer (EDS) and X-ray diffractometer (XRD). The corrosion behavior of the coatings immersed in 3.5%NaCl(mass fraction) solution for different time (30 min and 7 days) was investigated using potentiodynamic polarization curves and electrochemical impedance spectroscopy. The results show that after 30 minutes of immersion, the corrosion current densities of the pure aluminum coating and the pure aluminum/aluminum oxide composite coating are 3.7×10-6 A·cm-2 and 8.0×10-7 A· cm-2, respectively; after 7 days of immersion, the corrosion current densities are 9.0×10-6 A·cm-2 and 1.8×10-6 A·cm-2, respectively. Both the pure aluminum/aluminum oxide composite coating and the cold sprayed aluminum coating can effectively delay the corrosion of the magnesium alloy substrate. Among them, the corrosion resistance of the micro-arc oxidation composite coating is nearly 5 times of the cold sprayed pure aluminum coating. The further improvement in corrosion resistance is attributed to the excellent physical barrier effect of the micro-arc oxidation ceramic layer.

Keywords

• cold spray
• micro arc oxidation
• ac impedance
• magnesium alloy
• corrosion and protection