Study on the Superhydrophobic Surface Modification and Corrosion Resistance of Mg(OH)₂ Films on Magnesium Alloys by Cathodic Deposition

Abstract

 In order to prolong the service life of magnesium alloys， superhydrophobic coatings were prepared on the surface of ME20M rare earth magnesium alloy through cathodic deposition and superhydrophobic modification.A stearic acid ethanol solution was used for chemical modification of the cathodically deposited Mg(OH)2 films on the magnesium alloy.Single-factor experiments were conducted to investigate the effects of stearic acid concentration，solution temperature and immersion time on surface wettability，in order to determine the optimal modification process.The corrosion resistance of typical samples was evaluated using drop tests，full immersion corrosion tests and modern electrochemical testing techniques.The adhesion strength of the film to the substrate was assessed by the cross-cut method， and the surface microstructure and composition of the samples were analyzed using scanning electron microscopy (SEM)， fourier transform infrared spectrometer (FT-IR)and X-ray diffraction analyzer(XRD).Results showed that the cathode deposited Mg(OH)2 film could be rendered superhydrophobic by brief immersion in a low-concentration stearic acid solution， achieving a static contact angle (SCA) of up to 151.5° with distilled water and a rolling angle (SA) as low as 1.0°， exhibiting low viscosity.The combined treatment of cathodic deposition and hydrophobic modification could significantly improve the corrosion resistance of magnesium alloys.Compared with the blank sample， the discoloration time of the droplet on the composite treated sample was extended by nearly 25 times， the self-corrosion current density Jcorr in 3.5%NaCl solution was reduced by nearly 3 orders of magnitude， and the characteristic impedance modulus ｜Z｜0.1 Hz was increased by nearly 4 orders of magnitude.The surface micromorphology of cathodic deposition Mg(OH)2 thin film with hydrophobic treatment showed a sword-like structure at the micro/nano scale.There were obvious absorption peaks of -CH3 and -CH2- in the infrared spectrum of the sample.

Keywords

• magnesium alloy； cathode deposition； magnesium hydroxide film； superhydrophobicity； corrosion resistance