Preparation of superhydrophobic Li–Al-Ala LDH/SA film with enhanced corrosion resistance and mechanical stability on AZ91D Mg alloy

Abstract

Layered double hydroxide (LDH) films have attracted extensive attention in Mg alloy anti-corrosion due to their unique physical barrier function and ion exchange performance. However, most of the LDH films on Mg alloy have problems of harsh preparation conditions, poor anti-corrosion stability, and poor adhesion. In this paper, a typical Li–Al-alanine (Ala) LDH film has been successfully prepared on AZ91D Mg alloy surface under milder conditions using multi-arc ion plating and in-situ dipping for the first time. Then an improved vacuum impregnation further modified the Li–Al-Ala LDH film in an ethanol solution of stearic acid (SA) to improve its protective stability. The potentiodynamic polarization curves and electrochemical impedance spectra (EIS) showed that the Li–Al-Ala LDH/SA film's corrosion resistance is more than three orders of magnitude higher than that of the blank Mg alloy in 3.5 wt% NaCl, showing a highly increased corrosion resistance. The long-term immersion experiments found that the surface structure and corrosion resistance of the Li–Al-Ala LDH/SA film did not change much after immersion in 3.5 wt% NaCl for 432 h. The bonding force between the film and the Mg alloy substrate can reach grade 0 based on the standard from International Standardization Organization (ISO). And the hydrophobicity of the film can remain stable with the water contact angle (WCA) being steady at about 140° after a certain distance of external abrasion, showing excellent mechanical wear resistance. The study provides a new milder approach to fabricating superhydrophobic LDH films with durable anti-corrosion resistance, good adhesion, and mechanical stability on Mg alloy surface. Graphical abstract: [Figure not available: see fulltext.].