Corrosion resistance and hydrophobicity of myristic acid modified Mg-Al LDH/Mg(OH)2steam coating on magnesium alloy AZ31

A hydrophobic surface was successfully fabricated on the Mg-Al-layered double hydroxide (Mg-Al LDH)/Mg(OH)2-coated AZ31 magnesium alloy via an in-situsteam coating (SC) process and a subsequent surface modification with environment-friendly myristic acid (MA). The microstructure, composition and hydrophobicity of SC/MA composite coating were investigated by XRD, SEM, EDS, FTIR, and contact angle (CA) measurement. The corrosion behavior of the hybrid coating was evaluated by potentiodynamic polarization, EIS and hydrogen evolution test in 3.5 wt.% NaCl solution. The results showed that the LDH coating had nano-flake microstructure, which remained unchanged after modification with MA. The CA of the MA-modified coating surface reached up to 129°± 3.5°, and the corrosion current density of SC/MA-2 coating decreased about three orders of the magnitude compared to that of the substrate. It is proven that the modified surface has an effective anti-corrosion effect on AZ31 alloy. The formation mechanism and the corrosion mechanism of the coating were also discussed.