Corrosion resistance of Mg(OH)2/Mg–Al-layered double hydroxide coatings on magnesium alloy AZ31: influence of hydrolysis degree of silane

Abstract

Mg(OH)2/Mg–Al-layered double hydroxide (LDH) coatings were modified with methyltrimethoxysilane (MTMS) on magnesium alloys. Effect of hydrolysis degree of silane solution on coating formation was investigated. Chemical compositions and surface morphologies of the coatings were examined using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and field-emission scanning electronic microscopy (FESEM). Results indicated that the composite coatings consisted of polymethyltrimethoxysilane (PMTMS), LDH and Mg(OH)2. Electrochemical and hydrogen evolution measurements revealed that the composite coatings possessed good corrosion resistance, especially the ones prepared in a high hydrolysis degree of silane. The optimum corrosion resistance of the composite coating was LDH/PMTMS-3 coating, which had the lowest value of corrosion current density (5.537 × 10−9 A·cm−2) and a dense surface. Plausible mechanism for coating formation and corrosion process of MTMS-modified Mg(OH)2/Mg–Al-LDH coatings were discussed.