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

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 coati ng 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.

Biocorrosion resistance and biocompatibility of Mg-AI layered double hydroxide/poly(L-lactic acid) hybrid coating on magnesium alloy AZ31

A Mg-AI layered double hydroxide(Mg-AI-LDH)coating was firstly synthesized via an in-situ steam coating growth method on the AZ31 Mg alloy,and then was modified with poly(L-lactic acid)(PLLA)via dipping and vacuum freeze-drying.The microstructure and composition of LDH/PLLA hybrid coating were analyzed by XRD,SEM,EDS and FT-IR.The biocorrosion behavior of hybrid coating was evaluated by potentiodynamic polarization,electrochemical impedance spectroscopy(EIS)and hydrogen evolution test in the Hank's solution.The results showed that LDH/PLLA coatings exhibited a much dense layer compared to the unmodified Mg-AI-LDH coating with unobvious boundary between PLLA and LDH coatings.The corrosion current density of the LDH/PLLA-10 hybrid coating decreased three orders of magnitude in comparison to its substrate.It was proven that the existence of the PLLA coating further prolonged the service life of the Mg-AI-LDH coating.What's more,the MTT assay and livel dead staining showed that the LDH/PLL A-10 coating had good biocompatibility for Mouse NIH3T3 fibroblasts.The formation mechanism and the anti-corrosion mechanism of hybrid coatings were proposed.

Corrosion resistance of a silane/ceria modified Mg-Al-layered double hydroxide on AA5005 aluminum alloy

The present work aimed at assessing the electrochemical behavior and the corrosion inhibition performance of Mg-Al-layered double hydroxide(LDH)coatings modified with methyltrimethoxysilane(MTMS)and cerium nitrate on AA5005 aluminum alloy.The chemical compositions and surface morphologies of the coatings were investigated by XRD,FT-IR and FE-SEM,while their corrosion resistance was evaluated by electrochemical and immersion tests.An optimum corrosion resistance of the composite coatings was obtained by adding 10^−2 mol·L^−1 cerium nitrate.An excess addition of cerium nitrate resulted in a loose structure and poor corrosion resistance of the coating.The corrosion mechanism of the composite coatings was proposed and discussed.