Amino acid and TiO2 nanoparticles mixture inserted into sol-gel coatings: An efficient corrosion protection system for AZ91 magnesium alloy

•Preparation of sol-gel coatings from mixing TEOS and TEVS.•Application of the prepared coatings on AZ91 alloy to protect it from corrosion.•Incorporation of various amino acids as inhibitors into the coatings.•Improving the performance of the amino acid-containing coatings by TiO2 nanoparticles.•Investigation of the inhibition performance of the coatings by EIS measurements. This work is aimed to protect the commercial AZ91 magnesium alloy from corrosion in 0.05 M NaCl solution via a hybrid sol-gel coating prepared from mixing tetraethylorthosilicate (TEOS) and triethoxyvinylsilane(TEVS). The formation and morphological characteristics of the provided coatings areinvestigated by using Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). To improve the protection properties of the coating, a series of amino acids named as cysteine, serine, alanine, and arginine are introduced into the coating as green inhibitors. TiO2 nanoparticles are also added to the coating as surface modifier to reach a higher uniformity of the coating surface. The performance evaluation of the coating isdone by using electrochemical impedance spectroscopy (EIS)and potentiodynamic polarizationmeasurements. The obtained EIS data show that the presence of cysteine, serine, and alanine in the coating makes a significant increase in the corrosion resistance, whereasarginine exhibits no efficient inhibiting effects. Moreover, the addition of TiO2 nanoparticles to the amino acid-containing coating is found to leadto a much more enhancement in corrosion resistance, for example from Rct = 52.56 kΩ cm2 in the presence of 0.5 wt% cysteine to 224.09 kΩ cm2 in the presence of 0.5 wt% cysteine +1.0 wt% TiO2 after 2 h immersion in the aggressive solution.