•Octadecylamine and tetradecyl trimethyl ammonium bromide can effectively reduce the CO2 and H2S induced corrosion of steel.•A good synergistic corrosion inhibition effect of octadecylamine and tetradecyl trimethyl ammonium bromide is observed.•Molecular dynamic simulation technique was used to study the synergism of inhibitors.•The synergism of inhibitors was found correlative to the fraction free volume value of inhibitor film.•Co-adsorption process of inhibitors was studied to explain the synergistic mechanism.The corrosion inhibition performances of octadecylamine (OCT) and tetradecyl trimethyl ammonium bromide (TTAB) for carbon steels in H2S and CO2 brine solution were investigated by weight loss, potentiodynamic polarization, molecular dynamic simulation and XPS analysis. TTAB showed better inhibition effects on H2S and CO2 induced corrosion than OCT. Synergistic corrosion inhibition effect was found between OCT and TTAB with proper mass ratios and the best inhibition performance was achieved with 10 mg L−1 OCT and 20 mg L −1 TTAB. The synergism was correlative to the fractional free volume of the inhibitor film of OCT and TTAB.

•l-Cysteine can effectively retard the CO2 induced corrosion of carbon steel.•A good synergism of imidazoline derivative and l-cysteine is observed.•An adsorption model was proposed to elucidate the synergistic mechanism.The corrosion inhibition performance of imidazoline derivative (IM) and l-cysteine (CYS) on carbon steel in CO2-saturated brine solution was investigated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), weight loss, contact angle and X-ray photoelectron spectroscopy (XPS) measurements. The results show that the inhibition performance of individual IM is slight for CO2 induced corrosion, and can be strengthened greatly by combined use with Cys. The synergistic inhibition effect of IM and CYS is observed. An adsorption model involving the initial adsorption of CYS on carbon steel surface followed by IM was proposed to elucidate the synergistic mechanism.

•A synergistic effect of QB and 12-3OH-12 is found in our research system.•We discuss the relationship between addition and adsorption quantity of inhibitors.•There is a competitive adsorption between QB and 12-3OH-12.•A simple adsorption model is proposed based on the obtained results.Corrosion inhibition of a quinolinium quaternary ammonium salt and a Gemini surfactant, 1,3-bis(dodecyldimethylammonium chloride)-2-propanol, for mild steel in H2S and CO2 saturated brine solution was investigated by using polarization test, EIS and XPS. The synergistic effect is found between these two compounds when the Gemini concentration is less than 50 mg L−1 in the solution containing 100 mg L−1 quinolinium quaternary ammonium salt, and it disappears when the Gemini concentration is larger than 50 mg L−1. The synergistic mechanism is explained by competitive adsorption of these two compounds on steel surface.

•A novel approach to improve the corrosion resistance of PEO coating of Mg alloy was developed by adding GO in the electrolyte.•The incorporation of GO decreased the porosity of the PEO coating.•With 2 g/L GO in the electrolyte, the optimal corrosion resistance was achieved.Graphene oxide (GO) was added into the electrolyte during the preparation of the plasma electrolytic oxidation (PEO) coating on AZ31 magnesium alloy. The effects of the GO additive on the microstructure, phase composition, and corrosion resistance of the PEO coating were studied. The results demonstrated that GO successfully incorporated into the PEO coating and it was partially reduced to rGO during the PEO process. As a result, the number of micropores on the PEO coating was significantly decreased. Moreover, the electrochemical test revealed that the corrosion resistance of the PEO coating was markedly improved upon the incorporation of 2 g/L GO.