The enhancement of corrosion inhibition of galvanised steel by synergised leave extracts of Sida acuta (S.A.) and Jatropha curcas (J.C.) in 1.0 M HCl solution was investigated using the gasometric technique at 30 oC and 50 oC. Results obtained showed that complimenting plant extracts with galvanisation of steel enhanced the inhibition of Zinc in the protection of steel. Fourier transform infrared analysis confirmed the O-H functional group of alcohol at 3851 and 3436 cm-1 band. Surface morphology of the steel, synergised were studied with a scanning electron microscope (SEM) and electron dispersive X-ray spectroscopy (EDX). Analysis revealed the protection of the internal grains of the metal from dissolution into corrodents provided by the adsorbed film the extract. Inhibition efficiency improved from 57.57 % to 95.45 %, corrosion rate 0.454 cm3 /hr to 0.093 cm3 /hr for zinc-coated steel only to extract enhanced-zinc coated steel. Langmuir isotherm best explained the adsorption mechanism of extract of zinc surface. Zinc coated steel has a half-life less than 0.04531539 x 1010 minutes, while effective enhancement of Zinc coated steel with extract gave a half-life of 0.075132088 x 1010 minutes. This implies that the enhancement of galvanised (Zinc coated) steel with synergised extract improved the inhibitory characteristics of the composites over that of zinc coat alone, which corrodes in place of steel.
