THE USE OF Vernonia amygdalina (BITTER-LEAF) EXTRACT AS CORROSION INHIBITOR FOR AA7075 ALUMINIUM ALLOY IN HCl AND NaOH MEDIA

Abstract

The effect of machining on corrosion behavior of AA7075 in 0.5M HCl and 0.5M NaOH solution was investigated

using Gravimetric-based mass loss method at different concentrations of Vernonia amygdalina (inhibitor) and

exposure time of 72, 144, 216 and 288 hours. The alloy was sand cast by the conventional sand casting technique,

after which two sets of coupons of dimension 12 mm by 20 mm were obtained by orthogonal and oblique

machining operations at a cutting speed and feed rate of 556 rev/min and 4 mm/rev respectively. They were then

immersed in two different corrosive media (0.5M HCl and 0.5M NaOH) in the absence and presence of Bitter leaf

extracts (inhibitor) at different concentrations of 0.25M, 0.5M and 1.0M. From the results obtained, the

susceptibility of the coupons to corrosion when immersed in HCl solution in the presence of inhibitor was lower

compared to those exposed to NaOH solution. It was also observed that obliquely-machined samples were less

susceptible to corrosive attack than orthogonally-machined samples in NaOH solution at room temperature. The

maximum Inhibition Efficiencies (IE%) for the obliquely-machined samples were 88.9% and 82.1% in HCl and

NaOH respectively. Similarly, maximum IE% values of 90% and 80% were achieved for the orthogonally

machined samples in HCl and NaOH respectively.