Abstract: The corrosion inhibition of polymeric substance(agar-agar ) on sand cast AA7075  aluminium alloy in 0.5M solution of NaOH was studied using weight loss method. The alloy of composition 5.6%Zn, 2.5%Mg, 1.6%Cu, 0.23%Cr and the balance Al was sand cast. After casting, the alloy was cut and machined to corrosion coupons and immersed into 0.5M solution of NaOH containing  the inhibitor solution at temperatures of 25, 35, 45, 55 and 65˚C respectively. Results obtained revealed that agar-agar inhibited/retarded the corrosion rate of AA7075 in the concentration and temperature ranges studied. The maximum inhibition efficiency (%IE) of 78.89% was achieved at 25˚C, while the minimum inhibition efficiency (%IE) of 12.71% was obtained at 65˚C. It was evident from the result generated that the inhibition efficiency decreases with increase in experimental temperature. The activation energy of the inhibited system (E_ai = 2460KJ/mol) is greater than for the uninhibited system (E_au =1660KJ/mol) which further confirms that the presence of agar-agar retards the corrosion rates of AA7075 in 0.5M  NaOH solution.


KEYWORDS: Corrosion, inhibitors, adsorption, inhibition efficiency.