The inhibition of corrosion of an aluminum alloy in 5% sodium chloride solution at pH 5.5 and pH 3.2 (by acidification with acetic acid) was studied. Experimental methods were weight loss measurements and electrochemical tests. Three azo compounds, methyl yellow, methyl red and methyl orange, were shown to have some inhibiting effect. The protection was shown to be dependent upon the pH of the solution and was not the same for the three compounds. Their behavior was demonstrated to relate to acid/base equilibria, relative to colored indicators. Their inhibitive power was attributed to the formation of a protective compound between the aluminum ions and the nitrogen of the azo bond and, in the case of the methyl yellow, to the formation of a colloidal precipitate at the alloy's surface. -- AATA