Abstract: The effects of zinc additions on the corrosion susceptibility of aluminium alloys in varying concentrations of NaCl solution have been studied. Virgin aluminium alloys containing 1.0, 2.0, 2.5, 3.5 and 4.0% Zn by weight were cast and machined into cylindrical coupons of average surface area of 12.71 cm2. The initial weights of the coupons were determined and immersed in beakers containing 0.1, 0.25, 0.5 and 1.0 M NaCl solution. The set-ups were allowed to stand for six days with a set withdrawn 24 h for corrosion rate determination using standard procedures. The results showed that although the normal corrosion rate profile (for passivating metals) was observed as the reinforcing phase increased, the samples gained weight; indicating an all-through passivation, especially in the 2.5% Zn alloy. It is concluded that the passivation is a consequence of media supersaturation and preferential oxide (Al2O3) adsorption on the metal surface and that the 2.5% Zn composition may well represent the solvus line in Al -Zn binary systems.