The corrosion behaviour of aluminium alloy AlSi7Mg0.3 in artificial sea water with added 0, 20, 50 and 100 ppm of Na2S was investigated over the course of immersion of 42 days. Samples were taken at various times and their electrochemical and microstructural properties characterized. The corrosion current densities in all immersion solutions was very low, in the range of 10−7–10−9 A cm−2. The structure, composition and protectiveness of the so formed oxide layers were dependent on the Na2S concentration and immersion time. The presence of low sulphide concentration (