Effect of additional Cu and Mg in Al–Mn–Si alloy on intergranular corrosion susceptibility after heating at 200°C

Effect of additional Cu and Mg in Al–Mn–Si alloy on intergranular corrosion susceptibility (corrosion characteristics) has been investigated by SWAAT after heating at 600°C, followed by reheating at 200°C. Intergranular corrosion occured in Al–Mn–Si–Cu alloy after the heating for 1 to 10 h, while pitting corrosion was observed in Al–Mn–Si–Cu–Mg alloy. Intergranular corrosion in the former alloy was cause by selective dissolution of lacking zone containing less content of Cu. In the latter alloy precipitates including Cu were observed not only in grain boundary but also in grain even after shorter heating time at 200°C. Therefore,decreasing intergranular corrosion susceptibility of the alloy was caused by smaller potential difference between lacking zone and grain matrix. In conclusion, addition of Mg in Al–Mn–Si–Cu alloy has corrosion resistance improving effect after heating at higher temperature.