The effect of trace level copper content on intergranular corrosion of extruded AA6082-T6 alloys

The effect of trace level Cu content on intergranular corrosion in an acidified salt solution has been systematically studied in four AA6082-T6 extrusions containing 0.001, 0.02, 0.03 and 0.05 wt% Cu. Although these Cu concentrations are smaller than those expected to directly contribute to intergranular corrosion (IGC) in aged AA6082 alloys, IGC is observed in the present experiment even in alloy with the lowest Cu content. Whereas the extent of IGC is negligibly small in the alloy containing 0.001 wt% Cu, it increases with increasing Cu content. Profound IGC is observed in the alloy containing 0.05 wt% Cu. Microstructural characterization reveals Cu segregations along some grain boundaries in each alloy. The different alloys demonstrate differences in the size and number density of precipitates as well as in the width of precipitate free zones.