Microstructure and Intergranular Corrosion of Al-Mg-Si alloy under a Trace level copper content

The heat-treatable Al-Mg-Si alloys are extensively used owing to their high strength-to-weight ratio, good formability, and good corrosion resistance. However, susceptibility to intergranular corrosion (IGC) of extruded Al-Mg-Si alloys may increase by unfavorable heat treatment or unbalanced addition of certain alloying elements such as Cu and Zn. A small fraction of copper can communally be present in Al-Mg-Si alloys, which either is added to improve the mechanical properties or can be found as a trace element.
Microstructure and intergranular corrosion of recycled Al 6082-T6 under trace levels of Cu were investigated by microscopic investigations and intergranular corrosion (IGC) testing. Microstructure and corrosion morphology was analyzed using light optical microscopy, scanning electron microscopy, and transmission electron microscopy. Extruded profile of the alloy showed duplex microstructure with recrystallized grains on the surface, while a fully deformed structure near the center of the extruded profiles. Copper concentrations even down to 0.001 wt.% showed IGC in Al 6082-T6, and the degree of attack increased with an increase in copper content. TEM results showed that the susceptibility is due to the segregation of copper at the grain boundary and related precipitate free zone even at very low level of copper content, while the width of the precipitate free zone was a function of copper content.