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The influence of solution annealing (T4) and artificial aging (T6) on the corrosion properties of a technical Al-Mg-Si alloy was investigated. In the T4 condition, the material was not susceptible to intergranular corrosion; however, pitting was identified to occur. Subsequent artificial aging of the solution annealed and quenched alloys introduced susceptibility to intergranular corrosion. This phenomenon was attributed to two microgalvanic coupling situations: one that occurred between the noble Cu-phases located on the grain boundary and the anodic adjacent area and one between a Mg-and Si-depleted zone along the grain boundaries and the adjacent area. Pitting corrosion was proposed to occur as a result of the absence of these microgalvanic coupling situations, and therefore with the absence of a distinct, preexisting corrosion path in the solution annealed condition.

The susceptibility of the 6056 aluminum alloy in the solution annealed (T4) and artificially aged (T6) condition to intergranular corrosion (IGC) was investigated utilizing the established testing standard ISO 11846 B and an electrochemical procedure specified as ISO 11846C. The first method showed significant differences in the corrosion properties of the materials, namely a high pitting susceptibility of the T4 treated material and an exclusive intergranular attack in the artificially aged samples. The electrochemical technique was not suitable to confirm these distinct corrosion properties. However, an alloy specific adaption of the standard was conducted to give comparable results and to qualify the method for high Cu containing 6000 alloys.

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