Investigating the effects of pre-deformation and aging conditions on localised corrosion behaviour of aluminium alloy 6061 via electrochemical polarisation

Corrosion behaviour and intergranular corrosion (IGC) sensitivity of 6061 aluminium alloy were investigated using electrochemical polarisation. A 10% tensile stretching was carried out on as-quenched 6061 alloys to understand the effect of pre-deformation on precipitation during subsequent aging treatments. Grain boundary (GB) TEM micrographs were taken to correlate the relationship between the changes in microstructure and corrosion resistance. For artificially aged 6061 alloys, the introduction of the 10% pre-deformation reduces the corrosion rate, but is unable to change their IGC susceptible nature. Conversely, pre-deformation dramatically reduces the pitting depth and pit distribution of naturally aged 6061 alloys. Needle-like β″ precipitates were found homogeneously distributed in the matrix and the GB areas in the pre-deformed and naturally aged 6061-T3. It is suggested that strain-induced dislocations and misorientation sites cover the lack of vacancies around the as-quenched GBs, therefore promote homogeneous precipitation across the GBs which improves resistance against localised corrosion.