Local corrosion behaviour of high-strength 7XXX aluminium alloys

7xxx aluminium alloys (Al-Zn-Mg-Cu) are susceptible to localised corrosion like pitting, intergranular and exfoliation corrosion. Their susceptibility is strongly affected by heat treatments. In order to study localised corrosion in 7xxx alloys, solution heat treated and overaged (T76) tempers of AA7075 were characterised using complementary techniques like SEM-EDS, scanning confocal laser microscopy, OCP and potentiodynamic polarisation measurements, scanning Kelvin probe force microscopy and micro-capillary cell. The samples that underwent potentiodynamic polarisation showed localised attack at the intermetallics and intergranular and exfoliation corrosion. The SKPFM investigation proved that the attack at the intermetallics was caused by strong potential differences between intermetallics and matrix. Moreover, the SW60 temper showed higher potential differences between intermetallics and matrix than the T76 temper. The investigation with the micro-capillary cell showed the higher potential differences between intermetallics and matrix in the SW60 temper caused a shift in the negative direction of the local breakdown potentials for areas containing a few intermetallics. It is concluded that the heat treatment of AA7075 affects the localised corrosion at the intermetallics.