Effects of reduced surface grain structure and improved particle distribution on pitting corrosion of AA6063 aluminum alloy

Abstract

Abstract In this paper, the effects of equal channel angular pressing (ECAP) and age treatment on the evolution of surface grain structure and corrosion behavior of AA6063 were investigated. ECAP was conducted for up to 6 passes followed by aging treatment at 180 °C for 8 h. It is concluded that with increasing deformation, the grain size decreases with the change of the morphology and the number density of particles. Studying the equivalent circuits by the EIS method demonstrates occurrence of a combination of pitting and uniform corrosion. By increasing the number of deformations passes, corrosion resistance increases and pitting corrosion decreases which are due to fragmentation of particles. This is confirmed by cyclic polarization tests as the potential for re-passivation of pits reduces and pitting corrosion resistance improves with increasing deformation. The corrosion resistance decreases with age treatment despite of expecting an enhancement due to the reduction in dislocation density. It is attributed to the formation of a high density of particles that can act as prominent sites for unstable pits. Indeed, the potential for re-passivation of pits increases after age treatment and the pitting corrosion resistance weakens. The results were also confirmed by potentiodynamic polarization and immersion tests.