Effects of the extrusion ratio on the intergranular corrosion behaviour of 6082 aluminium alloy

Abstract

The intergranular corrosion behaviour and corrosion mechanism of 6082 aluminium alloy subjected to different homogenisation processes were investigated. The results show that with increasing homogenisation temperature and/or time, the amount of corrosion product, Al(OH)3, and the thickness of its layer gradually increase, the corrosion current density decreases, and the corrosion resistance increases. In addition, the corrosion current density of the forged alloy is much smaller than that of the extruded alloy, and thus, the forged alloy is more resistant to corrosion. Two kinds of secondary phase particles, Si and AlMnFeSi, are homogeneously distributed within the plastic deformation flow lines of the alloy. When the boundary between the secondary phase Si particles and the matrix is in contact with the corrosive agent, the matrix dissolves first and initiates the formation of corrosion cracks, as the matrix serves as an anode and the Si particles serve as a cathode in the micro-galvanic cell configuration. Moreover, the corrosion cracks develop into networks upon electrochemical corrosive coupling between the β″-Mg2Si precipitates and the precipitate-free zone (PFZ) located along the grain boundaries.