Anodising as pretreatment of durable aluminium: The behaviour of several aluminium alloys to filiform corrosion

Aluminium alloys AA 3005, AA 3103 and AA 6063 were anodised in sulphuric ac id under different conditions whereby a set of porous layers with varying t hicknesses was produced. The influence of porous layer thickness on the Fil iform corrosion behaviour was examined by means of the Lockheed rest. The f iliform corrosion behaviour as a function of time was investigated. It appeared that the alloys showed similar filiform corrosion behaviour sin ce for all alloys filiform corrosion was reduced considerably by increasing the porous layer thickness. The number of filaments N and the average fili form corroded surface R increase in time until a saturation level has been reached. However, the saturation level appeared to be different for each co mbination of alloy and porous layer thickness. The results indicate that th e mechanism for filiform corrosion is the same for all three aluminium allo ys.