Studies on the Electrochemical Behaviour of Al-Ni Alloys in Alkaline Solutions

The electrochemical behaviour of Al and Al-Ni alloy of different Ni % content below the eutectic, the eutectic and beyond the eutectic composition were investigated by potentiodynamic anodic polarization and potentiostatic current-time transient techniques in NaOH solutions complemented by metallugraphic examination. The anodic polarization behaviour of both Al and Ni was introduced for comparison. The results of anodic passivation parameters showed that the alloy of the eutectic composition has the highest resistivity against corrosion in all studied solutions. This may be attributed to the decrease of the anodic dissolution rates with increasing surface area ratios of the eutectic composition in the alloy. The main anodic dissolution reaction in all alloys is identified as a selective dissolution of the Al, α-phase, from the Al(α) + NiAl 3 (β) eutectic composition. The corrosion behaviour of the alloys below the eutectic composition is attributed to the bifunctional effect of Ni 2 + cations in the solution, which either promotes or inhibits the dissolution of the alloy, depending on the concentration of Ni 2 + cations dissolved in the solution.