Thermally Sprayed Aluminum-Zinc-Indium as a Corrosion Protection for Steel

For many years thermally sprayed Aluminum-Zinc-Indium has been used in sacrificial CP of the rebars in reinforced concrete. The high negative potential of the alloy and the presence of Indium as an activator have made an ideal solution to overcome the high ionic resistance of reinforced concrete.  AlZnIn ingots are also very popular for protection of steel structures in marine environments.  Today economic pressures, especially the high price of zinc, have led to a new evaluation of consumables used in CP - consumables now have high cost, whereas, in the past they have been treated as low cost and of no importance.  These world economic changes have led to the idea of using thermally sprayed AlZnIn alloys for the CP of all steel structures.  The ternary alloy system, AlZnIn can lead to many individual alloys but the present authors have chosen a trusted composition, that which has been used for many years in solid cast anodes.  Solid homogeneous wires have been made for arc-spraying and they behaved physically as pure aluminum wires - no extra allowances were made in the spraying process.  Adhesion to the steel surface was as good or slightly better than that of pure aluminum.  Corrosion testing confirmed the high negative potential of the system, when compared to zinc and to pure aluminum and the throwing power was found to be at least as good as that of zinc. The biggest advantage of the aluminum alloy, compared to zinc, was its significantly higher resitance to erosion-corrosion, expected because the alloy is much harder than zinc. At one time, AlZnIn alloys were considered to be 'special' but today they can now enter the mainstream of CP and many applications can be proposed.