Hard anodizing of AA2011-T3 Al-Cu-Pb-Bi free-cutting alloy: improvement of the process parameters

The free-cutting Al-Cu-Pb-Bi alloy AA2011-T3 has been anodized in a traditional sulphuric bath with the aim of producing hard and uniform oxides of technological interest. H2SO4 concentration, electrolyte temperature, Al3+ concentration and current density have been modified. The effect of each process parameter has been evaluated through Potential-vs-time plot, coating hardness, coating thickness, volumetric expansion-ratio and coating defectiveness. SEM analysis has shown that Bi-based intermetallics are the main responsible for the severe defective state. Higher H2SO4 concentration and higher current density have improved coating hardness and defectiveness, however potentiodynamic polarizations have revealed that they do not enhance corrosion resistance.