Production and Characterization of AAO/Ni-P Hybrid Coating on Aluminum Alloy and Evaluation of its Corrosion Behavior

In this research, firstly, an oxide coating was created on the aluminum 2024 substrate by anodizing method, and then, with the aim of improving the surface properties of the aluminum alloy as much as possible, an electroless nickel-phosphorus coating was applied on this oxide coating. This hybrid coating was further heat treated at 450 degrees Celsius. Coatings were characterized Field-Emission Scanning Electron Microscopy (FESEM), X-ray Diffraction (XRD) and Energy-dispersive spectroscopy (EDS). The results indicated the formation of amorphous alumina by anodizing method on an aluminum substrate that contained some sulfur according to the sulfuric acid solution used in the anodizing process. The nickel-phosphorus electroless coating had 9.4 wt.% of phosphorus. The effect of coatings on corrosion resistance was also evaluated using TOFFEL polarization test. Examining the results of these tests has shown that the corrosion performance of the aluminum substrate has improved because of the application of the hybrid coating. Conducting heat treatment of hybrid coating at 450 degrees caused a decrease in corrosion resistance because of the production of small galvanic cells on the surface of the coating.