In-Situ Laser Cladding of Al₂O₃ Reaction Coating on Aluminium Alloy 7075 for Corrosion Resistance Improvement

Abstract

The microstructure and corrosion behaviour of the thermite reaction coatings for the systems of Al–CuO–SiO₂, Al–Cr₂O₃–SiO₂, and Al–TiO₂–SiO₂ that produced by laser cladding on aluminium alloy 7075 have been studied. The results of the XRD analysis show that in all the three reaction coatings, α-Al₂O₃ and γ-Al₂O₃ phases were present together with various intermetallic phases and the corresponding reduced metal. A comparison of the polarisation curves of the untreated and the various coated specimens shows that except for the Al–CuO–SiO₂ system, the corrosion current density of the coated specimens was one order of magnitude lower than that of the untreated specimen, also a higher corrosion potential was obtained. The inferior corrosion resistance of the Al–CuO–SiO₂ system is attributed to galvanic corrosion occurred between the reduced metal, the intermetallic compounds and aluminium.