Laser cladding of Al2O3 coating on aluminium alloy by thermite reactions

Based on the principle of the thermite reaction of CuO and Al powders, an Al2O3 ceramic coating was produced on an aluminium AA7075 alloy substrate by means of laser cladding. SEM, XRD and TEM techniques were employed to study the phases of the coating. The results show that the top coating is a layer of Al2O3, below which is the fusion layer and the substrate. The Al2O3 layer primarily consists of the α-Al2O3 and γ-Al2O3 phases. The mechanism of the formation of the top Al2O3 layer is explained. It involves a series of thermite reactions and the decomposition of CuO powders. The amount of γ-Al2O3 phase present is considered to be governed by the solidification time available for the formation of the phase. Good interfacial bonding is achieved at the fusion layer/γ-Al2O3 phase interface.