Microstructure and interfaces of a reaction coating on aluminium alloys by laser processing

Abstract
This paper reports an approach to coat a ceramic layer on aluminium alloys by means of chemical reaction. The reaction product of Al₂O₃ layer of 100 µm in thickness has been formed using a powder mixture of silicon oxide and aluminium by laser processing. It turns out that the large amount of heat from the exothermic reaction has a predominate effects on the formation of the oxide layer. Further, the negative free energy of the reaction may promote the metal/oxide wetting. The micro-hardness and wear tests proved that the oxide layer is hard and strong. A mullite intermediate layer between aluminium and oxide have been identified by TEM. The atomic structure and defects of the reaction layer have been imaged at high resolution electron microscope.