Metal-Ceramic Interfaces in Laser Coated Aluminium Alloys

A novel process was developed to firmly coat an aluminium alloy, Al6061, with α-Al2O3 by means of laser processing. In this approach a mixture of SiO2 and Al powder was used to inject in the laser melted surface of aluminium. A reaction product α-Al2O3 layer of a thickness of 100 µm was created which was well bonded to the aluminium surface. Various interfaces, Al/α-Al2O3, Al/mullite and α-Al2O3/mullite, were studied by conventional transmission electron microscopy (CTEM) and high resolution electron microscope (HREM). It turns out that the presence of the Al/mullite interface may be essential to form a well bonded oxide layer and the high Si-content α-Al2O3 intermediate layer may be wetted better by liquid Al. Investigations of the interface structures and wetting phenomena during laser processing are presented and a simple correlation between wetting phenomena and interface strength is derived