Laser melt injection in aluminum alloys: On the role of the oxide skin

In this paper the method of laser melt injection of SIC particles into an a luminum substrate is investigated both experimentally and theoretically. An extremely small operational parameter window was found for successful inje ction processing. It is shown that the final injection depth of the particl es is controlled mainly by the temperature of the melt pool rather than by the particle velocity. A theoretical model that takes into account the wett ing behavior and the particle penetration processes is developed on the bas is of the observed particle velocity, thickness and area fraction of oxide skin that partially covers the surface of the heated aluminum melt pool. Th e model reveals the role of the oxide skin: it is relatively strong at low temperature and acts as a severe barrier for the injection process. It was found that preheating the aluminum substrate results in a higher temperatur e of the melt pool and partial dissolution of the oxide skin, through which the injected particles are able to penetrate. (C) 2000 Acta Metallurgica I nc. Published by Elsevier Science Ltd. All rights reserved.