Theoretical and practical aspects regarding Al - SiC particles composites obtaining by casting

摘要

The paper presents the principal aspects regarding the obtaining of the mixture aluminium - silicon carbide particles. It is discussed about the wetting conditions and the critical acceleration necessary for the incorporation of particles into the melt. The high values obtained for this parameter involve applying some methods to improve the wettability: the covering of the complementary material with a thin layer of Ni, the alloying of the aluminium melt, the overheating of the metallic bath and the heat treatment of the silicon carbide particles. Also, the mechanical stirring conditions necessary to realize the mixture are presented. The settling process of the silicon carbide particles in the melt as a function of particles size, shape and volumetric concentration is also analysed. The presence of complementary material leads to the growth of the mixture viscosity. Therefore, the liquid alloy was investigated like a continuous medium in connection with the apparent viscosity. The main aspects regarding the solidification of metallic composites processed by casting method based upon theoretical concepts, general knowledge about casting of composites and experimental data are discussed. Finally, the specific defects caused by an insufficiently controlled solidification process and prevention measures are shown.