SPRAY FORMING AND CHARACTERIZATION OF AL-GRAPHITE ALLOYS

Abstract

Spray forming, also called spray casting or spray deposition, is the inert gas atomization of a liquid metal stream into variously sized droplets which are then propelled away from the region of atomization by the fast flowing, atomizing gas. The droplet trajectories are interrupted by a substrate which collects and solidifies the droplets into a coherent, near fully dense preform. This method has many advantages over conventional techniques like casting, powder metallurgy etc. Aluminum is used for spray forming because aluminum alloys are difficult to prepare by other methods like powder metallurgy and casting. In spray forming technique, a molten metal stream of Aluminum is disintegrated by the energetic gas field created by an atomizer. The resulting droplets and graphite particles which are injected from other source are collected on the substrate to produce preforms. The present work concerns with this technique. This technique can be employed to produce a near net-shape of preform. Aluminum alloys are used in a wide variety of applications because of their attractive properties, such as a high strength to weight ratio, good corrosion resistance, high thermal and electrical conductivity, a low wear rate and good response to various finishing processes. Thus, these alloys are widely used in automotive and aerospace applications. Since graphite immensely improves the wear resistance of these alloys because of its high hardness, it has been concluded that higher graphite content leads to better wear resistance. Amongst several Al-alloys, aluminum graphite alloys has created interest for several applications in aerospace, automobile used as a bearing material and electrical equipment industries due to their low density to weight ratio, high specific stiffness, high thermal conductivity, high wear-resistance and low coefficient of thermal expansion (CTE).