HOT EXTRUSION OF ALUMINIUM POWDER

Abstract

Extrusion of metal powders is a well established forming process and its potential especially for shaping brittle powders into useful products was realised in the very early stages when filaments of electric bulbs were successfully manufactured. The application of this technique to softer metal powders like iron, copper and aluminium is a recent innovation. Although the experimental technique for producing extruded products from powder is well develop-ed, theoretical analysis of the process involved received little attention. The earliest attempt in this direction was initiated as late as 1970 when some well established theories of metal forming were applied to the extrusion of aluminium powder and its alloys. Application of the slip line field theory and upper bound analysis could predict the load required for extrusion which was lower than that required for the extrusion of cast billet into final product of the same geometry. It was emphasised that unlike the extrusion of a cast billet, powder billet during extrusion must necessarily be subjected to massive shear zones along slip lines in order that a strong and coherent product was obtained. Based on this reasoning the use of square edge dies Uiith relatively higher reduction ratios ( B.> 10 0l ) was favoured. Experimentation was confined mainly to a temperature of 300°C and the theoretical analysis employed had its own limitations because of simplified assumptions....................