THE INFLUENCE OF EXTRUSION-CONSOLIDATION VARIABLES ON THE INTEGRITY AND STRENGTH OF THE PRODUCT FROM PREALLOYED 7075 ALUMINIUM POWDER

Abstract

A study has been made of extrusion-consolidation processing variables for the production of sound material from spherical 7075 aluminium alloy powder (median particle size 132 μm) canned in evacuated cylinders at ～60% initial density. Maximum product integrity and tensile properties were obtained by extrusion at 644K (700°F)–700K (800°F) and 6:1–10:1 reduction ratio. At lower reduction ratios (2:1 and 3:1) the product exhibited gross cracking and was not completely dense. At a reduction ratio of 40:1, it had significantly poorer tensile properties, attributable to the formation, during extrusion and heat-treatment, of longitudinal cracks at the particle boundaries and to the microstructure produced within the particle grains by the thermomechanical conditions. In general, processing behaviour and product properties were either inferior to or, in some cases, equal to those of wrought material extruded for comparison under the same conditions. Inferior behaviour of the metal powder during processing and tensile testing results from the presence of a brittle oxide film on the surfaces of the particles. Suggestions for improving the processing behaviour of the metal powder and the properties of the extruded product are made.