The characterization of the flow of wet powder masses has been achieved using a ram extruder. Force/displacement curves obtained when material is forced through dies of varying length were found to exhibit three stages: (1) compression (2) steady state flow and (3) forced flow. To provide high quality extrudate it was found preferable to ensure that the compression stage was as short as possible and that steady state flow predominated. To produce these conditions, an optimum composition, die length and ram speed were required. The implications of these findings in relation to the provision of suitable formulations and production conditions for the preparation of spherical granules are discussed.

The characterization of wet powder masses suitable for extrusion/spheronization.

The application of capillary rheometry to the extrusion of wet powder masses

Extrusion is shown to be a thermally activated process in which mass transfer is important. Speed effects may be recognized in the mean equivalent strain rate and then combined with temperature eff...

Temperature and speed effects in hot extrusion of aluminium alloys

The quality of a powder compact depends on the uniformity of the particle size distribution throughout its volume and the retaining of a refined microstructure during the final consolidation process. This paper deals with the creation of uniform green compacts from powders and the dynamic consolidation process. An overview of basic issues and problems concerning the behaviour and handling of granular materials is presented, emphasising recent results on particle size segregation induced through vibrations and occurring in granular flows. The implications of segregation on the production of green compacts are introduced followed by a discussion of their formation via ultrasonic vibrations. The dynamic (shock) consolidation process to form dense compacts with metastable or refined microstructures from green compacts is described. A critical review and discussion of the kinetics and energetics in the shock consolidation process, including particle bonding and shock energy distribution, is presented.

Manufacture of powder compacts

Abstracts are not published in this journal

Extrudability of PM 2124/SiCp aluminium matrix composite

More than a hundred experiments have been performed to investigate the extrusion mechanism involved and the effect of process variables on the structure, substructure, and mechanical properties of the extrude when processing atomized aluminium powder of varying mesh size. It is demonstrated that extrusion pressure is largely independent of the final properties and that the ductility of the extrude may be controlled by the process variables. A mechanism that agrees with experimental observations is suggested to explain the extrusion mechanics. Transmission and scanning electron microscopy results also support the theses presented.

The extrusion of atomized aluminium powders

Materials that are difficult to cast and work may be prepared by using powder extrusion as a primary fabricating technique. The Al-Fe system was selected for study and is examined in detail. The effect of varying the extrusion conditions on the structure and substructure development and on the mechanical properties of the final product is investigated. It is shown that the mechanism of extrusion provides an explanation for the various properties observed, and that for this alloy the oxide content is not significantly property-controlling.

POWDER EXTRUSION AS A PRIMARY FABRICATING PROCESS FOR Al-Fe ALLOYS*

Four aluminium alloy powders were extruded in the temperature range 250–550° C and the strain-rate/flow-stress/temperature relationship analysed in terms of exponential functions. The results of ∼400 experimental runs indicate that the powder process is less strain-rate sensitive than is its conventional counterpart. The process is thermally activated and it appears that the rate-controlling mechanism is the climb of edge dislocations or the migration of jogged screw dislocations.

P. J. M. Chare

Papers

The extrusion of atomized aluminium powders

POWDER EXTRUSION AS A PRIMARY FABRICATING PROCESS FOR Al-Fe ALLOYS*

On thermal activation during extrusion of metal powders