The production of aluminium alloy composites using a cold isostatic press and extrusion approach

Whilst experimental results indicate that metal-matrix composites possess higher specific mechanical strengths, one of the main difficulties in implementing these materials on a large scale has been the costly and often complicated processes used. This paper presents the preliminary results obtained in developing a powder metallurgy process involving an approach based on the use of a cold isostatic press together with subsequent extrusion. Three systems have been compared: an unreinforced Al alloy system; an Al alloy-Ni short-fibres composite; and an Al alloy-Al₂O₃ p particulates composite. Mechanical mixing of the matrix powder and fibre reinforcement was followed by a high-pressure isostatic pressure compaction. Pressurization was done in the range of 10-400 MPa. The green compacts were extruded subsequently at 5-10 mm/min, and reduction ratios of 5 and 10, at both 400 and 500°C. Whilst the initial high-pressure compaction step was sufficient to reduce the porosity to as low as 5% when a pre-degassing step was used, both composite systems could not achieve porosity of less than 10% even after sintering at 600°C. However, by using the subsequent extrusion step, reduction to less than 5% porosity was achieved at 500°C, for both of the composite systems.