The effect of the tooling-workpiece interface condition on the metal flow in extrusions is shown to be of critical importance in the achievement of sound product. For 2:1 reduction ratio extrusions, the central burst defect is shown to occur when low fractional restraint interfaces are employed. Sound internal product is shown to occur when high frictional restraint interfaces are employed. In metal alloy powder compaction-extrusion processes, a low density core is shown to be associated with compaction at low extrusion ratios employing low frictional restraint interfaces. The experimental results are discussed in terms of recent theoretical analyses of metalworking processes which are based on the effect of the interface friction influencing the volume of the plastic deformation zone and the subsequent strain rate fields.

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