Extrusion limit diagrams: Effect of hmogenising conditions and extension to productivity analysis

Limit diagrams have been used for a number of years to illustrate and define the processing conditions for metal extrusion. Such diagrams show the working envelope for the process in terms of the ram speed, the extrusion ratio, and the Zener-Hollomon parameter. The present paper defines the effect of homo genis at ion on these diagrams by reference to some 7XXX alloys. Frequently, when extruding sections in which the properties are not particularly critical, it is the production rate that assumes greater importance. Mathematical expressions are developed which allow the maximum production rate to be expressed in terms of the cross-section of the extrudate and the extrusion preheat. Examples are given of both limit and production diagrams and it is shown that these are general forms which may be extended beyond the limit of the experimental alloys.