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Abstract
The development of an as-extruded structure has been examined for the conditions of the initial stages of extrusion. It is observed that an extrusion billet is subjected to considerable deformation before extrusion commences. The authors therefore discuss the product structure with reference to its length/diameter ratio and it is shown by inspection of electron micrographs that the popular concept that an as-cast structure is retained in the front portion of the extrude is incorrect. It is shown that the extrudate structure is fully developed before the ‘breakthrough’ pressure is attained and full product strength should therefore be obtained at an extrude length of about 9 diameters.