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Abstract
When a billet is extruded through a die with two holes of different diameter hut similar length of bearing surface, the extrusion through the larger hole is longer. The ratio of the length of the extrusion through the larger hole to the length through the smaller hole isproportional to the ratio of the external friction of the metal on the container and on the die to the resistance to flow of the metal itself. On this basis a simple, rapid test for extrudability was developed. The billets to be tested are extruded through a die with holes of different diameter. By measuring the length of extrusion through each hole, the formability of the material or the effect of external conditions (lubrication, surface finish, design of the die, etc.) can be measured. The higher the ratio of the length of the extrusion through the larger hole to the length of the one through the smaller hole, the better the extrudability, or the higher the external friction. This test correlates very well with the measurements of breaking pressure and extrusion speed but is more reliable and more sensitive to small variations: in an alloy of the Al-Mg-Si type (6063) a variation of magnesium content from 0·47 to 0·52% reduces the ratio some 8–10%.