アルミニウム押出棒の不均一流れ

Abstract

Most of extrusion defects are caused by inhomogeneous flow of materials during extrusion, and there are many singular phenomena resulted from inhomogeneous flow in the outer parts of the products. But few quantitative studies of the metal flow in extrusion, especially near the outer surface of the products with high reductions, have been made. The present work was carried out to study quantitatively the flow of aluminum extruded with high reductions. The redundant strain from center to surface of the products was evaluated and compared with the slip line field theory. The results are summarized as follows:1) By a unique method of extruding aluminum billets with high purity Au wires as flow line markers, redundant strain values in the outer parts of the extruded bars could be obtained quantitatively.2) It can be said, within the experimental errors, that the intervals between longitudinal markers of the billet are similarly reduced in the extruded rod. Consequently, the displacement in the direction of the diameter agrees with that in plane strain analysis by the slip line field theory.3) The flow lines of the products could be represented by a function, Y = a exp (bX), where X is the distance from the center line of the bar, Y is the hight of the marker from X-axis, and a and b are constants. On the other hand, the flow lines from the slip line field theory under equivalent conditions were represented as Y = mXn, where m and n are constants, irrespective of extrusion ratios and friction conditions.4) The redundant strain in the outer part of the product is almost ten times as much as that from the theory. This may give a clue to make clear the anomalous structure near the surface of the extruded metals.