On the Deep Drawing of Zinc Single Crystals

Abstract

In deep drawing, the operations involve two essentially different modes of deformation; the central regions of the blank crystals are stretch-formed over the punch head, while the outer parts are subjected to radial drawing between the die and the pressure plate. This experiment has been carried out to investigate the crystallographic behavior under these complex stresses given by the deep drawing of hexagonal close packed metal. The single crystals of zinc with 99.999% purity were deep drawn by using a hemispherical nose form on the punch at room temperature and at 200°C. As a result, the deep drawability deformed at room temperature depends extremely on the crystallographic angle of θ, the angle between the blank and the basal plane. The crystals having the angle of 30°\lesssimθ\lesssim60° showed a good deep drawability (the limiting drawing ratio larger than 1.5), while the other crystals fractured at the beginning stage of drawing with two modes of fracture. The crystals having the angle of θ\lesssim30° fractured by cleavage of the basal plane in the created twinns, while the crystals with the angle of θ\gtrsim60° fractured at the basal plane in the initial matrix.
At higher temperature drawing, larger limiting drawing ratio over 1.5 were obtainned and furthermore, most interesting earing pattern due to twinning were observed. The mechanism of arising these ears are discussed by the shear direction of twinns and the basal slip direction.