Improvement of Drawability at Room Temperature in AZ31 Magnesium Alloy Sheets Processed by Equal Channel Angular Rolling

Abstract

A new rolling process, so-called as equal channel angular rolling (ECAR) process, for fabricating the magnesium alloy sheets with an enhanced formability at room temperature is introduced. The ECAR device was designed so that it could feed the sheet with the preheated temperature of 673 K in a continuous manner at a relatively high speed of 0.43 m/s. A significant amount of the shear deformation could be achieved by passing the sheet through the mold with the oblique angle of 115°. The x-Ray spectra were examined to analyze the crystal orientation of the sheets, which indicates that the crystal orientation with non-basal plane was fabricated after ECAR processing. The grain was not refined and plenty of twins were brought out because of the low-shear deforming temperature. The high stress and low ductility for the ECARed specimens can be related to the presence of twins. In spite of having the similar optical microstructure, the elongation to failure for the ECARed specimens after annealing was above 33%, which was larger than that of about 20% for the as-received/annealed specimens. And the drawability for the ECARed/annealed specimens with the Erichsen value of 6.24 mm and the limiting drawing ratio of 1.6 can be obtained, which is improved dramatically than that of 4.18 mm and 1.2 for the as-received/annealed specimens, respectively. These can be related to the rotation of (0002) basal plane toward the rolling direction because of the shear deformation induced by ECAR process.