Grain refinement of high purity aluminium by asymmetric rolling

For the purpose of grain refinement, development of the microstructure of c oarse grain, high purity aluminium during cold asymmetric rolling has been studied by electron backscatter pattern (EBSP) analysis, as well as optical and transmission electron microscopy, and compared with that developed dur ing conventional rolling. In 91.3% asymmetrically rolled sheet, new fine eq uiaxed grains with an average size of similar to2 mum are evolved almost un iformly throughout the thickness. On the other hand, in conventionally roll ed sheet, the coarse fibrous structure is predominant. A change of grain bo undary misorientation distribution with an increase in reduction shows that the fraction of sub-boundaries below 10 degrees decreases linearly, and th at of the high angle boundaries above 15 degrees increases linearly. The fi ne grain evolution during asymmetric rolling seems to result from the devel opment of sub-boundaries into high angle boundaries promoted by a simultane ous action of two deformation modes, namely compression and additional shea r deformation. Fine grains evolved during asymmetric rolling are stable at temperatures below 423 K, Annealing at temperatures above 473 K results in remarkable grain growth.