Grain refinement of a 6061 aluminum alloy by asymmetric warm-rolling

Abstract

For the purpose of grain refinement, the development of the microstructure of 6061 aluminum alloys during asymmetric warm-rolling was studied by electron backscatter pattern (EBSP) analysis, as well as optical and transmission electron microscopy, and compared with that developed during conventional warm-rolling. In asymmetrically rolled sheets to a thickness reduction of 91.8% at 300°C, new fine grains with an average size of about 1 μm are evolved almost uniformly throughput the thickness. The fraction of fine grains in asymmetrically warm-rolling sheet increased with an increase in thickness reduction and a rise in temperature, whereas for conventionally warm-rolled sheet, the usual fibrous microstructure is predominant. The evolution of new fine grains during asymmetric warm-rolling seems to be due to the subgrain formation and the development of the subgrain into fine grain promoted by a simultaneous action of two deformation modes, namely compression and additional shear deformation. However, the obvious growth of fine grains was observed during solution treatment. For suppression of such a grain growth, scandium addition to 6061 alloy is effective.