Plastic Flow Properties and Microstructural Evolution in an Ultrafine-Grained Al-Mg-Si Alloy at Elevated Temperatures

An AA6082 alloy was subjected to eight passes of equal channel angular pressing at 100 degrees C, resulting in an ultrafine grain size of 0.2 to 0.4 mu m. The tensile deformation behavior of the material was studied over the temperature range of 100 degrees C to 350 degrees C and strain rate range of 10(-4) to 10(-1) s(-1). The evolution of microstructure under tensile deformation was investigated by analyzing both the deformation relief on the specimen surface and the dislocation structure. While extensive microshear banding was found at the lower temperatures of 100 degrees C to 150 degrees C, deformation at higher temperatures was characterized by cooperative grain boundary sliding and the development of a bimodal microstructure. Dislocation glide was identified as the main deformation mechanism within coarse grains, whereas no dislocation activity was apparent in the ultrafine grains.