Deformation twins in ultrafine grained commercial aluminum

Abstract

Abstract Deformation twins in an ultrafine grained commercial Al – Mg – Si alloy with nonequilibrium grain boundaries processed by equal channel angular pressing at room temperature have been observed by means of a transmission electron microscope and a high-resolution transmission electron microscope. It was found that deformation twins formed frequently at the intersections of several grain bands where the critical stress level is reached locally and a change in the dominant slip system may occur due to the significant plastic deformation. Deformation twinning was also observed to occur via partial dislocations emission from grain boundaries and grain boundary junctions in the ultrafine grained alloy. Twins and stacking faults formed by Shockley partial dislocations dissociated from 0° screw dislocations were characterized and analyzed. Three twinning mechanisms suggested by molecular dynamic simulations were identified and their relevance was discussed.