Grain Boundary Structure of Al–Mg Alloys Processed by High Pressure Torsion

Abstract

The structure of dislocation and grain boundary(GB) in nanostructured Al–Mg alloys processed by high pressure torsion(HPT) was characterized by means of transmission electron microscopy(TEM) and high-resolution TEM(HRTEM).The results show that the grains less than 100 nm have sharp GBs and are completely free of dislocations.In contrast,a high density of dislocation as high as 1017m- 2 exists within the grains larger than 200 nm and these larger grains are usually separated into subgrains and dislocation cells.These dislocations appear as dipoles and loops.Different GB structures including low/high angle non- equilibrium GBs,low angle equilibrium GBs and high angle Σ 9 equilibrium boundaries are characterized by HRTEM.The roles of the very high local dislocation density,the dislocation cells and the non-equilibrium GBs in grain refinement during HPT are analyzed and the refinement mechanisms associated with these structural features have been proposed.