Study On Grain Refinement Of High Purity Aluminum Plate Of Large-Size By Equal Channel Angular Pressing

Equal channel angular pressing (ECAP) is one kind of promising severe plastic deformation methods, which can produce ultra fine and even nano scale grains. An important advantage of ECAP is that simple shear deformation can be accumulated in the work piece without changing its size when pressing. At present, ECAP is mainly used in processing sample with small size. The cross section of the sample is always in the order of 100mm2, and this limits the further application of ECAP in industry.In order to find a short cut to fabricate the high purity aluminum sputtering target, using the self-designed mold, ECAP experiments of 5N high purity aluminum were carried out at room temperature by two routes T and W. The dimension of the plate is: 180mm*180mm* 22mm. After several passes ECAP, the microstructure evolution was investigated by OM, TEM and EBSD. Besides, shear mechanism of different routes and refinement mechanism were analyzed.It is found that the grain refinement and distribution in the middle part are better than in both ends. The grain on the shear plane was stratified along cross section of 5N aluminum plate. In the beginning, uniformity of grain distribution was determined by shear mode. Then accumulation of stress and strain plays a leading role. Combining the results of TEM and EBSD, refinement mechanism can be described as: original large grains;? large grains break up under shear rotation;? high density of dislocations lines accumulate at the grain boundary and form dislocation cells or walls; density of sub-grain increase and rotate to the high angle grain boundaries. After ECAP, cooper texture and rotated Goss texture appeared, then cube texture or rotated cube texture also developed, During ECAP, discontinuous dynamic recrystallization occurred.