Three-dimensional numerical analysis and experimental investigation of grain refinement in multi-pass equal channel angular pressing for round-workpieces

Equal channel angular pressing (ECAP) has the capability of producing ultra fine-grained (UFG) materials bellow the dimension of 1 μm. At present, it is one of the most important methods to get bulk UFG materials. Multi-pass ECAP processes for round workpieces are investigated by using numerical simulations and experimental studies in this paper. The deformation mechanism of ECAP for grain refinement is obtained. Three processing routes A, B and C are simulated in order to study the influence of the processing routes to the deformation uniformity of the workpiece. The finite element (FE) analysis results of the multi-pass ECAP process show that the different processing routes result in the different deformation distributions. The grain in the workpiece is refined obviously after multi-pass pressing. The microstructures of the processed material are more different than that of the microstructure of the annealing initial equiaxed grains. The microstructure evolution of the workpiece can be changed via different processing routes. It is found that route B can get a high angle grain boundaries distribution in the workpiece than other routes. The results of the analysis show that the process of grain refinement can be described as a continuous dynamic recovery and recrystallization. The microstructure evolutions of the grain refinement mechanisms and micro-structural characteristics for different multi-pass ECAP processing routes are verified by using OM (optical model) and TEM (transmission electron microscope) analysis. In addition, the experimental microstructure results are also consistent with FE analysis results.