Numerical simulation and experimental investigation of grain refinement behavior in equal channel angular pressing/extrusion process

The ultra-fine grained (UFG) materials have been widely investigated due to their mechanical properties such as super high strength and super high plasticity. The finite element simulation schemes are planned for the deformation mechanism of ECAP pressing. It will greatly affect the extrusion process when processing parameter changed such as die geometrical parameters and friction condition. It is considerable to determinate the range of die channel angle and die corner angle during ECAP process, and a moderate die corner angle is usually chosen. The friction condition of the ECAP should be lubricated as good as possible in the pressing on the basis of optimal die geometrical conditions. The ECAP process is a non-uniform shear deformation process in the cross-section of the workpiece for first-pass pressing. There have low angle grain boundaries along the cross-section of the grain microstructures. For the multi-pass pressing, although the pressing pass numbers are same, the processing routes were of important significance on the grain sizes and grain distribution and grain boundaries (GBs) orientations of workpieces. The formation mechanism of nanostructure was given for the ECAP through studying the deformation behavior and dislocation's evolution. The dislocation is one of the main defects in the processed materials, but the form of the dislocations and its density are difference for different processing route. The processed workpiece with high surface quality, refined grain microstructure and optimization grain boundaries were obtained with optimal processing parameters and routes.