Grain refinement mechanism analysis and experimental investigation of equal channel angular pressing for producing pure aluminum ultra-fine grained materials

Bulk ultra-fine grained (UFG) materials can be obtained by equal channel angular pressing (ECAP) process. Using our own commercial metal forming finite element code CASFORM/PC, ECAP process is analyzed numerically in this paper. The grain refinement mechanism is presented. The node mapping method is employed to realize the analysis of multi-pass ECAP process. Rules of acquiring the uniform deformation distribution of the final workpiece are put forward for pure aluminum material. The obtained results can offer valuable processing parameters and optimal processing routes of ECAP for producing UFG materials. Meanwhile, the microstructure evolutions of grain refinement mechanisms for different multi-pass ECAP processing routes are verified by using ECAP experiments and microstructure analysis. Through the numerical simulations and experimental studies, the uniformly deformed UFG materials with high angle grain boundary microstructure can be obtained by adjusting processing routes and parameters. The formation mechanism of nanostructure was given for the ECAP through studying the deformation behavior and dislocation's evolution. The process of grain refinement can be described as continuous dynamic recovery and recrystallization. From the viewpoint of the microstructure analysis, the grain refinement process is to control the dynamic balance of the generation and annihilation of the dislocations. From the viewpoint of the macro deformation analysis, the grain refinement process is to seek optimal processing routes.