Experimental and Finite Element Analyses of the Hydrostatic Cyclic Expansion Extrusion (HCEE) Process with Back-Pressure

It is generally known that severe plastic deformation processes with back pressure not only apply higher hydrostatic stress and more deformation compared to what a regular process can apply to a workpiece but also prevent surface defects in the workpiece during the process. Hydrostatic cyclic expansion extrusion (HCEE) was developed recently for processing long ultrafine-grained metals and alloys. This process applies relatively higher hydrostatic pressure and prevents the formation of defects at the same time dramatically decreases the process load by eliminating the friction. However, increasing the compressive hydrostatic pressure leads to enhance the mechanical properties by minimizing the initiation and propagation of defects. So, back pressure may be considered as a solution. In this paper, first, morphological investigation of HCEE processed aluminum without back pressure is conducted. Second, the plastic deformation behavior of the aluminum sample during this recently introduced process for producing longer samples with different external back pressures is investigated using the finite element method. The homogeneity within the workpiece was analyzed in terms of contours, path plot, and statistics of strain distribution under different conditions regarding back pressure. The simulation results shed some lights on the optimum design of HCEE for homogeneous and large severe plastic deformation.