The new machine for deformation of metals and alloys by Cyclic Extrusion Compression method has been presented. The special, 600 kN capacity press was designed and build to deform materials by the CEC way. The press is equipped by microprocessor control system for hydraulic steering and measurement of the forces exerted by tools. The microstructure of AlMgSi (6082) samples deformed by new CEC press showed the nanometric features such as dimension of grains below 100 nm and large disorientation between nanograins. The nanostructure was found after the 24 cycles of the CEC ( = 16). The simulation of plastic flow in CEC process was performed by a DEFORM software. The process has been modelled in relation to the technically pure aluminium and 6082 aluminium alloys deformed with the reduction of sample diameter from 10 to 8.5 mm and next increase from 8.5 to 10 mm in a single CEC cycle. It was found that at suitably selected values of counterforce the tensile circumferential stresses occurred behind the matrix where radial extrusion took place. Increasing the level of hydrostatic pressure it was possible to prevent an increase of the dangerous tensile stresses. Based on the data from numerical simulation of the CEC processes a special diagram has been prepared, which facilitates suitable choice of the counterforce level.
The influence of very large deformations on the properties and microstructures of A199.95 and A199.992 is investigated. The very large deformations are imposed by the cyclic extrusion-compression (CEC) method, which combines extrusion and compression processes. It is found that above true strains of 4 and 8 respectively, the compression proof stresses of A199.992 and A199.95 stabilize. The property stabilization appears to result from the increasing incidence of micro bands which leads to the final constancy of the microstructure parameters. The homogeneous chess-board like microstructure forms during the deformation by the CEC method, as the result of rearrangement of microstructure by the mutually crossing microbands leading to the final dominance of persistent macro shear bands.
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