چكيده به لاتين
In the present study, Equal Channel Angular Torsion Drawing (ECATD) has been introduced as a novel method for continuous grain refinement of wires. Commercial pure Al wires with initial diameter of 4mm, have been processed with the ECATD method for several passes. Then, the obtained properties and developed microstructures have been investigated experimentally. Microstructure study by light optical microscopy (LOM) as well as by EBSD method indicates that the grains size decreased from 100μm for the annealed sample to about 10μm in the center and below 2μm in the areas near the wire surface after four passes of the process (drawing speed: 3.8mm/rev, rotational speed: 21rpm and die intersection angle: 160º). The development of dislocations accompanied with generation of sub-grains and substructures created by intersection of deformation bands and micro-shear bands are the most significant microstructural changes. Microhardness measurement results reveal an increase in the hardness of the initial wires, especially in the areas near the wire surface. The tensile test results indicate an improvement in the yield and ultimate tensile strength of the processed wires. On the other hand, the results show that, depending on the parameters of the process, a wide range of elongation for the final wires can be achieved. There is a good agreement between experimental and numerical results regarding the strain distribution, resulting in the heterogeneity of the developed microstructure and the gradual change of hardness in the cross section of the deformed wires. The analytical results obtained by Upper-bound method for predicting the required force of the process are also in good agreement with the measured value of the experimental and numerical methods. Continuous grain refinement without longitudinal limitation and enhancing mechanical properties of wires are some advantages of the ECATD method, while reduction of cross section due to tensile stresses is a disadvantage. The results show that by optimizing the geometrical parameters of the ECATD die and using the proper combination of process parameters to achieve high production rate, the ECATD method could be used for fabricating wires with enhanced mechanical properties in industrial scale.
