Papers by Keyword: UFG Materials

Abstract: Processing by severe plastic deformation (SPD) may be defined as such metals forming procedure in which a very high strain is imposed on a bulk material. This paper investigates the effect of different equal channel angular pressing (ECAP) routes and number of ECAP passes on resulting microstructure, mechanical properties and creep behaviour of selected materials. The distinction between various ECAP routes (A, B and C) and the difference in number of ECAP passes applied may lead to variations both in the macroscopic distortions of the individual grains and in the capability to develop a reasonably homogeneous and equiaxed ultrafine-grained microstructure. Experimental materials were processed by ECAP at room temperature using a die with an internal angle of 90° between the two parts of the channel. The ECAP pressing was performed by different routes up to 12 ECAP passes. Tensile creep tests were conducted at temperatures 473 - 673 K and at different applied stresses on ECAP materials and, for comparison purposes, on their unpressed states. Microstructure of samples was characterized by scanning electron microscope (SEM) equipped with the electron backscatter diffraction (EBSD) unit. In conclusion, the ECAP processing route and number of applied ECAP passes could play an important role in creep behaviour and their effect may be different for particular materials. The highest differences in processing routes were revealed for materials especially at lower number of ECAP passes. However, a little apparent dependence of the creep properties was observed during subsequent pressing.

Abstract: ECAP is a large plastic deformation processing technology, ultrafine-grained materials can be prepared using ECAP process. This paper reviews the channel angular extrusion process application in aluminum alloy, copper alloy, magnesium alloy and composite materials and so on. Summarizes the influence of the central angle and mold inside corner radius, processing route, the coefficient of friction , extrusion speed, extrusion temperature, extrusion and steps on the ECAP. Also introduced a more advanced package sets-ECAP and continuous ECAP process.

Abstract: Different initial texture of ring rolled AA 2014 alloy was processed to one pass in Equal Channel Angular Extrusion (ECAE) at room temperature. The material flow/deformation characteristics as well as the degree of grain refinement, as a function of different initial grain morphological orientation are studied. Macroscopic and microscopic investigation by Optical Microscope (OM) confirms the significant variation in the shearing characteristics of grains in the billets in each orientations. OM observations also suggested that the severity of deformation was more in middle portions of the extruded billets. TEM observations made on the samples also confirmed the existence of regions which had undergone the different degree of dynamic recovery and recrystallisation after passing through shear deformation zone.

Abstract: An Ultrafine grain (UFG) microstructure is developed on the sheet of Al-2.4wt%Cu-0.3wt%Si alloy after three passes of accumulative roll bonding (ARB) process. The detailed of the microstructural features and phases at different strain condition has been studied by transmission electron microscopy (TEM). Observation indicates at the possibility of dynamic recovery and recrystallisation during the ARB processing itself. The material becomes ultrafine grains after three passes of ARB itself with the formation of dynamically recrystallised grains all over the sample. TEM evidence is presented in support of this proposal.

Abstract: With the development of the ECAP technology, the corrosion behavior of the UFG materials has been investigated in some degree. Two categories of corrosion behaviors of UFG material were discussed in this paper. The large proportion of the non-equilibrium grain boundaries and high residual stress inside of the grain were regarded as the key to affect the corrosion behavior of the UFG materials. The corrosion behavior was also affected by the ECAP factors especially the press pass number and the pressing temperature. Finally some prospects of making UFG materials combined with high mechanical property and good corrosion resistance by ECAP technology were expounded.

Abstract: In the paper, the study was conducted on the characteristics of microstructures and orientations of UFG pure copper and 6061 aluminum alloy prepared by AARB, ECAP and CECC severe plastic deformation processes, in which SEM, TEM, EBSD and X-ray diffraction techniques were employed. The result of the study shows that microstructures, mainly composed of subgrains and dislocation kinks, are profuse in the UFG materials by the three SPDs. These kinds of microstructures have the strength of the materials much enhanced and the toughness heavily decreased. In these processes, shear deformation makes gains get finer and finer with the existence of the preferred orientations in the prepared UFG materials. Nevertheless, CECC shows the heaviest effect on the grain refining and the preferred orientation weakening.