Papers by Keyword: ECAP

Abstract: Severe plastic deformation (SPD) has been known as a method for materials grain refining. Among its numerous techniques, equal channel angular pressing (ECAP) is the representative model for the theoretical analysis in the view of equipment design challenge. By rigid block model of plastic deformation zone, technological parameters such as high accumulative strain, hydrostatic stress, punch pressure and distribution of stress and strain state are estimated. A compressive hydrostatic pressure created by a friction force in a contact surface between a die and a workpiece, which is directly proportional to the strength of the treated material, prevents its fracture and increases punch pressure significantly. The paper presents a method used in metalworking for determining the main parameters. The solution can be used for the die design in comparing with other conventional technologies to overcome the difficulty.

Abstract: It is fundamental in thixoforming to have a refined microstructure that, when heated to the semisolid state, consists of a mixture of small spheres immersed in liquid as this ensures the best rheological properties. The present work therefore aims to analyze the rheological behaviour of aluminum-silicon-copper alloys, namely, Al5Si2.8Cu, Al6Si2.8Cu and Al7Si2.8Cu. The alloys were produced by conventional casting and then deformed by ECAP in one pass in a die containing two channels of the same cross-sectional area forming an angle of 120°. After being processed by ECAP, the alloys were heated to semisolid temperatures, i.e., temperatures corresponding to a solid fraction of 45 %, and kept in the semisolid state for 0, 30 and 90 s, after which they were subjected to hot compression tests. The structures of the three alloys had an excellent response to recovery and recrystallization mechanisms, with refined microstructures that led to the formation of very fine spheres immersed in liquid in the semisolid state. The best rheological behaviour was obtained for the Al5Si2.8Cu alloy, which had an apparent viscosity of the order of 10³ Pa.s. The findings suggest that this simple ECAP process is a promising route for the production of semisolid feedstock for use in thixoforming.

Abstract: The paper presents the results of a study of changes in the structure during equal-channel angular pressing (1 and 4 cycles) with a deformation rate of 320 mm/s. It was found that a significant structure refinement of copper M1 and Cu-1.1Cr alloy to an ultrafine-grained state occurs already after 1 ECAP cycle. A predominantly band structure with a transverse size of fragments of ~ 200-300 nm occurs. A specific feature of the structural state is alignment of low-and high-angle boundaries by dislocations and absence of unbonded dislocations in the body of fragments. After 1 cycle of ECAP, practically no dispersed particles are observed in the body of Cu-1.1Cr alloy grains, and the electrical conductivity does not change in this case. The maximum hardening of copper M1 is observed after 4 ECAP cycles-1320 MPa with an electrical conductivity of 89% IACS for Cu-1.1Cr alloy, the maximum hardening is achieved after 1 cycle of ECAP and aging at 450 °C for 1 h-1655 MPa with an electrical conductivity of 77% IACS.

Abstract: The paper analyzes the influence of various geometric factors on the destruction possibility of aluminum alloys during pressing in an equal-channel step matrix, which allows to obtain an ultrafine-grained structure. It is found that the angle of the junction of the matrix channels has a significant effect on the Cockroft-Latham damage criterion, in contrast to the length of the inclined channel of the matrix. The most optimal value of the joint angle is 135° - in this case, the metal is processed with a sufficiently high intensity at a low level of the fracture criterion. The length of the inclined channel of the matrix is recommended to use no more than 15 mm to reduce the level of damage.

Abstract: In this study, commercial Al-3%Mg aluminium alloy was subjected to ECAP processing using two different ECAP die configurations. The first one – conventional and the second one modified in which a part of the exit channel in the ECAP die, causes twist deformation, to impose extra shear strains to the sample. The local changes in microstructure were characterized by Light Microscopy, SEM equipped with an EBSD facility and TEM. Mechanical properties of the ECAP processed samples were compared based on hardness measurement. The results showed that when ECAP with modified die, the greater grain and crystalline refinement is possible. The microstructures exhibit high dislocation density within subgrains with non-equilibrium and Moiré boundaries. Moreover, the mechanical examinations display a significant improvement in hardness and calculated yield strength when the ECAP process is conducted using a modified die.

Abstract: In this study, selectively laser melted AlSi10Mg alloy was subjected to ECAP processing for the first time. Mechanical properties of the ECAP processed samples were compared based on hardness measurement, compression and wear tests. The results showed exceptional synergy of high yield strength ~382 MPa and strain to failure of ~48% of the SLM ECAP processed sample. This sample also offered approximately ~71% higher wear resistance, than an unprocessed one. The proposed novel route expands the opportunities of both technologies to produce materials with exceptional properties.

Abstract: The aim of this work was to analyse the microstructural nature of plasticity in ZnAl4Cu1 alloy and its dependence on the processing technology. The alloy condition was analysed after gravity casting, after forging and after ECAP processing. Two alloys with slightly different compositions were studied. For alloy A, the returnable material from a prominent Zn alloy producer was used. For B alloy input raw materials of relatively high purity were used. Tensile testing showed that in the as-cast alloy tensile strength had relatively low levels up to 211 MPa, and particularly low values of ductility only up to 2.5 % were found in B alloy, which was more polluted. By means of ECAP processing of the as-cast alloy, the tensile strength was improved by 50 % (Rm = 312 MPa). In the case of the purer A alloy the majority of samples improved to level A = 27.9 %. Forging of the as-cast alloy preserved strength on a level similar to the ECAP result, but ductility was improved to the level of 34.4 %, although alloy B had lower purity. Further significant ductility improvement was obtained through ECAP processing to A = 147 % of the as-forged alloy. The microstructure of ZnAl4Cu1 consists primarily of segregated η phase (rich in Zn) and fine eutectoid composed of η and alpha phases segregated mostly in dispersive state, but in places also in lamellar form. Close correlation between microstructure and processing method resulted from our fractographic study. In the case of ECAP processing of the forged state the finest microstructure was achieved, which was accompanied by higher plasticity and also by fine dimples of transcrystalline ductile fracture (DTDF).

Abstract: In this work, the consolidation of blended elemental powders of iron, manganese and aluminum (Fe-25Mn-15Al wt.%) was performed by Equal Channel Angular Pressing (ECAP). Samples were consolidated at room temperature in a Φ = 120° die by a single pass and a second pass in route A. Both samples were heat treated at 650 °C and water cooled. Prior to heat treatment, samples presented a dense but chemically inhomogeneous structure. Fe and Al particles were highly deformed, whereas, Mn was almost undeformed. Mn particles were partially shattered by friction with Fe and Al particles. After heat treatment, the samples were characterized by SEM-EDX and presented substantial interdiffusion along the particles interfaces. It is believed that higher deformations by ECAP may improve the sinterability of consolidated samples in order to densify and chemically homogenize it.

Abstract: Equal-channel angular pressing (ECAP) is an effective fabrication process to modify ultrafine grain size. It is believed that the smaller grain size could improve the mechanical properties. In the present work, the solution treatment applied to Al-Si-Cu-Mg-Mn alloy. Furthermore, two models of ECAP have been done through one-to-three pass at room temperature. The microstructures were observed by optical microscope (OM) and scanning electron microscope (SEM). The micro-hardness of longitudinal plane was analyzed by vickers hardness test. The strength of ECAP materials at room temperature was obtained by using tensile test. The results show that the ECAP process has improved mechanical properties of alloys, which were the hardness and ultimate tensile strength tend to increase since single pass stage.

Abstract: In the current study, consequence of ECAP on the toughness characteristics of the Al-Zn-Mg alloys was studied. Three set of Al-Zn-Mg alloys (5, 10 and 15% Zn and 2% Mg) were selected and ECAPed. Also, consequence of zinc on the toughness characteristics of the alloy, before and after ECAP was studied. After ECAP, grain size of the alloys decreased and significant rise in the strength and ductility of the alloys were noticed. Mainly, modulus of toughness of the alloys increased with successive ECAP passes. But, the modulus of toughness of the alloys decreased with rise in the zinc in the material.