Papers by Keyword: Equal Channel Angular Processing

Abstract: Mg-3Al-1Zn (AZ31) alloy samples with different starting textures have been processed using Equal Channel Angular Processing (ECAP) at 150°C and 200°C. The common temperature limit for ECAP of wrought AZ31 alloys has been reduced from 200°C to 150°C by suppressing tensile twinning activity. Twinning activity was reduced by either changing the starting texture or increasing the temperature. A crystal plasticity model was utilized to gain a better insight into the operating deformation mechanisms during ECAP. Suppression of tensile twinning and pronounced prismatic slip activity resulted in a crack-free, homogeneous deformation at 150°C. In addition, twinning, when exists, was shown to have a significant effect on the promotion of DRX and shear band formation.

Abstract: The effect of severe plastic deformation at ambient temperature on microstructures and mechanical properties of aluminum alloy 2519 was investigated by means of tensile test, micro-hardness test, optical microscopy and scanning electron microscopy. The results showed that tensile strength of as-queched 2519 alloy was greatly enhanced to nearly 550MPa (ultimate tensile strength, UTS) and 520MPa (yield strength, YS) by severe cold rolling or equal channel angular processing (ECAP) while the elongation decreased to 5%. The 2519 alloy could obtain quite well mechanical properties as much as 80 % and 12 passes cold rolling deformation. This indicated that pre-deformation by ECAP is effective in improving the mechanical properties of 2519 alloy by grain refinement, strain aging and high density dislocations.

Abstract: The microstructure and mechanical properties of AZ61-4Si magnesium alloy before and after equal channel angular processing (ECAP) were studied. Results show that the matrix α-Mg and divorced eutectic β-Mg₁₇Al₁₂ are refined and chinese script type Mg₂Si phases are broken to dispersed particles after ECAP. The mechanical properties of the alloy after ECAP are significantly improved. After 4 passes of ECAP, the yield strength is increased from 50MPa to 109 MPa, tensile strength from 129MPa to 237MPa, elongation from 6% to 22%, and hardness from 61.2HBS to71.5HBS. The modification mechanism for microstructure and mechanical properties of the experimental alloy by ECAP was analyzed.

Abstract: Equal channel angular pressing (ECAP) deformation for commercial pure titanium (CP-Ti) was successfully conducted using a conventional die with an angle of 90° between the channels at room temperature via route B, in which the billet was rotated 90° along its longitudinal axis between adjacent passes. Each billet was processed for two passes using a ram speed of 26mms-1. The microstructures and mechanical properties of these CP-Ti billets with an initial grain size of ~23μm processed by ECAP were investigated. Experiment results show thin parallel shear bands with a width of 0.3~0.4μm are generated after one ECAP pass, which are composed of large number of dislocation cell blocks. After the two ECAP passes, some various directional bands are generated and the equiaxed and smaller-than-average CBs in local areas begin to appear. In addition, the ultimate strength and microhardness are significantly enhanced to ~725MPa and ~2283MPa, respectively. Meanwhile good elongation of 18.0% to failure is still remained.

Abstract: Atomic force microscopy provides a useful tool for examining the flow processes occurring during the tensile testing of ultrafine-grained metals processed by equal-channel angular pressing (ECAP). This paper describes the results obtained from experiments conducted on a Zn-22% Al eutectoid alloy and high-purity (99.99%) aluminium. The results show these two materials behave in different ways in terms of the development of mesoscopic shear planes.

Abstract: Semi- solid (SS) processing technologies provide the production of metal parts with homogeneous, fine and globular – grained microstructure. This is one of the most successful and reliable methods to produce near net shape products exhibiting good mechanical properties. Production of feed stock with non-dendritic and spherical structure is the critical factors in semisolid forming. Among several processes to obtain a globular microstructure, the SIMA (strain induced melt activated) process is simple and advantageous with respect to equipment and eliminating the melting stage before reheating. In this research, Al (A356) has been used and in order to induce strain, ECAP (equal channel angular pressing) method has been applied. ECAP is a method in which a great strain is induced and severe plastic deformation without any changes in cross section area occurs. To induce larger strain, ECAP process was carried out on annealed specimens up to several passes in route A (no rotation of samples around linear axis between each pass) and Bc (90◦ rotation of samples around linear axis between each pass), in ambient temperature. The reheating condition was optimized and the comparison between different routes and number of passes was investigated. The microstructure evolution of deformed and reheated Al (A356) was characterized by SEM (Scanning electron microscopy) and optical microscopy. In addition, the relation between the induced strain with size and shape of particles has been studied.

Abstract: The low cycle fatigue(LCF) test was performed to characterize the influences of the equal channel angular pressing(ECAP) and subsequent annealing of Al 5052 alloy. In the present research, one group of Al 5052 alloy specimens was directly subjected to ECAP, while another was subjected to ECAP and subsequent annealing. It was found that the tensile strength of the Al 5052 alloy increased, while its elongation decreased, with increasing number of ECAP passes. The LCF test was conducted at constant total strain amplitudes of 0.5%, 0.7%, 0.9% and 1.1%. Only cyclic hardening was observed as the number of fatigue cycles increased at all strain amplitudes in the specimen without ECAP. However, the ECAPed specimens showed a slight amount of cyclic hardening in the beginning and then saturation until fracture.

Abstract: The effects of equal channel angular pressing (ECAP) and subsequent heat treatment on the low cycle fatigue properties of 6005 Al alloy were investigated. The ECAPed specimens showed cyclic softening, whereas the peak aged specimens showed cyclic hardening at all strain amplitudes. After ECAP, artificial aging was performed at 175°C to observe the change of the low cycle fatigue properties due to precipitation. The fatigue life and behavior of the unECAPed and ECAPed 6005 Al alloys were discussed in terms of the microstructural changes and aging conditions.

Abstract: The influence of various processing routes (casting, extrusion, ECAP) on microstructure evolution and electrochemical properties of the magnesium alloy AZ80 were investigated. Both extrusion and ECAP were found to result in significant grain refinement (by a factor of 100 in the ECAP alloy) of the as cast AZ80 alloy. The electrochemical impedance spectroscopy was used to characterize the electrochemical properties of the surface of different microstructure states of the alloy. After the exposure to the corrosion environment containig aggressive chloride ions (0.1M NaCl) a complex polarization layer consisting of two different layers was formed on the specimen surface. The first compact layer directly adjoined to the specimen surface while the second porous layer was formed on the first layer. Microstructure changes due to extrusion and equal channel angular pressing were found to influence the stability of these layers. In the as cast alloy the compact layer was broken already during the first 24 hours of the exposure, while the compact layer in the extruded specimen remained unchanged up to 72 hours of the exposure. In the ECAP specimen both layers remained stable even after 96 hours of the exposure and no degradation occurred. Enhanced electrochemical properties were therefore found in the ultrafine-grained ECAP specimen.

Abstract: Annealed oxygen-free and tough-pitch copper samples have been processed by equalchannel angular pressing (ECAP) by route BC. The samples included 8 x 8 mm section pieces and a 40 mm diameter bar. Thermal stability was assessed based on the changes in the standard mechanical properties (conventional yield strength, tensile strength, elongation, proportional elongation and contraction) after annealing at different temperatures for 1 hour. Thermal stability of the same grade of material has been found to be different for different batches and to depend on the structural conditions of deformed material. The zone of thermal stability for copper of the two grades of interest does not depend on the material’s chemical composition.