Papers by Keyword: Equal Channel Angular Processing

Abstract: In the present study the microstructure evolution of the aluminum alloy 3103 subjected to ECAP up to eight passes applying route Bc was investigated after deformation and subsequent isothermal annealing. The deformed and annealed states were analyzed by SEM, EBSD, optical microscopy and microhardness tests. It will be demonstrated that this ECAP deformed material shows an increased stability against discontinuous recrystallization with growing number of passes.

Abstract: In this study, susceptibility to SCC of nanostructured Cu-10wt%Zn alloys, produced by equal-channel angular pressing (ECAP) was investigated under the constant stress test in ammonia vapour, which has been well-known typical environment for IGSCC of Cu-Zn alloy. Billets having diameter of 20 mm and length of 100 mm were subjected to ECAP for eight passes at room temperature to obtain structure with grain size of about 100 nm. After ECAP, some of the billets were flush-annealed in 473 K for 60 seconds to decrease excessive unequilibrium dislocations at grain boundaries. Coarse grained specimens without ECAP and one-pass specimens were also tested for comparison. The specimens for SCC were tensioned by a constant load in ammonia vapour inside a glass chamber for 24 hours at room temperature. After the SCC tests, maximum length of cracks was evaluated by SEM. Specimen having UFG structure by 8-passes exhibited cracks in lower applied stress ratio, (=σa/σys) compared with 0- and 1-pass samples, where σa is applied stress and σys is yield stress, respectively. Most importantly, the specimen with annealed at 473K for 60s after ECAP cracked in higher applied stress. It became less sensitive to SCC after flush annealing although mechanical properties were not changed considerably. In our previous studies, we reported that the SCC of UFG copper produced by ECAP, and the sensitivity to SCC becomes lower by flush annealing. Results are discussed in terms of grain boundary state with or without extrinsic grain boundary dislocations

Abstract: Crack growth in AA6060 after two and eight equal-channel angular extrusions (ECAE), showing a bimodal microstructure and a homogenous ultrafine-grained microstructure, respectively, are compared to the coarse grained counterpart. Furthermore, an optimized condition, obtained by combining one ECA-extrusion and a subsequent short aging treatment is included. Fatigue crack growth behaviour in the near-threshold regime and the region of stable crack growth is investigated and related to microstructural features such as grain size, grain size distribution, grain boundary characteristics and ductility. Micrographs of crack propagation surfaces reveal information on crack propagation features such as crack path deflection and give an insight to the underlying microstructure. Instrumented Charpy impact tests are performed to investigate crack initiation and propagation under impact conditions. Due to the recovery of ductility during the post-ECAE heat treatment, the optimized condition shows improved fatigue crack properties and higher energy consumption in Charpy impact tests, when compared to the as-processed conditions without heat treatment.

Abstract: This paper reports on the microstructures and fatigue properties of ultrafine-grained (UFG) AM60 magnesium alloy processed by equal channel angular pressing (ECAP) at various temperatures. After ECAP processing, samples exhibited an increase in fatigue endurance limit, which correlates well with a decrease in grain size. In case of lowest ECAP temperature, the mean grain size is as small as 1 2m which leads to an increase in fatigue endurance limit by 70 % in comparison to coarse-grained alloy. The temperature of ECAP not only governs the grain size and misorientation angles of grain boundaries but also the volume fraction of precipitates, thus affecting the probability of twinning and grain growth after fatigue treatment.

Abstract: In this article we present the results of the experimental research and those of the processes developing the crystallographic texture of computer modeling in CP Ti in the process of 1-4 equal channel angular pressing (ECAP) passes along the route ВС. The goal of the research was to determine the active deformation mechanisms, depending on the strain degree, accumulated in the ECAP process. The research was carried out by the method of X-ray analysis and by computer modeling. Computer modeling was carried out on the example of visco-plastic self-consistent model. Thereby, the basal, the prismatic and the pyramidal (of the 1st and of the 2nd order) slip systems were considered as possible active slip systems. Besides, the possibility of activating the tensile and the compressive twinning systems were taken into consideration. As the result of the carried out experimental research, the objective laws of forming preferred orientations were determined. For the first time, with the help of computer modeling, made up to the 4th ECAP pass, it was shown that the crystallographic texture development processes in CP Ti in ECAP, realized at temperature of 723 K, can be explained by activation of the basal, prismatic and pyramidal (of the 1st order) slip systems and compressive twinning systems. Therefore, the increase of the ECAP passes can lead to amplification of contribution of the basal and prismatic slip systems, as well as the insignificant weakening of the contribution of pyramidal slip systems (of the 1st order). Moreover, the compressive twinning can become obvious only in the 1st ECAP pass.

Abstract: A fine-grained magnesium alloy AZ31was obtained through equal channel angular pressing (ECAP).Mechanical properties and the microstructures after deformation under tension and compression were investigated. The tensile strength, compressive strength and the elongation to failure of the fine-grained AZ31 are enhanced due to the reduction of grain size. The compressive ultimate strain (CUS) of the fine-grained AZ31 magnesium alloy is lower than that of the initial state due to the formation of shear bands during compression. The ECAP processed AZ31 magnesium alloy exhibited no tension/compression asymmetry in yielding.

Abstract: The microstructure evolution of an as-cast commercial Al-Mg-Sc-Zr alloy during Equal- Channel Angular Pressing (ECAP) at 325°C was investigated. In the early stages of deformation strain induced boundaries were created within the initial coarse grains and constitute the deformation bands. Repeated ECAP led to an increase of the number and misorientation of deformation bands. Further straining up to e~8 resulted in the formation of a new fine-grained structure with an average crystallite size of 1.2 /m. It is concluded that the progressive increase of the misorientation of deformation induced boundaries is the main mechanism of structure formation under high temperature ECAP.

Abstract: The present study is an assessment of the effects of precipitation heat treatments on tensile behaviour, work hardening (WH) characteristics and microstructural evolution of an Al-4%Cu alloy deformed by equal channel angular pressing (ECAP). Two ageing temperatures were employed (170 and 100oC) and their effect on strength and WH behaviour was compared with that exerted on the same alloy, but in two different initial conditions: quenched from solution temperature and slowly cooled before anneal. Grain and precipitate sizes of samples deformed by one and four ECAP passes and heat treated as described were measured employing transmission electron microscopy (TEM). It was concluded that the lower ageing temperature gives the best combination of strength and ductility, a high WH rate and, possibly, the smaller grain and precipitate sizes. The relative participation of the various hardening mechanisms to total strength was estimated from tensile tests and hardness measurements.

Abstract: The evolution of texture and deformation in the grains during one pass of equal-channel angular pressing (ECAP) was examined for fine grained high strength and low strength Al alloys and a coarse grained low strength Al alloy. The materials were analysed using electron back-scatter diffraction (EBSD). The results are consistent with the materials responding to the intense macroscopic shear stress by deformation of individual grains through movement of dislocations on one or more of the slip crystallographic slip planes {hkl} that are favourably oriented, combined with the rotation of grains to directions that bring main crystallographic slip planes parallel to the macroscopic shear direction and crystallographic slip directions parallel to two main shear directions. Contrary to reports claiming up to 4 slip systems are activated, it was observed that only the {111}<110> and {001}<110> shear systems are activated. Macroscopic shear deformation occurs on two shear planes: the main shear plane (MSP), equivalent to the simple shear plane, and a secondary shear plane which is perpendicular to the MSP.

Abstract: Single pass ECAP of pure Magnesium was performed and stopped after 50 % deformation; textures thereafter at the ingoing, the deformation and the outgoing channel were characterized by neutron radiation and related to the deformation mode. A gradient texture evolution was obtained, which was attributed to the inhomogeneous distribution of the effective stress and strain, and also the inevitable existence of friction.