Papers by Keyword: Equal-Channel Angular Pressing (ECAP)

Abstract: In this study, investigations into the deformation behavior of aluminum AA5083 at elevated temperatures were carried out on a newly developed test rig. The test rig was developed jointly with ZwickRoell GmbH & Co. KG (Germany) and is based on a Nakajima test carried out with heated dies. In this way, statements can be made about the lightweight potential of the alloy. Additionally, equal-channel angular pressing (ECAP) was performed to process the aluminum sheet metal. The conventional ECAP process is mainly used for bulk material in laboratory use and therefore is often not suitable for many industrial applications, especially for large series. The use of sheet metal allows a significant increase in the areas of application. It is documented in conventional ECAP that grain refinement is achieved by the severe plastic deformation. At room temperature this primarily increases the mechanical strength. Formability is improved in fine-grained materials, especially at elevated temperatures, which is related to diffusion-controlled deformation mechanisms and grain boundary sliding. The advantages of ECAP for sheet materials are thus also in lightweight construction and can even optimize the use of the AA5083 alloy. ECAP-route C was used for the process to provide the most homogeneous microstructure possible (180° rotation around the ECAP-axis after the first pass). Nakajima specimens were taken from the processed sheet materials to determine the Forming Limit Curve (FLC) compared to the reference material (four different specimen geometries). FLCs under elevated temperatures (250 °C, 375 °C) were performed on the novel Nakajima test bench. A special feature of the test rig is the rapid heating to avoid microstructural changes. Microscopic examinations were performed after the deformation to study the deformation mechanisms. Differences of the forming and fracture mechanisms between the reference alloy and the ECAP material were found.

Abstract: Equal-channel angular pressing (ECAP) is often used as effective tool for grain refinement for many different metallic materials. It is well known that grain size is an important microstructural feature influencing superplastic properties of fcc materials like aluminum alloys. The magnitude of introduced shear strain depends on geometrical parameters of the ECAP channel. In this contribution, the impact of different geometrical parameters of the ECAP channel on the resulting magnitude of introduced shear strain is analyzed. ECAP on AA5083 aluminum sheets with the dimensions of 200x200x1.8 mm3 is performed. Microhardness measurements reveal a considerable increase of hardness after ECAP and microstructural investigations by electron backscatter diffraction (EBSD) show the beginning formation of a deformation-induced substructure which is known to be a preliminary stage of the grain refinement process. It is assumed that this fine-grained microstructure results in an enhanced superplastic forming capability. Furthermore, a numerical model of the process based on the experimental results is established. The bending of the ECAP processed sheet metal as well as its microhardness are used for the validation of the model. The friction coefficient between the channel and the aluminum sheet significantly influences the results of the simulation. With the applied model different channel angles and inner corner radii are varied in order to determine a maximum magnitude of deformation resulting in sufficient grain refinement of the investigated material. With the help of the results gained in this study, suitable ECAP parameters for sheet metals can be derived that enable creating ultrafine-grained materials for superplastic forming operations.

Abstract: In this work, feasibility of friction-stir welding (FSW) for joining of heavily deformed 5083 aluminum alloy was studied. To produce work hardening condition, the commercially available material was homogenized to precipitate strengthening particles and then subjected to equal-channel angular pressing (ECAP) at 300 °C to a true strain of ~12 via B_C route and successive rolling at the same temperature to 80 pct. of thickness reduction. Despite the subsequent FSW resulted in significant microstructural changes in stir zone, joint efficiency was found to be 98 pct.

Abstract: Copper and copper alloys are widely used in engineering as structural materials because they have high electrical and thermal conductivity. In connection with the rapid growth of industry, special requirements are imposed on these materials, that is, they must withstand the contact mechanical loads without significant plastic deformation at elevated temperature and have stable high physical and mechanical properties. To improve the combination of strength, electrical conductivity, thermal stability, and wear resistance, low-alloyed Cu-Cr-Zr copper alloys have been subject to severe plastic deformation and aging. It the same time the analysis of the termo-stability of the formed ultrafine grained microstructure and properties is a topic task. In this work, a Cu-0.5Cr-0.2Zr (wt. %) alloy was quenched to form solid solution, equal channel angular pressed and cold rolled with following aging. The microstructure was studied, mechanical and electrical properties were also analyzed. The results showed that the ultimate strength of the Cu-Cr-Zr alloy increases with the degree of deformation at room temperature up to 630 MPa. Heat treatment at 450 ° C for 1 hour led to the precipitation of Cr and Cu₅Zr particles, which increases the strength up to 660 MPa, which is 2.5 times greater than the initial state. At the same time, sufficient electrical conductivity of 70% IACS is maintained. The thermal stability of the microstructure and properties of the alloy are investigated. The reinforced alloy maintains stable the microstructure and microhardness at 450 ° C for at least 5 hours. The change in microhardness is no more than 10%. That is in agreement with the requirements of industry.

Abstract: Microstructure, precipitation behaviour and mechanical properties of an Al-5.64Cu-0.33Mn-0.23Mg-0.14Zr-0.11Ti (in wt. %) alloy subjected to thermomechanical processing (TMP) involving equal-channel angular pressing (ECAP) at ambient temperature to total strains (ε) of ~1 and ~2 followed by aging at 180°C for 0-28 h have been investigated and compared with conventional aging at the same temperature (T6 state). TMP led to significant increase in yield stress (YS) and ultimate tensile strength (UTS) and decrease in elongation-to-fracture as compared to the peak-aged T6 state. The YS, UTS and δ values attained after ECAP to ε ~ 2 followed by peak ageing were ~510 MPa, ~540 MPa and ~7.6%, respectively. The changes in mechanical properties were related to microstructure evolution and precipitation behaviour. TMP conditions obtaining a high-strength state of the Al-Cu-Mg alloy are discussed.

Abstract: Three Zn-Al alloys, namely Zn-22Al, Zn-5Al and Zn-0.3Al, were subjected to equal-channel angular pressing (ECAP), and the effect of ECAP on their microstructure and room temperature (RT) superplastic behavior were investigated in detail referring to previous studies reported by the authors of the current study. ECAP remarkably refined the microstructures of three alloys as compared to their pre-processed conditions. While the lowest grain size was achieved in Zn-22Al alloy as 200 nm, the grain sizes of Zn-5Al and Zn-0.3Al alloys were ~540 nm and 2 µm, respectively, after ECAP. After the formation of fine/ultrafine-grained (F/UFG) microstructures, all Zn-Al alloys exhibited superplastic behavior at RT and high strain rates. The maximum superplastic elongations were 400%, 520% and 1000% for Zn-22Al, Zn-5Al and Zn-0.3Al alloys, respectively. It is interesting to point out that the highest RT superplastic elongation was obtained in Zn-0.3Al alloy with the largest grain size, while Zn-22Al alloy having the lowest grain size showed the minimum superplastic elongation. This paradox was attributed to the different phase compositions of these alloys. The formation of Al-rich α/α phase boundaries, where grain boundary sliding is minimum comparing to Zn-rich η/η and η/α phase boundaries of Zn-Al alloys, is the lowest level in Zn-0.3Al alloy among all the alloys. Therefore, it can be concluded that if it is desired to achieve high superplastic elongation in Zn-Al alloys at RT, keeping Al content at a possibly minimum level seems to be the most suitable way.

Abstract: In this paper we report a microstructure and strength properties investigations of a Cu-10 mass. % Zn alloy subjected to ECAP, with the aim of forming a UFG structure and enhancing the strength properties. The obtained results for this alloy having an average SFE value (35 mJ⋅m^-2) are compared with the results obtained for pure UFG copper with a high SFE value equaled to 78 mJ⋅m^-2. It is shown that the decrease in SFE value leads to more developed microstructure refinement, an increase in the density of dislocations and twins, which, in turn, provides an increase in strength characteristics.

Abstract: Effect of ultrasonic treatment (UST) with an amplitude of oscillating tension-compression stresses 100 MPa on the characteristics of superplastic deformation of Ti-6Al-4V alloy with an ultrafine grained (UFG) structure processed by equal-channel angular pressing (ECAP) is studied. During tensile tests at 600°C with initial strain rates in the interval from 10^-4 to 10^-3 s^-1, ultrasonically irradiated samples exhibit a reduced flow stress, higher values of the strain rate sensitivity coefficient and elongation to failure as compared to the samples tested directly after ECAP. Detailed studies of the microstructure of samples subjected to ECAP only and ECAP followed by UST revealed no considerable differences. It is suggested that the UST affected fine structure of the material bringing them to a state with a higher ability of relaxation of deformation-induced defects.

Abstract: The commercial Zr-modified 5083 aluminum alloy was homogenized to precipitate nanoscale Al₆Mn particles and then undergone to equal-channel angular pressing (ECAP) at 300 °C to a true strain of ~12 via B_C route. The obtained ultrafine-grained material was subjected to friction-stir welding (FSW). The welding variables were selected to provide reasonable homogeneous microstructure distribution across the weld zone and thus to ensure a highly uniform elongation during subsequent superplastic tests of the joints. Superplastic behavior of the obtained welds is discussed.

Abstract: Various contributions to the overall strength of the Cu-1Cu-0.7Al-0.2Zr alloy after the combined severe plastic deformation treatment have been calculated and compared with those after the standard industrial processing. Contrary to the common viewpoint, the SPD increases the strength not only due to the structure refinement, but also because of greater contribution of the dispersion strengthening. It is argued that this effect is linked to the deformation-induced phase transitions upon the SPD.