Multiple Equal Channel Angular Pressing Research Articles

Facing the Issues of Sheet Metal Equal‐Channel Angular Pressing: A Modified Approach Using Stacks to Produce Ultrafine‐Grained High Ductility AA5083 Sheets

A new approach for equal‐channel angular pressing (ECAP) of thin AA5083 sheets using two different orientations is investigated to address the issues of sheet metal ECAP. The method includes the deformation of a stack of 6 individual sheets supported by bulk material pieces placed on both sides of the stack. An excess length of the support materials and their pre‐deformation during an early stage of processing allows a buckling‐free deformation of the thin sheets for one of the investigated orientations. Multiple ECAP passes (up to N = 4) at room temperature following route C and microstructural analyses by electron back‐scatter diffraction are performed. Two passes of ECAP already result in considerable grain refinement with equiaxed grains, pronounced substructures and in an increased tensile strength at room temperature. At elevated temperatures (250 °C) a comparatively large elongation to failure (>130%) is found for the fine‐grained sheets. Diffusion‐controlled deformation mechanisms likely contribute to the deformation behavior of the investigated material. Scanning electron microscopy of the tensile specimens after testing reveals the formation of elongated and large cavities. These results highlight the suitability of the modified experimental method to produce (ultra)fine‐grained thin aluminum sheets with distinctly increased strength and ductility.

Characteristic Features of Physical and Mechanical Properties of Ultrafine-Grained Al–Mg Alloy 1560

Specimens of Al–Mg alloy 1560 of ultrafine-grained structure were obtained by the method of severe plastic deformation based on multiple equal-channel angular pressing. Impact on physical and mechanical properties of the processed material and fracture pattern of specimens was studied. Tensile tests showed an increase of the offset yield strength and resistance to rupture with decrease in the ultimate deformation. The obtained specimens have increased microhardness values compared to the initial ones. It was established that the last cycle of pressing determines the structural orientation of macroscopic shear bands occurring at an angle to the specimen longitudinal axis while passing connection of channels. It affects the physical and mechanical properties of the material and fracture pattern. The quality control of the obtained specimens by the method of ultrasonic defectoscopy and X-ray tomography confirmed the absence of macroand microdefects when following the matched optimal regime of processing.

Grain refinement kinetics and strengthening mechanisms in Cu–0.3Cr–0.5Zr alloy subjected to intense plastic deformation

The ultrafine-grained microstructures, mechanical properties and electrical conductivity of a Cu–0.3%Cr–0.5%Zr alloy subjected to equal channel angular pressing (ECAP) at a temperature of 400°C to a total strain of 1, 2, and 4 were investigated. The ultrafine-grained microstructure resulting from progressive increase in the misorientations of strain-induced low-angle boundaries during the multiple ECAP process is considered as a type of continuous dynamic recrystallization. The multiple ECAP process resulted in substantial strengthening of the alloy. The yield stress of CuCrZr alloy in the initial solution treated condition (ST) increased from 65MPa to 476MPa after four ECAP passes at 400°C. For the aged condition (AT), the yield stress increased from 170MPa to 511MPa after four passes. The strengthening was attributed to the grain refinement and high dislocation densities evolved via large strain deformation. Bacon–Kocks–Scattergood modification of the Orowan model is sufficient for acceptable description of the precipitation hardening of AT specimens during ECAP processing; this finding is in excellent agreement with the experimental data. The discrepancy between the experiment and model for ST specimens disappears after taking into consideration additional precipitating of the supersaturated solid solution during preheating and ECAP processing.

Strain path effects on the development of shear bands during shear tests in aluminum alloy processed by ECAP

ECAP (Equal Channel Angular Pressing) involves the pressing of a prismatic specimen through two channels with the cross-section identical to that of the specimen and intercepting at a certain angle. The specimen undergoes shearing over a single plane but no dimensional changes, leading to a possible anisotropy in the mechanical properties of the processed specimen. In addition, multiple ECAP passes lead to a severe refinement of the material structure, which is a function of the angle between the channels and the rotation of the sample in successive passes (the so-called “processing route”). An analysis is presented of the mechanical and microstructural anisotropy along three orthogonal axes in an aluminum alloy specimen processed along three different processing routes. The mechanical properties were evaluated through shearing tests, and the stress–strain curves thus determined indicated that the mechanical behavior of the commercial purity aluminum after ECAP depends on the processing route. The analysis of the specimen surfaces after testing revealed the presence of shearing bands whose orientation also depended on the processing route.

Deformation microstructures, strengthening mechanisms, and electrical conductivity in a Cu–Cr–Zr alloy

The ultrafine-grained microstructures, mechanical properties and electrical conductivity of a Cu–0.87%Cr–0.06%Zr alloy subjected to multiple equal channel angular pressing (ECAP) at temperatures of 473–673K were investigated. The new ultrafine grains resulted from progressive increase in the misorientations of strain-induced low-angle boundaries during the multiple ECAP process. The development of ultrafine-grained microstructures is considered as a type of continuous dynamic recrystallization. The multiple ECAP process resulted in substantial strengthening of the alloy. The yield strength increased from 215MPa in the original peak aged condition to 480MPa and 535MPa after eight ECAP passes at 673K and 473K, respectively. The strengthening was attributed to the grain refinement and high dislocation densities evolved by large strain deformation. Modified Hall–Petch analysis indicated that the contribution of dislocation strengthening to the overall increment of yield stress (YS) through ECAP was higher than that of grain size strengthening. The formation of ultrafine grains containing high dislocation density leads to a small reduction in electrical conductivity from 80 to 70% IACS.

Tube extrusion of AZ31 alloy with Sr additions

Abstract Three Mg alloys (AZ31, and AZ31 + 0.4 and 0.8 wt%Sr) were successfully hot extruded into tubes at 400 °C through a porthole die. Strontium (Sr) additions to AZ31 alloy reduced twining and the dynamically recrystallized grain size. However, Sr also increased the surface cracking tendency during extrusion. It was noted that the complex deformation path in the porthole die distributes the Sr-rich precipitates homogeneously across the microstructure and stringer formation is effectively avoided. The material flow in the die resembles that seen in multiple equal channel angular pressing (ECAP) routes and similar and significant effects on the final texture are observed. The material flow curvatures in the extrusion direction rotate the basal poles 25° from the radial direction. Two other texture components ( δ 1 , δ 2 ) are also formed in the welding zone by the circumferential flow of material. The maximum intensity of the orientation distribution function (ODF) is reduced with increasing level of Sr. Noteworthy, the maximum intensity in AZ31 + 0.8Sr occurs at the δ 1 component while for AZ31 and AZ31 + 0.4Sr, the maximum intensity is located at the basal components. With Sr, alloying, Al is depleted from Mg solid solution and grains deform more easily in the circumferential direction. As a result, selective workhardening–dynamic recrystallization (SWH–DRX) cycles leave more grains with unfavorable slip orientations (the δ components).

Strengthening and Toughening Effect on Tungsten Subjected to Multiple ECAP

This paper presents the research results of the grain refining effect on the ductile-to- brittle transition temperature (DBTT) of commercial purity tungsten. The as-received tungsten was subjected to eight passes of equal-channel angular pressing (ECAP) at decreasing temperatures from 1300 to 1150 °C. According to optical and TEM microscopy the average grain size was refined considerably from ~80 μm to ~1 μm. The mechanical tensile tests, carried out at various temperatures for the tungsten samples, showed that DBTT decreased approximately 80 °C as a result of microstructure refinement by ECAP, at the same time the strength also increased 50-100 % by grain refinement. SEM observation of the fractures confirmed the mechanical testing results.

Effect of equal channel angular pressing on microstructure, texture, and high-cycle fatigue performance of wrought magnesium alloys

Abstract The magnesium alloys AZ80 und ZK60 received from Dead Sea Magnesium in as-cast conditions were extruded at T = 350 °C using an extrusion ratio of ER = 22. The extruded bars were severely plastically deformed by equal channel angular pressing (ECAP). Multiple ECAP processing up to 8 passes was done. The ECAP-induced changes in grain size and grain size distribution were measured by transmission electron microscopy while changes in dislocation density and crystallographic textures were determined by positron annihilation spectroscopy and X-ray diffraction analysis, respectively. The strain induced by ECAP was found to influence the microstructural characteristics, in particular the grain size, the dislocation density, and the crystallographic texture, which in turn enhance (or deteriorate) the mechanical or fatigue response of both alloys.

3D finite element analysis on strain uniformity during ECAP process

The uniformity of plastic strain distribution in a workpiece after equal channel angular pressing (ECAP) was studied using finite element software ABAQUS in 3D. Processing parameters including the channel intersection angle Φ, channel outer curvature Ψ, pressing speed, friction and processing route were varied to study their effects on strain homogeneity. It was found that a single ECAP pass was unable to produce homogenous strains in a workpiece although strain distribution can be improved by selecting the appropriate processing parameters. Multiple ECAP passes improved strain homogeneity significantly.