Papers by Keyword: Equal Channel Angular Extrusion (ECAE)

Abstract: Development of high strength I/M Mg alloys has been tried by ECAE processing. The mechanical properties and microstructure of ECAE-processed Mg97Zn1Y2 alloy with LPSO (long-periodic stacking ordered) structure were investigated. The tensile yield strength and elongation of as-cast Mg97Zn1Y2 were improved substantially by ECAE process. ECAE-processed with yield strength of 290 MPa and elongation of 22 % was obtained. The microstructure of ECAE-processed Mg97Zn1Y2 alloy consisted of refined α-Mg with the grain size around 6.5 μm and finely dispersed LPSO phase. Furthermore, the some texture was formed by ECAE process. The improved mechanical properties seem to be originated by the microstructure refinement and texture.

Abstract: Equal channel angular extrusion (ECAE) is a processing method for introducing an ultrafine grain size into a material. In the present study, a two-step severe plastic deformation process was used to produce ultrafine grained copper with significantly enhanced strength. Equal channel angular extrusion was first used to refine the grain size of copper samples. The copper samples were further processed by cold rolling (CR) to a strain of 0.67 (about 50% reduction). This two-step process produced ultrafine grained copper with strengths higher than those of pure copper processed through ECAE only. This paper reports the microstructures and mechanical properties of the copper specimens processed by a combination of room temperature ECAE and CR. The effectiveness of initial processing by ECAE prior to cold rolling is discussed.

Abstract: Equal Channel Angular Extrusion (ECAE) with varying levels of applied backpressure was used to refine the microstructure of commercial automotive aluminium alloy 6016 at room temperature using route BC and a 90° die. Before processing, the alloy was solution heat treated at 560°C for 1 hour to produce an initial average grain size of ~190μm (in the furnace cooled condition) and ~200μm (in the water quenched condition). Two needle-like secondary phase precipitates were observed predominantly at grain boundaries and identified as α-Fe Al12Fe3Si2 and β-Fe Al5FeSi. The ability of Al 6016 to accumulate strain by simple shear was found to be dependent upon both the heat treatment condition and level of applied backpressure. The furnace cooled (FC) condition was found to accumulate higher strains than the cold water quenched (WQ) condition (under the same applied backpressure) with higher levels of backpressure allowing both conditions to accumulate greater equivalent plastic strains. A series of static annealing experiments were performed on as-processed material to investigate the grain stability of the ultrafine grained structure obtained after ECAE. Grain growth was observed to occur at 250°C in the FC condition of Al 6016 after 12 passes of ECAE where the average grain size approached 1μm. The engineering strain to failure in elevated temperature tensile testing was found to be dependent upon the number of passes of ECAE, test temperature, strain rate and level of applied backpressure. Increasing the number of passes and level of applied backpressure during ECAE and decreasing the strain rate during testing was found to produce the greatest tensile ductilities at 200°C (FC condition) and 300°C (WQ condition).

Abstract: Severe plastic deformation processes like equal channel angular extrusion (ECAE) have been widely investigated for their ability to produce nano/ ultra fine-grained microstructures. It is well known that submicron sized grains/ sub grains can be produced in most Al alloys using this technique. However, industrial applications of ECAE will depend heavily on the advantages conferred by this process when it is used as an intermediate processing step prior to conventional forming. In the current investigation, the influence of pre processing by ECAE on subsequent post processing by conventional cold extrusion has been investigated. ECAE extrusion was carried out on cylindrical specimens of AA 6101 using an ECAE die with a die angle of 120 degrees. Extrusion was carried out for three passes using two different processing routes. The ECA extruded specimens were subsequently subjected to conventional cold extrusion. The differences in extrusion pressures, which have a strong influence on industrial applications, were noted. Changes in microstructure and mechanical properties were also determined. The obtained results of mechanical properties and microstructure evaluation show that for high strains (strain ε ≈ 2.01), ECAE through some processing routes can be effectively used as an intermediate processing step prior to conventional cold extrusion to obtain a product with enhanced mechanical properties.

Abstract: Equal Channel Angular Extrusion (ECAE) has become a very popular tool for studying the evolution of microstructure and properties under severe plastic deformation. It is believed that the stress-strain characteristics are uniform in a cross-section of the billet and this uniformity of the stress-strain distribution ensures the uniformity of microstructure and mechanical properties in ECAE processed billet. However, some experimental data such as the fracture of the extruded billet, which is initiated at the inner surface of the sample, has caused doubts about uniformity of stress-strain distribution. This non-uniformity has been proved recently by Finite Element Simulation. In this paper the studies of the positive role of the applied back-pressure during ECAE are reviewed and the influence of a back-pressure on the uniformity of the stress-strain distribution, strain localisation, die corner filing, and the prevention of fracture is shown. The effect of back-pressure on grain refinement and improvement in mechanical properties is emphasized. The paper summarises our results from over seven years of work using a unique machine for ECAE with computer-controlled back-pressure and velocity of the backward punch.

Abstract: Various processing routes have been studied to develop the most efficient route toward microstructure refinement and texture homogenization. Most studies have focused on the central shear zone in round or square cross-section rods. However, the utility or application of these materials is subject to conditions across the entire rod. This study begins to investigate the development of recrystallization textures and microstructures across copper ECAE processed via route Bc through 16 passes. Although the recrystallized condition appears to be reasonably homogeneous after 4 or 8 passes, additional passes lead to stronger, heterogeneous recrystallization textures and coarsened microstructures.

Abstract: A submicron-grained (SMG) microstructure, with an average grain size of ~0.4 µm was produced by equal channel angular extrusion (ECAE). The SMG microstructure was composed of large dynamic recrystallized grains within a matrix of deformed elongated cells. Samples were annealed for various times at 473 K and then examined using transmission electron microscopy (TEM) and electron back scattered diffraction (EBSD). The results specify that a large recovery takes place during the first annealing times. Moreover, MET investigations show nucleation of grains which orientations are found in the recrystallized texture. The EBSD measurements established that, after 7min30s at 473 K, the microstructure is equiaxed and stable with an average grain size of about 2 µm.

Abstract: FCC metals with different stacking fault energy (SFE), namely Al, Ag and Cu have been investigated for the evolution of crystallographic texture during ECAE deformation using Route A. Different materials with different SFE result in their characteristic textures. The results have been analysed on the basis of microstructural features and related established concepts on texture evolution in FCC metals.

Abstract: Texture and microstructure were investigated after 1 pass equal channel angular extrusion (ECAE) of a single crystal cube oriented Ni billet. Neutron and X-ray diffraction were used to determine global and local textures, respectively. EBSD and TEM investigations were also carried out in order to study fine scale microstructural features. Substantial variations in texture and microstructure, resulting from different efficiencies in the shearing process, were locally recorded through the billet height. The deformation was heterogeneous on both micro and macro scales.