IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Equal Channel Angular Pressing (ECAP) is currently being widely investigated because of its potential to produce ultra-fine grained microstructures in metals and alloys. A sound knowledge of the plastic deformation and the strain distribution is necessary for understanding the relationships between strain inhomogeneity and geometry of the. Considerable research has been reported on finite element analysis of this process, assuming 2D plane strain condition. The 2D models are not suitable due to the component geometry, especially for workpiece with cylindrical cross section. In the present work 3D simulation of ECAP process was carried out for different inner corner radii for strain hardening aluminium alloy (AA 6101). Strain inhomogeneity is presented and discussed for all cases. Pattern of strain variation along certain radial lines in the body of work-piece is presented.

GENERAL

Department of Metallurgical and Materials Engineering

Transactions of the Indian Institute of Metals

Study of inner corner influence in equal channel angular pressing using 3D finite element simulation

Severe plastic deformation processes like the equal channel angular pressing (ECAP) process are currently the subject of extensive investigation and it has been established that ECAP is capable of producing ultrafine grained microstructures in Al alloys. However, practical applications of ECAP process will depend upon the advantages obtained when this process is combined with conventional forming techniques. In the current study, the advantages of the equal channel angular pressing (ECAP) process, when used as an intermediate processing step prior to conventional forming by cold extrusion, have been investigated. ECAP of Al alloy AA 6101 was carried out using a die with 105° die angle for three passes through two different processing routes and these specimens were subsequently processed through conventional cold extrusion. Mechanical property and microstructure data show that improved properties after cold extrusion are heavily dependent upon prior ECAP processing routes. Implications of the results for the processing of ultrafine grained materials are discussed. © 2006 Elsevier B.V. All rights reserved.

Journal of Materials Processing Technology

Influence of cold extrusion on the microstructure and mechanical properties of an aluminium alloy previously subjected to equal channel angular pressing

Groove pressing (GP) is a severe plastic deformation technique for producing ultra fine grain sized microstructures in metals and alloys. In the present study, groove pressing and a two-step process of groove pressing followed by cold rolling was used to investigate the potential of these processes to produce ultra fine grained copper with significantly enhanced strength. Mechanical and microstructure properties were evaluated after groove pressing and after groove pressing followed by cold rolling. The advantages conferred by groove pressing prior to cold rolling on producing copper with enhanced properties has been investigated.

Materials Science Forum

Microstructure and mechanical properties of commercial purity copper resulting from repeated groove pressing followed by cold rolling

The Equal Channel Angular Extrusion (ECAE) process is a promising technique for imparting large plastic deformation to materials without a resultant decrease in cross-sectional area. The die consists of two channels of equal cross section intersecting at an angle; the workpiece is placed in one channel and extruded into the other using a punch. In the present study, the suitability of this technique for processing of tubular specimen geometries has been investigated. Tubular specimens of an aluminum alloy were extruded to three passes through two processing routes using sand as a mandrel. The pressures required for extrusion were measured, and the mechanical properties of the extruded material were evaluated. The low extrusion pressures during ECAE of tubular specimens are due to the movement of the mandrel (sand) along with the specimen (drag friction acts in the same direction as the main punch force). On processing to three passes of ECAE (by inducing a strain of 0.9), the tensile strength, yield strength, and hardness are improved, and elongation to failure (percent) decreased as expected. The process requires low forming loads while ensuring retention of specimen shape. It is also possible to impart further deformation to the specimen using the same die. It is concluded that ECAE is a promising technique for improving properties of tubular specimens.

Journal of Manufacturing Processes

Equal channel angular extrusion of tubular aluminum alloy specimens - Analysis of extrusion pressures and mechanical properties

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.

Microstructure and mechanical properties resulting from cold rolling of equal channel angular extruded commercial purity copper

The equal channel angular pressing (ECAP) process is a promising technique for imparting a large plastic deformation to materials without a resultant decrease in cross sectional area. In the present study, the suitability of this technique for the processing of tubular specimens has been investigated. Commercially pure titanium was selected for the study. Tubular specimens were extruded to three passes using two processing routes through an ECAP die with an angle of 150°between the two intersecting channels. Sand was used as a mandrel during the pressing. Analysis of force-stroke diagram was carried out, work from registered force-stroke diagram was calculated and compared with theoretical calculations. The mechanical properties and the microstructure were also investigated. To determine the influence of surface area to volume ratio of the specimens (referred to as the shape difficulty factor, SDF), data obtained in the current study on ECAP of tubular CP-Titanium was compared with data available in the literature on Hooker extrusion and conventional solid extrusion of CP-Titanium. Improvement in mechanical properties was observed in both the Routes. The grain size was reduced from ∼18 μm to ∼12 μm. These investigations demonstrate that ECAP is a promising technique for improving properties of tubular materials while ensuring retention of shape (with the possibility of imparting further deformation to the specimen using the same die) and with low pressing pressures. © 2005 Elsevier B.V. All rights reserved.

Candidature of equal channel angular pressing for processing of tubular commercial purity-titanium

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 microstracture and mechanical properties were also determined. The obtained results of mechanical properties and microstracture 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.

Microstructure and mechanical properties resulting from conventional cold extrusion of equal channel angular extruded aluminium alloy AA6101

The Deformation and Processing of Structural Materials: A Volume in Woodhead Publishing Series in Civil and Structural Engineering

Aluminium and its alloys

Commercial purity aluminium was subjected to a severe plastic deformation technique called groove pressing at both room temperature and cryogenic temperatures. In both cases, submicron sized grain structures were obtained after deformation; there was no significant difference in microstructures obtained under room temperature and cryogenic temperature deformation conditions. © 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Scripta Materialia

Production of ultrafine grain sizes in aluminium sheets by severe plastic deformation using the technique of groove pressing

Commercial purity copper sheets were subjected to a severe plastic deformation technique called groove pressing (GP) to a strain of 3.48 at both room and cryogenic temperatures. The mechanical properties and microstructure were studied as a function of the number of passes. A deformed microstructure with cell sizes approximately 0.5 μm in size were obtained from a starting annealed grain size of 78 μm. © 2005 Elsevier B.V. All rights reserved.

Materials Science and Engineering A

Applicability of the groove pressing technique for grain refinement in commercial purity copper

The process of equal channel angular extrusion (ECAE) is being widely investigated because of its potential for producing ultrafine grained structures. In the present study, a commercial grade aluminum alloy (AA 6063) was subjected to ECAE for three passes using two different processing routes: Route A where the specimen orientation is kept constant between passes; Route B where the specimen is rotated by 180° about its longitudinal axis between passes. Each extrusion pass imparts an equivalent true strain of 0.67 to the specimen. Analysis of the force-stroke diagram was carried out and compared with theoretical predictions. The mechanical properties and microstructure were investigated. In order to facilitate comparison of these parameters with those of conventional forming techniques, conventional cold extrusion studies were also carried out using an extrusion die that imparts an equivalent true strain of 0.65 to the material. The calculated extrusion loads were in the same range as the values experimentally observed for the first pass. The extrusion pressures increased slightly for processing by Route A but decreased for Route B with increasing number of passes. By processing through Route A, the tensile strength increased and elongation to failure (%) decreased as expected, but the elongation to failure (%) increased from the second to third pass when processed through Route B. After conventional cold extrusion, the mechanical properties were observed to be more or less similar but much higher extrusion loads were required. This implies that the material can be subjected to the same amount of plastic deformation by ECAE but with lower press loads to refine grain size and improve strength. © 2002 Elsevier Science B.V. All rights reserved.

Analysis of forming loads, microstructure development and mechanical property evolution during equal channel angular extrusion of a commercial grade aluminum alloy

The feasibility of using the equal channel angular extrusion (ECAE) process for the breakdown of cast structures in commercial purity aluminium has been investigated. Billets of an as-cast coarse grained Al (99.7% pure) were subjected to ECAE at 500°C using a die that imparts an equivalent plastic strain of 0.67 per pass. Multiple extrusion passes were performed using two different processing routes: Route I in which the billet orientation was kept constant from pass to pass, and Route II in which the billet was rotated by 180° about its longitudinal axis from one pass to the next resulting alternately in shear in planes oriented at 120° to each other. Processing by Route I through five passes produced elongated grains showing evidence of dynamic recovery. Processing by Route II through five passes however produced largely equiaxed grains with a dynamically recovered substructure due to the intervention of static recrystallization during the reheating to extrusion temperature between passes. Both processing routes produced a dynamically recovered structure with equiaxed subgrains approximately 6μm in size. Sharp deformation textures were not obtained. The relevance of this technique to industrial processing is discussed. © 2001 Elsevier Science B.V. All rights reserved.

Development of microstructure and texture during high temperature equal channel angular extrusion of aluminium

A process for imparting large plastic deformation to materials without any significant decrease in cross-sectional area, called equal channel angular drawing (ECAD), has been studied. As-cast aluminum bars of commercial purity (99.9% pure) with extremely coarse grains (of the order of 2000 μm in size) were subjected to six ECAD passes (resulting in a plastic strain of approximately 3) using three different processing routes, in order to study the potential of ECAD to produce a fine-grained bar of higher strength with special textures. All three processing routes result in considerable strain hardening. Micro banding was a significant mode of plastic deformation. Micron-sized subgrains misoriented by approximately 1-4° are produced in all three routes. The shape of the subgrains varied from elongated to equiaxed depending on the processing route used. Strong deformation textures were not obtained. The suitability of the process to produce a fine-grained commercial purity aluminum bar of increased strength from an initially coarse-grained material is discussed. © 1999 Elsevier Science S.A.

World University root node

The development of microstructure and the influence of processing route during equal channel angular drawing of pure aluminum

A review of current research related to the understanding of extrusion welding phenomena is presented. Two types of extrusion welds: the transverse and longitudinal welds are discussed. Metal flow and die design optimization is needed in order to minimize the amount of scrap metal as a result of transverse welding taking place during the billet-to-billet extrusion process. The importance of understanding of longitudinal weld performance and its metallurgical characteristics as a function of the extrusion process parameters is presented. Results of the preliminary tests for a longitudinal weld obtained when a special test die was utilized are shown. An outline of proposed study involving laboratory simulation techniques to physically model the welding that occurs during extrusion of aluminum alloys through porthole dies is discussed. Mechanical properties of the welded samples need to be determined to investigate the influence of the extrusion parameters such as temperature, speed and die orifice location on weld quality. The relative performance of the welded region compared to adjacent regions needs to be addressed as well. A necessity for mechanical evaluation of weld integrity both in the as-welded and in the aged condition is also discussed.

TMS Annual Meeting

Welding phenomena in extruded aluminum hollow profiles

As-annealed, 2.47 mm ETP copper wire was drawn in five passes to 1.45 mm using carbide dies with nominal included angles of 8, 16 and 24 degrees. A single die, low speed drawing block was used, and the lubricant was fat-based and water soluble. Annealing was undertaken in a box furnace, for six minutes at temperatures ranging from 185 to 230°C. Annealing response and texture evolution were assessed by way of tensile tests, microhardness measurements and x-ray diffraction. Redundant strain accumulation was projected by way of deformation zone geometry, or Δ, analysis. The as-drawn wire reveals volumes of (111) and (200) fiber texture, as well as a significant volume of essentially randomly oriented grain structure. The ratio of (111) to (200) texture decreases as die angle increases. Increases in die angle and related redundant strain promote the development of random orientation and reduce the sharpness of the (111) and (200) texture components. Increases in die angle and related redundant strain also lower the annealing temperature range and cause non-uniform recrystallization, presumably due to redundant strain and texture gradients. The as-annealed 1.45 mm wire displays a large volume of randomly oriented grain structure for all three die angles. In the case of the as-annealed wire, increases in die angle are associable with a decrease in the volume percent of (111) fiber texture, a decrease in the sharpness of the (200) fiber texture, and an increase in randomly oriented grain structure.