Microstructural breakdown and scale-up effects in equal channel angular extrusion of cast copper

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Title: Microstructural breakdown and scale-up effects in equal channel angular extrusion of cast copper
Author: Kadri, Shabibahmed Jehangir
Abstract: The primary objectives of this study were : (1 ) to verify the effectiveness of ECAE to induce equal amounts of strain and grain refinement in bars of different cross -sectional areas , (2 ) to determine the effectiveness of ECAE in breaking down the as -cast macrostructure in CDA 101 Cu and in producing a homogeneous material containing micron -scale grains upon recrystallization , and (3 ) to determine a thermomechanical processing (TMP ) schedule (from the ones examined ) that produces the best microstructure in terms of grain size and uniformity . The effects of extrus ion route , levels of strain and intermediate heat treatment were investigated . To achieve the first objective , bars having square cross -sections of three different sizes , 19 mm , 25 mm and 50 mm , were processed up to eight ECAE passes through routes A , B , C and E . To achieve the second and third objectives , bars were processed up to eight ECAE passes with and without intermediate heat treatments through routes Bc , C , E and F . ECAE processing was carried out in a 90o extrusion die with sliding walls at an extrusion speed of 2 .5 mm /s . Recrystallization studies were carried out on the processed material to evaluate the recrystallization behavior and thermal stability of the material . The as -worked and recrystallized materials were characterized by Vickers microhardness , optical microscopy (OM ) and transmission electron microscopy (TEM ) . Results indicate that similar hardness values , sub -grain morphology and recrystallized grain size are generated in the three bars having different cross -sectional sizes processed through ECAE . ECAE is shown to induce uniform strain in all three billet sizes . ECAE is therefore shown to be effective in scale -up to a size of at least 50 mm , with larger billets giving better load efficiency . Results from the later parts of this study indicate that eight extrusion passes via route Bc produces the best microstructure in terms of grain size and microstructural uniformity . The routes can be arranged in the sequence Bc > E , F > C for their ability to produce a uniform recrystallized microstructure with small average grain size . Macroscopic shear bands are sometimes generated during extrusion depending upon the initial grain morphology and texture of the material .
URI: http : / /hdl .handle .net /1969 .1 /4341
Date: 2006-10-30

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Microstructural breakdown and scale-up effects in equal channel angular extrusion of cast copper. Available electronically from http : / /hdl .handle .net /1969 .1 /4341 .

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