Recrystallized grain size in severely deformed pure copper
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abstract
In this study, the effectiveness of ECAE for grain refinement of as-cast CDA 101 copper with large columnar grains is analyzed. Square cross-section bars were processed at room temperature with up to eight passes in 90 tooling through routes C, E, Bc and F. The effects of extrusion route, number of extrusions and annealing heat treatment are examined by optical microscopy, TEM imaging and Vicker's microhardness. TEM results indicate that some regions in the as-worked material are composed of nano-scale (-100 nm - 200 nm) elongated grains after a single pass. Additional strain improves microstractural uniformity but does not appreciably decrease the as-worked grain size of the most highly refined regions. The smallest possible recrystallized grain size is obtained after two extrusion passes but widespread heterogeneity exists in the microstracture. Higher levels of strain improve the uniformity of the recrystallized microstracture. Intermediate recrystallization heat treatments during multi-pass ECAE processing are found to promote a lower recrystallization temperature, a more rapid recrystallization transformation and a more uniform recrystallized microstracture. Little difference is seen in the recrystallized grain size ( 6u,m) produced through different thermo-mechanical processing schedules for four extrusions and above.
