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1.0 I N T R O D U C T I O N

THE evolution of dislocation substructures

at low to moderate strains during r o o m temperature deformation is well documented in the literature and has been reviewed by McElroy and Szkopiak. ~Published work in the field of microstructures and mechanical properties achieved by relatively large strain deformations is rather limited, but is available on: wire drawing in iron alloys, 2-7 Cu, 7 austenitic steel s and Ti, 9 torsional deformation in Fe-Ti ~~and Cu, H compression in Fe, ~2U 12 and Cu, 13rolling in Cu base alloys 14-17and A1,1s-Is rolling and wire drawing in Nb19and wire drawing in A1 alloys. 2~ Most of the detailed microstructural studies of low temperature high strain deformation have been carried out on BCC Fe alloys. 2-7,1~Linear hardening has been observed to true strains approaching 10 during r o o m temperature wire drawing. 4 The strengthening has been attributed mainly to cell size refinement and increasing misorientation between the cells. An attempt has been m a d e by Langford and Cohen 3 to independently calculate the contribution from these two factors to the overall strengthening and added in such a way as to be consistent with the modified Hall-Petch relation, o = Oo + K 1 L - 1 . It has been generally assumed that the behavior of F C C metals at large strains is f u n d a m e n tally different from BCC metals because of the greater extent of dynamic recovery in F C C metals which, it is thought, should result in a steady state microstructure and strength. However, rolling of Cu at r o o m temperS. K. VARMA is Visiting Assistant Professor, Mechanical Engineering Department, Texas A & M University, College Station, TX 77843, and B. G. LeFEVRE is with Bell Telephone Laboratories, Norcross, GA 30071. Manuscript submitted October 19, 1978.

ature has shown either linear hardening to true strains of 514 or work softening at true strains between 2 and 3.515,17 a c c o m p a n i e d by dynamic recrystallization? 5 A study on cold rolled AP s showed unusual fluctuations in hardness after a strain of approximately 1.2. Studies on certain conductor grade A1 alloys 2~ indicate that hardening persists up to true wire drawing strains (Cw) of 4 and that the yield strength is inversely related to the dislocation cell size according to the modified HallPetch Relation: o = o 0 + K s L -1 There is at present no consistent view of the hardening characteristics or the a c c o m p a n y i n g microstructures that develop during r o o m temperature deformation of F C C metals to large strains. Although it is clear that such factors as the m o d e (and uniformity) of deformation, strain rate and alloying additions are important, detailed information is lacking. The present work was undertaken to help clarify s t r e n g t h - - m i c r o structure characteristics of heavily deformed A1 at r o o m temperature and the effects of small additions of soluble and insoluble impurities. The alloys chosen were: 99.98* pure A1; A1-0.2 Mg, A1-0.6 Fe and EC A1. * All compositions refer to weigh