Evolution of microstructure and properties in alpha-brass after iterative processing

Abstract

Iterative strain-recrystallization cycles have been applied to alpha-brass in order to enhance ductility while maintaining tensile strength. Five iterations of 25 pct uniaxial strain followed by a 300 second anneal at 665 °C were used to achieve the desired properties. This article concentrates on assessment of the effect of the processing on microstructure evolution and crystallographic details of the grain boundary population, after each strain-recrystallization cycle. The overall aim of the work is to provide further knowledge on the mechanisms of grain boundary engineering. The results demonstrate that there is a distinctive pattern in both the Σ3 population density (in coincidence site lattice notation) and the proximity to the Σ reference structure, as a function of treatment cycle iteration. During the first two treatment cycles, the proportion of Σ3s drops, which the present work shows is an essential step to homogenize the microstructure in preparation for the subsequent treatment iterations required for the property enhancements to develop. It is proposed that this is a general feature of all grain boundary engineering by iterative processing where cold reduction is involved. Furthermore, Σ3ⁿ (n>1) boundaries do not build up in the microstructure concomitant with the Σ3 fraction because they are removed by the “Σ3 regeneration model.”