Effect of process variables on the structure of directionally recrystallized MA-6000

The effect of zone speed during directional recrystallization of MA-6000 in two conditions of extrusion has been investigated. Electron back-scattered patterns have been used to compare the microtextures developed and to characterize the longitudinal grain boundaries formed. h extrusions a [110] texture developed; in addition, small (<10μm) highly misoriented grains were detected, their frequency of occurrence decreasing with increasing zone traverse rate. A high density of small annealing twins was also observed after low traverse rates. It is suggested that both features are formed at the secondary recrystallization interface but fail to grow with the rest of the grain. at the minimum zoning rate, the high temperature extrusion material failed to directionally recrystallize but developed equiaxed grains. It is concluded that under these conditions, the rate of traverse exceeds the maximum growth rate of the grains. No microstructural differences were detected between the materials after differing extrusion conditions, and the origin of the difference in boundary mobility is considered to arise from solute pinning.