2006 Volume 55 Issue 11 Pages 1021-1026
In order to evaluate the strain rate dependence of the dynamic flow stress of 6061-T6 aluminum alloy, strain rate reduction tests are conducted in the strain rate range from about 2×104 to 4×104s−1, which is the strain rate range before reduction, and the reduction in strain rate is 58.6%. To eliminate an effect of elastic wave dispersion produced in a bar on the measured flow stress, a output bar being 2mm in diameter is employed. A steep increase in the flow stress was observed at the strain rate of about 2×104s−1. A simplified model for dislocation kinetics under dynamic plastic deformation is used which can represent a transition in the rate controlling mechanism of dislocation motion from a thermally activated process to a viscous drag. It is comfirmed that the steep increase in the flow stress of 6061-T6 observed at the strain rate of about 2×104s−1 is attributed to the rate dependence of the viscous drag on the dislocation motion and furthermore, the increase in the mobile dislocation density lowers a velocity of moving dislocations and shifts the transition region, or the strain rates in which the steep increase in the flow stress becomes to appear, to the higher strain rate side.
