Strain rate dependence of dynamic flow stress considering viscous\ndrag for 6061 aluminium alloy at high strain rates

Abstract

\nIn order to evaluate the strain rate dependence of the\ndynamic flow stress of aluminium alloys, 6061-O and -T6, high strain rate\ntests are performed at strain rates ranging from about 1000/s to 30000/s,\nand strain rate reduction tests are also conducted in the strain rate range\nfrom about 10000/s to 20000/s. A steep increase in the flow stress is\nobserved for 6061-O at the strain rate of about 5000/s. The above\nphenomenon, however, is not observed for 6061-T6 in the strain rate range\nwhere the strain rate reduction tests is conducted. A simplified model for a\ndislocation kinetics under a dynamic plastic deformation is used to consider\nthe deformation mechanism in the above strain rate ranges, which reveals\nthat the steep increase in the flow stress of 6061-O is attributed to the\nrate dependence of the viscous drag on the dislocation motion. It is\nestimated that the velocity of moving dislocation of 6061-T6 is lower than\nthat of 6061-O at a given strain rate, and that 6061-T6 is higher in a\nmobile dislocation density than 6061-O. The model predicts also that the\nincrease in the mobile dislocation density shifts the transition region, or\nthe strain rates in which the steep increase in the flow stress becomes to\nappear, to the higher strain rate side.\n