Abstract
The steady state creep of pure and commercial Al was studied at different working temp. in the range 340-475 deg C under a constant stress of 1.86 kgf mm -- 2. Superplasticity was detected at 410 and 390 deg C for pure Al and commercial Al, respectively. The effect of the grain dia. on superplasticity was investigated using commercial Al which showed higher peak values of strain rates than those of pure Al. It was found that polycrystalline samples with initially small grains were required to initiate superplasticity. The structural study of commercial Al revealed that superplastic behavior was associated with decreases in the initial grain dia. and in the initial lattice parameter. For pure Al the activation energy 37 plus/minus 1 kcal mole -- 1 and the strain rate sensitivity m = 0.5 characterizing the superplastic process were controlled by dislocation climb. The presence of impurities enhanced such a mechanism and the impurities acted as spherical centers facilitating grain boundary sliding through dislocation climb at these boundaries.11 refs.--AA