Superplasticity at High Strain Rates in Aluminum Alloys

摘要

The detailed experimental data of microstructural developments during the optimumthermomechanical treatments and superplastic properties in the wide deformation range have been investigated on fourteen P/M aluminum alloys with various chemical matrix compositions and different typed precipitate particles. It was revealed that the differences in both size and volume among the second phase particles, which increase with content of Zr, Cr, Mn or Y, affect on the recrystallization behavior, grain size and superplastic properties of these aluminum alloys. Some of them exhibited high-strain-rate superplasticity, so the optimizing processing methods in this proposal werevery powerful to provide the desired structures required for high-strain-rate superplasticity in these aluminum alloys. A theoretical interpretation, based on the experimental data by tensile test and the observed grain sizes, has been revealed that values in activation energy for all alloysare between 140 and 155 kJmol-1, which are similar to that for lattice self-diffusion of aluminum. Each mechanical data of each alloy can be presented by a single equation. It was postulated that superplastic flow in these P/M aluminum alloys was fundamentally controlled by a grain boundary sliding mechanism accommodated by dislocation climb controlled by lattice self-diffusion. However, for the statically recrystallized alloys consisted of the high-angle grain boundaries, the Dorn typed equation presents n=2, p=2 and D=D sub L, whereas for the dynamically recrystallized alloys with the low-angle grain boundaries, n=3, p=2 and D=D sub L. The consideration for deformation mechanisms with the accommodation helper by such a liquid has been applied on the aluminum alloys, but it remained unclear. The contribution by an accommodation helper to high-strain-rate superplasticity will be the further research subjects, includi.