Aluminum-lithium Alloy Electroluminescent High-speed Superplasticity

Based on the phenomenon of low deformating strain rate for alloys to exhibit superplasticity which is one of three great technical problems faced by present superplastic reseaches, it is first to apply electroplastic and electromigration theories in superplastic deformation in search of a new approach to enhance the strain rats of superlastic deformation of alloys. It was showed by the investigation of processes that, compared with the optimum tension result. in normal superplastic deformation, the strain rate of the 2091 Al —Li alloy in superplastic cold rolled state increased 40 times at the conditions of J=2.0× 10~2A/mm~2,f = 11Hz and T = 773K. It was also indicated that the superplastic properties of the 2091 Al— Li alloy in fully recrystallized, partially recrystallized and normally cold rolled states increased to some extent by applying current pulses. On the bases of the experimental results stated above, it is first to submit the concepts of electro—high striain rate superplasticity and electro—superplasticity.In the investigation of the effects of current pulses on recrystallization , it was first to employ TEM to observe the effect of current pulses on the dislocation structrue in the recrystallization. The grain size after fully recrystaliized and in superplastic deformation was observed and measured with a metallographic microscope and a linear intercept method respectively. Experimental results showed that, current pulses accelerated the recovery of dislocations and reduced the grain size after fully recrystallized and in the superplastic deformation. The theoretical studies on recrystallization kinetics suggested that current pulses increase the rate of recrystallization nucleation and decrease the growth rate of recrystallized nucleus, upon which, the kinetics equation for recrystallization under the action of current pulses is first established. On the basis of Pernvezentsev V N model, the grain growth model is established in the electro— high strain rate superplastic deformation of 2091 Al — Li alloy. The higer superplastic properties in normal cold rolled plates than superplastic plates by employing the dynamic recrystallization were first induced in order to simplify the superplastic pretreatment, which further lays a reliable experimental foundation for the determination of the research subject of dynamic recrystallization induced superplasticity.Electron probe measuring results showed that, current pulses made the heavy element Cu collect at the latitudinal grain boundary of the specimens. The observations of the metallographic microstructure in the specimen at failure showed that, current pulses increased grain isometry. It is indicated that current pulses promote the atomic diffusion in superplastic deformation. The relation between the density of current pulses and diffusion coefficient is formulated on the basis of the model of interstitial and vacancy...