Mechanism of Continuous Recrystallization under Superplasticity

The research falls roughly into the following two heads.(1)Continuous Recrystallization in a Superplastic Aluminum AlloyThe misorientations of subgrain boundaries evolved in the pancaked grains increase accompanied by a randomization of the initial texture，followed by a new grain development with high angle boundaries(HABs)at high strains.Increasing in the pre cold-rolled reduction results in a decrease in the flow stress and a rapid increase in total elongation。Grain boundary sliding(GBS)frequently takes place just after yielding even in the layered HABs parallel to the tensile axis。With further straining，GBS can bring about the rotation of subgrains near the HABs，leading to increase inMhe subgrain misorientation。It is concluded that nonrecrystallized and pancaked grain structure introduced by cold rolling is an important prerequisite not only for the appearance of superplasticity，but also for the dynamic evolution of new fine grains.(2)Dynamic Evolution of New Grains…More during Hot Deformation of Magnesium Alloy AZ31 The flow curve shows a rapid hardening and a stress peak at relatively low strain(ε_p=0。12)，followed by a strain softening and then a steady state flow in high strain.Fine grains are evolved at original grain boundaries corrugated at aroundε_p and developed rapidly during strain softening，finally leading to a roughly full evolution of equiaxial fine grains.On the other hand，kink bands are evolved at grain boundaries corrugated and also frequently in grain interiors even at around%。The misorientation of the boundaries of kink band increases rapidly during strain softening and approach a saturation value of around 43°in high strain。The average size of the regions fragmented by kink band is almost the same as that of new grains evolved in high strain，which scarcely changes during deformation。It is concluded therefore that new grain evolution can be controlled by a deformation-induced continuous reaction，i.e.continuous dynamic recrystallization(DRX)，although many characteristics of new grain evolution process and its relation to flow behaviors are apparently similar to those in conventional，i.e.discontinuous，DRX.Less：Less

The research falls roughly into the following two heads.( 1 ) Continuous Recrystallization in a Superplastic Aluminum AlloyThe misorientations of subgrain boundaries evolved in the pancaked grains increase accompanied by a randomization of the initial texture, followed by a new grain development with high angle boundaries (HABs) at high strains. Increasing in the pre cold-rolled reduction results in a decrease in the flow stress and a rapid increase in total elongation. Grain boundary sliding (GBS) frequently takes place just after yielding even in the layered HABs parallel to the tensile axis. With further straining, GBS can bring about the rotation of subgrains near the HABs, leading to increase inMhe subgrain misorientation. It is concluded that nonrecrystallized and pancaked grain structure introduced by cold rolling is an important prerequisite not only for the appearance of superplasticity, but also for the dynamic evolution of new fine grains.(2) Dynamic Evolution of New Grains … More during Hot Deformation of Magnesium Alloy AZ31The flow curve shows a rapid hardening and a stress peak at relatively low strain (ε_p=0. 12), followed by a strain softening and then a steady state flow in high strain. Fine grains are evolved at original grain boundaries corrugated at around ε_p and developed rapidly during strain softening, finally leading to a roughly full evolution of equiaxial fine grains. On the other hand, kink bands are evolved at grain boundaries corrugated and also frequently in grain interiors even at around %. The misorientation of the boundaries of kink band increases rapidly during strain softening and approach a saturation value of around 43゜ in high strain. The average size of the regions fragmented by kink band is almost the same as that of new grains evolved in high strain, which scarcely changes during deformation. It is concluded therefore that new grain evolution can be controlled by a deformation-induced continuous reaction, i.e. continuous dynamic recrystallization (DRX), although many characteristics of new grain evolution process and its relation to flow behaviors are apparently similar to those in conventional, i.e. discontinuous, DRX. Less