The Mechanism Of Twinning And Recrystallization In As-cast Magnesium Alloys At Different Temperature And Strain-rate During The Plane Strain Compression

As the lightest structural material at present,magnesium and its alloy materials have many advantages,such as low density,high specific strength,high specific stiffness,excellent damping,anti-magnetic,shielding and heat dissipation,are widely used in aerospace,automobile,electrical and electronic communication industries.Currently,magnesium alloy products are mainly cast products.If the magnesium alloy is processed by extrusion,rolling or other deformation processing,its mechanical properties will be greatly improved.However,the deformability of magnesium alloys is poor at room temperature,so the magnesium alloys are usually processed at medium or high temperatures.The Plane Strain Compression experiment can well simulate the rolling process,avoid the problem of uneven rolling plate force and reduce the phenomenon of plate thickness.This thesis selects the AZ31 magnesium alloy as the research object at the temperatures of300?and 400?,strain rates of 10s^-1,80s^-11 and 160s^-1,as-cast AZ31 magnesium alloy sheets were tested by Plane Strain Compression.Using optical metallographic microscope and Scanning Electron Microscope equipped with Electron Back Scattering Diffraction,probe by the micro structures close to and far away from the crack boundary area of twinning and recrystallization calibrated and analized the effect of AZ31 magnesium alloy on twinning and recrystallization behavioris discussed.The relationships between twinning and recrystallization behaviors and macroscopic stress-strain curves were clarified.The main conclusions are as follows:?1?Under 400?,because of the local stress concentration besides the crack boundary area within twinning than far away from the crack boundary area within the twinning is more active.Within the grain near the crack boundary,because of the{10-11}-{10-12}twinning?DTW?are generated in large quantities,the induced twinning dynamic recrystallization?TDRX?forms a term chain structure with smooth boundary on the basis of the original twinning.With the increasing of the strain rate,the number of twinning increases gradually,and the strain rate sensitivity of twinning is more significant.In addition to twinning,dynamic recrystallization also showed rate sensitivity.With a higher strain rate of 80s^-11 and 160s^-1,the flow stress inside the material also increased,and the dynamic twinning recrystallization became more active.The stress-strain curve shows that the failure strain in the Plane Strain Compression experiment first decreases with the increase of the strain rate and then increases with the increase of the strain rate,and this phenomenon largely depends on the competition between twinning induced hardening and twinning recrystallization?TDRX?induced softening.Therefore,the competition mechanism between twinning and recrystallization can be controlled by controlling the strain rate.?2?Under 300?,the Plane Strain Compression Test speciments in the twinning also shows significant strain rate sensitivity.Because of the local stress concentration,the twinning recrystallization besides the crack boundary and at the crack tip of the material was more active than the far away from the crack boundary side,and showed the same strain rate sensitivity at the crack tip.In addition to strain rate sensitivity,twinning recrystallization is also closely related to temperature.Because of the condition of 300?specimen of flow stress is higher,and the flow of the higher stress promoted the twinning recrystallization process,the process effectively refine the grain size.So the 300?relative to 400?is more conducive to the formation of twinning recrystallization,significantly improve the plasticity of magnesium alloy AZ31 as-cast processing capacity.The both strain rate and temperature can affect twinning and recrystallization in magnesium alloy materials.Therefore,the temperature and strain rate sensitivity of twinning and twinning-induced recrystallization in coarse grains can further reveal the microscopic of the plastic deformation of coarse magnesium and alloy,it can provide quantitative basis for the deformation process.