Research On Microstructure Of Ultrafine-grained Aluminium Alloy During Preparation And Annealing

As a new type of large plastic deformation method for efficiently preparing regular shape ultrafine-grained materials,large strain extrusion machining has attracted the attention of researchers.Due to shear and extrusion,the microstructure of the ultrafine-grained material changes significantly and has an important effect on its mechanical properties.At the same time,the ultrafine-grained material prepared by the process has a small size,and the influence of external heat is involved in the subsequent utilization,so the microstructure evolution of the ultrafine-grained material during the heat treatment is also required.Therefore,in order to study the microstructure and mechanical properties of ultrafine-grained materials during preparation and annealing process,this study analyzed the influences of tool rake angle and chip thickness compression ratio,annealing temperature and time on the microstructure and mechanical properties of ultrafine-grained aluminum alloy.The main contents of this study are as follows:(1)The process of large strain extrusion machining was analyzed by finite element simulation.The influences of tool rank angle and chip thickness compression ratio on the effective strain,strain rate,stress,temperature and the main cutting force of the ultrafine-grained aluminum alloy during the preparation process were studied.The results show that,with the decrease of the tool rank angle or the increase of the chip thickness compression ratio,the plastic deformation of the aluminum alloy will be more severe and the strain will be greater;(2)Scanning electron microscopy and electron backscattered diffraction(EBSD)were used to observe the evolution of microstructure of ultrafine-grained aluminum alloy during the preparation process and the hardness value was measured.The influences of tool rake angle and chip thickness compression ratio on microstructure and mechanical properties of ultrafine-grained aluminum alloy were investigated.The results show that,as the rake angle of the tool decreases or the compression ratio of the chip thickness increases,the grain size of the ultrafine-grained aluminum alloy will get smaller and the hardness value will be higher.(3)The ultrafine-grained aluminum alloys prepared by large strain extrusion machining were annealed.The microstructure evolution of ultrafine-grained aluminum alloy during annealing was observed by scanning electronic microscopy and electron backscatter diffraction(EBSD)and the hardness value was measured.The influences of annealing temperature and annealing time on the microstructure and mechanical properties of ultrafine-grained aluminum alloys were investigated.The results show that,with the increase of annealing temperature,the ultrafine-grained aluminum alloy undergoes recovery,nucleation and grain growth,and the hardness values are correspondingly slightly fluctuated,abruptly decreased and slowly decreased.With the prolonged annealing time,the ultrafine-grained aluminum alloy is entering the recovery stage,the point defects and dislocations are reduced,the dislocation density is reduced,and the grain size and hardness values are not changed significantly.