The Study On Compression And Bending Mechanical Behavior Of Ultrafine Crystal 6061 Aluminum Alloy

With the increasing severity of energy and environmental problems,the importance of lightweight design is becoming more and more prominent.Aluminum alloy,as an important lightweight material,has been widely used in aerospace,high-speed rail,automobile,electronic and electrical appliances and even robots and other fields.However,its strength is not high.Such as micro screw,micro gear,micro pin and other parts of the micro motor system as well as the lower limbs of multi-legged robot,will produce a large plastic deformation and then seriously affect the normal service of these parts when it is used in uniaxial compression,it will produce large plastic deformation,which will seriously affect the normal service of multi-legged robot.To this end,it is urgent to improve the strength of the aluminum alloy and to investigate whether the modified aluminum alloy can meet the service requirements of the pressure-bearing structural members.Multi-direction forging technology makes the material have large plastic deformation and refines grain size by applying large stress,which is simpler and more efficient than other large plastic deformation techniques and can significantly improve the strength and hardness of metal materials.Therefore,the ultra-fine grain 6061 aluminum alloy was prepared by multi-direction forging at room temperature.It is considered that the equal pressure structure of the lower extremity of the multi-pedal robot may be unbalance loading and the bending effect may occur,the mechanical behavior of the superfine crystal 6061 aluminum alloy under uniaxial compression and three-point bending load is studied.The evolution of surface strain of 6061 aluminum alloy during bending deformation is also studied by means of digital image correlation technology(DIC).Finally,the fatigue life of ultra-fine grain 6061 aluminum alloy under compression stress control is predicted based on SWT model.The main research results are as follows:1.Ultra-fine grain 6061 was prepared by multidirectional forging test at room temperature.After three forging cycles,the refinement effect of the material distribution uniform,the grain size is refined from 40?m to about 1?m,and the hardness is increased from 87.28 HV to 140.14 HV2.Through the compression test before and after forging of 6061 aluminum alloy and the pressure-compression fatigue test under stress control,it is found that the uniaxial compression characteristics of ultra-fine grain are obviously different from those of coarse grain,the yield stress is high and the strain rate is insensitive;The ratcheting strain of superfine grain and the increasing rate of ratcheting strain in the initial stage of cycle increase and slow down with the increase of stress ratio,while the coarse grain is on the contrary,while the ratcheting strain of superfine grain increases and slows down with the increase of stress ratio.3.Through the comparative study of three-point bending test and bending fatigue test,it is found that the bending strength of ultra-fine grain increases,but the plasticity decreases obviously and the strain rate is more sensitive.The bending fatigue life of ultra-fine grains is significantly higher than that of coarse grains.The bending fatigue fracture mode of the original sample is the combination of trans-crystalline rupture and microovoid.The fracture mode of the specimen after three cycles of forging is trans-crystalline rupture.