Preparation And Properties Of 6061 Ultrafine Grain Aluminum Alloy By Ultrasound Assisted Equal Channel Angular Extrusion

As a very efficient method of large plastic deformation,equal-diameter angular extrusion(ECAP)has been developed and perfected continuously since it was put forward.Although ECAP can obtain ultrafine-grained materials and obviously improve the strength and hardness of the materials,ECAP also has many disadvantages,such as uneven distribution of materials and generally poor thermal stability of materials.Ultrasound is a high frequency vibration with a frequency of more than 20 KHz,which is widely used in medical,industrial,aerospace and other fields.The influence of ultrasound energy on the deformation behavior of metal alloys has been a hot topic for scientists.Because ultrasound waves release a large amount of energy and heat during action,these energies enter the local regions of metals,such as vacancies,dislocations and grain boundaries,which make the tissue activity of metal materials enhanced,the internal tissue movement intensified,and the properties changed.Meanwhile,ultrasound vibration will reduce the friction force between the metal material and the mold,and then reflect that the extrusion pressure is obviously reduced during the extrusion process.Therefore,this thesis solves these problems by ultrasound assisted equal-diameterangle extrusion(ultrasound-assisted ECAP),or US-ECAP,.The research contents and results are as follows:1.Feasibility of the US-ECAP is discussed based on the simulation US-ECAP of deform-3d software and the traditional one.And determine the corresponding parameters.2.This thesis,the traditional ECAP die is designed as a symmetrical split free sleeve die with a certain taper,and it is matched with the die sleeve with a conical inner hole.due to the effect of the gravity of the die itself,the two hoops together produce a pre-tightening force,and during the extrusion process,with the increase of the extrusion pressure,the closing force will become larger,which can solve the problem of flange existing ECAP the traditional die.3.Compared the extrusion pressure,hardness and thermal stability of ECAP and US-ECAP extruded 6061 aluminum alloy,the results show that the US-ECAP is better than that of US-ECAP;Meanwhile by means of the Metallographic Test,XRD?transmission electron microscope,the reason why the hardness of the ultrafine-grained material obtained is greater than that of the ECAP ultrafine-grained material is revealed from different scales.Thermal stability tests using different annealing temperatures showed that the recrystallization volume fraction of the US-ECAP.