The Plastic Flow Machining Process And Mechanical Properties Of Gradient Structural Pure Aluminum

Industrial pure aluminum has good plasticity and lower strength,and has a higher performance improvement space.The introduction of gradient ultrafine/nanocrystalline structure can not only effectively improve its strength,but also maintain its good ductility.The plastic flow machining method,as a newly proposed process,can prepare ultrafine-grained metal sheets,plates or strips with a gradient structure from bulk metal materials in one step.Therefore,in this paper,the method of combining simulation and experiment is used to deeply study the plastic flow machining process and mechanical properties of gradient structural pure aluminum.The main research results obtained in this paper are as follows:(1)The thermal-mechanical coupled finite element model of plastic flow machining was established.According to the finite element analysis,the pure aluminum material suffers severe shear deformation during the plastic flow machining process,and formed an obvious strain gradient on the thickness layer of the laterally extruded "fin" material.Simultaneously,the influence rules of extrusion thickness,extrusion speed and back press on the material forming process were analyzed.The results show that as the extrusion thickness increases,the highest equivalent strain decreases,the low-strain zone is more widely distributed,and the material flowing to the lateral extrusion channel gradually increases;as the extrusion speed increases,the equivalent strain rate gradually increases,the temperature gradually increases;as the back pressure increases,the equivalent strain in the low-strain zone decreases,and the equivalent strain in the high-strain zone remains basically unchanged,and the material flows to the lateral extrusion channel gradually increases.(2)The actual processing experiment was carried out,the forming material was successfully prepared by the plastic flow machining process,and the microscopic observation sample was made,and the material was microscopically observed by metallographic microscope to analyze the mechanism of microstructure evolution during the plastic flow machining process.The results show that when the workpiece material passes through the deformation zone near the extruding block,the grains will be extruded and sheared,and then elongated and broken,finally refined.Away from the side of the extruding block,the strain received is relatively small,so the elongated crystals are the main,and the refinement is relatively incomplete,thus forming a gradient distribution in the grain size.(3)Isothermal annealing heat treatment at different temperatures on the prepared samples was performed,the micro hardness tester was used to test the hardness of the material surface,and the universal electronic tensile testing machine was used to test the tensile properties of the material.The mechanical properties and thermal stability of the gradient sample were studied.The results show that the hardness of the gradient sample is distributed in a gradient on the thickness layer,the strength is significantly improved relative to the raw material,and maintains good ductility;the greater the extruded thickness of the gradient sample,the lower the tensile strength,the better the ductility;when the annealing temperature is below 200°C,the gradient sample still maintains higher strength and ductility,has good thermal stability;as the temperature rises above 250°C,the hardness gradient of the gradient sample gradually loses,the strength decreases significantly and the ductility gradually increases.