Research On Preparing Semi-solid Billet Of Aluminum Alloy By Using Severe Plastic Deformation Induced And Isothermal Spheroidization

With the requirement of lightweight and energy-saving,7005 aluminum alloy are widely used in aerospace,machinery,automotive,energy,national defense and other fields due to its good physical and chemical properties.At present,traditional forming technology of aluminum alloy include solidification and plastic forming,mechanical properties can’t be satisfied in solidified forming technology,and the plastic forming can’t be used to produce workpiece with complex sharp.Semi-solid metal forming technology is a net-shape forming technology,it has been used in the manufacture of high-quality workpiece,and the semi-solid forming of 7005 aluminum alloy will become the mainstream metal forming method in the future.During semi-solid processing of metal,it is the key to fabricating high-quality semi-solid billets of metal.In this dissertation,equal channel reciprocating extrusion process and isothermal treatment experiment are used to prepare semi-solid billets of 7005 aluminum alloy by using severe plastic deformation induced and isothermal spheroidization,the effects of extrusion temperature,heat treatment,isothermal temperature and isothermal time on the microstructure and mechanical properties of the materials were studied,explore the optimum process parameters of billet preparation.In this paper,Deform-3D software is used to simulate the process of equal channel reciprocating extrusion,and the stress and strain changes of the material are obtained when the punches is in different displacement.We had also simulate the effect of different extrusion temperature and the state of superposition other billet.It is found that the stress and strain of the material increase as the displacement of the punch increases during the extrusion process.With the increase of extrusion temperature,the stress and strain of the material are smaller,and the stress concentration area becomes smaller.When two pieces of billets are extruded,abnormal strain and stress concentration zone are formed at the contact between the billets.In this section,equal channel reciprocating extrusion process was employed to refine the grains of 7005 casting aluminum alloy.With the help of metallographic microscope,tensile test machine,electron backscatter diffraction(EBSD)technique and scanning electron microscope(SEM),the influence of the parameters on the microstructure and mechanical properties of the billet was studied,the results show that the equal channel reciprocating extrusion process increased mechanical properties of materials and it’s microstructure was refined well.In the experiment of stacking billets the grain size was refined better with the increase of deformation.The continuous extrusion experiments shows that the grain size of billets decreases first and then increases with the increase of extrusion temperature.When the extrusion temperature is 400 degrees,the extrusion effect is better.By semi-solid isothermal treatment experiment and with the help of metallographic microscope,IPP image processing software and Energy Dispersive Spectrometer(EDS),the grain evolution rule of the microstructure of the material during isothermal treatment was analyzed.The results show that with the increase of the isothermal temperature and isothermal time,the grain size and grain shape coefficient keep increasing,when the temperature is high,the grain size will be reduced.Fe,Mn,Cu and other elements to form eutectic phase,in the isothermal process,eutectic phase melt quickly into liquid phase.The optimum process parameters: extrusion temperature is 400℃,heated to 610℃ for 20 min or 615℃ for 15 min.Based on these analysis of experiment,a new method was put forward for fabricating high-quality semi-solid billets of 7005 aluminum alloy,which named large deformation strain induced isothermal spheroidization effect.