Research On Thixoforging Of AlSi7Mg Aluminum Alloy Semi-solid Billet Fabricated By RAP

Forming methods of aluminum alloys include mainly plastic processing and solidification processing,which are difficult to meet the requirements of excellent performance and complex shape at the same time.Semi-solid processing has comprehensive advantages such as low forming force and near net forming,which can solve the above dilemma.AlSi7Mg aluminum alloy is a typical cast aluminum alloy with a large solid-liquid interval.In the field of semi-solid processing,the liquid phase method is commonly used to fabricate semi-solid billets of it,and there is little literature on the solid phase method.Based on the reasons above,this paper explores the possibility of fabricating semi-solid billets of AlSi7Mg aluminum alloy and thixoforming through the Recrystallization and Partial Remelting(RAP)method in the solid phase method,in order to broaden the application range of fabricating semi-solid billets and forming materials by RAP and explore new semi-solid processing technology,and further study the structure and properties of AlSi7Mg aluminum alloy semi-solid billet at high solid phase rate.The specific research is as follows:In this paper,the RAP method is used to fabricate semi-solid billets of AlSi7Mg aluminum alloy ingots,and the metallographic microscope and IPP software are used to study the grains.The influences of the deformation temperature and the amount of deformation on the average grain size and shape factor of semi-solid billet during warm deformation are studied.According to the principle of minimum average grain size,the optimal upsetting parameter under the selected parameters is that the deformation temperature is 240 ? and the deformation amount is 38.65%,and the suboptimal upsetting parameter is the deformation temperature is 260? and the deformation amount is 38.65%.Then,based on the parameters above,the evolution of the semi-solid structure is studied,and the effects of isothermal temperature and isothermal time on the average grain size and shape factor are studied.The results show that under the conditions of isothermal temperature of 581??599? and isothermal time of 2?26min,the average grain size distribution is between 64?117?m and the shape factor distribution is 0.76?0.89,which meets the relevant requirements of semi-solid billets.This study confirmed that the RAP method is feasible for fabricating semi-solid billets of AlSi7Mg aluminum alloy.The true stress-strain curves of AlSi7Mg aluminum alloy under high temperature and semi-solid temperature conditions are input into Defrom-3D finite element software in table form.The changes of strain field,stress field and temperature field in the process of thixoforging are studied,and the influence of different parameters on the simulation results is studied to obtain the optimal parameter group under the selected parameters.At the same time,the comparison between semi-solid die forging and hot die forging shows the advantages of semi-solid thixoforming forging technology.According to the parameters determined by small billets,upsetting is performed under the condition that the large billet samples are free of defects,and the billets are performed according to the size of the shaped part.According to the simulation results,the optimal parameter group under the selected parameter conditions is used to formulate the process,and the thixoforging experiment is carried out to obtain the intermediate product of the part that has not been strengthened by heat treatment.Their metallographic structure and mechanical properties are analyzed by RAP method.