Research On Continuous Rheo-extrusion Forming Process And Two-stage Aging Heat Treatment Of 7075 Aluminum Alloy

As countries"emission peak","carbon neutrality"strategic objectives,energy conservation and emissions reduction becomes increasingly urgent demand,it also represents the automobile,aircraft and high-speed lightweight material on more and more important.7000series aluminum alloy has a series of advantages such as small density,high strength,good corrosion resistance,is an important material"to aluminum steel",7075 aluminum alloy as a typical representative of 7000 series aluminum alloy,after heat treatment,its tensile strength generally reaches more than 500MPa,7075 aluminum alloy relying on excellent performance is more and more used in high strength structural parts.But because of its high degree of alloying,wide temperature range of solidification characteristics,appear easily in the process of forming segregation,cracking and other defects.Therefore,it is of great significance to explore the high quality forming process of 7075 aluminum alloy.The effect of different process parameters on the surface quality and microstructure of7075 aluminum alloy wire with diameter 9.5mm by continuous rheo-extrusion process was systematically researched in this paper.Illustrated the different process parameters on the mechanism of impact,finally obtained the optimization of continuous rheo-extrusion forming process parameters.On this basis,the experimental scheme of heat treatment of 7075 aluminum alloy with solution treatment and two-stage aging system was researched.The research results show that the forming quality of 7075 aluminum alloy can be effectively improved by preheating the cavity and the mold to 300℃and holding for a period of time,and the microstructure can be made more uniform.Products with excellent surface quality and good mechanical properties can be obtained in the range of extrusion wheel speed of 0.039m·s^-1～0.063m·s^-1 and pouring temperature of 710℃～750℃.In the speed range of0.039m·s^-1～0.063m·s^-1,the higher the rotation speed of the extrusion wheel,the larger the deformation of the microstructure and the grain,the lower the uniformity,the higher the tensile strength,and the elongation decreases.In the range of pouring temperature of 710℃～750℃,the higher the pouring temperature is,the grain size of the microstructure increases slightly,the number of second phases decreases slightly,the tensile strength first decreases and then increases,and the elongation first decreases and then increases.The optimized process parameters of 7075 aluminum alloy continuous rheo-extrusion are:preheating cavity and mold to 300℃,pouring temperature of 750℃,extrusion wheel speed of 0.047m·s^-1,and its tensile strength under these process parameters is 373.73 MPa,the elongation is 12.09%.At 470℃for 90 min of solution treatment,the T（Al Zn Mg Cu）phase is undergoing obvious redissolution,and the T phase is not dissolved obviously and the grains continue to grow after prolonging the solution time,in this solid solution system,theθ（Al₂Cu）phase is the main insoluble phase.Under the two-stage aging system,second-stage aging temperature has the most obvious effect on the tensile strength.When the first-stage aging system is the same,and the second-stage aging time is 14h,the tensile strength of the alloy at the second-stage aging temperature of 150℃is 50.90 MPa higher than that at 180℃,and the elongation is 0.44%lower.Obtain the optimized two-stage aging heat treatment process parameters of7075 aluminum alloy.After solution treatment at 470℃/90min and double-stage aging at 110℃/5h+150℃/14h,the tensile strength of rheologically extruded 7075 aluminum alloy reaches523.44MPa,and the elongation reaches 9.96%.