Effect Of Secondary Extrusion Deformation On Microstructure And Properties Of 7075 Aluminum Alloy

7xxx aluminum alloy has been widely used in the aerospace industry.With the continuous development of advanced aerospace equipment,higher requirements are imposed on 7xxx aluminum alloy.Researchers have developed a variety of new 7xxx aluminum alloys by optimizing composition and deformation heat treatment processes.Combined with the current research status,this paper mainly studies the effect of secondary extrusion deformation on the microstructure and properties of 7075 aluminum alloy.Specific research contents include:(1)Evolution of microstructure and properties of 7075 aluminum alloy during homogenization annealing,primary and secondary extrusion;(2)Effect of the solution treatment on the microstructure and properties of primary and secondary extrusion 7075 aluminum alloy.The results show that:(1)After solution treating(475?×1h)and aging(120?×12h),the tensile properties of the samples are not significantly different between samples of the primary and secondary extrusion.The yield strength,the tensile strength and the elongation of the primary extrusion specimen were 666.6MPa,723.8MPa,and 11.9%,respectively.Homogenization before the primary extrusion and different homogenization annealing system after the primary extrusion seems have little effect on the tensile properties of secondary extrusion specimens.The yield strength of secondary extrusion is on the range of 648.6MPa and 684.8MPa.The tensile strength of secondary extrusion is on the range of 712.0MPa and 733.0MPa,and the elongation of secondary extrusion on the range of 9.3%and 11.9%.(2)During solid solution treating at different temperatures(490?-530?),the number and size of the over-fired phase increase with the increase of the solution temperature,but on the same conditions the number and size of the over-fired phase in the primary extrusion sample was significantly higher than that of the secondary extrusion sample.(3)During the solid solution treating at different temperatures(490?-530?),percentage of recrystallization area increased with the increasing of solution temperature.After solution treatment at 490?,500?,510? and 520?,the percentage of recrystallization area of the primary extruded sample was 8.31%,8.94%,9.46%,and 21.85%respectively;the percentage of recrystallization area of the secondary extrusion samples were 16.85%,19.13%,38.79%,and 39.46%respectively.(4)After aging treatment at different temperatures for 1h and 120?×12h,the strength and elongation of the primary extruded sample decreased with increasing solid solution temperature.After solution treatment at 490?,500?,510? and 530?,the yield strengths were 675.8MPa,672.8MPa,651.0MPa,and 164.5MPa respectively,the tensile strengths were 733.5MPa,723.9MPa,713.9MPa,and 478.3MPa,respectively,and the elongations were 11.3%,11.2%,9.5%,0.7%respectively.After aging treatment at different temperatures for 1h and 120?×12h,the strength and elongation of the secondary extruded sample increase at the beginning and then decrease with increasing of temperature.After solution treatment at 490?,500?,510? and 530?,the yield strengths were 678.5MPa,688.4MPa,683.6MPa and 428.5MPa respectively,the tensile strengths were 734.7MPa,748.1 MPa,741.2MPa and 594.2MPa respectively,and the elongations were 11.3%,11.6%,13.2%and 1.6%respectively.