Effect Of Solution Process On Microstructure And Properties Of Spray-deposited 7055 Aluminum Alloy Extruded Bar

7000 series high-strength aluminum alloy has the advantages of higher specific strength,specific stiffness,better stress corrosion resistance,etc.,and is widely used in aviation and aerospace fields.Spray forming technology was applied to the preparation of 7000 series aluminum alloy in the 1990s.Spray forming 7055 series aluminum alloy has the advantages of uniform structure,fine grains,and no obvious segregation.Moreover,its mechanical properties and stress corrosion resistance can be improved by solution aging treatment.At present,most of the grains and recrystallized structures observed in the solid solution process are metallographic corrosion methods.It is difficult to quantitatively analyze the average grain size and recrystallized volume fraction during the solid solution process,which reduces the rationality of the solid solution process.Aiming at this problem,this paper takes spray forming 7055aluminum alloy extruded bar as the research object,and uses electron backscatter diffraction(EBSD)technology to quantitatively analyze the average grain size and recrystallized volume fraction of the alloy under different solid solution processes;use SEM pictures and images-Pro-plus software quantitatively analyzes the content of the second phase of the alloy under different solid solution processes,which provides a basis for improving the mechanical properties and stress corrosion resistance of the alloy.The research results show that there are MgZn₂ phase,S(Al₂CuMg)phase and Al₇Cu₂Fe phase in the extruded state of 7055 aluminum alloy.The area fraction of the second phase of the extruded alloy is 10.3%,the recrystallized volume fraction is 69%,the average grain size is 2.5?m,and the hardness value is 88HV.In the single-stage solution treatment stage,MgZn₂ is almost completely re-dissolved after solution treatment at 460?/2h;S phase is almost completely re-dissolved after solution treatment at 480?/2h;Al₇Cu₂Fe phase is treated at 500?/2h after solution treatment Still exist.After 470?/2h solution treatment,the remaining second phase area fraction is 0.57%,the recrystallized area fraction is 80%,the average grain size is 3.8?m,and the hardness value is 152HV.Compared with other single-stage solid solution processes,after solution treatment at 470?/2h,the area fraction of the second phase is lower,the volume fraction of recrystallization is lower,and the average grain size is smaller.Through the above quantitative analysis and hardness test,it is finally determined that470?/2h is the best single-stage solid solution process.After 7055 aluminum alloy undergoes the primary solution treatment at 440?/4h,there are still a small amount of MgZn₂phase,a large amount of S phase and Al₇Cu₂Fe phase in the alloy;after 490?/30min secondary solid solution treatment,MgZn₂ phase and S phase in the alloy Basically re-dissolved,the morphology of Al₇Cu₂Fe phase changed little.After the alloy is solution treated at 440?/4h+490?/30min,the residual second phase area fraction is 0.23%,the recrystallized area fraction is 79.9%,the average grain size is 4.0?m,and the hardness value is 186HV.Compared with other two-stage solid solution process,after the alloy is solid solution treated at440?/4h+490?/30min,the area fraction of the second phase is lower,the volume fraction of recrystallization is lower,and the average grain size is smaller.Through the above quantitative analysis and hardness test,it is finally determined that440?/4h+490?/30 min is the best two-stage solid solution process.The tensile strength of 7055 aluminum alloy after 470?/2h+120?/18h(single-stage solution+aging)heat treatment is 624MPa,and the elongation is 9%;after440?/4h+490?/30min+120?The tensile strength of the alloy after/10h(two-stage solution+aging)heat treatment is 673MPa,and the elongation is 14%;the fracture modes of the alloys in the two states are mixed fracture(intergranular fracture+transgranular fracture).