Theoretical Study On Hardenability Of 7000 Series Aluminum Alloy And Microstructure And Properties Effect Of Mg?Zr And Cu On Rolled 7000 Series Ultra High Strength Aluminum Alloy

7000 series aluminum alloy has been widely used in all walks of life because of its excellent performance after being developed.Research and development of 7000 series aluminum alloy is always a hot spot in the field of metal.Because of the application of 7000 series aluminum alloy in aerospace and automotive fields,large structural parts not only need aluminum alloy has high strength and good plasticity,but also have good hardenability.Eight kinds of ultra-high strength rolling 7000 series aluminum alloy which were developed independently were used as experimental materials in this paper.Effects of Mg,Zr and Cu on microstructure and properties of 7000 ultra-high strength aluminum alloy subjected to rolling treatment were investigated by using the control variable method.The main factors affecting the hardenability of 7000 series aluminum alloy were also investigated preliminarily in this paper.Hardness test,tensile test,inter-granular corrosion test,exfoliation corrosion test and end quenching test were carried out to test the properties of alloys.XRD,metallographic observation,EBSD,SEM and EDS were carried out to study the microstructure of alloys.The main research work and conclusions are as follows:(1)The main factors which affect hardenability of 7000 ultra-high aluminum alloy were investigated by using end-quenching experiment,SEM and EDS.The results show that Mg,Zn / Mg,Zn + Mg + Cu,the content of Zr,Si and the sum of the atomic radius difference(the sum of the atomic volume difference)of Zn,Mg and Cu has a great influence on the hardenability of the 7000 aluminum alloy.Zr,Si and high atomic radius difference(the sum of the atomic volume difference)can reduce the hardenability of the alloy.Qualitative analysis showed that when the content of Zr and Si is high,the alloy cannot maintain good hardenability even if the sum of the atomic radius difference of the alloy is small.When the content of Zr and Si is low,the alloy can also maintain good hardenability even if the sum of the atomic radius difference is high.In order to improve the hardenability of 7000 series aluminum alloy,it is necessary to reduce the sum of the atomic radius difference of the alloy,and to control the Zr content and Si content in the alloy at a lower level.Quantitative analysis using standard multivariate linear regression method showed that the factors affecting the hardenability of 7000 aluminum alloy can be sorted as Mg>?R>Zn/Mg>Zn+Mg+Cu> Si>Zr>Fe in order of their influence ability.Mg,Zn and Mg are beneficial to the hardenability of 7000 series aluminum alloy.?R,Zn + Mg + Cu,Si and Zr are harmful to the hardenability of 7000 series aluminum alloy.(2)Three kinds of 7000 series aluminum alloy with excellent comprehensive properties were developed.The composition of this aluminum alloy is Al-8.95Zn-x Mg-1.18Cu-0.44 Zr.The content of Mg are 2.57%,2.21% and 1.89%.Effect of Mg on microstructure and properties of 7000 ultra-high aluminum subjected to rolling treatment were investigated.The results show that aluminum alloy has best overall properties when the content of Mg element is 2.21%.The strength of T6 and T76 aging state aluminum alloy can reach 651.7MPa and 645.6MPa respectively.The alloy also has excellent plasticity properties.The elongation rates of two aging state aluminum can reach 10.7% and 15.4% respectively.The hardenability of the alloy is good too.The end-quenching depth is 85 mm.Mg can promote recrystallization significantly.It can reduce the effects of dislocation and low-angle grain boundaries strengthening.However,Mg can improve solid solution and aging strengthening.Mg can change the shape of elongated grains due to hot pressing and rolling,which change the elongated grains to equiaxed grains.So that Mg can also improve exfoliation corrosion performance of rolled alloy significantly.However,it reduces inter-granular corrosion ability of aluminum alloy.(3)Three kinds of 7000 aluminum alloy with excellent comprehensive properties were developed.The composition of this aluminum alloy is Al-8.86 Zn-2.33Mg-1.79 Cu-x Zr.The content of Zr are 0.382%,0.462% and 0.573%.Effect of Zr on microstructure and properties of 7000 ultra-high aluminum subjected to rolling treatment were investigated.The results show that aluminum alloy has best overall properties when the content of Zr element is 0.382 %.The strength of T6 and T76 aging state aluminum alloy can reach 649.9 MPa and 650.8 MPa respectively.The elongation rates of two aging state aluminum can reach 6.2% and 7.6% respectively.The hardenability of the alloy is good too.The end-quenching depth is 105 mm.Zr can inhibits recrystallization and refine grains.It can improve the effects of dislocation and low-angel grain boundaries strengthening.However,Zr can reduce solid solution and aging strengthening.When the content of Zr is greater than 0.382%,Zr reduce the strength of aluminum alloy.Zr also makes it difficult for elongated grains due to hot pressing and rolling to change to equiaxed grains because of its recrystallization-inhibiting function.So that Zr can reduce inter-granular and exfoliation corrosion performance of rolled alloy.(4)Two kinds of 7000 aluminum alloy with excellent comprehensive properties were developed.The composition of this aluminum alloy is Al-8.44 Zn-1.8Mg-x Cu-0.148 Zr.The content of Cu are 1.28% and 2.36%.Effect of Cu on microstructure and properties of 7000 ultra-high aluminum subjected to rolling treatment were investigated.The results show that aluminum alloy has best overall properties when the content of Cu element is 2.36 %.The strength of T6 and T76 aging state aluminum alloy can reach 648.0 MPa and 615.2 MPa respectively.The elongation rates of two aging state aluminum can reach 16.4 % and 19.3 % respectively.The hardenability of the alloy is good too.The end-quenching depth is 120 mm.Cu can improve recrystallization.It can improve the ratio of low-angel grain boundaries and improve the effects of low-angle grain boundaries strengthening.So Cu can improve plastic processing hardening ability of alloy.Cu can significantly improve the solid solution aging precipitation strengthening of aluminum alloy and further improve the strength of aluminum alloy.Cu can also improve the plasticity of aluminum alloy.Besides Cu can improve inter-granular and performance of rolled alloy while reduce exfoliation corrosion performance.