| Al-Zn-Mg-Cu aluminum alloy is widely used in aerospace(aircraft),transportation(automobile,rail transportation)and other fields because of its high strength and toughness,high specific strength and good corrosion resistance.The research on the microstructure and properties of super aluminum alloy,especially the super strength aluminum alloy of 800 MPa strength level,has always been the goal pursued by research scholars.In this thesis,the optimum design of alloy composition,heat treatment regulation(solid solution+aging),deformation processing anisotropy are studied.The effect of different Zn/Mg and Cu/Mg on hardenability of cast aluminum alloy and the microstructure and properties of aluminum alloy rolling material was studied.The super strong aluminum alloy with large size extrusion material was prepared by selecting the alloy components with better comprehensive properties(Al-11.2 Zn-3.0 Mg-1.3 Cu-0.2 Zr).The effects of six solid solution processes and three aging processes on the microstructure and properties of the super strong aluminum alloy were studied.Finally,the microstructure and properties of the super alloy with hot compression extruded material were studied.The grain,undissolved phase,dislocation,hardness,electrical conductivity,hardenability,mechanical properties and corrosion resistance of the materials were studied.The details are as follows:(1)The effects of different Zn/Mg and Cu/Mg on the cast state and microstructure and properties of Al-x Zn-3.0 Mg-y Cu-0.2 Zr aluminum alloy were studied.The Zn/Mg values were 3.13,3.73 and 4,respectively,and Cu/Mg values were 1.43 and 0.77,respectively.The heat treatment process was:solid solution(470~oC×2 h)+T6(121 ~oC×24 h).The results show that:For the cast aluminum alloy,the increase of Zn/Mg and Cu/Mg would reduce the quenching sensitivity of the alloy.In addition,the hardenability of the alloy was negatively correlated with the sum of the alloy atomic radius difference,that is,the greater the sum of the alloy atomic radius difference,the worse the alloy hardenability.For aluminum alloy rolling materials,increasing the Zn/Mg value of the alloy will promote the recrystallization and grain growth of the alloy,and play a strong hardening effect on the alloy.When the value of Cu/Mg is 0.77 and Zn/Mg rises from 3.13 to 3.73,the hardness is increased by 8.8 HV and the strength increased by 49.268 MPa.However,when Zn/Mg increased to 4,the hardness and strength decreased.In addition,the addition of Zn/Mg will also reduce the intergranular corrosion resistance and exfoliation corrosion resistance.Increasing the Cu/Mg value also increased the recrystallization and grain growth of the alloy,and reduced the strength,hardness and exfoliation corrosion resistance of the alloy,but would improve the toughness and intergranular corrosion resistance of the alloy.(2)The microstructure and properties of large size ultra strong aluminum alloy extrusion material(theoretical design component:Al-11.2 Zn-3.0 Mg-1.3 Cu-0.2 Zr)in six solid solution processes and T6(121 ~oC×24 h),T76(121 ~oC×5 h+153 ~oC×16 h)and T7X(121~oC×5 h+133 ~oC×16 h)aging processes were studied.The results showed that:the unmelting phase in the alloy decreases with the increase of solid solution temperature and the time of solid solution,and decreases slowly at G3(450 ~oC×2 h+460 ~oC×2 h+472 ~o C×2 h),and the grain size of the alloy increases;the hardness reaches the maximum in the G3 solution process,and the electrical conductivity tends to decrease.The strength of the alloy after aging treatment at T6,T76 and T7X showed a trend of increasing and then decreasing,and reached the maximum at G3,G4(450 ~oC×2 h+460 ~oC×2h+470 ~oC×2 h+475 ~oC×2 h),and the elongation gradually reduced.In addition,with the increase of solid solution temperature and the increase of solid solution time,the intergranular corrosion resistance of the alloy increased,and the resistance to exfoliation corrosion first increased and then decreased,and the best value was found under the solution treatment of G3 and G4.Therefore,the heat treatment process with the highest strength in this test is G3 solid solution+T7X aging,at this time the tensile strength of the alloy is 827.9MPa,the elongation at post is 8.1%,the maximum depth of intergranular corrosion is 126.9 mu m,and the exfoliation corrosion is EA grade.The hardenability of the alloy was studied under the heat treatment process,and the single end quenching depth was 35.145 mm.(3)The microstructure and properties and anisotropy of super high strength aluminum alloy under hot compression extrusion solid solution(G3)aging(T7X)were studied.The resulted show that the microstructure of the aluminum alloy extrusion material had obvious difference(The grains in Y direction are equiaxed,and the grains in X and Z directions are banded),and the internal dislocation is only retained in the direction of X,but the difference between the hardness and the conductivity of the alloy is not very large.In addition,the tensile properties of the alloy also had obvious anisotropy,and the tensile strength of the Z direction increased by about 122 MPa compared with the Y direction,and the elongation increased by157%.The corrosion resistance of the alloy also exists in the anisotropy.The Z direction had the best intergranular corrosion resistance,the corrosion depth was167.46 um,while the anti peeling corrosion in the Y direction was the best,only a slight peeling phenomenon occurs,and the peeling corrosion grade was PC grade.This thesis creatively verified the internal relation between the total of the alloy atomic radius difference and the hardenability,and realized the effective control of the alloy composition,microstructure(unmelting phase,gold phase,dislocation),heat treatment and performance.The 800 MPa grade super strong aluminum alloy was prepared by conventional process. |
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