| Al-Zn-Mg-Cu high strength aluminum alloy with high strength, low density,good weld ability and good working properties are widely used in the aerospace field. And their properties are closely related with precipitated phase during ageing.In this paper, combined with actual factory production and mechanical properties of7055 alloy, the precipitation phase is controlled with heat treatment. The optimum heat treatment process was determined. Analysis of microstructure in different parts of a large ring on this basis, combined with Ansys finite element simulation,analysis quenching process of temperature and stress field, so as to reveal the microscopic mechanism of large rings in different parts of the performance difference.The results show that as the solution temperature increases, tensile strength and yield strength first slowly increased, reaching a peak at 470℃, further raising the temperature to 480 ℃, the tensile strength and yield strength decreased, and elongation alloys with solid solution the rise of temperature increases. The solution temperature reaches 460 ℃, the elongation reaches a maximum(about 30%).Two-stage solution experiments showed that the alloy after 450 ℃, 60 min after-treatment solution was heated to different temperatures 60 min solution can improve the tensile strength and yield strength of the alloy. In the second solution temperature solution temperature also have a similar effect. Best two-stage solution process level solution alloy processing solution 450 ℃ 60 min, secondary solution is480 ℃ solution 60 min, tensile strength and yield strength increased by 19% and22% higher than the single-stage solution.The results show that the alloy with 470 ℃ 4h solution treatment, aging process significantly affects the mechanical properties of the alloys decreased with the increase of the alloy after aging temperature and aging time, with the yield strength and tensile strength of the alloy are first increased while the elongation decreased significantly after 470 ℃ alloy solution and 120 ℃ aging 4h, tensile strength reached 660 MPa, yield strength of 605 Mpa, elongation of 21%.XRD analysis showed that the microstructure alloys mainly consist of α-Al,Al2Zn3Mg3, Mg Zn2(η’ phase) and Al2 Cu Mg phase(S phase) composition, after the solution treatment, Al2Zn3Mg3 diffraction peak intensity phase decreased, and diffraction peaks disappear completely at 480 ℃. After 480℃ 4h solution phase Mg Zn2 Al2 Cu Mg phase.7055 aluminum alloy after aging 120 ℃ 4h, in matrix precipitates as fine spherical η’ phase; aging 8h, two precipitates in the matrix appear, one for sphericalη’ phase, another needle η phase, precipitates to η’ phase-based, spherical η’ phase disappears, precipitated phase needle η. Aging 24 h, needle-like precipitates η phase all the crude into a rod of η phase.SEM observation showed that after ring rolling, some coarse second phase be crushed and distributed in a certain direction. XRD patterns and EDS show coarse second phase Mg Zn2(η) phase, Al2 Cu Mg phase and Al2Zn3Mg3 phase. Alloy forging ring in different parts of the second phase precipitates are different with the parts and there is a change on the precipitation type and amount of phase distribution ring surface of the second phase distribution is more dispersed.Ansys finite element simulation ring quenching stress field and temperature field, where in the temperature field symmetrical, gradually decreases from the surface and inside the huge temperature gradient. Irregular distribution of ring stress field due to the difference in the cooling rate, at the edge of the ring is always peak stress region, the greater the temperature gradient, the higher the surface peak stress.The stress field in the tensile stress and the pressure caused by thermal stress resulted from plastic deformation of the ring, the plastic deformation after occur in the initial period of hardening. |
PDF Full Text Request