| 7075 aluminum alloy belongs to high strengrh Al-Zn-Mg-Cu series alloy,which can be strengthened by aging.Owing to excellent room temperature strength and good overall performance,they has been widely applied in the aviation,military,automotive,electronics and other fields.In this paper,the effects of solution time and single stage aging on the microstructure and properties of 7075 aluminum alloy were studied by means of heat treatment furnace,thermal simulation test machine,SEM and EDS,selected the under-aged process which suitable for thermal deformation.The thermal simulation test was carried out on the under-aged 7075 alloy,the rheological constitutive equation and thermal processing of the 7075 aluminum alloy were established,and analyzed the microstructure after deformation.The results of the study show that:(1)Most of the second phase in the alloy has been dissolved in the matrix with the extension of the solution time at 470°C.The second phase has a good solid solution effect when the solution time is 2h,the appropriate solution is 470°C×2h.(2)With the prolongation of single-stage aging and the temperature rise,the peak of strength presented under different aging processes.When the aging temperature is higher than 120°C or the aging time is longer than 24 h,the performance of the alloy showed a different degree of decline.When the aging process is 120°C×24h,the tensile strength,yield strength and hardness of the alloy are: 642.61 MPa,549.2MPa and 207 HV respectively.The elongation of the alloy is 10.36% under this aging condition.(3)Compared the under-aged stage of 105°C,120°C and 135°C,the 120°C aging is superior to the other two temperatures at the same aging time,with 120°C×16h under-aged the tensile strength of the 7075 aluminum alloy is more than 620 MPa,the elongation of the 7075 aluminum alloy can be maintained at 11% or more,which is of reference value for the subsequent thermal deformation test.(4)120°C×16h under-aged 7075 aluminum alloy in the thermal compression test,the deformation of the initial stress with the real strain increases rapidly increased to the peak stress,in the subsequent deformation of the true stress will continue to decline to steady state.During the thermal deformation of the alloy,rheological stress increases with the increase of strain rate while decreases with the increase of deformation temperature.At the same strain rate,with the increase of temperature,the recrystallized grains have a tendency to grow.At the same deformation temperature,the lower strain rate will make the intergranular slip and dislocation movement more sufficient time to carry out,so the high deformation temperature and low strain rate is conducive to the dynamic recrystallization.(5)The stress factor ?=0.0091MPa-1,the deformation activation energy Q= 230.805kJ/mol,the stress index n=5.926,the structural factor A=4.84×1017s-1,the material parameters can be obtained with the Arrhenius flow stress equation represented by the hyperbolic sine function and the constitutive equation of the material flow stress represented by the Z parameter.(6)The unstable areas of the alloy is mainly concentrated in the high strain rate low temperature region and the high strain rate high temperature region.Unstable areas of the high temperature high strain rate region increases with the increase of the true strain.Nonuniform structure and deformation defects exist in the unstable areas.The suitable deformation conditions of the alloy are: deformation temperature 400°C~ 450°C,strain rate 0.01s-1~0.001s-1,multi-channel and small strain are better processing methods for deformation. |
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