欠时效对7075铝合金组织性能及热变形行为的影响研究

发布时间：2018-05-17 02:19

本文选题：7075铝合金 + 欠时效　；参考：《南昌航空大学》2017年硕士论文

【摘要】：7075铝合金属于可时效强化型Al-Zn-Mg-Cu系超高强度铝合金,其优异的室温强度和良好的综合性能,使其在航空,军事,汽车,电子等领域得到了广泛的应用。本文利用热处理炉、热模拟试验机、SEM、EDS等设备,研究了固溶时间和单级时效对7075铝合金组织及性能的影响,确定了适合用来热变形的欠时效工艺。通过对欠时效态7075合金进行热模拟试验,建立了7075铝合金在欠时效状态下的流变应力本构方程和热加工图,并分析了变形组织,结果表明:(1)在470°C下随固溶时间的延长,合金中的大部分第二相已经溶于基体中,固溶时间为2h时固溶较完全,适宜的固溶工艺为470°C×2h。(2)随着单级时效的时间延长和温度升高,在不同时效工艺下均存在强度峰值,当时效的温度高于120°C或时效时间大于24h时,合金的抗拉强度和屈服强度均呈现不同程度的下降。当时效制度为120°C×24h时,合金的抗拉强度、屈服强度和硬度分别为:642.61MPa、549.2MPa和207HV,此时延伸率为10.36%。(3)对比105°C、120°C、135°C三种温度的欠时效阶段,120°C时效在同样的时效时间时,强度和塑性均优于其他两个温度,其中120°C×16h的欠时效态7075铝合金在抗拉强度大于620MPa时,能够保有11%以上的延伸率,作为后续热变形试验的研究具有一定参考价值。(4)在120°C×16h欠时效态7075铝合金的热压缩试验中,变形初期真应力随着真应变的增加而迅速增加至峰值,在随后的变形中真应力会不断下降至趋于稳态。合金的热变形过程中,真应力随应变速率的提高而变大,随变形温度的升高而变小。在相同的应变速率下,随着温度升高,不断驱动再结晶晶粒形核和长大,在相同的的变形温度下,较低的应变速率,会使晶间滑移和位错的运动有更充分的时间进行,故高的变形温度和低的应变速率有利于动态再结晶的进行。(5)合金的应力因子α=0.0091MPa-1,变形激活能Q=230.805kJ/mol,应力指数n=5.926,结构因子A=4.84×1017s-1,将这些材料参数带入可得到用Arrhenius双曲正弦函数表示的流变应力方程和用Z参数表示的材料流变应力本构方程。(6)合金的热变形流变失稳区主要集中在高应变速率低温区域和高应变速率高温区域,高应变速率高温区域的流变失稳面积随着真应变的增大而变大,失稳区组织不均匀且存在变形缺陷。该合金的适宜变形条件为:变形温度400°C~450°C,应变速率0.01s-1~0.001s-1,采用多道次+小应变量的加工方式进行变形。
[Abstract]:The 7075 aluminum alloy belongs to the aging strengthened Al-Zn-Mg-Cu system ultra high strength aluminum alloy, its excellent room temperature strength and good comprehensive performance, make it in aviation, military, automobile, electronics and other fields have been widely used. In this paper, the effects of solution time and single stage aging on the microstructure and properties of 7075 aluminum alloy have been studied by means of heat treatment furnace and thermal simulation test machine, etc. The underaging process suitable for thermal deformation has been determined. Based on the thermal simulation test of underaged 7075 alloy, the constitutive equation of rheological stress and hot working diagram of 7075 aluminum alloy under underaging state are established. The deformation microstructure is analyzed. The results show that the solution time of 7075 aluminum alloy increases with the increase of solution time at 470 掳C. Most of the second phases in the alloy have been dissolved in the matrix, and the solution is more complete when the solution time is 2 h. The suitable solution process is 470 掳C 脳 2h.f.) with the increase of the single stage aging time and the increase of temperature, there is a peak value of strength in different aging processes. When the aging temperature is higher than 120 掳C or the aging time is longer than 24 h, the tensile strength and yield strength of the alloy decrease in varying degrees. When the aging system is 120 掳C 脳 24 h, the tensile strength, yield strength and hardness of the alloy are: 642.61 MPA and 207HVrespectively, and the elongation is 10.36%. The tensile strength and plasticity of the underaged 7075 aluminum alloy at 120 掳C 脳 16 h are superior to those of the other two temperatures. When the tensile strength is greater than 620MPa, the elongation of 7075 aluminum alloy can retain more than 11%. The study as a follow-up hot deformation test has certain reference value.) in the thermal compression test of 7075 aluminum alloy with underaging state of 120 掳C 脳 16 h, the initial true stress of deformation increases rapidly to the peak with the increase of true strain. During subsequent deformation, the true stress will decrease to steady state. During hot deformation, the true stress increases with the increase of strain rate and decreases with the increase of deformation temperature. At the same strain rate, the recrystallization grain nucleation and growth are driven continuously with the increase of temperature. At the same deformation temperature, the lower strain rate will make the movement of intergranular slip and dislocation more sufficient time. Therefore, high deformation temperature and low strain rate are favorable to dynamic recrystallization. The stress factor 伪 (0.0091MPa-1), the deformation activation energy (Q) 230.805kJ / mol, the stress exponent nr 5.926, and the structural factor A4.84 脳 1017s-1 are favorable for dynamic recrystallization. The Arrhenius hyperbolic sinusoidal function can be obtained by using these parameters. The flow stress equation and the constitutive equation of material rheological stress expressed by Z parameter are mainly concentrated in the high strain rate low temperature region and the high strain rate high temperature region in the hot deformation rheological instability region of the alloy. The rheological instability area in the high strain rate region increases with the increase of true strain, and the microstructure is not uniform and there are deformation defects in the instability zone. The suitable deformation conditions of the alloy are as follows: the deformation temperature is 400 掳C, and the strain rate is 0.01s-1n 0.001s-1.The deformation is carried out by means of multi-pass small strain.
【学位授予单位】：南昌航空大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.21;TG166.3

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