预变形对7075铝合金时效成形微观组织及力学性能的影响

发布时间：2018-04-11 03:22

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

【摘要】：在航空工业迅猛发展的当前,对飞机整体壁板的成形提出越来越高的要求,而时效成形是飞机整体壁板类工件成形的有效方法。研究材料预变形后对时效成形件性能的影响,是对传统时效成形工艺的发展和创新,具有重要的理论意义和工程实用价值。本文以T6态的7075铝合金薄板为研究对象,研究了在预变形、预变形加固溶处理以及最终形变热处理条件下,材料未时效态、时效态及时效成形态的力学性能及微观组织。研究结果表明:T6态的7075铝合金时效成形回弹率会随预变形量的增加而减小。当预变形量为7%时试样回弹率达到最小,为21.02%,比预变形量为0时回弹率下降了64.88%,此时的7075铝合金拥有良好的成形性能,但是其强度相比未时效态的试样会大幅度下降。通过透射电镜可以发现,未时效态试样晶内析出相主要是由强化相GP区和η'相构成,晶界析出相细小连续,晶界无析出带不明显,经过时效成形后,强化相GP区和η'大部分消失了,出现了粗大的η相,晶界变为断续分布,晶界析出相尺寸变大,使合金强度低于未时效态试样。对T6态的7075铝合金进行固溶处理,其固溶处理后力学性能得到了提升,未时效态预变形量为2%的时试样延伸率高达22.33%,比T6态母材延伸率提高了31.35%。在固溶处理的基础上对合金施加预变形,最后时效成形,发现其回弹率也会随预变形量的增加而减小。预变形量在7%时回弹率达到最小,为38.30%,此时试样的成形性能也很好,且其强度比时效态预变形量为7%时提高了20.89%。在固溶处理→预变形→人工时效的基础上,通过在预变形前加预时效,发现终时效、时效成形态后合金的强度得到了大幅度的提高。通过透射电镜可以发现预时效可以为基体提供均匀分布的细小弥散相GP区和少量的η'相,而GP区会为终时效时强化相η'相的均匀形核提供条件,同时时效、时效成形后η'相会被球化,球化的均匀分布的η'相会使合金的力学性能得到改善。最终形变热处理工艺下7075铝合金时效成形回弹率也会随试样预变形量的增加而减小,但是最小回弹率只有62.66%,成形性能相比其他两个工艺发生了下降,总的说来,预变形对时效成形回弹率的减小是有益的。
[Abstract]:With the rapid development of aviation industry, higher and higher requirements are put forward for the forming of aircraft integral wall plates, and aging forming is an effective method for forming aircraft integral wall panels.It is of great theoretical significance and practical value to study the effect of pre-deformation of materials on the properties of aging forming parts, which is important to the development and innovation of traditional aging forming process.In this paper, the mechanical properties and microstructure of 7075 aluminum alloy sheet in T6 state were studied under the conditions of pre-deformation, pre-deformation strengthening solution treatment and final thermomechanical treatment.The results show that the springback rate decreases with the increase of pre-deformation of 7075 aluminum alloy.When the pre-deformation is 7, the springback rate of the sample reaches the minimum (21.02), which is 64.88% lower than that of the pre-deformation 0. The 7075 aluminum alloy has good formability, but its strength will be greatly reduced compared with the unaged specimen.It can be found by TEM that the precipitated phase is mainly composed of strengthening phase GP region and 畏 'phase. The precipitated phase at grain boundary is fine and continuous, and there is no obvious precipitation band at grain boundary.Most of the GP region and 畏'of the strengthened phase disappeared, and the coarse 畏 phase appeared, the grain boundary became discontinuous distribution, and the size of precipitated phase at the grain boundary became larger, which made the strength of the alloy lower than that of the unaged sample.The mechanical properties of 7075 aluminum alloy in T6 state were improved after the solution treatment. The elongation of 7075 aluminum alloy was 22.33 when the pre-deformation of aging state was 2%, which was 31.35% higher than that of T6 base metal.On the basis of solution treatment, the alloy was pre-deformed and the springback decreased with the increase of pre-deformation.The springback rate of the sample reaches the minimum at 7 and is 38.30. The formability of the sample is also very good, and its strength is 20.89% higher than that of the aging predeformation of 7.On the basis of the artificial aging of solution treatment and pre-deformation, it is found that the strength of the alloy has been greatly improved after the final aging and aging into shape by adding pre-aging before pre-deformation.It is found by TEM that preaging can provide uniform distribution of small dispersed phase GP region and a small amount of 畏 'phase for the matrix, while GP region can provide conditions for homogeneous nucleation of the strengthened phase 畏' phase at the end of aging, and aging at the same time.After aging forming, 畏 'phase will be spheroidized, and the mechanical properties of the alloy will be improved by the uniformly distributed 畏' phase of spheroidization.Under the final thermomechanical treatment process, the springback rate of aging forming of 7075 aluminum alloy will also decrease with the increase of sample pre-deformation, but the minimum springback rate is only 62.66, and the formability of 7075 aluminum alloy decreases compared with the other two processes.Pre-deformation is beneficial to the reduction of springback.
【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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