【作者】 张艳秋；

【导师】 单德彬；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2008， 博士

【摘要】 铝合金盘饼类锻件广泛应用于航空领域。近年来,为了满足减重的需要,该类零件多被设计成复杂形状的整体结构件,并且对锻件的精度和组织性能的要求越来越高,对于一些重要的受力构件,还要求锻件流线按照零件的几何外形分布。铝合金盘饼类锻件由于局部金属流程较长、金属变形流动复杂且难以控制,非常容易出现充不满和折叠等缺陷。特别是一些关键受力的盘饼类锻件,由于流线多要求沿径向或环向分布,而原始坯料的流线通常沿轴向分布,还非常容易产生流线露头、涡流和穿流等缺陷。此外,该类锻件由于形状复杂,各部位金属变形程度不均匀,再加上坯料及变形方案等的影响,将使锻后组织和性能难以控制。目前,对于复杂盘饼类锻件缺陷的形成机理及组织性能控制方面的研究还不够深入,且没有系统的理论进行指导。本文采用有限元模拟和实验相结合的方法深入系统地研究了7A09铝合金复杂盘饼类锻件等温成形过程中缺陷形成的机理,揭示了成形方案及热处理工艺对锻件组织性能的影响规律。采用热模拟实验方法研究了7A09铝合金的高温变形行为,获得了该合金的高温流变方程,绘制了7A09铝合金的热加工图,并结合变形组织确定了该合金等温成形的最佳工艺参数。采用数字化技术设计了复杂盘饼类锻件的等温精密成形方案和模具,实现了模具设计制造的一体化,提高了模具设计质量和加工精度,缩短了模具设计、制造周期,降低了成本。采用有限元模拟和实验相结合的方法分析了复杂盘饼类锻件成形时模膛的充填规律,研究了成形方案对成形质量的影响,揭示了该类锻件等温成形时充不满、折叠、粗晶、流线露头、涡流、穿流和穿筋等缺陷形成的机理,提出了复杂盘饼类锻件缺陷控制的有效措施,并采用优化工艺获得了尺寸精度、表面质量和内部流线均合格的7A09铝合金复杂盘饼类锻件。采用光学显微镜、扫描电子显微镜及透射电子显微镜等现代分析方法,通过大量实验研究了变形工艺对7A09铝合金复杂盘饼类锻件组织和性能的影响。实验结果表明,制坯时变形程度、摩擦条件和终锻前的坯料厚度、锻造火次等都对锻件最终的组织性能有很大的影响,制定等温成形工艺方案时必须考虑这些因素的影响,才能获得更优良的锻件组织和性能。研究了各种热处理工艺对7A09铝合金复杂盘饼类锻件多火次等温锻造锻件组织性能的影响规律。结果表明,对于7A09铝合金复杂盘饼类锻件,采用常规过时效处理能够获得较好的综合性能,采用合理的双级时效或回归再时效制度可以在保证良好的塑性条件下获得更优良的强度、硬度和抗应力腐蚀性能。更多还原

【Abstract】 Aluminum alloy disk forgings have been widely used in aircraft domains. In recently years, the parts are designed mostly as integral structures with complex shape in order to lighten the weight of aircraft. Moreover, there are higher and higher requirements for the precision, the microstructures and properties of the forgings, and as for some important structrural parts which bear loading, it is also demanded that the flow lines distribute along geometrical shapes of the forgings. As for aluminum alloy complex shape forgings, the defects such as underfilling and folding are very likely to happen because of the long flow distance of some local metal, the complexity and controlling difficulty of metal deformation and flow. Especially for some key stressed disk forgings, the defects such as flow line outcrop, flow line vortex and fibre breaking are very likely to occur because the required radial or circumstantial flow lines result from the original bars with the axial flow lines. Furthermore, the metal deformation of each location is inhomogeneous because of the complex of the forgings and the influence of billet as well as the deformation scheme, which will make it difficult to forecast the forged microstructures and properties. It has not beeen studied profoundly on the forming mechanics of the defects, the microstructures and mechanical properties control of this kind of forgings at present, and it has been no systemic theories to guide so far. Therefore, in this dissertation, the defect mechanism of 7A09 aluminum alloy disk forging with complex shape were studied profoundly and systemically by combining FEM simulation with experiment, and the influence laws of forming scheme and heat treatment on microsturctures and properties of the forgings were disclosed.The hot deformation behavior of 7A09 aluminum alloy was investigated by means of thermal simulating experiments, and constitutive equation of flow stress of the alloy at high temperatures was obtained. What’s more, the hot processing maps of 7A09 aluminum alloy were drawn, and the optimal process parameters of isothermal forming of the alloy were established by combining the processing maps with deformed microstructures.The forming scheme and dies of isothermal precision forming for disk forging with complex shape were designed by means of digital technology. The integrated designing and manufacturing of dies was realized, which enchanced the design quality and manufacturing precision of dies, shortened the design and manufacturing period of dies, and reduced the costs. By combining FEM simulation with experiments, the cavity filling laws of forming disk forgings with complex shape were analyzed, the influences of billet schemes on forming qualities were studied, the occuring mechanisms of the defects arising in isothermal forming, such as underfilling, folding, coarse grain, flow line outcrop, flow line vortex, fibre breaking and rib breaking, were revealed, and the valid measures to control the forging defects of disk forgings with complex shape were put forward. What’s more, 7A09 aluminum alloy disk forgings with complex shape were obtained by optimal process, which are acceptable on not only size precision, but also surface qulity and interior flow lines.The analytical methods such as optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM) were used to study the influence of forming process on microstructures and mechanical properties of 7A09 aluminum alloy disk forging with complex shape through a lot of experiments. The experimental results show that the final microstructures and mechanical properties of the forgings were significantly influenced by deformation extent as well as friction condition during preforming, and by billet thickness and fire times during die forging. Thereby more excellent microstructures and mechanical properties can be gained only by considering these factors in determining the process schemes of isothermal forming.The influence laws of heat treatment on microstructures and mechanical properties of forgings formed by multi-fires isothermal forging were studied. The results show that proper combination properties can be obtained by adopting conventional overageing treatment for 7A09 aluminum alloy disk forgings with complex shape. By reasonable two-stage ageing or retrogression and reageing treatment, better strength, hardness and stress corrosion resistance can be gained under the condition of good plasticity.更多还原