It is well known that applying severe plastic deformation methods on the precipitation hardenable aluminum alloys at room temperature is very difficult because of crack formation and segmentation of the specimen during the processes. In this study, several procedures were experimentally examined for performing the cyclic close die forging (CCDF) and improving the mechanical properties of AA7075. The experimental tests revealed that supersaturated solid solution of AA7075 after water quenching is formable for only about 5 min and performing the CCDF process in this limited time is possible. Optical and scanning electron microscopy and transmission electron microscopy were used to study the microstructure of the processed samples. It was observed that by applying two passes of CCDF, the grain size of the material reduced from 30 µm to about 200–300 nm. In addition, the X-ray diffractometer results demonstrated that Guinier–Preston zone picks of the processed samples are very weak and the equilibrium η-phase does not exist in none of the suggested procedures. Furthermore, it was found that by combining CCDF and aging processes according to the proposed procedures, the mechanical properties of the processed AA7075 were improved when compared with the AA7075-T6. To put it more clearly, micro-hardness, yield strength and ultimate tensile stress of the processed sample were improved as much as 38.6%, 25% and 23%, respectively.

中文翻译：

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组合循环闭模锻造和时效工艺对AA7075组织和力学性能的影响

众所周知，在室温下对析出硬化铝合金应用剧烈的塑性变形方法是非常困难的，因为在此过程中试样会形成裂纹和分段。在这项研究中，对执行循环闭模锻造 (CCDF) 和提高 AA7075 机械性能的几种程序进行了实验检查。实验测试表明，水淬后 AA7075 的过饱和固溶体仅可形成约 5 分钟，并且在此有限时间内进行 CCDF 工艺是可能的。使用光学和扫描电子显微镜以及透射电子显微镜来研究加工样品的微观结构。据观察，通过应用两次 CCDF，材料的晶粒尺寸从 30 µm 减小到大约 200-300 nm。此外，X 射线衍射仪的结果表明，处理过的样品的 Guinier-Preston 区拾取非常弱，并且在所有建议的程序中都不存在平衡 η 相。此外，发现根据所提出的程序将CCDF 和老化工艺相结合，与AA7075-T6 相比，加工后的AA7075 的机械性能得到了改善。更明确地说，加工后的样品的显微硬度、屈服强度和极限拉伸应力分别提高了 38.6%、25% 和 23%。X 射线衍射仪的结果表明，处理过的样品的 Guinier-Preston 区拾取非常弱，并且在所有建议的程序中都不存在平衡 η 相。此外，发现根据所提出的程序将CCDF 和老化工艺相结合，与AA7075-T6 相比，加工后的AA7075 的机械性能得到了改善。更明确地说，加工后的样品的显微硬度、屈服强度和极限拉伸应力分别提高了 38.6%、25% 和 23%。X 射线衍射仪的结果表明，处理过的样品的 Guinier-Preston 区拾取非常弱，并且在所有建议的程序中都不存在平衡 η 相。此外，发现根据所提出的程序将CCDF 和老化工艺相结合，与AA7075-T6 相比，加工后的AA7075 的机械性能得到了改善。更明确地说，加工后的样品的显微硬度、屈服强度和极限拉伸应力分别提高了 38.6%、25% 和 23%。