Characterization of the Isothermal Precipitation Kinetics of an Al-Zn-Mg-Cu Alloy
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AL-ZN-MG-CU alloys, also known as 7xxx series super high-strength Al alloys, are now widely used in modern aerospace, high-speed train, and automotive fields due to the their outstanding comprehensive properties and lightweight structures for energy conservation.[1–3] Over the last decades, numerous studies have focused on the intricate precipitation sequences, morphology, and structures under various aging treatments which were generally accepted to be the key factors of high strength.[4–8] Based on modern diffraction analysis and electron microscopy observations, the precipitation sequences in Al-Zn-Mg-Cu alloys were basically believed to follow[4–7] supersaturated solid solution (SSSS) fi Guinier–Preston (GP) zones fi g¢ fi g. Recently, Liu et al.[7] also argued that an intermediate phase was presented between g¢ and g phases based on high-resolution transmission electron microscopy (HRTEM) characterization. Further, the microstructure evolution of Al-Zn-Mg-Cu alloys during higher
FULIN JIANG is with the College of Materials Science and Engineering, Hunan University, Changsha 410082, China and also with the Department of Materials Science and Engineering, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4L7, Canada. Contact e-mail: [email protected] HATEM S. ZUROB, GARY R. PURDY, and XIANG WANG are with the Department of Materials Science and Engineering, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4L7, Canada. HUI ZHANG is with the Hunan Province Key Laboratory for Spray Deposition Technology and Application, Hunan University, Changsha 410082, China. Manuscript submitted October 28, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
temperature solution treatment, welding, and subsequent cooling processes was also well investigated.[8–11] However, the precipitation kinetics between typical aging and solution treatment is not adequately understood, which involves the temperature range of industrial hot working process.[12–15] As indicated in our earlier contributions,[16–18] the non-isothermal precipitation kinetics of 7150 Al alloy was examined over a wide range of temperature. The initial material state, i.e., As-Received (AR), Furnace Cooled (FC), and Water Quenched (WQ) had a strong influence on precipitation reactions that occurred during heating. The complex precipitation reactions, which were dependent on cooling/heating routes, might also affect dynamic and static flow behavior during hot deformation.[12,14,15] In the present contribution, the effect of isothermal holding on precipitation in alloy 7150 is examined with initial heating route that is contrary to general cooling route after solution treatment or welding.[8–11,17,18] Isothermal kinetics studies can often be related more closely to fundamental processes. For better designing, the alloy and industrial processing (especially elevated holding during multistage hot working or after hot working), the precipitation kinetics at elevated temperature holding was studied by comparing with that at lower temperature (typ
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