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Wanfu Guo,Youping Yi,Shiquan Huang,Hailin He,Jie Fang 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.1
Large 2219 Al–Cu alloy transition rings are extensively utilised in launch vehicles. However, coarse-grained structures andagglomerated Al2Cusecond-phase particles considerably decrease the ductility of large 2219 Al–Cu alloy rings manufacturedusing the conventional hot rolling process. In this study, 10%–40% warm rolling deformation was applied to elucidatethe evolution of grain structures, characteristics of the Al2Cusecond-phase particles, and the influencing mechanisms ofductility. The results indicate that increased warm rolling deformation can facilitate dynamic recrystallisation and yield moresub-grains, which leads to the appearance of numerous finer and more equiaxed recrystallised grains after solution heattreatment; however, the homogeneity of the grain structure is decreased. With increased warm rolling deformation, Al2Cusecond-phase particles are more dispersed and more completely fragmented; furthermore, the dispersed and fragmentedAl2Cuparticles are more thoroughly dissolved during solution heat treatment. By the combined action of grain structuresand second-phase particles, the main fracture mode transitions from intergranular fracture into transcrystalline fracture. Thisresults in elongation in the axial and circumferential directions increasing steadily with increased warm rolling deformation;elongation in the radial direction initially increases, and finally decreases due to the appearance of glide planes. Samples thatexperience a warm rolling deformation of 30% exhibit the best overall elongation.
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Yang Yang,Chun Li,Wanfu Zhang,Xueyan Guo,Quanyong Yuan 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.4
A 2D unsteady numerical simulation with dynamic and sliding meshing techniques was conducted to solve the flow around a threeblade Vertical axis wind turbine (VAWT). The circular wakes, strip-like wakes and the shedding vortex structures interact with each other result in an extremely unstable performance. An airfoil with a trailing edge flap, based on the NACA0012 airfoil, has been designed for VAWT to improve flow field around the turbine. Strategy of flap control is applied to regulate the flap angle. The results show that the flapped airfoil has an positive effect on damping trailing edge wake separation, deferring dynamic stall and reducing the oscillating amplitude. The circular wake vortices change into strip vortices during the pitch-up interval of the airfoils. Examination of the flow details around the rotating airfoil indicates that flap control improves the dynamic stall by diminishing the trend of flow separation. Airfoil stall separation has been suppressed since the range of nominal angle of attack is narrowed down by an oscillating flap. Vortices with large intensity over rotational region are reduced by 90 %. The lift coefficient hysteresis loop of flapped airfoil acts as an O type, which represents a more stable unsteady performance. With flap control, the peak of power coefficient has increased by 10 % relative to the full blade VAWT. Obviously, the proposed flapped airfoil design combined with the active flow control significantly has shown the potential to eliminate dynamic stall and improve the aerodynamic performance and operation stability of VAWT.
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Grain Refinement and Thermal Stability of 2219 Aluminum Alloy in the Warm Deformation Process
Xianchang Mao,Youping Yi,Shiquan Huang,Wanfu Guo,Hailin He 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.11
2219 Al alloy is an important material for manufacturing launch vehicles, and its grain structure has a substantial effecton the performance of storage tank transition rings. In this work, warm compression tests (100–350 °C) of 2219 Al alloywere carried out, a grain refinement model of warm deformation was established, and the evolution and thermal stability ofthe static recrystallized grain size D were analyzed. The results showed that static recrystallization is the main mechanismof grain refinement, and that the nucleation rate and grain refining effects were significantly improved by decreasing thedeformation temperatures (T). The established model was found to be accurate, and the predicted and experimental valuesexhibited high degrees of coincidence. When T and the amount of deformation (Δd) were respectively 150 °C and 70%, thevalue of D was reduced from 60 μm to 21 μm. Additionally, when the solution treatment time was increased from 0 to 4 h,there was a slight change in the values of D (high thermal stability) when T was lower than 250 °C and Δd was greater than20%, but they significantly increased when Δd was less than 10%.
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Jianwu Huang,Youping Yi,Shiquan Huang,Fei Dong,Wanfu Guo,Dengliang Tong,Hailin He 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.5
2219 Al–Cu alloy transition rings are widely used in launch vehicles. However, the coarse and agglomerated second-phaseAl2Cuparticles significantly deteriorate the mechanical properties and ductility of 2219 Al–Cu alloy rings manufactured bytraditional thermal deformation processes. In this study, cryogenic deformation (− 190 °C) is applied for the manufacturingof 2219 Al–Cu alloy rings to alleviate this problem. The effects on the evolution of second-phase Al2Cuparticles and themechanical properties of the T8-aged samples were examined in comparison with the results of room-temperature (25 °C)and conventional thermal deformation at 480 °C. The results indicate that cryogenic deformation can effectively producehigh-density dislocations and strongly crush coarse particles, promoting the dissolution of Al2Cuparticles and improving theirdistribution in the Al matrix when combined with subsequent solution treatment and rolling processes. As the deformationtemperature was decreased from 480 to −190 °C, the area fraction of the coarse particles was decreased from 1.55 to 0.47%,while their mean size was decreased from 11.8 to 8.3 μm. Correspondingly, the uniformity and density of the precipitatesafter T8 aging were improved. Thus, the mechanical properties of the T8-aged samples were improved with decreasingdeformation temperatures; the average ultimate tensile strength, yield strength, and elongation were increased by 20 MPa,22 MPa, and 3.1% at room temperature.
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