Effects of Cryogenic Deformation on Second-Phase Al2Cu Particles and Mechanical Properties of 2219 Al–Cu Alloy Rings

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.

Investigations on the influence of control devices to the separation characteristics of a missile from the internal weapons bay

Shiquan Zhu,Zhihua Chen,Hui Zhang,Zhen-gui Huang,Huanhao Zhang 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.5

To ensure the safe separation process of a missile from internal weapons bay, the control device is mounted in front of the internal weapons bay to control the separation process. Based on the coupling of Navier-Stokes (N-S) equations and six-degrees-of-freedom (6DOF) rigid-body motion equations, the separation process of missile under four different conditions (free separation, and rectangle, prism and wedge control) was numerically simulated. The separation process and flow fields were obtained, the aerodynamic parameters and trajectory parameters of four cases compared. Our results show that, the control device can improve the aerodynamic characteristics of the flow field, enhancing the safety of the missile separation. The wedge control device has the best control effect and makes the missile stable, the rectangular and prism control devices have strong bow shock wave and make the pitch angle of the missile large.

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%.

Effects of Warm Rolling Deformation on the Microstructure and Ductility of Large 2219 Al–Cu Alloy Rings

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.

Experimental and Theoretical Investigation on the Forming Limit of 2024-O Aluminum Alloy Sheet at Cryogenic Temperatures

Chenguang Wang,Youping Yi,Shiquan Huang,Fei Dong,Hailin He,Ke Huang,Yanzhen Jia 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.12

Cryogenic forming, a new technology used to manufacture aluminum alloy thin-walled parts, has attracted much attentionin recent years. This work presents an experimental and theoretical study of 2024-O aluminum alloy sheet forming limit atcryogenic temperatures and provides an effective method for accurate prediction of forming limit curves (FLCs) at cryogenictemperatures. Uniaxial tensile experiments at different temperatures were carried out between 20 °C and − 196 °C to obtainthe constitutive equation of the material at cryogenic temperatures. The Marciniak–Kuczynski (M–K) model was used topredict FLCs at cryogenic and room temperatures. The constitutive equation and yield functions are used in the model. Theeffects of different yield criteria (Mises, Hill-48, Barlat89, Gotoh, and Yld2000-2d) on the prediction results of FLC areanalyzed. These prediction results were verified by the Nakazima test, and it was found that the Yld2000-2d yield criterion isthe most accurate for FLC prediction. Finally, the M–K model is combined with this criterion to predict the FLC at differenttemperatures. It was found that the lower the temperature, the higher the FLC curve and the better the sheet formability, andthe increase is more obvious at extremely low temperatures.

Investigation of Quench Sensitivity and Microstructure Evolution During Isothermal Treatment in 2195 Al–Li Alloy

Zhiwu Zhang,Youping Yi,Wen You,Shiquan Huang,Yonglin Guo,Hailin He 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.6

To investigate the quenching sensitivity of the 2195 Al–Li alloy rolled sheet and guide the design of the quenching process,the time–temperature-property (TTP) curves of this material were researched through interrupted quenching experiments. The differential scanning calorimetry (DSC) and transmission electron microscope (TEM) were used to characterize theevolution of precipitates during isothermal treatment. The results of this essay demonstrated that the nose temperature of 2195Al–Li alloy is around 370 °C and the temperature range of quenching sensitivity is 340 °C to 400 °C. The microstructureobservation revealed that the T1particles precipitate and grow rapidly at the temperature from 340 to 400 °C, which is dueto the high nucleation rate of phase and fast solute diffusion kinetics, especially at the nose temperature. The needle-shapedθ′/θ″ and T1particles grow up quickly as the isothermal preservation time prolonged, leading to the decrease of the supersaturatedsolid solution of the matrix. This will reduce the number of the age-induced precipitate and weaken the subsequentage hardening effect. Therefore, the rate of cooling should be increased in the quenching sensitivity range (340–400 °C) toinhibit the precipitation of the second phase and obtain excellent mechanical properties. While in other temperature ranges,the cooling rate should be decreased appropriately to reduce residual stress. The appropriate average cooling rate is recommendedto be around 13 °C s−1 at the temperature from 340 to 400 °C.

Influence of Forging Temperature on the Microstructures and Mechanical Properties of a Multi-Directionally Forged Al–Cu–Li Alloy

Hailin He,Kanghua Chen,Youping Yi,Wen You,Yonglin Guo,Bingxiang Wang,Jiaguo Tang,Research Institute of Light Alloy, Central South University,Shiquan Huang 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.2

Optimization of forging process to improve the microstructure and mechanical properties of 2195 Al–Cu–Li alloy forgingsis an urgent issue. In this study, a homogenized 2195 alloy ingot was subjected to multi-directional forging (MDF), annealing,and forging at 500 °C, 420 °C, and 240 °C with a 50% reduction in cross-sectional area, followed by a T8 heat treatment(involving solution, quenching, cold compression, and aging). The microstructural evolution during the process and thefinal mechanical properties in three orthogonal directions were examined. The results showed that the grain structures ofthe alloy were significantly refined after MDF by dynamic recrystallization (DRX), but the structure was thermally unstableand formed coarse grains during subsequent annealing by static recrystallization (SRX). The T8-treated samples forged at500 °C, 420 °C, and 240 °C obtained fine and uniform grain structures by DRX, inhomogeneous grain structures by partialSRX, and uniform, equiaxed grain structures by full SRX, respectively. The average grain size of the forging increased withdecreasing forging temperature because more significant SRX occurred for the forging that was deformed at lower temperatures. The grain structures had minimal influence on precipitation behavior and strength but had a significant influence onelongation. The fine and uniform grain structures improved the elongation; whereas, the inhomogeneous grain structures,which contained extremely large grains, significantly deteriorated the elongation. The uniform, equiaxed grain structuresdecreased the anisotropy in three orthogonal directions and maintained fine elongation even though the average grain sizeof the forging was the largest.