2017 Vol.37(5)

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2017, 37(5): 0-0.
[Abstract](81) [PDF 877KB](8)
Molecular Dynamics Simulation Connections and Mechanical Properties of Cu/Al Explosion Shock Interface
Yan ZHANG, Wanshen XIAO
2017, 37(5): 1-6. doi: 10.11868/j.issn.1005-5053.2017.000014
[Abstract](267) [FullText HTML] (65) [PDF 3842KB](5)
Based on the molecular dynamics (MD) method, transient explosive welding process of Cu/Al junction point was revealed from the microscopic aspect, and mechanical properties and machinability of the Cu/Al nano-weldment were studied. The results show that kinetic energy is converted into internal energy in the system after the collision. The heterogeneous atoms penetrate into each other and the diffusion effect of copper atoms is better than aluminium atoms. The elastic modulus of the nano-weldment is 64.56 GPa, which is between copper's and aluminium's; however, its yield strength is less than those of the two monocrystals. Interactions between dislocations and disordered lattices cause the stress strengthening in the plastic deformation stage, which causes that the stress values of the weldment is larger than those of the two monocrystals. This strengthening mechanism is also reflected in the cutting process, and the weldment has the highest average cutting force 117.80 nN. A mass of dislocations nucleate in the disordered lattice areas of the weldment, and they spread at 45¯ to the cutting direction. However, dislocations pile up when their propagation is hindered by the disordered lattices and interface, which leads to the work hardening effect.
Microstructure and Mechanical Property of Aluminum Alloy Plate AA 7055
Junzhou CHEN, Shenglong DAI, Liang ZHEN
2017, 37(5): 7-14. doi: 10.11868/j.issn.1005-5053.2016.000176
[Abstract](282) [FullText HTML] (48) [PDF 7073KB](8)
Through-thickness microstructure and mechanical property of AA 7055-T7751 aluminum alloy plate were investigated by using electron backscattered diffraction (EBSD), transmission electron microscope (TEM) and small angle X-ray scattering(SAXS). The results indicate an inhomogeneous distribution of microstructure through the thickness. The degree of recrystallization decreases gradually from 69% to 19.1%, as deepening from the surface to the center of the plate. The size of subgrains decreases from 10 μm at the surface to around 2 μm at the center. Strong texture of rolling type is observed near the center but the intensity decreases gradually as nearing the surface and the shear texture becomes the dominant. High density of plate-like η' phases are observed in the alloy, indicating the sufficient precipitation. η' precipitates of this condition are around 3.7 nm in radius, 1-3 nm in thickness and are found coherent with the Al matrix with a coherent strain of 0.0133, showing a strong strengthening effect. The heterogeneity in grain scale does not influence the distribution and the morphology of precipitates. The yield strength (L direction) varies linearly along the thickness direction of the plate, fitting an equation of σy=-38.7S+604.8 (0≤S≤1). The variation of yield strength is related to the heterogeneity of grain structure.
Interphase Constituent of Laminated Composites Ti46Zr26Cu17Ni11
Bingtong XU, Rongxia ZHANG, Wei WU, Fulong CHEN
2017, 37(5): 15-21. doi: 10.11868/j.issn.1005-5053.2016.000172
[Abstract](274) [FullText HTML] (53) [PDF 3772KB](3)
Thermal analysis of the Ti46Zr26Cu17Ni11 amorphous ribbon prepared by melt spinning was conducted by using DSC. Accordingly the amorphous alloy was treated by vacuum heat treatment at 693 K ( < Tg), 753 K (Tg-Tx1) and 813 K (> Tx1) for different time to analyze the crystallization behavior. Taking Ti46Zr26Cu17Ni11 amorphous alloy, TA2 and pure Al as raw materials, laminated composites were fabricated by Gleeble-3500 thermal simulator at 873 K, 10 MPa and 8 h. The phase composition, precipitation order and properties of interface layers were investigated by SEM, TEM, micro hardness tester, combined thermodynamics and element diffusion theory. The results indicate that the glass transition temperature Tg of Ti46Zr26Cu17Ni11 amorphous is 720 K and the initial crystallization temperature Tx1 is 788 K. The I phase is crystallized from the amorphous at first, followed by a ternary or quaternary Laves phase and a TiNi phase precipited. After hot pressing, the interface between pure Al and crystallization layer is divided into two parts, which are Al3Ni with small thickness and Al3(Ti0.6Zr0.4) with fine grain and uniform microstructure. The interfaces are straight and there are no defects, with a thickness ratio of about 6.5:1 compared with interface layer between pure Ti with Al. The hardness of Al3(Ti0.6Zr0.4) and Al3Ti are 564.2HV and 579.8HV respectively. The plasticity of Al3(Ti0.6Zr0.4) layer is better.
Thermo-physical Properties and Mechanical Properties of Burn-resistant Titanium Alloy Ti40
Yunjin LAI, Pingxiang ZHANG, Saifei ZHANG, Kaixuan WANG, Qiang LEI, Shewei XIN, Yongjian ZHENG, Qiming TAN
2017, 37(5): 22-28. doi: 10.11868/j.issn.1005-5053.2016.000159
[Abstract](276) [FullText HTML] (35) [PDF 2459KB](3)
As a functional material of burn-resistant titanium alloy, the physical properties of Ti40 alloy were first reported. The chemical compositions of Ti40 alloy ingots by VAR were uniform. The microstructures of Ti40 alloy slab manufactured by HEFF+WPF were uniform. The results show that the room temperature tensile strength of Ti40 alloy is 950 MPa degree. The properties of high temperature heat exposure, creep resistance and lasting time are good at 500 ℃. In the range from room temperature to 600 ℃, Young's modulus and shear modulus are decreased linearly with increasing the temperature, Poisson's ratio is increases slowly as the temperature rises, and linear thermal expansion coefficient and average linear expansion coefficient is increase as the temperature rises.
Infrared Emissivities and Microwave Absorption Properties of Perovskite La1-xBaxMnO3(0≤x≤0.5)
Jiawei LIU, Jianjiang WANG, Baocai XU, Yongshen HOU, Haitao GAO
2017, 37(5): 29-34. doi: 10.11868/j.issn.1005-5053.2017.000031
[Abstract](204) [FullText HTML] (53) [PDF 2425KB](9)
La1-xBaxMnO3(0≤x≤0.5) with perovskite-type structure as a microwave and infrared multi-functional material has been successfully prepared by sol-gel method. The effects of Ba incorporation on the stucture, electrical conductivity, infrared emissivity and microwave-absorbing properties were investigated in detail by XRD, 4-point probes resistivity measurement system, IR-2 infrared-emissivity analyzer and vector network analyzer. XRD results show that the perovskite structure of LaMnO3 is hardly changed when the doping concentration (x) of Ba2+ is less than or equal to 0.5 and when the doping concentration increases, the lattice distortion increases. The incorporation of Ba in LaMnO3 leads to the decrease of electrical conductivity, while the infrared emissivities are decreased. Moreover, microwave-absorbing properties in the frequency range of 2-18 GHz are sensitive to Ba content. The optimal reflection loss calculated from the measured permittivity and permeability is 32 dB at 10.8 GHz with a thickness of 2.0 mm when the doping amount of Ba2+ is 0.3. It is possible to make Ba-doped lanthanum manganites achieve compatible camouflage capability for radar and infrared wave-band.
Effect of Rotation Rate on Microstructure and Properties of Friction Stir Welded Joints of Al/Cu Clad Plates
Ke QIAO, Kuaishe WANG, Wen WANG, Nan WU, Tianqi LI, Wei GUO
2017, 37(5): 35-40. doi: 10.11868/j.issn.1005-5053.2016.000123
[Abstract](256) [FullText HTML] (42) [PDF 3706KB](6)
Al/Cu clad plates were joined by friction stir welding (FSW), and the effect of rotation rate on microstructure and mechanical properties of joints was investigated. The results show that the laminar structure of aluminum and copper is generated in the weld. With increase the of rotation rate, the grain sizes of aluminum and copper are increased respectively. The average microhardness of the Al/Cu plates exceeds that of the as-received metal of 33.0 HV, and ultimate tensile strength is 127.21 MPa in the nugget zone when rotation rate is 1180 r/min. The microhardness of copper in the nugget zone is 99.7 HV, reached 82.05% of the microhardness of received metal, and void defect is main reason responsible for the decrease of mechanical properties of joints.
Performances of Fatigue Crack Growth for Aluminum Friction Stir Welds and Base Materials
Hongshan QIN, Xinqi YANG
2017, 37(5): 41-47. doi: 10.11868/j.issn.1005-5053.2016.000125
[Abstract](186) [FullText HTML] (56) [PDF 5134KB](7)
The fatigue crack propagation performances for friction stir welded AA7075-T6 and LC4CS (a Chinese brand aluminum alloy similar to AA7075-T6) joints and their corresponding base materials have been investigated. It was found that the fatigue crack growth rates (da/dN) for AA7075-T6 welded joints along the weld center line, advanced and retracted side regions are all slower than that of LC4CS alloy, but the da/dN values along the perpendicular direction of weld for both alloys are the approximate same values. The da/dN along the weld center line is the lowest, the second is that of retracted and advanced side and the da/dN along the vertical direction of weld is the highest. The da/dN of AA7075-T6 FS welds is slower at the range of low load ΔK compared to base material, but for the range of high ΔK, the da/dN of AA7075-T6 base material is slower. The fracture surface of crack growth along the weld center line is obviously different from that of advanced and retracted side regions and base materials. The typical fatigue striations can be observed across the surface of fatigue crack stable growth for advanced and retracted side regions and base material, but not any fatigue striation can be found along the fatigue fracture surface of weld center line. The resistance of fatigue crack propagation for AA7075-T6 FS welds is better than that of LC4CS welds and the fine and equiaxed grains at nugget region have no good benefit to reduce the da/dN of AA7075-T6 and LC4CS FS welds.
Effect of Pretreatment Process on Properties of Aerospace Al-Li Alloy Sulfuric Acid Anodic Film
Baohong HAN, Qi ZHANG, Zhihua SUN, Chen LUO, Bo YU, Zhihui TANG
2017, 37(5): 48-54. doi: 10.11868/j.issn.1005-5053.2017.00002
[Abstract](125) [FullText HTML] (45) [PDF 3176KB](8)
Aiming at a new Al-Li alloy, by the use of optical microscope, SEM and EDS, we analyzed the effects of different pretreatment processes including alkali corrosion and tri-acid deoxidation on the appearance, corrosion resistance and fatigue properties of sulfuric acid anodic oxide coatings. which provided a theoretical basis for the design, selection, application and surface protection of Al-Li alloy structural components. We found that the corrosion degree of the Al-Li alloy surface by alkali corrosion was deeper than that of the tri-acid deoxidation process. The corrosion resistance at the grain boundary was poor, so the mesh surface morphology of the anodic oxide film was formed. The fatigue life of the samples treated with alkali corrosion was lower than that of the tr-ioxic acid treatment, the fatigue life of the samples subjected to sulfuric acid anodic oxidation is different. The effect of different pretreatment on the corrosion resistance of the sulfuric acid anodic oxide layer of Al-Li alloy is not significant.
Effect of Liquid Natural Rubber on Properties of Natural Rubber/Silica Composite Prepared by Wet Compounding
Fan HE, Xin JI, Tianyuan YUAN, Shuangquan LIAO
2017, 37(5): 55-62. doi: 10.11868/j.issn.1005-5053.2017.000004
[Abstract](234) [FullText HTML] (33) [PDF 5052KB](7)
Natural rubber/silica composites (NR/SiO2) was prepared by wet compounding technology with liquid natural rubber(LNR) as compatibilizer. Curing characteristics, processing properties, filler dispersion and mechanical properties were investigated.The results showe that the optimum cure time is decreased 4.16 min, the processing properties of the composites were improved with the incorporation of LNR; better silica dispersion in NR in presence of LNR; the when silica is 60 phr, tensile strength and tear strength of the vulcanizates were increase 25.73% and 66.59%respectively; as far as the dynamic mechanical properties are concerned, the W(NR/SiO2) composites with LNR owned a combination of high wet skid resistance and low rolling resistance. It is revealed that LNR has better compatibility, which is attributed to LNR reaction with both NR and SiO2 to form compatibilizing interface.
BA9916-Ⅱ/CCF300 Composite Stiffened Plate Hygroscopic Characteristics
Xianhang ZHANG, Shulin LI, fei Chang, Lekun LI, Junjie YIN, Xiangfei TAN, Yao XIAO
2017, 37(5): 63-69. doi: 10.11868/j.issn.1005-5053.2017.000038
[Abstract](213) [FullText HTML] (59) [PDF 3094KB](3)
In order to study the moisture absorption characteristics of BA9916-Ⅱ/CCF300 composite stiffeners, Carrying out the moisture absorption experiment in 70℃/85%RH hot and humid environment. Fick moisture absorption model based on thethickness partition is put forward.The mass diffusion model is used for moisture absorption behavior of the finite element simulation.The result show that: Moisture absorption model is put forward based on the thickness of fick moisture absorption model can better describe the moisture absorption behavior of the structure of the type, the analysis is of the high precision; But as a result of composite stiffened plate's staging phenomenon of moisture absorption. There is a certain deviation of Fick moisture absorption model on the structure hygroscopic behavior later described; The Hygroscopic power curve and water concentration distribution results of the finite element simulation is verified the rationality of the hygroscopic model based on thickness division, better expressing the real process of moisture absorption and moisture distribution.
Preparation of Silicon Rubber/2, 2'-(3-methyl-4-dihydro-1, 3, 2-benzoxazine)Propane Ablative-resistant Composites and Its Ablative Structure
Yimin DONG, Zhengshuai YIN, Yong LI
2017, 37(5): 70-76. doi: 10.11868/j.issn.1005-5053.2016.000169
[Abstract](193) [FullText HTML] (38) [PDF 3471KB](7)
Benzoxazine resin is a new generation of anti-ablation resin with high char yield and high-temperature oxidation resistance. Using high temperature vulcanized silicon rubber as ablation resistance matrix and 2, 2'-(3-methyl-4-dihydro-1, 3, 2-benzoxazine)propane as anti-ablation resin, silicon rubber/polybenzoxazine anti-ablation composite was prepared by blending method. The mechanical properties were tested, and the ablation structure and the composition of the composite were investigated by DSC, SEM, FT-IR and Raman.Experimental results show that the polybenzoxazine resin can improve the ablation resistance property of silicone rubber composite. The composite has good ablation resistance and mechanical property when the addition of polybenzoxazine resin reaches 20 phr. After ablated by oxygen acetylene flame, the ablation layer is divided into three obvious layers as surface ceramic layer, pyrolysis carbonization layer and base layer. The surface ceramic layer formed in the progress of ablation plays a positive role in the ablation property of the composite material.
High Temperature Low Cycle Fatigue Properties and Failure Mechanism of a TiAl Alloy
Chengli DONG, Huichen YU, Zehui JIAO, Fantao KONG, Yuyong CHEN
2017, 37(5): 77-82. doi: 10.11868/j.issn.1005-5053.2017.000075
[Abstract](304) [FullText HTML] (37) [PDF 4337KB](4)
Total strain range controlled low cycle fatigue (LCF) experiments were conducted at 750 ℃ to investigate the effects of the duplex and fully lamellar microstructure on fatigue behavior and life of a TiAl alloy, and the total strain range-life equation was employed to predict LCF life of the alloy. The results show that the mean stress produced at hysteresis loop of TiAl alloy with DP is less that of TiAl alloy with FL at the same temperature and applied strain. The total strain range-life equation is able to predict the fatigue life of the alloy, and the predicted life is located between ±2 scatter band of the experimental life. In addition, the fatigue source of TiAl alloy with DP is located near center of the specimen while that of TiAl alloy with FL is located on subsurface of the specimen, and the failure mechanisms are obviously different between the two types of the TiAl alloy.
Prior Particle Boundary of PM FGH96 Superalloy and Its In-situ High-cycle Fatigue at Elevated Temperature
Jingyi ZHOU, Changkui LIU, Wenxia ZHAO, Zhen ZHENG, Yan ZHONG
2017, 37(5): 83-89. doi: 10.11868/j.issn.1005-5053.2016.000130
[Abstract](238) [FullText HTML] (50) [PDF 8878KB](10)
The influence of different grades of prior particle boundary (PPB) in PM FGH96 superalloy during high-cycle fatigue test at 550 ℃ was investigated by the in-situ fatigue test in SEM. The results show that the PPB in P/M FGH96 superalloys by plasma rotating electrode process (PREP) + hot isostatic press (HIP) is constituted of large size γ' and carbide. There are no significant effect on the initiation and propagation of high cycle fatigue crack in different grades of PPB. Crack initiation is initiated in the grain interior, and the propagation is transgranular or intergranular, which is influenced by the angle between the grain boundary and the stress axis. In the fast crack growth zone and the transient zone, the fracture characteristics of serious grade PPB FGH96 superalloy are transgranular and along PPB globular surfaces.
Comparison Study on Interlaminar Shear Strength Testing Methods of CFRP under Hygrothermal Aging Conditions
Chao SHUANG, Lulu LIU, Zhenhua ZHAO, Yupu GUAN, Wei CHEN
2017, 37(5): 90-98. doi: 10.11868/j.issn.1005-5053.2017.000009
[Abstract](168) [FullText HTML] (43) [PDF 5086KB](8)
The effects of hygrothermal aging on the interlaminar shear strength of T700/TDE-85 composites were studied by short-beam method and double-incision method. The relationship between moisture absorption and aging time was discussed, and the fracture surface morphology was analyzed. The experimental results show that the moisture absorption law of the two specimens is in accordance with Fickle's second law, but the saturated moisture absorption rate and moisture absorption time are different. The moisture absorption rates and saturated moisture absorption rates of the specimens of double incision method are higher than those of the short beam method. The interlaminar strength of double-incision test is more obvious than that of short-beam under hygrothermal aging conditions, the interlaminar shear strength retention rates of short-beam method's specimens are 74.5%, 61.0%, 53.2% and 50.6% at 500 h intervals and the interlaminar shear strength retention rates of double-incision method's specimens are 60.9%, 38.3%, 42.6% and 33.0% at 500 h intervals. The failure mode of short-beam specimen is more complicated than that of double-incision with the increase of hygrothermal aging time.

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