2016 Vol. 36, No. 6

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2016, 36(6): .
First-principle Calculations of Mechanical Properties of Al2Cu, Al2CuMg and MgZn2 Intermetallics in High Strength Aluminum Alloys
Fei LIAO, Shitong FAN, Yunlai DENG, Jin ZHANG
2016, 36(6): 1-8.
Structural stabilities, mechanical properties and electronic structures of Al2Cu, Al2CuMg and MgZn2 intermetallics in Al-Zn-Mg-Cu aluminum alloys were determined from the first-principle calculations by VASP based on the density functional theory. The results show that the cohesive energy (Ecoh) decreases in the order MgZn2 > Al2CuMg > Al2Cu, whereas the formation enthalpy (ΔH) decreases in the order MgZn2 > Al2Cu > Al2CuMg. Al2Cu can act as a strengthening phase for its ductile and high Young's modulus. The Al2CuMg phase exhibits elastic anisotropy and may act as a crack initiation point. MgZn2 has good plasticity and low melting point, which is the main strengthening phase in the Al-Zn-Mg-Cu aluminum alloys. Metallic bonding mode coexists with a fractional ionic interaction in Al2Cu, Al2CuMg and MgZn2, and that improves the structural stability. In order to improve the alloys' performance further, the generation of MgZn2 phase should be promoted by increasing Zn content while Mg and Cu contents are decreased properly.
Thermal Simulation Test of AA-FGH95 Superalloy
Xuqing WANG, Mincong ZHANG, Junpeng LUO, Zichao PENG, Junying SHENG, Jian YAN
2016, 36(6): 9-14.
The hot deformation behavior of AA-FGH95 superalloy was investigated by hot compressive tests on Gleeble-1500D thermal simulation test machine in different temperatures and strain rates. The true stress-strain curves were obtained, and based on the deformation data, the constitutive equation and processing map of FGH95 superalloy were built. The deformation active energy of AA-FGH95 is Q=695.78 kJ/mol. The results show that the simulated maximum stresses are in agreement with the experimental data, and the average error is about 6%. Based on the processing map, the safety processing parameters of 1070-1100℃ and 0.01-0.001 s-1 are confirmed. When the temperature reached 1100℃, the maximum strain rate increased to 0.5 s-1.
Inhomogeneity of Microstructure and Properties of 7085-T651 Aluminum Alloy Extra-thick Plate
Chengbo LI, Kezhun HE, Fengxuan SONG, Shengdan LIU, Shengqiang CAO, Xinming ZHANG
2016, 36(6): 15-22.
Inhomogeneity of microstructure and properties of 7085-T651 aluminum alloy extra-thick plate were investigated by tensile properties, exfoliation corrosion, optical microscopy(OM), composition analysis, scanning electron microscopy(SEM),differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The results show that the microstructure, tensile property and exfoliation corrosion in different layers of 7085-T651 aluminum alloy of 110 mm thick are inhomogeneous. For the 1/4 thickness layer, the tensile strength is the minimum, 540 MPa, and the resistance to exfoliation corrosion of this layer is the worst, with exfoliation corrosion classification of EB. For the core layer, the tensile strength is the maximum, 580 MPa. The resistance to exfoliation corrosion of the surface layer is the best, with exfoliation corrosion classification of EA. For the 1/4 thickness layer, it has the largest recrystallized fraction up to about 47.7% and the grain size is about 105 μm; there are equilibrium phase particles precipitated on grain boundaries or within grains; the size of aging precipitates is small; and thus both mechanical properties and resistance to exfoliation corrosion are the worst. For the core layer, it has the smallest recrystallized fraction of about 14.8% and there are a large amount of sub-grains; the fraction of residual phase Al7Cu2Fe almost reaches up to about 1.43%; the size of the equilibrium phase on grain boundaries, the size of aging precipitates and the width of PFZ are large, and therefore good mechanical properties and bad resistance to exfoliation corrosion are obtained.
Superplastic Deformation of TC6 Alloy
Ling DING, Zhilu WANG, Qianjiang SUN, Jian CHEN, Gaochao WANG
2016, 36(6): 23-28.
The superplastic tensile tests of TC6 alloy were conducted in the temperature range of 800-900℃ by using the maximum m value superplasticity deformation (Max m SPD) method and the constant strain rate deformation method at the strain rate range of 0.0001-0.1 s-1. The stress-strain curve of the tensile tests was obtained and the microstructure near the fracture were analyzed by metallographic microscope. The result shows that the superplasticity of TC6 alloy is excellent, and the elongation increases first and then decreases with the increase of strain rate or temperature. When the temperature is 850℃ and strain rate is 0.001 s-1 at constant stain rate tensile tests, the elongation reaches up to 993%. However, the elongation using Max m SPD method at 850℃ is 1353%. It is shown that the material can achieve better superplasticity by using Max m SPD tensile compared to constant stain rate tensile under the same temperature. The superplastic deformation of TC6 alloy can enhance the dynamic recrystallization behavior significantly, the dynamic recrystallization behavior is promoted when strain rate and temperature are increased.
Mechanism of Grain Refinement of Pure Titanium by Friction Stir Welding
Fuyang GAO, Yan YU, Zhiying LIU, Peng JIANG, Yufan GUO
2016, 36(6): 29-34.
Reliable connection of 5 mm pure titanium was achieved by friction stir welding, and the microstructure of the welded joint was studied by optical microscopy(OM), scanning electron microscopy(SEM) and transmission electron microscopy(TEM). The results show that the welded area can be divided into the weld nugget zone, thermo-mechanically affected zone, heat affected zone and base metal. According to the structure of each district, the dynamic recrystallization process of pure titanium during friction stir welding was analyzed. Because of high stacking fault energy, dislocations generated by friction stir of titanium cannot be completely decomposed. When there is a hindrance, it can continue to move only through slip and climb. By the effect of friction stir repeatedly, the dislocation tangles are accumulated and piled up, so the dislocation density continuously increases, which will produce new grain boundaries and form fine grains, and then the grain refinement is achieved.
Effect of Heat Treatment on Microstructure and Hardness of 9Cr13Mo3Co3Nb2V Steel
Dengping HUO, Zhikai LIANG
2016, 36(6): 35-39.
Effect of heat treatment on the microstructure and hardness of 9Cr13Mo3Co3Nb2V steel was studied systematically by metallographic examination and hardness testing. The results show that after quenching, cryogenic treatment and multiple tempering, the retained austenite of 9Cr13Mo3Co3Nb2V steel is adequately transformed into tempered martensite, and the significant secondary hardening effect is brought. Consequently the steel gains stable microstructure and high hardness. Secondary carbide begins to precipitate and the secondary hardening effect emerges when the tempering temperature is above 350℃, and the tempering hardness reaches the maximum value when tempering temperature range is from 480℃ to 520℃.
Effect of High Velocity Arc Spraying Parameters on Properties of FeNiCrAl Coating
Haoliang TIAN, Changliang WANG, Zhihui TANG, Shicheng WEI, Binshi XU, Minhong QUE
2016, 36(6): 40-47.
FeNiCrAl coating is a kind of surface wear resistant material for shaft parts. Microstructure, adhesive strength, phase composition and microhardness were analyzed in order to study the influence mechanism of spraying parameters on coating properties. The relation among the spraying current, coating microstructure and cohesive strength was studied in detail. The results shown that the spraying current is very important to obtain the dense coating (porosity of 8.76%) with cohesive strength of 52.3 MPa and an excellent coating is prepared by spraying current 200 A, spraying voltage 34 V and spraying distance 160 mm. The hardness of coating is 626 HV0.1 and about 1.6 times as that of the matrix. The effective mechanism is relevant to the scatter distribution of the Fe-Al intermetallic compound and Cr0.19Fe0.1Ni0.11 solution in the coating.
Influence and Simulation Study of Surface Coating Damage on Pitting Corrosion of 7B04 Aluminum Alloy
Chenguang WANG, Yueliang CHEN, Yong ZHANG, Guixue BIAN
2016, 36(6): 48-53.
Self-corrosion and pitting corrosion of 7B04 aluminum alloy at different environment conditions were studied by electrochemical test with simulating surface coating damage on 7B04 aluminum alloy. The forming conditions of pitting corrosion after contacting 7B04 aluminum alloy with TA15 titanium alloy were analyzed by finite element method which was based on the mathematical model of galvanic corrosion. The results indicate that the pitting potential of 7B04 aluminum alloy is influenced by Cl- concentration and pH value. Pitting corrosion of 7B04 aluminum alloy in self-corrosion condition can occur in neutral solution(mass fraction of NaCl>5%) or in acidic solution(mass fraction of NaCl=3.5%). The potential rises when 7B04 aluminum alloy contacts with TA15 titanium alloy which results in the occurrence probability of pitting corrosion. The occurrence probability of pitting corrosion is increased. The pitting corrosion of 7B04 aluminum alloy initiates and propagates when the area ratio of cathode and anode is greater than 40 in neutral solution(mass fraction of NaCl=3.5%). The potential of 7B04 aluminum alloy decreases slowly with the increase of the distance between cathode and anode, and the decline of the potential is not over 2 mV at distance within 10 m.
Influence of Acid Etching on Wettability of Ion-exchanged Aluminosilicate Float Glass
Xiaoyu LI, Liangbao JIANG, Lei LI, Yue YAN
2016, 36(6): 54-60.
The influence of acid etching time on wettability of ion-exchanged aluminosilicate float glass was investigated. The contact angle, roughness and surface composition were measured. The results show that the contact angle increases to a maximum value in the first 7 min and then decreases with the corrosion time. The main reason that cause the change of the contact angle is the change of surface roughness and the content of fluorine atom. The contact angle on the tin side is always larger than that on the air side which is caused by the tin ions on the tin side.
Tribological Investigation of SiC/Al Composite under Dry Sliding Friction
Liquan DAI, Guoqiu HE, Shiquan LÜ, Yun YE, Xiaoshan LIU, Qi LU
2016, 36(6): 61-67.
The effect of sliding distances on aluminum matrix composite reinforced by silicon carbide particle with volume fraction of 9% was investigated. Friction behavior and wear resistance of the composite with distances of 5000 r, 10000 r and 20000 r were studied under dry sliding conditions of the same speed and load(200 r/min, 45 N). The results show that the friction coefficient in long-range sliding process displays three stages:wearing zone, stable zone and accelerating zone. The matrix surface produces severe adhesion because of the rising temperature and then leads plastic areas, in which both friction coefficient and wear rate are increased.
Effect of Twice Hole Expansion on Fatigue Property of Ti1023 Alloy
Guangyong YANG, Meng LI, Yinggang SONG, Guoxin LU, Lijun HUANG
2016, 36(6): 68-73.
The property of the surface layer of twice hole expansion Ti1023 alloy was analyzed by TEM, X-ray and roughness tester, and the strengthen mechanism of the bushing hole expansion was discussed. The results indicate that the roughness(Ra1.722→0.349 μm), hardness(Hv32→38) and residual stress distribution of the hole are improved by twice hole expansion techniques,and the fretting wear fatigue(fatigue limits 385→619MPa) of Ti1023 alloy is improved.
Preparation of Ag/TiO2/ITO UV Detector and Its Photoelectronic Properties
Songyan DAI, Hongfei QI, Dabo LIU, Lejin TENG, Fei LUO, Ye TIAN, Dongsheng CHEN
2016, 36(6): 74-78.
TiO2-based UV detectors with Ag antidot/TiO2/ITO sandwich structure were prepared by RF magnetron sputtering and colloidal crystal template technology. The microstructure and photoelectronic properties of the UV detectors were investigated by SEM, XRD, four point probe and semiconductor parameter instrument. The experimental results show that pore size of Ag antidot has an obvious effect on the photoelectronic properties of the detectors. With the increase of pore size, the dark current increases and the response time is prolonged, while the photocurrent is increased at first, then is decreased. Meanwhile, it is found that photoelectronic properties are optimum when the pore size is 4.2 μm. Antidot array electrodes with large pore size possess higher electrical conductivity, lower ultraviolet transmittance and higher recombination probability of electron-hole pair. Therefore, the pore size variation exhibits significant effluence on the photoelectronic properties of the UV detector.
Damage Effects of Electron Irradiation with Different Energy on Mechanical Properties of Polyethylene Heat-shrinkable Sleeves
Yuming LIU, Chunqing ZHAO, Man LI, Kai ZHANG, Zicai SHEN
2016, 36(6): 79-85.
Damage effects of electron irradiation with different energy on mechanical properties of polyethylene heat-shrinkable sleeves were studied by irradiating the sleeves with 45 keV, 1 MeV and 2 MeV electrons respectively. The mechanical property degradations of the sleeves before and after radiations were present. X-ray photoelectron spectra (XPS), scanning electronic microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were used to analyze the element contents, the morphologies and the molecular structures of the samples to study the damage mechanism of the sleeves. A degradation model for the changes of the mechanical properties of the sleeves in electron radiation environment was proposed. It is shown that the increase of irradiation degradation of the polyethylene causes the sleeves' mechanical properties. For the penetration depth of different energy electrons in polyethylene is different, only a shallow layer the sleeves is affected by 45 keV energy electrons, while 1 MeV and 2 MeV energy electrons are penetrated the sleeves and cause the sleeves great damage. The mechanical properties of the sleeves are decreased by about 30% to 40% after 45 keV energy electron irradiation, and decreased by about 100% after 1 MeV and 2 MeV energy electron irradiation.
Effects of Starch on Properties of Alumina-based Ceramic Cores
Fengguang LI, Shiyan TANG, Fuchu LIU, Zitian FAN
2016, 36(6): 86-91.
In order to improve the poor leachability of alumina-based ceramic cores, different amount of starch was added to the specimens as pore former. Alumina-based ceramic cores were prepared by hot injection technology using corundum powder as base material, paraffin wax and beeswax as plasticizer, silica powder and magnesium oxide powder as mineralizing agent, wherein the parameters of the hot injection process were as follows:temperature of the slurry was 90℃, hot injection pressure was 0.5 MPa and holding time was 25 s. The effects of starch content on the properties of alumina-based ceramic cores were studied and discussed. The results indicate that during sintering period, the loss of starch in the specimens makes porosity of the alumina-based ceramic cores increase. When starch content increases, the room-temperature flexural strength of the ceramic cores reduces and the apparent porosity increases; the volatile solvent increases and the bulk density decreases. After being sintered at 1560℃ for 2.5 h, room-temperature flexural strength of the alumina-based ceramic cores with starch content of 8%(mass fraction) is 24.8 MPa, apparent porosity is 47.98% when the volatile solvent is 1.92 g/h and bulk density is 1.88 g/cm3, the complex properties are optimal.
Feasibility of Penetrant Testing on Surface Axial-Radial Cracks of GH4169 Super Alloy Turbine Disk
Haiyan QIAO, Xuedong REN, Yiwei SHI, Chunhu TAO
2016, 36(6): 92-96.
The post emulsifiable and water-washable fluorescent penetrant testing were carried out with ZL-27A and ZL67 respectively. Ultrasonic cleaning by detergent were used for 30 minutes before penetrant. The parts were immersed and drained for 60 minutes. The macroscopic and microscopic characteristics of cracks were researched using the split mirror and scanning electron microscope. The results show that the outgrowth of high temperature oxidation plugs up the forging cracks. Thus the penetrant testing is not effective in detecting this type of cracks.