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      20 December 2012, Volume 0 Issue 12 Previous Issue    Next Issue
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    Surface Protection of Friction Stir Welding Joint for AZ31 Magnesium Alloy Coated by Microarc Oxidation
    XUE Wen-bin, CHEN Ting-fang, LI Yong-liang, ZOU Zhi-feng, LIU Xiao-long, ZHAO Yan-hua
    2012, 0 (12): 1-6.  
    Abstract ( 637 ( PDF (3233KB)( 596 Citation
    A uniform ceramic coating on friction stir welding (FSW) joint of AZ31 magnesium alloy was fabricated by microarc oxidation (MAO) in silicate electrolyte. Microstructure, phase constituent and microhardness profile of the MAO coating at the different zones of FSW joint were analyzed. The influence of microarc oxidation surface treatment on corrosion behaviors of FSW joint was evaluated by immersion and potentiodynamic polarization tests. The results show that hardness of stir zone is higher than that of base alloy, but the hardness of heat-affected zone is lower than that of base alloy. However, the microhardness of MAO coating at different zones of FSW joint is the same, which is about seven times higher than that of AZ31 base alloy. After immersion test in 3.5%NaCl(mass fraction) solution, the serious pitting corrosion on heat-affected zone takes place, but no pitting corrosion is observed on the MAO coating surface. In addition, the heat-affected zone of FSW joint has a lower corrosion potential and higher corrosion current density, but the corrosion current density of MAO coating at different zones is very close, which is much lower than that of bare AZ31 magnesium alloy. So the MAO surface treatment can significantly improve the corrosion resistance of FSW joint of AZ31 magnesium alloy.
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    Research and Revise on Constitutive Equation of 7050-T7451 Aluminum Alloy in High Strain Rate and High Temperature Condition
    HUA Yong-zhi, GUAN Li-wen, LIU Xin-jun, CUI Hai-long
    2012, 0 (12): 7-13.  
    Abstract ( 749 ( PDF (2036KB)( 579 Citation
    The flow stress behavior of 7050-T7451 aluminum alloy at high temperature and high strain rate was investigated by split Hopkinson pressure bar (SHPB) and quasi-static test system. The strain hardening parameters were obtained by the quasi-static test experiment data.The strain rate hardening parameter at various strain rates (400-2500s-1) and room temperature,and the thermal softening parameter at various temperatures where strain rate is 2500s-1,were obtained by the split Hopkinson pressure bar experiment data.A new thermal softening equation is proposed to revise the Johnson-Cook constitutive equation ,where the a quintic polynomial equation is choosed as the new thermal softening equation.According to the comparison between predict curves and experiment curves of stress-strain at various temperatures,the modified constitutive equation can fit the experiment date well.
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    Early Failure of Shaft Bearings
    GUAN Wen-xiu, JIANG Tao, TAO Chun-hu, ZHANG Bing, LIU De-lin, HU Chun-yan
    2012, 0 (12): 14-20.  
    Abstract ( 893 ( PDF (2827KB)( 734 Citation
    Based on analyzing some classic early failure cases of shaft bearings, the common factors contributing to early failure of shaft bearing were discussed and summarized. Local burning caused by improper abrasive machining may lead to early failure of shaft bearings. Improper dimension matching, pits caused by pull-off carbide, foreign material, and improper assembly were other common causes. In addition, the effect of lubrication and loading on failure of shaft bearings was analyzed. In order to improve service life and reliability of shaft bearing, design,manufacture, machining process, and the use of process must be fine.The suitable process parameters and effective preventive measures are needed especially in grinding process and assembly.
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    Failure Analysis on 0Cr17Ni4Cu4Nb Screw
    HU Chun-yan, LIU Xin-ling, TAO Chun-hu, HE Yu-huai
    2012, 0 (12): 21-23,28.  
    Abstract ( 453 ( PDF (1782KB)( 403 Citation
    A precipitation-hardening stainless steel 0Cr17Ni4Cu4Nb screw was fractured. The feature and cause of the screw were analyzed by micro and macro observation on fracture surfaces, metallographic examination, hardness testing and energy spectrum analysis. The results show that the fracture mode of the screw is fatigue failure. Failure and fatigue testing screw have the same feature of quasi-cleavage and intergranular in source zone, and the intergranular feature is more obvious in failure screw. The main cause of the intergranular feature should be relevant to the material properties and the complex stresses such as pretighening force, tensile stress, bending stress of screw thread roots.
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    Influences of Stress Amplitude on Fatigue Behavior of As-annealed Mg-3Al-2Sc Alloy
    SHA Gui-ying, HAN Yu, LIU Teng, LI Zhao-hua, WANG Jie
    2012, 0 (12): 24-28.  
    Abstract ( 521 ( PDF (2001KB)( 376 Citation
    The stress-controlled fatigue tests for the Mg-3Al-2Sc alloy after anneal treatment were carried out under different stress amplitudes. The effect of stress amplitude on the behavior of fatigue crack propagation and fracture mechanism was investigated. The results showed that, in the stress range of 12-75MPa and at the stress ratio of 0.2, fatigue fracture life of the Mg-3Al-2Sc alloy decreases and the fatigue crack growth rate increases with the increasing stress amplitude. The cleavage fracture is the main mechanism in the crack initiation stage of the alloy. In the crack propagation stage, the predominant fracture mode is the quasi-cleavage fracture. However, for the final fracture stage, the main fracture mode is quasi-cleavage fracture at lower stress amplitude, but the fracture mode is mainly micro-voids aggregation fracture at higher stress amplitude.
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    TIG Welding Heat Efficiency for AZ31B Magnesium Alloy
    CHU Ya-jie, CHEN Jian, LI Xiao-quan, WU Shen-qing, YANG Zong-hui
    2012, 0 (12): 29-32,38.  
    Abstract ( 574 ( PDF (1935KB)( 340 Citation
    The AZ31B magnesium alloy welded joint were carried out on tungsten inert gas(TIG) welding with filler, and arc heat efficiency and melting efficiency were studied in terms of process parameters (welding current in the range of 120-200A, welding voltage in the range of 11-15V and welding speed in the range of 3-11mm/s), and the effects of welding process parameters, arc heat efficiency and melting efficiency on the microstructure of welding joint were analyzed. The results showed that the arc efficiency values ranged from 0.56-0.82 in terms of welding process parameters. Melting efficiency increased with both increasing welding current and speed. The analyses revealed a strong influence of the TIG welding process on cross-section shape of the fusion zone (the depth B and width H) and also on the microstructure of the welding zone.
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    Impact Behavior and Fracture Mechanism of Ductile Cast Iron with Minor Nickel Addition at Low Temperature
    CHEN Jiang, HUANG Xing-min, GAO Jie-wei, DONG Hai, DAI Guang-ze
    2012, 0 (12): 33-38.  
    Abstract ( 702 ( PDF (3579KB)( 329 Citation
    Utilizing laser confocal microscopy,SEM, instrumented impact and other experimental methods, the influence of nickel content(0.0%-0.9%,mass fraction, the same below) on the microstructure and low temperature impact toughness of ductile cast iron(DCI) was investigated. The fracture mechanism of DCIs was studied further at different temperatures by using scanning electronic microscopy (SEM). The results show that ductile-to-brittle transition temperature of as-annealed DCIs with 0.7% Ni content is lower than -60℃, the impact energy of Charpy-type test is still higher than 12J at -70℃. Minor Ni addition of proper quantities might favor the grain refinement and matrix strengthen, low temperature impact toughness properties of DCIs are markedly improved.
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    Effect of Heat Treatment on Microstructures and Mechanical Properties of Extruded GWZ661 Alloy
    ZHEN Rui, SUN Yang-shan, WANG Zhang-zhong, FANG Xin-xian, SHI Wei
    2012, 0 (12): 39-44.  
    Abstract ( 606 ( PDF (2696KB)( 585 Citation
    A quaternary alloy with composition of Mg-6Gd-6Y-1Zn (mass fraction/%) was prepared by conventional casting and extrusion. The microstructure and aging behavior of the alloy were investigated. The results showed that the as-cast microstructure of the alloy consisted of the α-Mg matrix, Mg24(GdYZn)5 eutectic and Mg12Y1Zn1 phase. After extrusion the Mg12Y1Zn1 phase were stretched along the direction of extrusion, and the 14H-LPSO phase distributed between Mg12Y1Zn1 strips. Solid solution treatment at high temperature above 500℃ resulted in the dissolution of Mg12Y1Zn1 phase into the matrix and increase of the 14H-LPSO phase. When solution treated alloys was aged at temperature of 225℃ (T6 treatment), the 14H-LPSO phase and β' precipitated appear in microstructure. Aging of as extruded alloys (T5 treatment) also caused the formation of β' precipitates,however the volume fraction of 14H-LPSO phase was lower than that in specimens after T6 treatment. High tensile strength combined with good ductility was obtained from the alloy after T6-aging.
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    Effect of Second-phase Particles on Texture Evolution of Low Carbon Al-killed Steel
    ZHUANG Dong-dong, WANG Zuo-cheng, ZHANG Jian-qiang, CHEN Kun, LIU Jin-yuan, GU Guo-gang
    2012, 0 (12): 45-49.  
    Abstract ( 528 ( PDF (2106KB)( 306 Citation
    Microstructure, mechanical properties and the content of different types of texture were investigated by means of TEM, tensile test and XRD. After cold rolling of 73% overall reduction and annealing at 700℃ for 4h, yield strength, tensile strength and r value of 2# sample is 28MPa higher, 19MPa higher and 0.24 lower than those of 1# sample. The results show that the content of the texture of {111} for 1# sample increases obviously after the cold rolling and annealing process, the content of texture of Goss decreases, and texture strength of {100} increases after the cold rolling process and decreases after the annealing process obviously. The precipitation of Al2O3 particles in 2# sample during the annealing process inhibits the precipitation of AlN particles, changes the mechanism of nucleation as nuclear particle shape. The increasing texture content of {100} and Goss, decreasing texture content of {111}, reducing value of r after annealing, which are not beneficial to deep-drawing performance. At the same time, small Al2O3 particles causes fine-grain strengthening and precipitation strengthening, and yield strength and tensile strength obviously increase.
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    Structure and Anti-corrosion Properties of Cold Sprayed Al Coatings on ZM6 Magnesium Alloy
    LIU De-xin, SHI Zhong-chuan, ZHANG Xiao-yun, LU Feng, SUN Zhi-hua, TANG Zhi-hui
    2012, 0 (12): 50-54,60.  
    Abstract ( 649 ( PDF (2734KB)( 419 Citation
    In order to improve anti-corrosion properties of magnesium alloy, Al coating on the ZM6 magnesium alloy was prepared by cold spray.The morphology and properties of coating were studied by scanning electronic microscope (SEM), energy dispersive spectroscopy(EDS) and micro-hardness tester. The electrochemical method and the neutral salt-spray test were used to evaluate the corrosion resistance of coating. The results indicated that pure Al coatings with high density were obtained on the surface of ZM6 alloy by means of cold spray technology successfully and the porosity was 0.8%. The micro-hardness was 59.8, which was higher than that of ZM6 alloy. Bonding force reached 21MPa.The corrosion resistance of coatings was superior to that of ZM6. Corrosion potential of ZM6 shifted positively by about 700mV after being cold sprayed Al, and salt-spray fog resistance reached 200 hours. ZM6 with coatings got long-life protection.
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    Contact Corrosion and Protection Between TC4-DT Titanium Alloy and Dissimilar Materials
    YANG Yong-jin, ZHANG Xiao-yun, LIU Ming-hui
    2012, 0 (12): 55-60.  
    Abstract ( 884 ( PDF (2531KB)( 441 Citation
    The susceptibility to galvanic corrosion between TC4-DT titanium alloy and dissimilar materials such as aluminum alloys, steels and their anodized composites were studied by measuring current density of the mentioned couples. The results indicated that galvanic corrosion was easily produced when TC4-DT titanium alloy was in direct contact with aluminum alloys or steels. TC4-DT titanium alloy was prohibited to contact with aluminum alloys and steels directly. It was necessary to protect for aluminum alloys and steels when TC4-DT titanium alloy was used. The anti-corrosion property can be high by anodizing both titanium alloy and aluminum alloys. Also there was a relatively decrease in the galvanic corrosion sensitivity through anodizing titanium and plating steels with a Cd-Ti layer.
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    Effects of Mullite Fiber Content on Friction and Wear Properties of Ceramic-based Friction Material
    WANG Fa-hui, LIU Ying
    2012, 0 (12): 61-65.  
    Abstract ( 532 ( PDF (2103KB)( 497 Citation
    Ceramic-based friction material with 0%-24% (mass fraction) mullite fiber reinforcement was prepared by nitrogen protection hot-pressing sintering. The effect of mullite fiber content on friction and wear properties of ceramic-based friction material was studied on the XD-MSM constant speed friction tester. The worn surfaces morphology after tests was observed by scanning electron microscopy (SEM), and wear mechanism was discussed. The results show that mullite fiber could increase friction coefficients of ceramic-based friction material, and with increasing mullite fiber contents, friction coefficients continuously increase. While the wear rates also increase with increasing mullite fiber contents at high temperature. The dominant wear mechanism of ceramic-based friction material without mullite fiber is brittle spalling and fatigue wear, accompanying with abrasive wear; the main wear type converts into adhesion wear and abrasive wear when adding mullite fiber into ceramic friction material.
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    Optical and Room-temperature Ferromagnetic Properties of ZnO and Fe Doped ZnO
    HE Xiao-wen, MENG Da-wei, LIU Chang-zhen, YU Xiao-hong, CHEN Long, XIE Jing
    2012, 0 (12): 66-70.  
    Abstract ( 735 ( PDF (1393KB)( 402 Citation
    The samples of Zn1-xFexO (0.00≤x≤0.10) were synthesized by co-precipitation method. The structure, optical and ferromagnetic properties were examined using X-ray diffractometer, infrared spectrometer, UV-Vis spectrophotometer, fluorescence spectrometer and vibrating sample magnetometer. The results showed that all the samples exhibited the hexagon wurtzite structure without any secondary phases. The absorptivity of samples reached to 95% in ultraviolet bands and the absorption rate in visible bands increased obviously with doping, and the band gap of Zn1-xFexO decreased from 3.20eV to 3.11eV. The photoluminescence characteristics of Zn1-xFexO showed the ultraviolet emission and blue emission peaks. Evident reduction of the photoluminescence intensity was caused by Fe doping, while the location of the main peaks did not move. The samples exhibited obvious room temperature ferromagnetism and the magnetism decreased with the increasing of Fe concentration.
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    Fast Evaluation of Fatigue Behavior of Q235 Steel by Infrared Thermography and Energy Approach
    FAN Jun-ling, GUO Xing-lin, WU Cheng-wei, DENG De-wei
    2012, 0 (12): 71-76.  
    Abstract ( 776 ( PDF (2289KB)( 433 Citation
    The infrared thermography was used to rapidly determine the fatigue parameters of Q235 steel undergoing uniaxial cyclic stress, and a good agreement was achieved between the predicted results and the results from the traditional fatigue testing methods. Based on the assumption of the limiting energy theory, the energy approach based on Miner’s law was advanced to predict the residual fatigue life of samples. The results show that the infrared thermography and the energy approach can be used to rapidly determine the fatigue limit and the S-N curve in a short test period; and that the residual fatigue life can be accurately predicted by the energy approach based on Miner’s law with clear physical meaning.
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    Numerical Simulation of Damage for Cr35Ni45Nb Steel Ethylene Cracking Furnace Tube at Action of Coupled Multiple Factors
    SHEN Li-min, GONG Jian-ming, JIANG Yong
    2012, 0 (12): 77-82,88.  
    Abstract ( 640 ( PDF (2076KB)( 306 Citation
    Based on the continuum damage mechanics (CDM), a user subroutine of ABAQUS coded by FORTRAN was developed for simulating the damage process of Cr35Ni45Nb steel ethylene cracking furnace tube at action of coupled creep-carburization under 1050℃. The results showed that the inner surface of tube generated micro-cracks firstly at action of coupled creep-carburization. However, the rupture initiated from the outer surface at action of single creep. The Von-mises stress and maximum principal stress along the inner surface decreased initially and then increased with time at the action of single creep. And the Von-mises stress and maximum principal stress along the outer surface increased with time, which caused the damage rate of outer surface to be higher than that of inner surface. The Von-mises stress and maximum principal stress along the inner surface decreased with time at action of coupled creep-carburization, which was contrary to the outer surface.
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    Low Cycle Fatigue Behavior of 500MPa Grade Acicular Ferrite Steel
    ZHENG Hong-wei, TANG Di, WU Hui-bin, YANG Liu, LIU Li-hua
    2012, 0 (12): 83-88.  
    Abstract ( 488 ( PDF (3995KB)( 352 Citation
    Low cycle fatigue tests for 500MPa grade acicular ferrite steel were conducted with smooth rotundity-section specimens under fully reversed total strain control cycling at room temperature. Cyclic stress-strain behavior, strain-life feature and cyclic stress response were investigated through the tests. The results show that when Δεt/2 equals to 0.35%, the tested steel quickly achieves cyclic saturation, and the stress amplitudes remains almost constant. When Δεt/2 is less than 0.35%, the tested steel shows cyclic softening until failure. When Δεt/2 is higher than 0.35%, the tested steel shows cyclic hardening which is followed by cyclic softening until failure. Observations of fracture surface show that fatigue cracks initiate with multi-initiation sites from one side of the specimen surface, and fatigue crack propagation is mainly in the sharpening-blunting mechanism of Laird.
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    Microstructure and Texture Evolution of Low-carbon Cr-Mo Deep Drawing Dual-phase Steel
    WANG Zhi-gang, ZHAO Zheng-zhi, ZHAO Ai-min, YE Jie-yun, CHENG Jun-ye, HUANG Yao
    2012, 0 (12): 89-94,101.  
    Abstract ( 560 ( PDF (2961KB)( 419 Citation
    Microstructure and texture evolution of low-carbon Cr-Mo deep drawing dual-phase steel were investigated by using microstructure observation, TEM and XRD. The results show that, the finish-rolling process conducted in austenite no-recrystallization zone promoted the formation of {112}〈111〉 component. The intensity of {001}〈110〉,{112}〈110〉 and {223}〈110〉 orientations were steadily enhanced during cold rolling.The formation of sharper 〈111〉//ND, {554}〈225〉 and {332}〈113〉 textures during annealing was favorable to improve the deep draw-ability of dual-phase steel. When intercritical annealed at 820℃ and 860℃, the intensity of γ-fibre was slightly different. The difference of intensity between {111}〈110〉 and {111}〈112〉 texture tended to increase at high-temperature annealing, causing by the solution-carbon of bainite and the variant selection from austenite to bainite. The high-temperature coiling process induced precipitation of Mo-based carbide in hot-rolled strips, and re-dissolution during the holding stage in annealing process, which not only facilitated the formation of recrystallization textures, but also improved the second phase transformation.
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    Inhibitive Self-assembled Monolayers on Steel
    WANG Hai-ren, CHEN Feng, QU Jun-e, JIANG Yan, GUO Xing-peng
    2012, 0 (12): 95-101.  
    Abstract ( 608 ( PDF (898KB)( 478 Citation
    Self-assembly method is widely used in surface engineering, nanotechnology,membrane technology and bioscience,and it is play an important role in future materials’ development. Self-assembly technology has become the focus of research in recent years. As a widely used engineering materials, the research of steel inhibitive self-assembled monolayers(SAMs) is important. The SAMs on steel not only has good orientation, closely ordered, thermodynamic stability and low cost,but also has high corrosion inhibition efficiency. Therefore, the inhibitive self-assembled monolayers on steel attracts many researchers’ attentions .This paper reviewed three aspects of the latest research progress including the main self-assembly systems, the influenced factors and characterization technique on steel,and then development of the self-assembled monolayers is prospected.
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