ISSN 0412-1961
CN 21-1139/TG
Started in 1956

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    DEVELOPMENT OF HIGH STRENGTH ALUMINUM ALLOYS AND PROCESSING TECHNIQUES FOR THE MATERIALS
    ZHANG Xinming, DENG Yunlai, ZHANG Yong
    Acta Metall Sin, 2015, 51 (3): 257-271.  DOI: 10.11900/0412.1961.2014.00406
    Abstract   HTML   PDF (7777KB) ( 2231 )

    The fundamental theories for the development of high strength aluminum alloys and processing techniques for the materials are briefly reviewed in this paper. It specifically focuses on alloying design, casting, homogenization, solution treatment, quenching, pre-stretching and ageing that have been extensively studied recently. Based on these discussions, some perspectives and suggestions have been proposed, which will benefit the development and applications of high strength aluminum alloys.

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    EFFECTS OF ELECTROMAGNETIC STIRRING WITH LOW CURRENT FREQUENCY ON RE DISTRIBUTION IN SEMISOLID ALUMINUM ALLOY
    LIU Zheng, LIU Xiaomei, ZHU Tao, CHEN Qingchun
    Acta Metall Sin, 2015, 51 (3): 272-280.  DOI: 10.11900/0412.1961.2014.00347
    Abstract   HTML   PDF (6085KB) ( 719 )

    When solidification of Al alloy melt was disturbed by electromagnetic field, its microstructure and properties were influenced by the diffusion and distribution of the solute and refinement in the melt. So it was necessary to study the metallurgical behavior of RE with electromagnetic stirring and to probe its diffusion and distribution under the forced convection in the melt. The magnetic induction intensity in the electromagnetic crystallizer and its variations with current frequency were simulated by Maxwell 2D software. The distribution of RE in the A356-Y alloy melt and its effect to the microstructure were studied with low frequency electromagnetic stirring. The results indicated that current frequency with stronger magnetic induction could be obtained during the range of low frequency under the working frequency. The slurry of semisolid A356-Y alloy was prepared by electromagnetic stirring at the frequency. The size and shape factor of the primary phase in the alloy were below 65 mm and above 0.80, respectively, which could satisfy the requirement of semisolid alloy rheoforming. The distribution of Y enriched at the edge of the ingot along its radius direction by the driving of electromagnetic field, but was effected by the frequency. Y presented the enriching at the edge of the ingot with the increase of the frequency under the range of the frequency tested.

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    INTERFACE STRUCTURE AND MECHANICAL PRO-PERTIES OF FRICTION STIR WELDING JOINT OF 2099-T83/2060-T8 DISSIMILAR Al-Li ALLOYS
    LIU Fenjun, FU Li, ZHANG Wenyuan, MENG Qiang, DONG Chunlin, LUAN Guohong
    Acta Metall Sin, 2015, 51 (3): 281-288.  DOI: 10.11900/0412.1961.2014.00297
    Abstract   HTML   PDF (8394KB) ( 760 )

    Al-Li alloys are widely applied in aircraft structures owing to their unique properties, such as low density, high strength and stiffness, outstanding low temperature performance, corrosion resistance and superplasticity. 2099-T83 and 2060-T8 are two new Al-Li alloys which have great potential to fabricate the fuselage panels of aircraft. The application of traditional fusion welding on joining Al-Li alloys is limited by cavity, high thermal stress, high thermal strain and low joint strength produced during melting and solidification. Friction stir welding (FSW) is an innovative solid-state joining technology. Compared with traditional fusion welding, FSW is capable of achieving high-quality welded joint in similar or dissimilar high-strength aluminum alloys due to its excellent performance, such as low energy consumption, low stress and strain, fewer metallurgical defects and distortion under reasonable processing parameters. Weld nugget zone (WNZ), thermo-mechanically affected zone (TMAZ) and external heat affected zone (HAZ) will be produced in the FSW joint. The micromorphologies and bonding interface among WNZ, TMAZ and HAZ have a significant effect on mechanical properties of welding joint. In this work, lap joints of 2099-T83 and 2060-T8 Al-Li alloy with 2 mm thickness were achieved by FSW. The interface microstructure of joints obtained by employing different tool rotation speeds and pin lengths was characterized by OM and SEM. The results showed that the obvious bonding interface was observed in the weld zone, and the bonding interface changed from smooth to zigzag with the rotation speed raising from 600 r/min to 800 r/min and pin length decreasing from 3.0 mm to 2.5 mm. In addition, micro-hardness of the weld zone was lower than the parent metal, and the lowest micro-hardness appeared in the transition region between the thermo mechanically affected zone and the weld zone (WZ) and the results of peel tests showed that the average failure load of joint with serrated bonding interface was up to 654 N. The failure occurred in the transition zone between the TMAZ and WZ of the 2060-T8 side, and the toughness-brittleness fracture mode appeared. Furthermore, the microhardness of the weld zone improved, while the failure load of the FSW joint with serrated bonding interface decreased 20% under artificial aging treatment with the temperature of 150 ℃ and the holding time of 20 h. The brittleness fracture mode existed in this condition. The pin length had a great effect on the morphology of bonding interface and mechanical property of welded joint.

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    INFLUENCE OF PRE-DEFORMATION ON THE PRECIP- ITATION BEHAVIORS OF Al-Mg-Si-Cu ALLOY FOR AUTOMOTIVE APPLICATION
    CUI Li, GUO Mingxing, PENG Xiangyang, ZHANG Yan, ZHANG Jishan, ZHUANG Linzhong
    Acta Metall Sin, 2015, 51 (3): 289-297.  DOI: 10.11900/0412.1961.2014.00348
    Abstract   HTML   PDF (1795KB) ( 734 )

    To reduce the weight of car body, Al-Mg-Si-Cu alloys have been widely used to produce outer body panels of automobiles due to their favorable high strength-to-weight ratio, corrosion resistance, weldability and good formability. Al-Mg-Si-Cu alloys belong to age-hardenable aluminium alloys, whose strength derives mainly from the matrix precipitation during aging treatments. However, their bake hardening response still need to be further improved to enhance their dent resistance. A novel thermo-mechanical treatment consisting of conventional pre-aging, pre-deformation and re-aging was developed to enhance the tensile properties and bake hardening increment of Al-Mg-Si-Cu alloys. In this work, the effect of pre-deformation on the precipitation behaviors of Al-Mg-Si-Cu alloy was studied by DSC, mechanical property measurement and TEM. The results show that, the GP zone dissolution rate decreases with increasing pre-deformation during the slow heating up process for the pre-aged alloy, the corresponding activation energies of 0, 5% and 15% pre-deformed alloy calculated by Avrami-Johnson-Mehl method are 137.1, 189.5 and 141.3 kJ/mol, respectively. If the pre-deformed alloys are directly bake hardened at 185 ℃ for 20 min, precipitation and bake hardening increment can be greatly improved by pre-deformation (the highest bake hardening increment is 160 MPa), but the bake hardening increment rate gradually decreases if the pre-deformation is above 10%. In addition, the GP zone dissolution rates of pre-deformed alloys after bake hardening treatment are much lower when the heat treatment temperatures are below one certain value, but if the treatment temperatures above it, the corresponding GP zone dissolution rates are higher than that of alloy without pre-deformation, finally, the activation energy changes from high value to low value even can be observed in the ln[(dY/dT)φ/f(Y)]-1/T curve. For the precipitation in the alloys, with increasing pre-deformation, its activation energy gradually decreases, corresponding gradually increase of precipitation rate.

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    CORROSION FATIGUE MECHANISM OF NUCLEAR-GRADE LOW ALLOY STEEL IN HIGH TEMPERATURE PRESSURIZED WATER AND ITS ENVIRONMENTAL FATIGUE DESIGN MODEL
    WU Xinqiang, TAN Jibo, XU Song, HAN En-Hou, KE Wei
    Acta Metall Sin, 2015, 51 (3): 298-306.  DOI: 10.11900/0412.1961.2014.00421
    Abstract   HTML   PDF (6558KB) ( 482 )

    The service degradation and life assessment of key components in light water reactor nuclear power plants (NPPs) mainly depend on the accumulation of service property data of component materials, understanding of environmental degradation mechanism, and construction of evaluation models or methods. The current ASME design fatigue code does not take full account of the interactions of environmental, loading and material's factors. In the present work, based on the corrosion fatigue tests in simulated NPPs' high temperature pressurized water, the environmental fatigue behavior and dominant mechanism of nuclear-grade low alloy steel have been investigated. A design fatigue model was constructed by taking environmentally assisted fatigue effects into account and the corresponding design curves were given for the convenience of engineering applications. The process for environmental fatigue safety assessment of NPPs' components was proposed, based on which some tentative assessment cases have been given.

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    INFLUENCE OF PULSED MAGNETIC TREATMENT ON MICROSTRUCTURES AND MECHANICAL PROPERTIES OF M42 HIGH SPEED STEEL TOOL
    MA Liping, LIANG Zhiqiang, WANG Xibin, ZHAO Wenxiang, JIAO Li, LIU Zhibing
    Acta Metall Sin, 2015, 51 (3): 307-314.  DOI: 10.11900/0412.1961.2014.00295
    Abstract   HTML   PDF (8503KB) ( 459 )

    Magnetic treatment of tools is a novel method to increase tool life in which the tool is magnetized before cutting or the cutting is performed in a magnetic field. The method has many attractive features, such as short treatment time and no pollution. However, this approach has not been widely applied yet, since the mechanism of magnetic treatment of tools is not clear and treatment results are affected by many factors. Therefore, it is important to study the mechanism of magnetic treatment of tools. This work aims to study the influence of pulsed magnetic treatment on microstructures and mechanical properties of M42 (W2Mo9Cr4VCo8) high speed steel, which is a typical tool material which contains high amounts of cobalt. So it can show a stronger magnetism in the process of pulsed magnetic treatment. Changes of dislocation configuration, carbide distribution and microstructure before and after magnetic treatment were characterized by TEM and laser scanning confocal microscope. Moreover, Rockwell hardness and micro-hardness were measured to quantitatively investigate the influence of magnetic treatment on the mechanical properties. Results showed that after pulsed magnetic treatment the lattice of material was distorted, the carbide was precipitated, and the microstructure and crystalline grain were refined. The changes of microstructure led to changes of mechanical properties, of which the Rockwell hardness and micro-hardness were significantly increased. The maximum increase of Rockwell hardness was 2.9 HRC. Ultimately, the strengthening mechanisms of high speed steel were analyzed based on dislocation theory. It was shown that the subjected force of dislocations due to the magnetic treatment could overcome the centripetal restoring force and the Peierls stress of dislocations. Therefore, dislocations proliferated by the Orowan dislocation strengthening mechanism, and dislocation density increased. The dislocation configuration determined from TEM micrographs was in good agreement with the discussion of dislocation mechanisms.

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    PRECIPITATION BEHAVIOR OF CARBIDE DURING HEATING PROCESS IN Nb AND Nb-Mo MICRO-ALLOYED STEELS
    ZHANG Zhengyan, LI Zhaodong, YONG Qilong, SUN Xinjun, WANG Zhenqiang, WANG Guodong
    Acta Metall Sin, 2015, 51 (3): 315-324.  DOI: 10.11900/0412.1961.2014.00424
    Abstract   HTML   PDF (7269KB) ( 1080 )

    As an important carbide forming element, Nb plays an important role in steel. Precipitated Nb can restrain the austenite grain growth during soaking process and provide precipitation strengthening after g /a phase transformation. Precipitated or dissolved Nb can inhibit recrystallizaton of deformed austenite. Recently, both Nb and Mo are added in steel to enhance the role of Nb. However, these kinds of researches mostly focused on continual cooling process of g /a transformation or isothermal process during tempering, and precipitation behavior of MC-type carbide in steel containing Nb and Mo during reheating process and the effect of Mo on precipitation of NbC in ferrite were rarely reported. Therefore, in this work, precipitation behaviors of MC-type carbide and the synergistic effect of Nb and Mo in steel containing Nb or Nb-Mo during reheating process at the heat rate 20 ℃/min were investigated by means of Vickers hardness test, SEM, HRTEM and DSC. The results show that both Nb and Nb-Mo steels have hardness peaks at 300 and 700 ℃, which are attributed to the precipitation of e-carbide and MC-type carbide, respectively. The MC-type carbide precipitates at about 650 ℃ during reheating process, which is in a good agreement with the nose temperature of MC-type carbide calculated by Avrami equation. (Nb, Mo)C particle forming in Nb-Mo steel during precipitation has a small mismatch with ferrite matrix compared with NbC, leading to the decrease of interfacial energy. Thus, the precipitation kinetic of MC-type carbide in Nb-Mo steel is faster than that in Nb steel, which results in the denser and finer MC-type carbide and higher precipitation strengthening effect.

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    CARBON SEGREGATION BEHAVIOR OF HIGH-CARBON HIGH-ALLOY STEEL DURING DEEP CRYOGENIC TREATMENT USING 3DAP
    XIE Chen, WU Xiaochun, MIN Na, SHEN Yunliang
    Acta Metall Sin, 2015, 51 (3): 325-332.  DOI: 10.11900/0412.1961.2014.00430
    Abstract   HTML   PDF (4824KB) ( 366 )

    Deep cryogenic treatment (DCT) is a supplement to conventional heat treatment, which usually involves cooling the material to liquid nitrogen temperature around -196 ℃ for a given soaking time and then heating back to the room temperature. As claimed in many pioneering researchers, DCT can evidently improve the hardness and wear resistance of high-carbon high-alloy steel and has been widely used to die steels, cutting tools, carburizing steels and barrels. The improvement of mechanical properties by DCT can be attributed to the transformation from retained austenite to martensite, the fine dispersion of nanoscale carbide precipitate and the removal of residual stresses. However, the nanoscale carbide precipitate is still lack of evidence and the interpretation of carbon segregation behavior during DCT is still unconvincing. In this work, the high-carbon high-alloy steel SDC99 is first austenized at 1030 ℃ for 30 min and then immersed in liquid nitrogen for 8 h and finally tempered at 210 ℃ for 2 h. The spatial distributions of carbon atom and alloy element concentration in quenched, DCT treated and tempered samples are analyzed by three dimensional atom probe (3DAP), respectively. In addition, the axial ratio and carbon content of martensite are studied using XRD and the carbide morphology before and after DCT are also observed in situ by SEM. The results indicate that after quenching from 1030 ℃ to room temperature, the volume fraction of retained austenite in SDC99 is about 21.1%. The retained austenite is soft and unstable which can easily transfer to martensite at lower temperatures. Carbon atoms will segregate slightly due to self-tempering. However, other alloy atoms do not segregated with carbon atoms. After quenching from 1030 ℃ to room temperature and then cooling in nitrogen for 8 h, the volume fraction of retained austenite in SDC99 will decrease to 7.4%. Carbon atoms will segregate along the twin boundary of martensite and form a segregation area with a thickness about 5~10 nm.There is no carbide precipitate after DCT. Furthermore, carbon atoms segregate again during heating up back to room temperature from -196 ℃. After tempering at 210 ℃ for 2 h, the volume fraction of retained austenite is almost 5.4%. Both carbon and alloy atoms will segregate during tempering at 210 ℃. With the increase of tempering time, the carbon segregation will aggravate and result in a C-rich phase or form the M23C6 carbide combined with other alloy element. This is one of the main reasons increasing the wear resistance of tool steels.

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    IMPROVING THE INTERGRANULAR CORROSION RESISTANCE OF THE WELD HEAT-AFFECTED ZONE BY GRAIN BOUNDARY ENGINEERING IN 304 AUSTENITIC STAINLESS STEEL
    YANG Hui, XIA Shuang, ZHANG Zilong, ZHAO Qing, LIU Tingguang, ZHOU Bangxin, BAI Qin
    Acta Metall Sin, 2015, 51 (3): 333-340.  DOI: 10.11900/0412.1961.2014.00552
    Abstract   HTML   PDF (7166KB) ( 863 )

    The heat-affected zone (HAZ) produced by welding in stainless steel has higher susceptibility to intergranular corrosion, which is attributed to the Cr depletion induced by grain-boundary carbide-precipitation. The grain boundary engineering can be used to control over the grain boundary structure, which has significant influence on the carbide precipitation and the associated Cr depletion and hence on the susceptibility to intergranular corrosion. The grain boundary network in a 304 austenite stainless steel can be controlled by grain boundary engineering (GBE) with 5% tensile deformation and subsequent annealing at 1100 ℃ for 30 min. The total length proportion of Σ3n coincidence site lattice (CSL) boundaries was increased to more than 75%, and the large-size highly-twinned grain-cluster microstructure was formed through the treatment of GBE. Specimens were welded by gas tungsten arc-welding. Then the microstructure and the corrosion resistance of HAZ were characterized. The result showed that the high proportion of low ΣCSL boundaries and the optimum grain boundary character distribution were stable in the HAZ of the grain boundary engineered stainless steel, and the grain size was nearly the same. The weld-decay region of GBE samples performed better intergranular corrosion resistance during the intergranular corrosion immersion experiment and electrochemical potentiokinetic reactivation (EPR) test. The reported results indicated that the grain boundary engineering can effectively improve the intergranular corrosion resistance of the heat-affected zone in 304 austenitic stainless steel.

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    MICROSTRUCTURE EVOLUTION AND MECHANICAL PROPERTIES OF TC1 ALLOY FABRICATED BY PLASMA ARC COLD HEARTH MELTING DURING ROLLING PROCESS
    LIU Mengying, CHANG Hai, XU Feng, XU Zhengfang, YANG Zhao, WANG Ning, GAN Weimin, FENG Qiang
    Acta Metall Sin, 2015, 51 (3): 341-348.  DOI: 10.11900/0412.1961.2014.00575
    Abstract   HTML   PDF (12869KB) ( 237 )

    Plasma arc cold hearth melting (PAM) is an effective technology to produce high purity titanium alloy ingots which are widely used in aeronautic and astronautic industries. To date, the development of PAM in our country is still at initial stage. It is necessary to investigate the melting parameters of PAM and the following thermal mechanical processing of the ingots fabricated by PAM. In this study, the TC1 alloy ingots casted by PAM were cogged at b transus temperature and then rolled by unidirectional rolling and cross rolling in the a+b phase field. The typical widmanstatten structure of cast-ingots turned to transformed b morphology after cogging at b transus temperature in which the a phases forms in smaller colonies of laths. After the unidirectinal rolling in the a+b phase field, the a colonies were distorted and the a laths re-arranged along the rolling direction, while they had weaker directivity after cross rolling. The sheets rolled by both unidirectional and cross rolling showed typical prismatic texture. After annealing treatment below the b transus temperature, the a phases turned to equiaxial morphology. The ambient yield strength of the sheet in transverse direction was significantly higher than in rolling direction, which could be attributed to the strong prismatic texture introduced by hot rolling process.

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    HIGH TEMPERATURE CREEP DEFORMATION MECHANISM OF BSTMUF601 SUPERALLOY
    SUN Chaoyang, SHI Bing, WU Chuanbiao, YE Naiwei, MA Tianjun, XU Wenliang, YANG Jing
    Acta Metall Sin, 2015, 51 (3): 349-356.  DOI: 10.11900/0412.1961.2014.00293
    Abstract   HTML   PDF (3313KB) ( 413 )

    Muffle tube is the core component in a large bright annealing muffle furnace. A lot of defects will be found on the muffle tube after long-term application under high temperature, self-weight and uneven temperature conditions, and among them creep deformation is serious, directly affecting the usability and life expectancy of muffle tube. High temperature creep and rupture properties are important indicators of the muffle tube material, and BSTMUF601 nickel-based superalloy materials are commonly used in a muffle tube. Because of good oxidation resistance at high temperatures, high strength and good creep resistance, nickel-base superalloy materials are taken seriously especially its creep mechanism. For different alloys or alloys in different conditions, the conclusions about creep mechanism are different. So the research of each alloy is necessary. Creep tests of BSTMUF601 superalloy for elevated temperature were carried out under different temperatures and stresses. The creep deformation characteristic of BSTMUF601 superalloy was investigated based on the creep curves. And then, a creep constitutive model for elevated temperature was proposed by introducing a modified θ projection method, which contained three stages of creep. The predicted results by using the model are in good agreement with the experimental results. The average relative error of the model fitted is 1.86%. Compared with the model ignored the second stage of creep and the model ignored the first stage of creep, the average relative error is reduced 0.10% and 6.02%, respectively. It is indicated that the model will be a wider range of application whereas the prediction precision is not reduced. Dislocation structure and its distribution for creep specimens and void evolution for creep rupture specimens have been carried by analyzing the microscopic structure. The results show that the creep stress index is close to 5 during the steady-state creep stage for different temperatures. The dislocation climb mechanism controlls the creep deformation process. There is no stacking fault or microtwin observed in phase or matrix. Cracks originate from the cavities at grain boundary and along the boundary, which lead to fracture. Grain boundary fracture is the main creep rupture mechanism.

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    MODELLING OF PLASTIC DEFORMATION ON COUPLING TWINNING OF SINGLE CRYSTAL TWIP STEEL
    SUN Chaoyang, GUO Xiangru, HUANG Jie, GUO Ning, WANG Shanwei, YANG Jing
    Acta Metall Sin, 2015, 51 (3): 357-363.  DOI: 10.11900/0412.1961.2014.00298
    Abstract   HTML   PDF (1125KB) ( 699 )

    Twinning induced plasticity (TWIP) steel exhibits high strength and exceptional plasticity due to the formation of extensive twin under mechanical load and its ultimate tensile strength and elongation to failure-ductility-value can be as high as 50000 MPa%. Therefore, the TWIP steel can still maintain high energy absorption performance and impact resistance when its thickness is reducing to the half. The high work hardening plays a dominant role during deformation, resulting in excellent mechanical properties. The deformation mechanisms, responsible for this high work hardening, are related to strain-induced microstructural changes, which are dominated by slip and twinning. Different deformation mechanisms, which can be activated at different stages of deformation, will strongly influence stress-strain response and microstructure evolution. In order to understand the effects of slip and twinning during plastic deformation process, it is important to explore the microstructure evolution of those two deformation mechanisms and their influences on macroscopic deformation during this process. In this work, a crystal plasticity constitutive model of TWIP steel coupling slip and twinning was developed based on the crystal plasticity theory. In this model, the volume fraction of twin and its saturation value were introduced in order to consider the effect of twinning on hardening and slip, respectively. The constitutive model was implemented and programed based on the ABAQUS/UMAT platform. It was applied to simulate the plastic deformation process of single crystal for typical orientation microstructures under simply loading condition. The microscopic mechanism of plastic deformation of single crystals with different orientations was analyzed, and then the influence of slip-twinning system startup states on macroscopic plastic deformation was investigated. The saltation of stress for brass and S orientations was paid attention especially, the stress steep fall for copper single crystal was also reproduced during tensile tests. The results show that when the volume fraction of twin is small, its effect on strain hardening should be ignored; however, its impact becomes gradually obvious with the increase of volume fraction of twin; when the volume fraction of twin reaches saturation value, twinning increment is zero, the slip directions in crystal must change, another slip system will be activated as a result of stress dropping suddenly.

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    INFLUENCE OF THE COMPOSITION OF Zn-Al FILLER METAL ON THE INTERFACIAL STRUCTURE AND PROPERTY OF Cu/Zn-Al/Al BRAZED JOINT
    YANG Hao, HUANG Jihua, CHEN Shuhai, ZHAO Xingke, WANG Qi, LI Dehua
    Acta Metall Sin, 2015, 51 (3): 364-370.  DOI: 10.11900/0412.1961.2014.00522
    Abstract   HTML   PDF (4687KB) ( 496 )

    The Cu/Al dissimilar metal joint is a compound structure that can efficiently decrease manufacturing costs, reduce product weight, and integrate the advantages of both metals. For the excellent comprehensive properties, the Cu/Al dissimilar metal joint has broad application prospects in air conditioners, refrigerators, cables, electronic components, solar collectors, et al. Brazing is considered as a promising method to join the Cu/Al dissimilar metal for lower residual stress, lower costs, higher precision and better adaption to the structure of joint. Meanwhile, the Zn-Al filler metal is considered as the relatively ideal filler metal due to better property of the Cu/Zn-Al/Al joint. However, the influence of the composition of the Zn-Al filler metal on the interfacial structure near Cu substrate and property of the Cu/Al joint has not been investigated. In this work, the Cu/Al joints were brazed by Zn-15Al, Zn-22Al, Zn-28Al, Zn-37Al and Zn-45Al filler metals, respectively. The influences of the composition of Zn-Al filler metals on the interfacial structure near Cu substrate of the Cu/Al joints were investigated, and the relationships of the composition of the Zn-Al filler metals, the interfacial structure and the shear strength of the Cu/Al joints were described systematically. It was found that the interfacial structure of the Cu/Zn-15Al/Al brazed joint was Cu/Al4.2Cu3.2Zn0.7. For thinner Al4.2Cu3.2Zn0.7 layer (2~3 μm), the shear strength of the joint was higher (66.3 MPa). With the increase of Al content of the filler metal, the thickness of Al4.2Cu3.2Zn0.7 layer at the interface was increased for Cu/Zn-22Al/Al joint, even some CuAl2 phase can be found nearby the Al4.2Cu3.2Zn0.7 layer of Cu/Zn-28Al/Al joint, and the shear strength of the Cu/Al joints were decreased correspondingly. When the Cu/Al joint was brazed by the Zn-37Al filler metal, the interfacial structure near Cu substrate was transformed into Cu/Al4.2Cu3.2Zn0.7/CuAl2. For higher brittleness of CuAl2 layer, the shear strength of the joint was decreased obviously (34.5 MPa). Finally, the interfacial structure of the Cu/Zn-45Al/Al joint was transformed into Cu/CuAl2, the interfacial structure lead to the lower shear strength of the joint, which is only 31.6 MPa.

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    EFFECT OF Mo CONTENT ON THE MICROSTRUC-TURE AND PROPERTIES OF CrMoN COMPOSITE COATINGS
    QI Dongli, LEI Hao, FAN Di, PEI Zhiliang, GONG Jun, SUN Chao
    Acta Metall Sin, 2015, 51 (3): 371-377.  DOI: 10.11900/0412.1961.2014.00549
    Abstract   HTML   PDF (4694KB) ( 976 )

    Ceramic coatings are usually used as protective coatings to improve performance and durability of tools and components now. Compared with conventional TiN based hard coating, CrN based coating like Cr-X-N (X=Ti, Al, Si, C, B, Ta, Nb, Ni) is a more interesting choice because of low friction coefficient, superior oxidation resistance and excellent corrosion resistance under severe environment conditions. The CrMoN is among these coatings and attractive since self-lubricating phase MoO3 may be formed in tribological process. However the effect of Mo content on structure and tribological properties of CrMoN coatings is not still clear. In the present study, CrMoN composite coatings with different Mo content were deposited on M2 high speed steel (HSS) substrates by DC reactive magnetron sputtering. The effect of Mo content on the microstructure and properties was investigated systematically, including the chemical composition, phase structure, chemical valence, cross-section morphologies, microhardness and tribological properties. The results showed that the phase transformation of the as-deposited coatings occurred with the increase of Mo content. The phase structure changed to (Cr, Mo)N substitutional solid solution based on CrN-type firstly, and then to mixed phase with g-Mo2N as main phase, and a small amount of elemental bcc-Mo phase appeared when the Mo content is 69.3%. The microhardness of the CrMoN composite coatings always increased until the highest hardness when the Mo content reached to 45.4%, and then decreased; a relatively low friction coefficient was obtained compared with that of the CrN coating when more than 45.4%Mo content was doped. The reason is that the more MoO3 lubricant phase could be formed in tribological process.

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    EFFECTS OF CHLORIDE ION ON THE ELECTRO- CHEMICAL BEHAVIOR OF Pb-Ag-RE ALLOY ANODE
    ZHONG Xiaocong, JIANG Liangxing, LÜ Xiaojun, LAI Yanqing, LI Jie, LIU Yexiang
    Acta Metall Sin, 2015, 51 (3): 378-384.  DOI: 10.11900/0412.1961.2014.00548
    Abstract   HTML   PDF (3307KB) ( 383 )

    Corrosion and oxygen evolution behavior of Pb-Ag-RE alloy anode has been comparatively investigated in H2SO4 solution without Cl- and with 500 mg/L Cl- by galvonostataic polarization, SEM, XRD, EIS and Tafel scanning. The results show that anodic layer on Pb-Ag-RE anode formed in electrolyte with Cl- exhibits ‘volcanic vent'-like holes, and the metallic substrate in this electrolyte shows obvious localized corrosion feature with large numbers of corrosion pits. In addition, the presence of Cl- decreases the amount of PbO2 on the surface of anodic layer. It also inhibits the formation and adsorption of oxygen evolution intermediates, and further enhances the charge transfer resistance of oxygen evolution reaction. Therefore, Cl- is detrimental to the corrosion resistance and oxygen evolution reactivity of Pb-Ag-RE alloy anode. Consequently, the Cl- concentration in electrolyte should be reduced as low as possible during industrial operation.

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