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cold metal transfer(CMT) technology-An overview

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Defence Technology（防务技术） 2018年第1期14卷 28-44页

作者： S.Selvi A.Vishvaksenan E.Rajasekar Mechanical Engineering Institute of Road and Transport Technology Automobile Engineering Institute of Road and Transport Technology

cold Metal Transfer technology has revolutionized the welding of dissimilar metals and thicker materials by producing improved weld bead aesthetics with controlled metal deposition and low heat-input. In this study, the process, weld combinations, laser-CMT hybrid welding and applications of CMT welding are critically reviewed. Microstructure and other weld characteristics have been discussed at length for various base metal combinations. Particularly, the welding of aluminium and steel with better results has been possible with CMT Welding. The results reviewed in this article indicate that the CMT-Laser hybrid welding is more preferable to Laser or Laser hybrid welding. CMT welding has found applications in automobile industries, defence sectors and power plants as a method of additive manufacturing.

关键词： cold metal transfer [CMT]Welding Laser-CMT welding Additive manufacturing Composite joint Metal inert gas[MIG] Metal active gas[MAG]

Joining of dissimilar metals between magnesium AZ31B and aluminum A6061-T6 using galvanized steel as a transition joining layer

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Journal of Iron and Steel Research(International) 2022年第4期29卷 677-686页

作者： Wei Li Jing-huan Chang Bao-feng Wen Rui Cao State Key Laboratory of Advanced Processing and Recycling of Non-Ferrous Metal Lanzhou University of TechnologyLanzhou 730050GansuChina Department of Materials Science and Engineering Lanzhou University of TechnologyLanzhou 730050GansuChina

A galvanized steel is used to join Mg AZ31B alloy and Al A6061-T6 alloy as a joining transition layer by cold metal transfer(CMT)method.Firstly,to optimize the process variables,extensive welding tests were performed by a design of experiment method.Then,microstructures,joining mechanisms and tensile properties were characterized and analyzed.Results indicated that Mg and Al alloys can be joined by using galvanized steel as a joining transition layer and cold metal transfer welding method.The formed joint is called as a Mg–steel–Al CMT joint.By using galvanized steel transition joining layer,Mg–Al brittle intermetallics Al12Mg17 and Al3Mg2 were inhibited.The properties of Mg–steel–Al CMT joints have been improved after optimizing the welding variables.The strength of Mg–steel–Al CMT joint is comparable to those of Al–Al joint and Mg–Mg joint.The strength of Mg–steel–Al CMT joint can reach 100%that of Al–Al joint and Al–steel joint,and reach 90%that of Mg–Mg joint and Mg–steel joint.The optimized Mg–steel–Al CMT welded joint with galvanized steel transition layer is fractured at the heat affected zone of Al base metal rather than at the weld-brazed interface,due to softening of Al base metal.

关键词： cold metal transfer Mg alloy Al alloy Galvanized steel Transition joining layer Dissimilar metal joining

Correlating particle impact condition with microstructure and properties of the cold-sprayed metallic deposits

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Journal of Materials Science & Technology 2020年第5期40卷 185-195页

作者： Yujuan Li Yingkang Wei Xiaotao Luo Changjiu Li Ninshu Ma State Key Laboratory for Mechanical Behavior of Materials School of Materials Science and EngineeringXi’an Jiaotong UniversityXi’an710049China Joining and Welding Research Institute Osaka UniversityOsaka 567-0047Japan

Inter-particle bonding is an important factor affecting the property of cold sprayed metallic deposit.Because the interface bonding between particles in deposit is directly determined by plastic strain of particles during spraying,Cu deposits were made at series of impact velocities of 578 m s^-1 to 745 m s^-1 and 807 m s^-1 to correlate particle impact condition with microstructure and properties of the deposits.Results show that as the average particle impact velocity increases from 578 m s^-1 to 745 m s^-1 and 807 m s^-1,the deposition efficiency of feedstock powder increases from 58%to 84%and even to 95%.Although all three deposits reveal dense microstructure due to the high ductility of Cu,the deformation degree of the deposited particles remarkably increases with increasing impact velocity.The enhanced plastic deformation of the deposited particles leads to more dispersed oxide scale and thereby stronger interparticle bonding with the strength of the deposit along the deposition direction increasing from 25.8 MPa to 148.5 MPa.The electrical and thermal conductivities at through-thickness direction of the deposit at particle impact velocity of 807 m s^-1 are 78%IACS,295 W m^-1 K^-1,respectively.

关键词： cold spray Particle impact velocity Deposition efficiency Electrical conductivity Thermal conductivity Mechanical property

Study of the impact of the compaction and curing temperature on the behavior of cold bituminous recycled materials

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Journal of Traffic and Transportation Engineering(English Edition) 2019年第4期6卷 349-358页

作者： Apparao Gandi Alberto Cardenas Djibril Sow Alan Carter Daniel Perraton Department of Construction Engineering Ecole de Technologie SuperieureMontrealQC H3C 1K3Canada Department of Construction Engineering University of ThiesThiesSenegal

In most countries, there is a low temperature limit to lay down hot asphalt mixes because if it is too cold, it becomes impossible to get proper compaction. For cold recycled bituminous mixture(CRM), there is little information on the effect of the low temperature on their behavior. The goal of this study is to evaluate, in laboratory, the impact of the compaction and curing temperature on the behavior of CRM. To do so, CRM containing 50%reclaimed asphalt pavement(RAP) and 50% natural aggregates treated with foamed asphalt or bituminous emulsion were mixed and cured at different temperature between 0 and23℃ for up to 10 days before being tested in indirect tension. The results show that for all mixes, a cure at lower temperature means lower tensile strength, but the decrease is more noticeable for emulsion treated materials than for foamed treated mixes. The trend is not as obvious for Marshall stability results. A second cure at ambient temperature was also done, and the analysis of the results showed that the decrease in mechanical performance remains important even after a second cure at higher temperature for all mixes treated with bituminous emulsion, but there is some mechanical gain for mixes treated with foamed asphalt.

关键词： cold recycled materials Bituminous emulsion Foamed asphalt Curing Marshall stability Indirect tensile strength

Deciphering impacts of climate extremes on Tibetan grasslands in the last fifteen years

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Science Bulletin 2019年第7期64卷 446-454页

作者： Dan Liu Tao Wang Tao Yang Zhengjie Yan Yongwen Liu Yutong Zhao Shilong Piao Key Laboratory of Alpine Ecology Institute of Tibetan Plateau Research Chinese Academy of Sciences Center for Excellence in Tibetan Plateau Earth Sciences Chinese Academy of Sciences School of Life Sciences Lanzhou University College of Urban and Environmental Sciences and Sino-French Institute for Earth System Science Peking University

Climate extremes have emerged as a crucial driver of changes in terrestrial ecosystems. The Tibetan Plateau, facing a rapid climate change, tends to favor climate extremes. But we lack a clear understanding of the impacts of such extremes on alpine grasslands. Here we show that extreme events(drought,extreme wet, extreme cold and extreme hot) occurred at a frequency of 0.67–4 months decade^(-1) during2001–2015, with extreme precipitation predominantly occurring in June-to-August and extreme temperatures in May. Drought and extreme wet cause opposite and asymmetric effects on grassland growth,with drought-induced reductions greater than increases due to extreme wet. Grassland responses to extreme temperatures, which predominantly occur in May, show a dipole-like spatial pattern, with extreme hot(cold) events enhanced(reduced) growth in the eastern plateau but slightly reduced(enhanced) growth in the western plateau. These opposite responses to extreme temperatures over the eastern plateau are explained by the possibility that the occurrence of extreme cold slows the preseason temperature accumulation, delaying the triggering of spring phenology, while extreme hot hastens the accumulation. In the western plateau, in contrast, positive responses to extreme cold are induced by accompanying high precipitation. Furthermore, high extremeness of climate events generally led to a much lower extremeness in growth response, implying that the Tibetan grasslands have a relatively high resistance to climate extremes. The ecosystem models tested could not accurately simulate grassland responses to drought and extreme temperatures, and require re-parameterization before trust can be placed in their output for this region.

关键词： Drought Extreme cold Extreme hot Growth response Alpine grasslands Tibetan Plateau

cold plumes trigger contamination of oceanic mantle wedges with continental crust-derived sediments:Evidence from chromitite zircon grains of eastern Cuban ophiolites

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Geoscience Frontiers 2018年第6期9卷 1921-1936页

作者： J.A.Proenza J.M.González-Jiménez A.Garcia-Casco E.Belousova W.L.Griffin C.Talavera Y.Rojas-Agramonte T.Aiglsperger D.Navarro-Ciurana N.Pujol-Solà F.Gervilla S.Y.O’Reilly D.E.Jacob Departament de Mineralogia Petrologia i Geologia AplicadaUniversitat de BarcelonaC/Martíi Franquès s/n08028BarcelonaSpain Departamento de Mineralogía y Petrología Universidad de GranadaFacultad de CienciasFuentenueva s/n 18002GranadaSpain Instituto Andaluz de Ciencias de la Tierra(CSIC-UGR) Avda.de las Palmeras 4E-18100ArmillaGranadaSpain ARC Centre of Excellence for Core to Crust Fluid Systems(CCFS) GEMOC National Key CentreDepartment of Earth and Planetary SciencesMacquarie UniversitySydneyNSW 2109Australia John de Laeter Centre Curtin UniversityPerthWA 6102Australia Geocycles-Earth System Research Center Institut fur GeowissenschaftenJohannes Gutenberg-UniversitatBecherweg 21D-55099 MainzGermany Departamento de Geociencias Universidad de los AndesBogotáColombia

The origin of zircon grains, and other exotic minerals of typical crustal origin, in mantle-hosted ophiolitic chromitites are hotly debated. We report a population of zircon grains with ages ranging from Cretaceous(99 Ma) to Neoarchean(2750 Ma), separated from massive chromitite bodies hosted in the mantle section of the supra-subduction(SSZ)-type Mayari-Baracoa Ophiolitic Belt in eastern Cuba. Most analyzed zircon grains(n = 20, 287 ± 3 Ma to 2750 ± 60 Ma) are older than the early Cretaceous age of the ophiolite body, show negativeε_(Hf)(t)(-26 to-0.6) and occasional inclusions of quartz, K-feldspar,biotite, and apatite that indicate derivation from a granitic continental crust. In contrast, 5 mainly rounded zircon grains(297±5 Ma to 2126±27 Ma) show positive εHf(t)(+0.7 to +13.5) and occasional apatite inclusions, suggesting their possible crystallization from melts derived from juvenile(mantle)sources. Interestingly, younger zircon grains are mainly euhedral to subhedral crystals, whereas older zircon grains are predominantly rounded grains. A comparison of the ages and Hf isotopic compositions of the zircon grains with those of nearby exposed crustal terranes suggest that chromitite zircon grains are similar to those reported from terranes of Mexico and northern South America. Hence, chromitite zircon grains are interpreted as sedimentary-derived xenocrystic grains that were delivered into the mantle wedge beneath the Greater Antilles intra-oceanic volcanic arc by metasomatic fluids/melts during subduction processes. Thus, continental crust recycling by subduction could explain all populations of old xenocrystic zircon in Cretaceous mantle-hosted chromitites from eastern Cuba ophiolite.We integrate the results of this study with petrological-thermomechanical modeling and existing geodynamic models to propose that ancient zircon xenocrysts, with a wide spectrum of ages and Hf isotopic compositions, can be transferred to the mantle wedge above subducting slabs by cold plumes.

关键词： Zircon U-Pb geochronology Chromitites cold plumes Ophiolites Cuba

Synthesis and properties of SrFe_(12)O_(19) obtained by solid waste recycling of oily cold rolling mill sludge

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International Journal of Minerals,Metallurgy and Materials 2019年第5期26卷 642-648页

作者： Bo Liu Shen-gen Zhang Britt-Marie Steenari Christian Ekberg Institute for Advanced Materials and Technology University of Science and Technology Beijing Nuclear Chemistry and Industrial Material Recycling Department of Chemistry and Chemical Engineering Chalmers University of Technology

The aim of this study was to develop a new approach for the preparation of environmentally friendly, high-value products from oily cold rolling mill(CRM) sludge. Utilizing oily CRM sludge as a source of iron, strontium hexaferrite(SrFe_(12)O_(19)) powders were prepared by multi-step processes involving acid leaching, chemical conversion treatment, and synthesis by a citrate precursor. The influences of citric acid dosage and the pH of the sol system on the formation, crystallite size, and magnetic properties of the obtained SrFe_(12)O_(19) powders were investigated. High saturation magnetization(74.8 mA·m^2·g^(–1)) and intrinsic coercivities(614.46 mT) were achieved for pH 7.0 of the sol system, for which the molar ratio of citric acid dosage to the total dosage of Fe^(3+) and Sr^(2+) was 1.5. This study presents a new approach to utilizing oily CRM sludge, and even refractory iron-containing solid waste.

关键词： strontium ferrite oily cold rolling mill sludge magnetic properties citrate precursor method recycling

Microstructuring of titanium surfaces with plasma-modified titanium particles by cold spraying

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Particuology 2019年第3期17卷 90-104页

作者： P. Breuninger F. Krull S. Buhl A. Binder R. Merz M. Kopnarski B. Sachweh S. Antonyuk Technische Universitat Kaiserslautern Institute of Particle Process Engineering Kaiserslautern Germany BASFSE Ludwigshafen Germany IFOS GmbH Institute for Surface and Thin Film Analysis GmbH Kaiserslautern Germany

Although the deposition mechanisms of the cold spray process are well studied, few reports regarding the use of surface-modified particles exist. Herein, titanium particles 3-39 μm in size and with an angular shape were modified in a plasma-enhanced chemical vapor deposition process in Ar, Ar-C2H2, and N2 plasmas. After Ar-C2H2 and N2 treatments, the respective presence of TiC and TiN on the particle surface was confirmed via transmission electron microscopy and energy-dispersive X-ray, X-ray photoelectron, and Raman spectroscopies. The powders were deposited on titanium substrates by cold spray experiments, where unmodified particles up to 10(xm in size exhibited a successful surface bon ding. This finding was described by an existing analytical model, whose parameters were achieved by computational fluid dynamics simulations taking the particle shape factor into account:. A good deposition of plasma-modified particles up to 30 μm in size was experimentally observed, exhibiting an upper size limit larger than that predicted by the model. Higher surface roughness values were found for plasmamodified particles, as determined by 3D scanning electron microscopy. The water contact angle indicated that argon treatment influenced the wettability. Tribological tests showed a decrease of the initial friction coefficient from 0.53 to 0.47 by microstructuring.

关键词： Chemical vapor deposition cold spray Surface modification Computational fluid dynamics

Tuning of activated sludge in winter based on respirogram profiles under standard and site temperatures

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Journal of Environmental Sciences 2019年第5期31卷 330-338页

作者： Zhihua Li Zhenyu Hang Qian Zhang Shuangshuang Zhang Tianyu Zhang Hanqing Yu School of Environmental and Municipal Engineering Xi'an University of Architecture and Technology Department of Mathematical Sciences Montana State University CAS Key Laboratory of Urban Pollutant Conversion Department of Chemistry University of Science & Technology of China

Respirograms of activated sludge OUR_ x^Tand OUR_x^(20)were measured under site(T) and standard(20°C) temperatures, respectively, and the predicted standard temperature respirogram OUR_( x,cal)^(20)was also calculated using the Arrhenius equation. These respirogram profiles reveal more information than effluent quality. A decrease of OUR_ x ^(20)is a critical alarm signal for the loss of pollutant removal capacity, and a sudden increase of the predicted value OUR_( x,cal)^(20)is an alarm signal for the unrecoverable deterioration of biomass. The sign of OUR_x^(20)–OUR_(x,cal)^(20)can be used for selection of tuning strategies. For example, a negative value of OUR_x^(20)–OUR_( x,cal)^(20)indicates that doubling biomass is difficult,thus strategies such as extending the reaction time with limited available biomass is preferred. The findings in this study elucidated the respiration profile of activated sludge under changes of temperature and can be effectively used for the stable operation of Wastewater Treatment Plants under cold temperatures and seasonal variations.

关键词： Activated sludge cold temperature shocking Oxygen uptake rate(OUR) Respirogram Seasonal variations