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Microstructures and mechanical properties of Al-Cu-Mn alloy with La and Sm addition

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Rare Metals 2012年第4期31卷 332-335页

作者： chen, zhongwei chen, Pei Ma, Cuiying State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi'an 710072ShaanxiPR China

The effect of single addition of La or Sm on the microstructures and mechanical properties of an Al-Cu-Mn alloy were investigated by microstructure characterization and tensile *** results show that addition of La or Sm into the Al-Cu-Mn alloy can remarkably increase the density of θ' phase and refine the microstructure,and thus,improves the mechanical properties at room *** addition results in a more considerable increase in the density and refinement of θ' phase than Sm *** addition has a more significant contribution on the mechanical properties of the Al-Cu-Mn alloy than Sm *** addition,a new phase of Al_6Cu_6La is formed in the Al-Cu-Mn alloy with La addition.

关键词： microstructure mechanical property Al-Cu-Mn alloy lanthanum samarium

Secondary Solidification Behaviour of AA8006 Alloy Prepared by Suction Casting

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Journal of Materials Science & Technology 2011年第9期27卷 769-775页

作者： zhongwei chen Hailing Zhang Yimin Lei State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi＇an 710072 China

Solidification behaviour of AA8006 aluminium alloy in suction casting has been investigated by field emission scanning electron microscopy with energy dispersive spectroscopy （EDS）. It is found that there is a secondary solidification process of the remaining liquid in located region of α-Al dendrites, and the cooling rate influences not only the solidification of the primary α-Al dendrite, but also the secondary solidification process of the remaining liquid. With the primary solidification being responsible for the formation of the relatively large α- Al dendrite, a fine and homogeneous microstructure is observed in the secondary solidification. Furthermore, because of the presence of the fine microstructure, the eutectic reaction is confined into small intergranular areas, inducing the formation of the laminar eutectic phase in the primary solidification region and fibrous eutectic phase in the secondary solidification region. EDS analysis shows that the content of Fe is higher in the secondary solidification region, and the enrichment of the solute element further confirms the existence of the secondary solidification.

关键词： Secondary solidification Suction casting AA8006 alloy Microstructure

Eutectic nucleation in Al-7 wt pct Si-Mg casting alloys

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Acta Metallurgica Sinica(English Letters) 2012年第5期25卷 340-346页

作者： chen, zhongwei Ma, Cuiying Zhao, Jing Northwestern Polytech Univ State Key Lab Solidificat Proc Xian 710072 Peoples R China

The nucleation of eutectic crystals of hypoeutectic A1-7 wt pct Si-Mg casting alloys modified by Ce and Sr was studied by using differential scanning calorimeter （DSC） and scanning electron microscope （SEM）. DSC results were applied to calculate the values of activity energy and nucleation work of eutectic nucleation for the alloys. These values were decreased and the eutectic nucleation frequency was increased with the addition of Ce and Sr to the alloys. Moreover, the morphology of eutectic silicon in the modified alloys was partially or fully modified as fine, fibrous or coral, and DSC plots show that the eutectic undercooling of A1-7 wt pct Si-Mg alloys were increased with additions of modified agents. The mechanism of eutectic modification is combined actions of the accelerated nucleation and the restricted growth.

关键词： Al-Si-Mg alloy Eutectic nucleation Ce and Sr addition DSC

A Model for Evaluation of Grain Sizes of Aluminum Alloys with Grain Refinement Additions

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Journal of Materials Science & Technology 2007年第5期23卷 619-622页

作者： zhongwei chen Zhi HE Wanqi JIE State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi＇an 710072 China

Based on the assumption that the nucleation substrates are activated by constitutional undercooling generated by an adjacent grain growth and solute distribution during the initial solidification, a model for calculation of the grain size of aluminum alloys with the grain refinement is developed, where the nucleation is dominated by two parameters, i.e. growth restriction factor Q and the undercooling parameter P. The growth restriction factor Q is proportional to the initial rate of constitutional undercooling development and can be used directly as a criterion of the grain refinement in the alloys with strong potential nucleation particles. The undercooling parameter P can be regarded as the maximum of constitutional undercooling △Tc. For weak potential nucleation particles, the use of RGS would be more accurate. The experimental data of the grain refinement of pure aluminum and AlSi7 alloys are coincident predicted results with the model.

关键词： Grain refinement Constitutional undercooling Nucleation Aluminum alloys

Simulation of microwave’s heating effect on coal seam permeability enhancement

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International Journal of Mining Science and Technology 2019年第5期29卷 785-789页

作者： Huang Jinxin Xu Guang chen Yinping chen zhongwei Department of Mining Engineering and Metallurgical Engineering Western Australian School of MinesCurtin UniversityKalgoorlie 6430Australia State Key Laboratory of Coal Resources and Safe Mining China University of Mining and TechnologyXuzhou 221116China School of Mechanical and Mining Engineering The University of QueenslandBrisbane 4072Australia

As hydraulic fracturing was forbidden in some countries due to possible negative environmental impacts and enhanced coalbed methane(ECBM)was restricted by in-situ conditions,microwave heating was proposed to enhance coalbed *** of the mechanisms of improving coal permeability with microwave irradiation is that thermal expansion caused by microwave *** study the influence of microwave’s heating effect of coal samples,the simulations were conducted using a coupled electromagnetic,thermal and mechanical model in this *** temperature,Von-Mises stress and strain distribution of coal sample are recorded every 10 *** permeability distribution is also obtained based on the relationship between strain and permeability from *** was found that volume average temperature,stress,strain and permeability increase almost linearly with *** average permeability increased from 1.65 10×16 m^2 to 3.63 10×16 m^2 under 2.45 GHz and 500Wmicrowave radiation after 300 *** significant increase proved microwave to be effective in coal seam permeability enhancement.

关键词： Microwave heating Permeability enhancement Thermal stress Numerical simulation COMSOL Multiphysics

Solid Oxide Electrolysis of H_(2)O and CO_(2) to Produce Hydrogen and Low‑Carbon Fuels

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Electrochemical Energy Reviews 2021年第3期4卷 508-517页

作者： Yun Zheng zhongwei chen Jiujun Zhang College of Sciences Institute for Sustainable EnergyShanghai UniversityShanghai 200444China Department of Chemical Engineering University of WaterlooWaterlooON N2L 3G1Canada

Solid oxide electrolysis cells(SOECs)including the oxygen ion-conducting SOEC(O-SOEC)and the proton-conducting SOEC(H-SOEC)have been actively investigated as next-generation electrolysis technologies that can provide high-energy conversion efficiencies for H_(2)O and CO_(2) electrolysis to sustainably produce hydrogen and low-carbon fuels,thus providing higher-temperature routes for energy storage and *** research has also focused on the promotion of SOEC critical components to accelerate wider practical *** on these investigations,this perspective will summarize the most recent progress in the optimization of electrolysis performance and long-term stability of SOECs,with an emphasis on material developments,technological approaches and improving strategies,such as nano-composing,surface/interface engineering,doping and in situ *** technical challenges are also analyzed,and future research directions are proposed to achieve SOEC technical maturity and economic feasibility for diverse conversion applications.

关键词： Solid oxide electrolysis cells Hydrogen production Carbon dioxide reduction Proton conductive electrolyte Optimization strategies

Effect of strontium on primary dendrite and eutectic temperature of A357 aluminum alloy

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China Foundry 2010年第2期7卷 149-152页

作者： chen zhongwei Zhang Ruijie State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi＇an 710072 Shaanxi China Faculty of Life Science Northwestern Polytechnical University Xi＇an 710072 Shaanxi China

Solidification process of A357 alloy with Sr addition was investigated in this *** particular,the effects of strontium and cooling rate on α-Al dendrite and Al-Si eutectic characteristic temperature were characterized by differential thermal analysis(DTA).Sr addition not only modifies the Al-Si eutectic,but also affects the morphology and structure of primary α-Al *** decreases the growth temperature of α-Al dendrite and Al-Si eutectic,and it also affects the dendrite growth *** has been found that such effect becomes more significant with higher cooling rate.

关键词： solidification differential thermal analysis(DTA) A357 aluminium alloy strontium modification

Effects of water content, water type and temperature on the rheological behaviour of slag-cement and fly ash-cement paste backfill

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International Journal of Mining Science and Technology 2020年第3期30卷 271-278页

作者： Yue Zhao Abbas Taheri Murat Karakus zhongwei chen An Deng School of Civil Environmental and Mining EngineeringThe University of AdelaideAdelaide 5005Australia School of Mechanical and Mining Engineering The University of QueenslandBrisbane 4072Australia

The pumping ability and placement performance of fresh cemented paste backfill(CPB) in underground mined cavities depend on its rheological properties. Hence, it is crucial to understand the rheology of fresh CPB slurry, which is related to CPB mixture design and the temperature underground. This paper presented an experimental study investigating the effects of binder type, content, water chemical properties and content, and temperature, on the rheological properties of CPB material prepared using the tailings of a copper mine in South Australia. Portland cement(PC), a newly released commercially manufactured cement called Minecem(MC) and fly ash(FA) were used as the binders added to the mine tailing materials. Various amounts of two different water types were added to the mixtures in the preparation of backfill material slurry. Six different temperatures ranging from 5 to 60 °C were to investigate the effect of temperature on CPB rheology. Overall, the increasing water content and decreasing temperature lead to lower yield stress. Based on the results obtained from the rheological properties of CPB slurry, it was found that at room temperature(25 °C), with regards to the unconfined compressive strength(UCS) performance, the replacement of 4% PC mixed CPB(28 days UCS 425 k Pa) to 3% MC mixed CPB(28 days UCS 519 k Pa), reduced the slurry yield stress from 210.7 to 178.5 Pa. The results also showed that the chemical composition of water affects the yield stress of CPB slurry and that MC mitigates the negative effect of mine-processed water(MW) and thus lead to improve the rheological properties of the slurry. However, the results suggested that the rheological properties of a mixture using MC is very sensitive to the water volume and temperature change. Therefore, using MC in backfill requires better quality control in slump mixing.

关键词： Cemented paste backfill Minecem Rheology Yield stress Fly ash Portland cement

In-situ Observation of Tensile Fracture in A357 Casting Alloys

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Journal of Materials Science & Technology 2014年第2期30卷 139-145页

作者： zhongwei chen Xiaolei Hao Yu Wang Kai Zhao State Key Laboratory of Solidification Processing Northwestern Polytechnical University

The mechanism of damage evolution and fracture in A357 casting alloys was investigated by in-situ scanning electron microscopy （SEM） tensile testing. Different microstructures of A357 casting alloys were produced by eutectic Si modification and T6 heat treatment. It is shown that microcracks in these alloys are predominantly formed in eutectic Si particles. Large and elongated eutectic Si particles in unmodified alloy show the greater tendency to cracking, whereas cracking of small and round eutectic Si particles in Sr modified and T6 heat treated alloys is relatively lag. The crack mainly propagates along the broken eutectic Si particles in unmodified and Sr modified alloys or along the deepened shear bands in T6 heat treated alloy with accumulating the applied strain. The results were discussed in terms of Weibull statistics and the fracture models were established.

关键词： A357 casting alloy Eutectic silicon In-situ scanning electron microscopy (SEM) Fracture mechanism