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The characterization of fe-rich phases in a high-pressure die cast hypoeutectic aluminum-silicon alloy

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journal of materials science & Technology 2020年第16期47卷 54-62页

作者： x.y.jiao C.f.liu Z.P.guo g.D.Tong s.L.ma y.Bi y.f.Zhang s.m.xiong school of materials science and Engineering Tsinghua UniversityBeijing 100084China Key Laboratory for Advanced materials Processing Technology Tsinghua UniversityBeijing 100084China China fAW foundary Co. LTDChangchun 130011China

Both microstructural characteristics and fracture behavior of fe-rich phases in a high-pressure die-cast hypoeutectic Al-si alloy were *** was focused on the morphology and formation mechanism of fe-rich phases,together with their influence on *** show that primary ferich phases exhibited in blocky shape precipitated from liquid while secondary fe-rich phase in a large net shape was distributed along eutectic boundary participating in a ternary eutectic *** synchrotron x-ray tomography characterization,three fe-rich phases with different morphologies,i.e.,polyhedral shape,fine compact shape and Chinese script-type shape were extracted along the radial *** slow-shot speed promoted the polyhedral fe-rich phase to precipitate in slow-shot sleeve while decreased the formation of fine compact and Chinese script-type fe-rich phases in die *** of a worse deformation compatibility,polyhedral fe-rich phases fractured and became stress concentration sources before the failure of the casting.

关键词： hypoeutectic Al-10si fe-rich phases fracture morphology high pressure die casting

One kind motion of controllable constrained Birkhoffian system:the absence of constraints

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Acta mechanica sinica 2020年第3期36卷 735-741页

作者： j.Chen f.x.mei s.x.liu y.x.guo school of Aerospace Engineering Beijing Institute of TechnologyBeijing 100081China school of Physics Liaoning UniversityShenyang 110000China

This paper is devoted to discuss the motion of controllable constrained Birkhoffian system along with its absence of *** first step is to establish the autonomous and non-autonomous differential equations of motion of the system,based on Pfaff-Birkhoff ***,the existence of constraint multipliers are exhaustively ***,the definition of one kind motion of the system,called free motion,is given,which is described and analyzed by the absence of constraints that are determined by constraint *** 2 illustrates that one system can realize its free motion by selecting proper control *** particular,theorem 2 provides that one system can naturally realize free motion when we consider the integral of the unconstrained Birkhoffian system as the constraints of constrained Birkhoffian ***,the results obtained are illustrated by several examples.

关键词： Constrained Birkhoffian system Kinematic control Absence of constraint free motion

Characterization of high-pressure die-cast hypereutectic Al-si alloys based on microstructural distribution and fracture morphology

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journal of materials science & Technology 2019年第6期35卷 1099-1107页

作者： x.y. jiao j. Wang C.f. liu Z.P. guo g.D. Tong s.L. ma y. Bi y.f. Zhang s.m. xiong school of materials science and Engineering Tsinghua University Beijing 100084 China state Key Laboratory of Automobile safety and Energy Tsinghua University Beijing China China fAW foundry Co. Ltd. Changchun 130011. China

The fracture behavior of high-pressure die-cast hypereutectic(hPDC) Al-si alloys was investigated using a high-resolution laboratory CT and synchrotron x-ray tomography with a particular focus on the influence of hPDC microstructure. Results showed that microstructure of the alloy was mainly comprised of primary silicon particles(PsPs), Al dendrites, Cu-rich phases and pores. most of the coarse PsPs, Cu-rich phases and pores were located in the center of the specimen. The rapid solidification of hPDC led to a heterogeneous microstructural feature. Elemental Cu was enriched in the frontiers of solid-liquid interface, causing the formation of large size dendritic arms. The pores were formed in the interdendrites which endured high stress intensity under high applied stress. microcracks were originated from pores and further connected Cu-rich phases causing intergranular fracture. PsPs worked as obstacles causing piling-up dislocations in the phase interface. In the regions where large size of PsPs enriched in, PsPs ruptured rather than debonded from matrix, indicating transgranular fractures of PsPs. microcracks originated around pores and PsPs tended to converge on the main cracks to decrease the energy required for crack propagation.

关键词： hypereutectic Al-si alloy Primary silicon particles Porosity fracture morphology high pressure die casting

Unusually high corrosion resistance in mo_(x)CrNiCo medium entropy alloy enhanced by acidity in aqueous solution

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journal of materials science & Technology 2023年第8期139卷 59-68页

作者： s.shuang g.j.Lyu D.Chung x.Z.Wang x.gao h.h.mao W.P.li Q.f.he B.s.guo x.y.Zhong y.j.Wang y.yang Department of mechanical Engineering College of EngineeringCity University of Hong KongKowloon TongKowloonHong KongChina state Key Laboratory of Nonlinear mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China school of Engineering science University of Chinese Academy of SciencesBeijing 101408China state Key Laboratory of solidification Processing Center of Advanced Lubrication and Seal MaterialsNorthwestern Polytechnical UniversityXi’an 710072China Unit of structures Department of Materials Science and EngineeringKTHStockholm SE-10044Sweden Thermo-Calc software Råsundav.18SolnaSE-16767Sweden Department of materials science and Engineering College of EngineeringCity University of Hong KongKowloon TongKowloonHong KongChina Institute of Advanced Wear&Corrosion Resistant and functional materials Jinan UniversityGuangzhou 510632China Department of Advanced Design and system Engineering College of EngineeringCity University of Hong KongKowloon TongKowloonHong KongChina

high corrosion resistance of alloys is essential for their structural applications;however,most alloys suffer from degradation of their corrosion resistance with the increasing acidity of their ***,we developed a series of medium-entropy alloys(mEAs)in this work,which ex-hibit high strength,superior fracture toughness and ultra-high corrosion resistance,outperforming the variety of corrosion resistant alloys hitherto *** interestingly,our mEAs exhibit an unusual anti-corrosion behavior and their corrosion resistance increases with acidity in Cl−containing *** extensive thermodynamic calculations,density functional theory(DfT)simulations and experi-ments,we reveal that the unusual anti-corrosion behavior of our mEAs can be attributed to their surface chemical complexity,which facilitates the physio-chemical-absorption of h_(2)O and O_(2)and thus the rapid formation of metastable medium entropy passive films that contain the lowest amount of defects,as compared to the passive films on conventional alloys reported in the literature.

关键词： Corrosion Passivation Alloy design multi-principal element alloys medium-entropy alloys

Towards the diffusion source cost reduction for NdfeB grain boundary diffusion process

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journal of materials science & Technology 2020年第1期36卷 50-54页

作者： h.x.zeng Z.W.liu j.s.Zhang x.f.liao h.y.yu school of materials science and Engineering South China University of TechnologyGuangzhou 510640China

Aiming at improving the performance/cost ratio in grain boundary diffusion process(gBDP),the critical RE containing Pr-Al-Cu alloy,less expensive RE containing La-Al-Cu alloy and non-RE Al-Cu alloy were employed as the diffusion *** preliminary results show that the coercivity was successfully enhanced from 1000 kA/m to 1695,1156 and 1125 kA/m by Pr70Al20Cu10,La70Al20Cu10 and Al75Cu25(at.%) alloys diffusion,respectively,due to the formation of(Nd,Pr)-fe-B,La2 O3 and c-Nd2 O3 phases respectively,after *** is also found that the corrosion resistance can be improved by Al-Cu diffusion due to the positive effects of Al and Cu elements in grain *** present results demonstrated the various coercivity enhancement mechanisms for the gBDP based on different diffusion sources,and provided feasible solutions for cost reduction of gBDP and NdfeB production by saving RE resource.

关键词： grain boundary diffusion Cost reduction Coercivity microstructure Corrosion resistance

mICROsTRUCTURE AND mEChANICAL PROPERTy DEVELOPmENT IN ThE sImULATED hEAT AffECTED ZONE Of V TREATED hsLA sTEELs

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Acta metallurgica sinica(English Letters) 2006年第1期19卷 57-67页

作者： y. T. Chen A.m. guo L.x. Wu j. zeng P.h. li National Enterprise Technology Center Wuhan Iron and Steel （Group） Co.Wuhan 430080 China

The simulated heat affected zone （hAZ） of the high strength low alloy （hsLA） steels containing 0%, 0.047%, 0.097% and 0.151% vanadium, respectively, were studied with gleeble-2000 thermomechanical simulator to determine the influence of vanadium addition on the mechanical properties of the hAZ. The hAZ simulation involved reheating the samples to 1350℃, and then cooling to ambient temperature at a cooling rate of 5℃/s ranging from 800 to 500℃ （△8/5=60s）. The mechanical properties including tensile strength and -20℃ impact toughness were conducted. The microstructures of the base steel and the simulated hAZs were investigated using optical microscope, scanning electron microscope （ sEm ） and transmission electron microscope （TEm）. Based on the systemutic examination, the present work confirmed that about 0.05% vanadium addition to low carbon low alloy steels resulted in expected balance of strength and toughness of the hAZ. And more than 0.10% levels addition led to detrimental toughness of the hAZ sEm study showed that the simulated 0.097% and 0.151%V hAZs consisted of more coarse ferrite plates with greater and more m-A constituents along austenite grain and ferrite plate bound- aries. The impact fracture surfaces of the simulated 0.097% and 0.151%V hAZs showed typically brittle mode with predominant cleavages. The size of the facet in the fracture surface increased with increasing vanadium level from 0.097% to 0.151%.As a result, the simulated 0.151% V hAZ has the lowest impact toughness of the four specimens.

关键词： vanadium high strength low alloy (hsLA) steel mechanical property,heat affected zone (hAZ)

New methods to find solutions and analyze stability of equilibrium of nonholonomic mechanical systems

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Acta mechanica sinica 2018年第6期34卷 1136-1144页

作者： j.Chen y.x.guo f.x.mei school of Aerospace Engineering Beijing Institute of TechnologyBeijing 100081China school of Physics Liaoning UniversityShenyang 110000China

A large proportion of constrained mechanical systems result in nonlinear ordinary differential equations,for which it is quite difficult to find analytical *** initial motions method proposed by Whittaker is effective to deal with such problems for various constrained mechanical systems,including the nonholonomic systems discussed in the first part of this paper,where in addition to differential equations of motion,nonholonomic constraints *** final equations of motion for these systems are obtained in the form of corresponding power ***,an alternative,direct method to determine the initial values of higher-order derivatives(q)0,(q)0,…is proposed,being different from that of *** second part of this work analyzes the stability of equilibrium of less complex,nonholonomic mechanical systems represented by gradient *** discuss the stability of equilibrium of such systems based on the properties of the gradient *** advantage of this novel method is its avoidance of the difficulty of directly establishing Lyapunov functions aimed at such unsteady nonlinear ***,these theoretical considerations are illustrated through four examples.

关键词： Nonholonomic system Initial motions gradient system Lyapunov function stability

Improved mechanical properties and strengthening mechanism with the altered precipitate orientation in magnesium alloys

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journal of magnesium and Alloys 2022年第5期10卷 1256-1267页

作者： y.j.Wan y.zeng y.C.Dou D.C.hu x.y.Qian Q.zeng K.x.sun g.f.Quan Key Laboratory of Advanced Technologies of materials Ministry of EducationSchool of Material Science and EngineeringSouthwest Jiaotong UniversityChengdu 610031China College of materials science and Engineering Sichuan University of Science and EngineeringZigong 643000China Department of materials The University of ManchesterOxford RoadManchester M139PLUnited Kingdom

Aging prior to twinning deformation was proposed to alter the precipitate orientation of the plate-shapedβ-mgAlfrom(0002)basal planes(named basal plates)to■prismatic planes(named prismatic plates)in AZ31 mg *** experimental results showed that the compressive yield strength(Cys)of the sample containing prismatic plates increased 40 mPa and the compression ratio raised by 22%compared to that containing basal *** underlying strengthening mechanism was analyzed via a yield strengthen(ys)model with a function of grain size,precipitate characters(size,oritention,fraction)and schmid factor(sf).It revealed that the improvement of Cys was mainly attributed to the altered precipitate orientation and refined grain size produced by twinning ***,the prismatic plates always have a stronger hardening effect on basal slip than basal plates under the same varites of precipitate diameter and ***,the decreased CRss ratio of prismatic slip to basal slip revealed that the activity of non-basal slip in mg alloy might be *** activated slip systems provided more mobile dislocations,contributing to the large compression ratio of the mg rolled sheet with prismatic plates.

关键词： Precipitate orientation Precipitation strengthening grain boundary strengthening yield strength model

magnetic properties and magnetocaloric effects in(ho_(1-x)y_x)_5Pd_2 compounds

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Chinese Physics B 2019年第5期28卷 293-299页

作者： x f Wu C P guo g Cheng C R li j Wang y s Du g h Rao Z m Du school of materials science and Engineering University of Science and Technology Beijing school of materials science and Engineering Guilin University of Electronic Technology guangxi Key Laboratory of Information materials

The crystal structure, magnetic and magnetocaloric properties of(ho_(1-x) y_(0.5))_5 Pd_2 compounds are investigated. All the compounds crystallize in a cubic Dy_5 Pd_2-type structure with the space group fd3 m and undergo a second order transition from spin glass(sg) state to paramagnetic(Pm) state. The spin glass transition temperatures T_g decrease from 26 K for x = 0 to 13 K for x = 0.5. In the Pm region, the reciprocal susceptibilities for all the compounds obey the Curie–Weiss law. The paramagnetic Curie temperatures(θp) for ho_5 Pd_2,(ho_(0.75) y_(0.25)_5 Pd_2, and(ho_(0.5) y_(0.5))_5 Pd_2 are determined to be 32 K, 30 K, and 22 K, respectively, and the corresponding effective magnetic moments(μeff) are10.8 μB/ho, 10.3 μB/RE, and 7.5 μB/RE, respectively. magnetocaloric effect(mCE) is anticipated according to the maxwell relation, based on the isothermal magnetization curves. for a magnetic field change of 0–5 T, the maximum values of the isothermal magnetic entropy change-?smof the(ho_(1-x)y_x)_5 Pd_2(x = 0, 0.25, and 0.5) compounds are determined to be 11.5 j·kg^(-1)·K^(-1), 11.1 j·kg^(-1)·K^(-1), and 8.9 K j·kg^(-1)·K^(-1), with corresponding refrigerant capacity values of 382.3 j·kg^(-1), 336.2 j·kg^(-1), and 242.5 j·kg^(-1), respectively.

关键词： (ho1-xyx)5Pd2 compounds magnetic transition magnetocaloric effect