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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

High strength Al_(0.7)CoCrFeNi_(2.4)hypereutectic high entropy alloy fabricated by laser powder bed fusion via triple-nanoprecipitation

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Journal of Materials Science & Technology 2024年第20期187卷 141-155页

作者： Zhaowen Geng Chao Chen Miao Song Jinru Luo Jiaxuan Chen Ruidi Li Kechao Zhou Cent South Univ State Key Lab Powder MetChangsh1410083China Suzhou Laboratory Suzhou215004China

Eutectic high-entropy alloys,composed of FCC/B2 phases with a narrow solidification interval and excel-lent fluidity,have become a new hotspot in additive ***,their microstructures exhibit significant sensitivity to processing parameters,feedstocks,and composition,ultimately limiting the alloys’engineering ***,a hypereutectic Al_(0.7)CoCrFeNi_(2.4)alloy with a low cracking sus-ceptibility index was designed by Thermo-Calc calculation and fabricated by laser powder bed *** show that the as-printed Al_(0.7)CoCrFeNi_(2.4)alloy manifests a stable cellular structure,coupled with appreciable ultimate tensile strength(≥1200 MPa)and ductility(≥20%)over a wide range of process-ing *** aging at 800℃for 30 min,outstanding strength(1500 MPa)and elongation(15%)were *** mechanical properties after aging stem from a triple strengthening mecha-nism,i.e.,L1_(2) nanoprecipitates and rod-shaped B2 particles within the FCC matrix,along with Cr-enriched spherical nanoparticles in the B2 ***,hierarchical structure,i.e.,FCC dominated matrix,a discontinuous B2 phase,a precipitation-free zone in the B2 phase,and a K-S orientation relationship be-tween FCC and B2,facilitate to maintain excellent *** results guide designing HEAs by AM with controllable microstructures and outstanding mechanical properties for industrial applications.

关键词： Laser powder bed fusion hypereutectic High entropy alloys Nanoprecipitation Strengthening mechanism

Mechanical properties of hypereutectic Al-Si alloy by semisolid processing

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中国有色金属学会会刊：英文版 2000年第4期10卷 441-444页

作者：李树索赵爱民毛卫民钟雪友北京科技大学北京

Semisolid hypereutectic Al Si alloy billets were obtained by electromagnetic stirring, in which microstructure of primary silicon gets rounder and there are a large number of rosette α phases appearing. Compared with conventional gravity die casting alloys, the tensile strength and elongation of semisolid forming hypereutectic Al Si get obviously improved. Change of primary silicon morphology of semisolid hypereutectic Al Si alloy made by electromagnetic stirring is the main reason of better tensile strength, and a large number of rosette α phases precipitation is the main reason of better elongation.

关键词： semisolid processing hypereutectic Al Si alloy tensile strength elongation

Semi-solid characteristics and thixoforming of hypereutectic Al-Si alloy

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中国有色金属学会会刊：英文版 2000年第3期10卷 309-313页

作者： LIU Chang ming(刘昌明) HE Nai jun(何乃军) LI Hua ji(李华基) Chongqing Univ Sch Mech Engn State Key Lab Mech Transmiss Chongqing 400044 Peoples R China

Effects of processing parameters on microstructure evolutions by mechanical stirring, procedures for obtaining thixotropy in semi solid slurries, and procedure for thixoforging component, were investigated in hypereutectic Al Si alloy. It is shown that 605 ℃ was the proper temperature for stirring treatment of this alloy, at which the coarse and plate primary Si crystals were effectively changed to globular crystals with a mean diameter of 200 μm after 50 min stirring, that billets with excellent thixotropy were obtained after 50 min remelting at 575 ℃, in which solid fraction of matrix and primary Si crystals was about 60%, and that a perfect near net shape component of disc casting was obtained by thixoforging.

关键词： hypereutectic Al Si alloy primary Si crystals thixoforming

Effect of deformation on microstructure and conductivity of hypereutectic aluminum-silicon alloy

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稀有金属材料与工程 2011年第S3期40卷 47-50页

作者： Wang Yuxin 1, 2 , Zhang Yu 1 , Yang Ying 1 , Liao Wenjun 1 , Lu Wei 1 , Yan Biao 1 , Gao Wei 2 , Chen Weiwei 2 1 Tongji University, Shanghai 200092, China 2 The University of Auckland, PB 92019, Auckland, New Zealand Tongji Univ Shanghai Key Lab D&A Met Funct Mat Sch Mat Sci & Engn Shanghai 200092 Peoples R China Univ Auckland Auckland 1 New Zealand

Plastic deformation of sprayed alloy is an effective method to fabricate the hypereutectic aluminum-silicon alloy which combines good conductivity and toughness. In this study, Al-20Si-0.35 RE (wt%) alloy was synthesized by spray atomization and deposition technique. The sprayed deposition and over-spray powder were hot-extruded and plastic deformed respectively. Microstructure and conductivity were systematically performed in order to understand the influence of deformation on microstructure and conductivity of the hypereutectic alloy. The Si particles are refining and uniformly distributed in the Al matrix due to the proper addition of rare earth metal and the rapid solidification preparation method. The microstructure of plastic deformed alloy has invariably indicated that severe plastic deformation lead to the even refinement of microstructure. Both the conductivity of over-spray powder extrusion and sprayed deposition extrusion were obviously improved after plastic deformation. Possible mechanisms of deformation on microstructure and conductivity of hypereutectic aluminum-silicon alloy are discussed.

关键词： hypereutectic Al-Si alloy deformation hot-extrusion conductivity

Effect of Cu-Ni and Cu-Ni-Mn on the Microstructural and Mechanical Behaviour of As-Cast Non-Inoculated hypereutectic Grey Iron

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Journal of Minerals and Materials Characterization and Engineering 2020年第2期8卷 27-46页

作者： Seidu Ojo Adama Sumaila Onigbajumo Adetunji Department of Metallurgical and Materials Engineering Federal University of Technology Akure Ondo State Nigeria Ajaokuta Steel Company Limited (ASCO) Ajaokuta Complex Kogi State Nigeria School of Mechanical Medical and Process Engineering Queensland University of Technology Brisbane Australia

The hypereutectic region of grey cast iron has received very little attention especially for designing cast products by researchers. Due to its high carbon equivalence, hypereutectic grey iron poses some challenges especially its tendency for grey to white transition (GWT) at this level of carbon content. However, hypereutectic grey iron possesses inherent properties that could be easily utilized for improved performance in automobile engines and brake pad system. Significantly, they could be modified for superior hardness, strength and toughness. This study presents the effect of microalloying on the mechanical behaviour of hypereutectic grey cast iron with carbon equivalence above 4.5. The first part of this work presented in this paper considers the addition of Cu-Ni and Cu-Ni-Mn to series of as-cast hypereutectic grey cast iron and their hardness and tensile strength were studied and compared. A total of 33 cast samples were obtained with the control sample. The examination of the micrographs revealed that graphite eutectics cells of Type A and A + D were obtained in the resulting microstructure. Results analyses showed that the ferrite forming tendency of silicon was suppressed due to the high carbon content of the as-cast hypereutectic grey iron coupled with the absence of inoculation which plays a great role in the graphite flake type, network, size and distribution. Cu-Ni microalloying was also confirmed to promote hardness with the hardening effect limit of nickel observed at 1.3% composition. For Cu-Mi-Mn addition, excess and free sulphur in the hyper- eutectic grey iron results in reverse effect of manganese on strength, hardness, reduced graphite flake size and shape.

关键词： hypereutectic Grey Iron Microstructure Hardness Tensile Strength Inoculation Graphitization Cast Iron Alloying

Comparative cyclic oxidation behaviour and effect of oxides on hardness of wear resistance coating alloys T-401 and T-900

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Journal of Iron and Steel Research International 2019年第10期26卷 1069-1079页

作者： Abdul Rehman Yang Liang Mohammad Hassan Shirani Bidabadi Zheng Yu Chi Zhang Hao Chen Zhi-gang Yang Key Laboratory of Advanced Materials Ministry of EducationSchool of Materials Science and EngineeringCollaborative Innovation Center of Advanced Nuclear Energy TechnologyTsinghua UniversityBeijing 100084China

The investigated alloys are newly developed Tribaloy alloys with enhanced crack and oxidation resistance over the traditional Tribaloy *** cyclic oxidation performance and effects of complex oxides on the hardness of cobaltbased Tribaloy alloys T-401(hypoeutectic)and T-900(hypereutectic)were *** results showed that T-900 alloy has a lower oxidation rate as compared to T-401 alloy at 800 and 1000℃,which attributed to the formation of dense continuous Cr2O3 layer with an upper thinner continuous layer of CoCr2O4 and NiCr2O4 *** 1000℃,T-401 alloy exhibited poor oxidation resistance due to severe spallation after 3 cycles(45 h).After oxidation,T-900 alloy exhibits 98%and 18%lower mass gain than T-401 alloy at 1000 and 800℃,*** T-900 alloy,relationship between mass gain and thickness of oxide layer revealed that mass will increase 0.162 mg/cm2 for every 1-μm increase in the oxides *** SiO2 oxide was observed at 800 and 1000℃for both ***,the extent of internal Si oxides increased with increasing oxidation temperature from 800 to 1000℃.Consequently,internal oxidation of Si led to the formation of Laves phase-depleted region near oxide/alloy interface in T-900 alloy at 1000℃.Thus,hardness of T-900 alloy decreased from 618 to 392 HV beneath the oxide/alloy interface at 1000℃,whereas hardness of T-900 and T-401 alloys after cyclic oxidation test at 800℃increased from 618 to 855 and 519 to 685 HV,respectively.

关键词： Tribaloy Hypoeutectic alloy hypereutectic alloy Cyclic oxidation Depletion Nitride Hardness

Preparation and Characterization of High Conductivity Aluminium Silicon Alloy

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稀有金属材料与工程 2011年第S3期40卷 185-187页

作者： Liao Wenjun1, 2, Wang Yuxin1, Yu Zhang1, Yang Yinhui1, Dong Gang1, Yan Biao1 1Tongji University, Shanghai 200092, China 2Shanghai Electric Group Co., Ltd. Central Academe, Shanghai 200070, China Tongji Univ Shanghai Key Lab D&A Met Funct Mat Sch Mat Sci & Engn Shanghai 200092 Peoples R China Shanghai Elect Grp Co Ltd Cent Acad Shanghai 200070 Peoples R China

hypereutectic aluminum-silicon alloy powder of Al-20Si-0.35RE was synthesized by using the inert gas atomization technique. This powder was ball milled for different time and hot extruded subsequently. The microstructure and electrical conductivity of alloy were studied by powder particle size analyzer, scanning electron microscope, X-ray diffraction and bridge resistance instrument respectively. It is indicated that the powder got by spray method have a better homogeneous distribution. The proper RE amount and milling time improved the conductivity due to either microstructural refining or decreasing of Si solid solubility in Al matrix. The conductivity changed with ball milling time, while unique high conductivity (75%IACS) could be achieved after milling for 12 h and hot-extruded 3 times. This kind of high conductivity aluminum-silicon alloy will be a potential conductor material which could be extensively used in the electrical engineering field.

关键词： hypereutectic Al-Si alloy gas atomization hot-extrusion conductivity

Microstructural characteristics of Al-20Si-2Cu-0.4Mg-1Ni alloy formed by rheo-squeeze casting after ultrasonic vibration treatment

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Transactions of Nonferrous Metals Society of China 2012年第12期22卷 2863-2870页

作者：吴树森钟鼓安萍万里中江秀雄华中科技大学材料成形与模具技术国家重点实验室武汉430074 早稻田大学材料科学与工程系

A swash plate for air conditioning compressor of cars was formed by rheo-squeeze casting with semi-solid Al-Si alloy slurry prepared by ultrasonic vibration process, and the microstructure of this alloy was investigated. Besides the microstructures of primary Si particles and α(Al)+β-Si eutectic phases, non-equilibrium α(Al) particles or dendrites are discovered in the microstructure of the Al-20Si-2Cu-0.4Mg-1Ni alloy. Rapid cooling generated by squeeze casting process rather than the pressure is considered as the main reason for the formation of non-equilibrium α(Al) phase. The sound pressurizing effect of ultrasonic vibration also enables the non-equilibrium α(Al) phases to form above eutectic temperature and grow into non-dendritic spheroids in the process of semi-solid slurry preparation. Non-equilibrium α(Al) phases formed in the hypereutectic Al-Si alloy with ultrasonic vibration treatment, consist of round α(Al) grains formed above the eutectic temperature and a small amount of fine α(Al) dendrites formed under the eutectic temperature. The volume fraction of primary Si particles is decreased significantly by the effect of ultrasonic vibration through increasing the solid solubility of Si atoms in α(Al) matrix and decreasing the forming temperature range of primary Si particles. The average particle diameter and the volume fraction of primary Si particles in microstructure of the swash-plate by rheo-squeeze casting are 24.3 μm and 11.1%, respectively.

关键词： Al-Si alloy hypereutectic ultrasonic vibration squeeze casting non-equilibrium α(Al) semi-solid slurry