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Effect of alloying elements and processing parameters on the Portevin–Le Chatelier effect of Al–Mg alloys

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International Journal of Minerals,Metallurgy and Materials 2015年第2期22卷 175-183页

作者： Peng-cheng Ma Di zhang Lin-zhong Zhuang ji-shan zhang State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing

The effects of alloying elements and processing parameters on the mechanical properties and Portevin-Le Chatelier effect of A1-Mg alloys developed for inner auto body sheets were investigated in detail. Tensile testing was performed in various Zn and Mg contents under different annealing and cold-rolling conditions. In the results, the stress drop and reloading time of serrations increase with increasing plastic strain and exhibit a common linear relationship. The increase rates of stress drop and reloading time increase with increasing Mg or Zn content. The alloys with a greater intensity of serrated yielding generally exhibit a greater elongation. The stress drop and reloading time of serrations decrease with increasing grain size in the case of the annealed samples. The cold-rolled sample exhibits the most severe serra- tion because it initially contains a large number of grain boundaries and dislocations.

关键词： aluminum-magnesium alloys Portevin-Le Chatelier effect alloying elements processing parameters mechanical properties

Microstructure evolution and phase transformation of traditional cast and spray-formed hypereutectic aluminium-silicon alloys induced by heat treatment

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International Journal of Minerals,Metallurgy and Materials 2010年第3期17卷 297-306页

作者： Long-gang Hou Yuan-hua Cai Hua Cui ji-shan zhang State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing Beijing 100083 China School of Materials Science and Engineering University of Science and Technology Beijing Beijing 100083 China

Microstructural evolution and phase transformation induced by different heat treatments of the hypereutectic aluminium-silicon alloy, Al-25Si-5Fe-3Cu （wt%, signed as 3C）, fabricated by traditional cast （TC） and spray forming （SF） processes, were investigated by differential scanning calorimetry （DSC） and scanning electron microscopy （SEM） combined with energy dispersive X-ray spectroscopy and X-ray diffraction techniques. The results show that A17Cu2Fe phase can be formed and transformed in TC- and SF-3C alloys between 802-813 K and 800-815 K, respectively. The transformation from β-Al5FeSi to δ-Al4FeSi2 phase via peritectic reaction can occur at around 858-870 K and 876-890 K in TC- and SF-3C alloys, respectively. The starting precipitation temperature of δ-Al4FeSi2 phase as the dominant Fe-bearing phase in the TC-3C alloy is 997 K and the exothermic peak about the peritectic transformation of δ-Al4FeSi2→β-Al5FeSi is not detected in the present DSC experiments. Also, the mechanisms of the microstructural evolution and phase transformation are discussed.

关键词： hypereutectic Al-Si alloy spray forming cast microstructure phase transformation

Microstructure characterization in a sensitized Al-Mg-Mn-Zn alloy

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Rare Metals 2018年第2期37卷 129-135页

作者： Chun-Yan Meng Di zhang Ping-Ping Liu Lin-Zhong Zhuang ji-shan zhang State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing School of Materials Science and Engineering University of Science and Technology Beijing

Alloying elements, present in the aluminum solid solution or the precipitates, influence the corrosion resistance of A1-Mg-Mn-Zn alloys. In this study, sensi- tizing treatment was applied to an A1-Mg-Mn-Zn alloy to modify the precipitation at the grain boundaries or in the grains. Transmission electron microscopy （TEM） and scanning electron microscope （SEM） were used to characterize various second-phase particles and determine their orientation relationship with the A1 matrix. After sensitizing treatment, z-phase （Mg32（Al, Zn）49） is observed to precipitate along the grain boundaries in a coarser size, producing a discontinuous grain boundary precipitate structure. In addition, Mn-rich particles are found to form with various shapes, such as global, plate and rhombus.

关键词： Al-Mg-Mn-Zn alloy Mg32(A1, Zn)49 phase A16(Mn, Fe) phase Microstructure characterization

Twinning Behavior of a Basal Textured Commercially Pure Titanium Alloy TA2 at Ambient and Cryogenic Temperatures

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Journal of Iron and Steel Research International 2016年第1期23卷 74-77页

作者： jin-ru LUO Xiao SONG Lin-zhong ZHUANG ji-shan zhang State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing

Twinning greatly affects the microstructure and mechanical performance of titanium *** twinning behavior of a basal textured commercially pure titanium TA2 plates rolled to 4% reduction at the ambient and cryogenic temperatures has been *** of the rolled samples were investigated by optical microscope（OM）and the twinning analysis was carried out based on orientation data collected by electron back-scatter diffraction（EBSD）.{1122}contraction twins,{1124}contraction twins and {1012}extension twins have been *** mode activity varied with rolling *** is considered as the dominant deformation mechanism during rolling at both temperatures for the strain *** proportion of grains activates twinning during cryorolling,and greater number and more diverse types of twins are observed;manifestly related to the suppression of dislocation slips at the cryogenic temperature.{1122}contraction twins are the dominate twin type within samples rolled at both ***{1124}contraction twins are observed in the cryorolled sample while there are only a few in the sample rolled at room temperature.A few tiny{1012}twins have been identified in both samples.{1124}contraction twins are preferentially activated at cryogenic deformation temperature and the{1012}extension twins may result in local strain accommodation.

关键词： titanium rolling twinning cryogenic temperature

Microstructure and mechanical properties of cryorolled AZ31 magnesium alloy sheets with different initial textures

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International Journal of Minerals,Metallurgy and Materials 2016年第7期23卷 827-834页

作者： jin-ru Luo Ya-qiong Yan ji-shan zhang Lin-zhong Zhuang State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing

AZ31 magnesium alloy sheets with different strong textures were cryorolled at the liquid-nitrogen temperature to the strain of 4% and 8%. The microstructure and texture of the rolled sheets were investigated via scanning electron microscopy（SEM）, electron backscatter diffraction（EBSD）, and X-ray diffraction（XRD）. The mechanical properties of the sheets were tested through in-plane uniaxial tensile tests at ambient temperature. The tensile stress was exerted in the rolling direction（RD） and transverse directions（TD）. The microstructural and textural evolutions of the alloy during cryorolling were investigated. Due to active twining during rolling, the initial texture significantly influenced the microstructural and textural evolutions of the rolled sheets. A {10 12} extension twin was found as the dominated twin-type in the cryorolled samples. After cryogenic rolling, the ductility of the samples decreased while the strength increased. Twinning also played an important role in explaining the mechanical differences between the rolled samples with different initial textures. The samples were significantly strengthened by the high stored energy accumulated from cryorolling.

关键词： magnesium alloy cryorolling microstructure mechanical properties twinning

Hot Deformation Behavior and Processing Map of Spray Formed M3∶ 2 High Speed Steel

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Journal of Iron and Steel Research International 2016年第5期23卷 501-508页

作者： Lin LU Long-gang HOU Hua CUI jin-feng HUANG Yong-an zhang ji-shan zhang State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing State Key Laboratory of Non-ferrous Metals and Process General Research Institute for Non-ferrous Metals

Hot deformation behavior of a new type of M3∶ 2 high speed steel with niobium addition made by spray forming was investigated based on compression tests in the temperature range of 950-1 150 ℃ and strain rate of 0. 001-10 s^（-1）. A comprehensive constitutive equation was obtained,which could be used to predict the flow stress at different strains. Processing map was developed on the basis of the flow stress data using the principles of dynamic material model. The results showed that the flow curves were in fair agreement with the dynamic recrystallization model. The flow stresses,which were calculated by the comprehensive constitutive equation,agreed well with the test data at low strain rates（ ≤1 s^（-1））. The material constant（ α）,stress exponent（ n） and the hot deformation activation energy（ Q_（HW）） of the new steel were 0. 006 15 MPa^（-1）,4. 81 and 546 kJ·mol^（-1）,respectively. Analysis of the processing map with an observation of microstructures revealed that hot working processes of the steel could be carried out safely in the domain（ T = 1 050-1 150 ℃,ε = 0. 01- 0. 1 s^（-1））with about 33% peak efficiency of power dissipation（ η）. Cracks was expected in two domains at either lower temperatures（〈 1 000 ℃） or low strain rates（ 0. 001 s^（-1）） with different cracking mechanisms. Flow localization occurred when the strain rates exceeded 1 s^（-1） at all testing temperatures.

关键词： high speed steel spray forming hot deformation processing map niobium

Microstructure, mechanical, and corrosion properties of extruded low-alloyed Mg–xZn–0.2Ca alloys

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International Journal of Minerals,Metallurgy and Materials 2019年第10期26卷 1274-1284页

作者： Ying-zhong Ma Chang-lin Yang Yun-jin Liu Fu-song Yuan shan-shan Liang Hong-xiang Li ji-shan zhang State Key Laboratory for Advanced Metals and Materials University of Science and Technology BeijingBeijing100083China State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an 710072China Center of Digital Dentistry Peking University School and Hospital of StomatologyBeijing 100081China Second Clinical Division Peking University Hospital of StomatologyBeijing 100081China

The microstructure, mechanical, and corrosion properties of extruded low-alloyed Mg xZn 0.2Ca (x=0, 1.0, 2.0, 3.0) alloys were investigated in this study. Findings from scanning electron microscope, X-ray diffraction and transmission electron microscopy results indicate that the amount of ternary Ca2Mg6Zn3 phase, as the only secondary phase in 1.0Zn, 2.0Zn, and 3.0Zn alloys, gradually increases with the addition of Zn, while the Mg2Ca phase was observed in the Mg 0.2Ca alloy only. Zn has a strong effect on the orientation and intensity of textures, which also influence mechanical behaviors, as revealed by electron back-scatter diffraction. Among all the alloys, the Mg 2.0Zn 0.2Ca alloy obtains the maximum tensile strength (278 MPa) and yield strength (230 MPa). Moreover, Zn addition has an evident influence on the corrosion properties of Mg xZn 0.2Ca alloy, and Mg 1.0Zn 0.2Ca alloy exhibits the minimum corrosion rate. This paper provides a novel low-alloyed magnesium alloy as a potential biodegradable material.

关键词： magnesium alloy Mg Zn Ca alloy extrusion microstructure mechanical properties corrosion properties textures

Mechanical properties and constitutive behaviors of as-cast 7050 aluminum alloy from room temperature to above the solidus temperature

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International Journal of Minerals,Metallurgy and Materials 2016年第8期23卷 949-958页

作者： Qing-ling Bai Hong-xiang Li Qiang Du ji-shan zhang Lin-zhong Zhuang State Key Laboratory for Advanced Metals and Materials University of Science and Technology BeijingBeijing 100083China SINTEF Materials and Chemistry TrondheimNorway

The mechanical properties and constitutive behaviors of as-cast AA7050 in both the solid and semi-solid states were determined using the on-cooling and in situ solidification approaches, respectively. The results show that the strength in the solid state tends to increase with decreasing temperature. The strain rate plays an important role in the stress–strain behaviors at higher temperatures, whereas the influence becomes less pronounced and irregular when the temperature is less than 250°C. The experimental data were fitted to the extended Ludwik equation, which is suitable to describe the mechanical behavior of the materials in the as-cast state. In the semi-solid state, both the strength and ductility of the alloy are high near the solidus temperature and decrease drastically with decreasing solid fraction. As the solid fraction is less than 0.97, the maximum strength only slightly decreases, whereas the post-peak ductility begins to increase. The experimental data were fitted to the modified creep law, which is used to describe the mechanical behavior of semi-solid materials, to determine the equivalent parameter fGBWL, i.e., the fraction of grain boundaries covered by liquid phase.

关键词： aluminum alloys mechanical properties constitutive relations fitting

Effect of cryogenic rolling and annealing on the microstructure evolution and mechanical properties of 304 stainless steel

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International Journal of Minerals,Metallurgy and Materials 2017年第6期24卷 638-645页

作者： jin-tao Shi Long-gang Hou jin-rong Zuo Lin-zhong Zhuang ji-shan zhang State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing Beijing 100083 China

Metastable 304 austenitic stainless steel was subjected to rolling at cryogenic and room temperatures, followed by annealing at different temperatures from 500 to 950°C. Phase transition during annealing was studied using X-ray diffractometry. Transmission electron microscopy and electron backscattered diffraction were used to characterize the martensite transformation and the distribution of austenite grain size after annealing. The recrystallization mechanism during cryogenic rolling was a reversal of martensite into austenite and austenite growth. Cryogenic rolling followed by annealing refined grains to 4.7 μm compared with 8.7 μm achieved under room-temperature rolling, as shown by the electron backscattered diffraction images. Tensile tests showed significantly improved mechanical properties after cryogenic rolling as the yield strength was enhanced by 47% compared with room-temperature rolling.

关键词： stainless steel cryogenic rolling annealing microstructural evolution mechanical properties recrystallization