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Influence of MnS particles on the behaviors of grain boundary migration in Fe-3%Si alloys

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Chinese Science Bulletin 2009年第21期54卷 4537-4540页

作者： mao weimin AN ZhiGuo LI ShuXia State Key Laboratory of Advanced Metals and Materials University of Science and Technology Beijing Beijing 100083 China

The precipitation behaviors of MnS particles at 900℃ in a hot deformed Fe-3%Si alloy were observed statistically. The ratio of MnS particles on dislocations and in grain boundaries was calculated based on a model concerning the second phase precipitation in supersaturated solid solution. It was indicated that the precipitation of MnS particles on dislocations prevailed. The coarsening process of MnS particles in grain boundaries determined the boundary mobility during the secondary recrystallization. However, the density difference of precipitated MnS particles inside the grains on both sides of a boundary will determine the migration direction of the boundary as well, besides the grain size effect. It was observed that the densities of MnS particles in two neighboring grains were commonly different, and the boundary tended to move towards the area with lower particle density. The factors, e.g. dislocation densities in differently oriented grains will affect the density of precipitated particles, in which the Goss grains with higher particle density could grow more easily.

关键词：粒子密度迁移行为夹杂物粮食合金 Si 铁密度差异

Changes of crystallinity and spherulite morphology in isotactic polypropylene after rolling and heat treatment

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Journal of University of Science and Technology Beijing 2008年第4期15卷 514-520页

作者： Juan Jia weimin mao Dierk Raabe School of Materials Science and Engineering University of Science and Technology Beijing Beijing 100083 China Max-Planck-Institut fur Eisenforschung Max-Planck-Str. 1 Düsseldorf 40237 Germany

The spherulite morphology of the rolled and subsequent heat-treated isotactic polypropylene （iPP） was observed by polarized microscopy, and the crystallinity evolution of materials was also measured by the wide angle X-ray scattering （WAXS）. Rolling led to the oblate spherulites in the deformed iPP samples. The sheared crystalline lamellae broke apart into sets of crystalline blocks during rolling. As a result, the crystallinity of the iPP samples was greatly reduced during deformation, which induced the unclear spherulites and spherulite boundaries. Subsequent heat treatment resulted in the strong reerystallization of the rolled iPP samples. But the recrystaUizatinn in this work only meant the rearrangement of the macromolecule along the unbroken crystalline lamellae and the existing small crystalline blocks in the deformed spherulites. Heat treatment did not change the shape of the spherulites formed during deformation. The recrystallization also resulted in very clear spherulites and spherulite boundaries.

关键词： isotaetic polypropylene (iPP) rolling heat treatment X-ray diffraction crystallinity spherulites

Opposite Relationship between Orientation Selection and Texture Memory in the Deformed Electrical Steel Sheets during α→γ→α Transformation

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Journal of Materials Science & Technology 2017年第12期33卷 1522-1530页

作者： Louwen Zhang Ping Yang weimin mao School of Materials Science and Engineering University of Science and Technology BeijingBeijing 100083China

The undesired {111} texture component for the magnetic properties mainly exists in the sheets of electrical steels by the conventional process, whereas the sheets with the non-{111} texture can be obtained by α→γ→α transformation. In this paper, we mainly investigate the opposite relationship between orientation selection and texture memory in the deformed ultra-low carbon steel sheet during →→ transformation annealing. A 0.5 mm thick hot-rolled sheet is directly subjected to transformation. The result shows that the specific transformation textures are not possible to generate in the sheets without deformation. Besides, transformation annealing is conducted on the recrystallized sheets in hydrogen and vacuum, respectively. The near {100} and {110} grains have the growth advantage at the atmosphere/metal interface, and the initial ferrite textures are retained in vacuum. Cold-rolled sheets with different thicknesses are annealed for transformation in vacuum, hydrogen and nitrogen, *** near {100} and {110} textures are still the preferential orientations at the atmosphere/metal interface. When the surface grains have sufficiently large growth advantage, the {111} grains developed by texture memory effect will be annexed. Otherwise, the {111} grains at the center layer of the sheets are hard to be replaced, and they are retained after α→γ→α transformation cycle. The results of deformed sheets annealed with different heating rates in hydrogen show that the growth of initial recrystallization grains has a great effect on variant selection.

关键词： Orientation selection Texture memory Electrical steels α→γ→α transformation Electron back-scatter diffraction

Inhomogeneous Distribution of Second Phase Particles in Grain Oriented Electrical Steels

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Journal of Materials Science & Technology 2011年第12期27卷 1120-1124页

作者： Yang Li weimin mao Ping Yang Department of Materials University of Science and Technology Beijing Beijing 100083 China State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing Beijing100083 China

The second phase particles were observed during the whole manufacturing process of conventional grain oriented electrical steels, exhibiting that the areal density of particles in the center was obviously higher than that on the surface at each manufacturing stage. After hot rolling, the approximately equiaxed grains formed upon recrystallization were present on the sheet surface while the deformation structures were retained in the central part. Thus, the dislocation density on the surface was evidently lower than that in the center and this trend became more noticeable after the first cold rolling. Since new precipitates were mainly nucleated at dislocations during both hot rolling and annealing following cold deformation, the difference in dislocation density resulted in the inhomogeneous distribution of particles through the thickness of sheet. According to this, Goss grains, which were usually found near the surface, tended to grow up more easily during the secondary recrystallization treatment.

关键词： Grain oriented electrical steel Precipitation Recrystallization Dislocation

Preparation for Semi-Solid Aluminum Alloy Slurry under Weak Electromagnetic Stirring Conditions

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Journal of Materials Science & Technology 2006年第4期22卷 447-451页

作者： weimin mao Yuelong BAI Guoxing TANG School of Materials Science and Engineering University of Science and Technology Beijing Beijing 100083 China

The effects of pouring temperature, short electromagnetic stirring with low strength and then soaking treatment on the microstructure of AISi7Mg alloy were investigated. The results show that if AlSi7Mg alloy is poured at 630 or 650℃ and meanwhile stirred by an electromagnetic field at a low power for a short time, the pouring process can be easily controlled and most solidified primary α-Al grains become spherical and only a few of them are rosette-like. Weak electromagnetic stirring makes the temperature field more homogeneous and makes the primary α-Al grains disperse in a larger region, which leads to the spherical microstructures of primary α-Al grains. When the AISi7Mg alloy is soaked or reheated at the semisolid state, the primary α-Al grains ripen further and they become more spherical, which is favorable to the semi-solid forming of AlSi7Mg alloy.

关键词： AlSi7Mg alloy Semi-solid Pouring temperature Electromagnetic stirring Microstructure

Effect of pouring height on the solidified microstructure of AlSi7Mg alloy

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Journal of University of Science and Technology Beijing 2006年第4期13卷 324-328页

作者： weimin mao Yuelong Bai Hai Lin Materials Science and Engineering School University of Science and Technology Beijing Beijing 100083 China

The effect of different pouring heights and evenly soaking process in the liquidus and solidus range on the solidified microstructure of AlSi7Mg alloy has been studied. The results show that if the pouring temperature is 630 or 650℃ and the pouring height is 40 mm, the microstructure of the solidified melt is not homogeneous and there are many rosette-like primary α-Al grains. But if the pouring height is increased to 400 mm, the solidified microstructure becomes more homogeneous and favorable to obtain spherical primary α-Al grains in the solidified melt. With further being evenly soaked in the liquidus and solidus range for some time, the temperature difference between the melt center and the melt periphery can be controlled within ±2℃ and the primary α-Al grains will evolve into more spherical grains. The theoretical analysis indicates that the higher pouring height promotes the melt flow motion and makes the temperature field in the melt more homogeneous and restrains the large rosette primary α-Al grains. This flow motion can also promote the ripening effect and the primary α-Al grains in the melt are gradually changed into spherical grains. It can be concluded from the experiments that pouring at an appropriate superheat and from a proper height is a good new method for preparing the semisolid slurry of AlSi7Mg alloy, its process control is easy and the preparation cost is lower.

关键词： AlSi7Mg alloy semisolid pouring height solidification flow motion

Compressive Deformation of Semi-Solid AZ91D Magnesium Alloy

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Journal of Materials Science & Technology 2005年第4期21卷 505-509页

作者： weimin mao Aimei YIN Xueyou ZHONG Foundry Institute School of Materials Science and Engineering University of Science and Technology Beijing Beijing 100083China

The compression tests of semi-solid AZ91D Mg alloy have been conducted on a parallel-plate viscometer. The results are as follows. With increasing the compression temperature, the deformation rate or the strain rate of the specimens rises, but the compressive stress continuously decreases; the deformation strain is obviously linear with the compressive stress and independent on compression temperature under a given compression load. In the wake of the compression load being added, the compressive strain increases but the compressive stress decreases clearly; the deformation strain is obviously linear with the compressive stress under different compression load. The mathematical apparent viscosity model about the semi-solid compressed AZ91D Mg alloy has been established, i.e ηapp =2004.2exp（15.61 fs）γ^***^-1.3511

关键词： Semi-solid AZ91D magnesium alloy Compressive deformation

Influence of Surface Oxide Films on Elastic Behaviors of Straight Screw Dislocations Parallel to the Surface of Pure Aluminum

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Journal of Materials Science & Technology 2007年第3期23卷 392-394页

作者： weimin mao Dong LI Yongning YU Department of Materials University of Science and Technology Beijing Beijing 100083 China State Key Laboratory of Advanced Metals and Materials University of Science and Technology Beijing Beijing 100083 China

The image stress of straight screw dislocations parallel to the medium surface covered by thin heterogeneous films was analyzed and deduced, in order to calculate the image shear stress. The relationship between image stress and distance from the screw dislocation to the interface of pure aluminum and its oxide covering was calculated based on the analysis. It was shown quantitatively that a sign conversion of the image stress appears in the case of thin oxide covering, while dislocation would pile up near the interface because of the possible slips of the screw dislocations induced by the image stress, which might break down the very thin oxide covering. Further investigation on edge dislocations or other dislocation configurations need to be done.

关键词： Dislocation Image force Interface Surface Aluminum Oxide film Stress

Tensile behavior of AA3104 aluminum sheets at low deformation degree

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Journal of University of Science and Technology Beijing 2005年第5期12卷 422-426页

作者： Quancang Ma weimin mao Huiping Feng Materials Science and Engineering School University of Science and Technology Beijing Beijing 100083 China State Key Laboratory for Advanced Metals and Materials University of Science and Technology Beijing Beijing 100083 China

The texture of a rolled AA3104 aluminum sheet was measured by the X-ray transmission method. The Lankford values or r values （ratio of plastic strain） and yield strengths in directions of 0, 15, 30, 45, 60, 75, and 90° to RD （rolling direction） of the sheet were tested during tensile loading at a strain of 2%. γ values were predicted by the Sachs model and the reaction stress model in consideration of the measured texture. The simulated results indicate that r values calculated by the Sachs model are more exactly approaching with the experimental values on the whole than those predicted by the reaction stress model. The deformation behavior of the AA3104 aluminum sheet reveals characteristic predicted by the Sachs model, which should be resulted from the sheet geometry different from bulk material as well as the low tensile deformation degree.

关键词： γ value yield strength texture AA3104 aluminum sheet tension deformation