Research on fractal characteristics of primary phase morphology in semi-solid A356 alloy

Semi-solid slurry of A356 alloy was prepared by low superheat pouring and slightly electromagnetic stirring, and the fractal characteristics of morphology in semi-solid primary phase was researched. The fractal dimensions of primary phase morphology in the semi-solid A356 alloy were calculated by the program written to calculate the fractal dimensions of box-counting in the image of solid phase morphology in semi-solid metal slurry. The results indicated that the morphology of primary phase in semi-solid A356 prepared by low superheat pouring and slightly electromagnetic stirring is characterized by fractal dimension, and the primary phase morphology obtained by the different processing parameters has different fractal dimensions. The morphology of primary phase at the different position of ingot has different fractal dimensions, which reflected the effect of solidified conditions at different positions in the same ingot on the morphology of semi-solid primary phase. Solidification of semi-solid alloy is a course of change in fractal dimension.

Filling ability of semi-solid A356 aluminum alloy slurry in rheo-diecasting

The effects of slurry temperature, injection pressure, and piston velocity on the rheo-filling ability of semisolid A356 alloys were studied by the reho-diecasting methods. The results show that the slurry temperature of the semi-solid A356 aluminum alloy has an important effect on the filling ability; the higher the slurry temperature, the better is the filling ability, and the appropriate slurry temperature for rheo-filling is in the range of 585-595℃. The injection pressure also has a great effect on the filling ability, and it is appropriate to the rheo-filling when the injection pressure is in the range of 15-25 MPa. The piston velocity also has a great effect on the filling ability, and it is appropriate to the rheo-filling when the piston velocity is in the range of 0.072-0.12 m/s. The filling ability of the slurry prepared by low superheat pouring with weak electromagnetic stirring is very good and the microstructural distribution in the rheo-formed die castings is homogeneous, which is advantageous to the high quality die casting. 2008 University of Science and Technology Beijing. All rights reserved.

Plasma-metabolite-based machine learning is a promising diagnostic approach for esophageal squamous cell carcinoma investigation

The aim of this study was to develop a diagnostic strategy for esophageal squamous cell carcinoma(ESCC)that combines plasma metabolomics with machine learning algorithms.Plasma-based untargeted metabolomics analysis was performed with samples derived from 88 ESCC patients and 52 healthy controls.The dataset was split into a training set and a test set.After identification of differential metabolites in training set,single-metabolite-based receiver operating characteristic(ROC)curves and multiple-metabolite-based machine learning models were used to distinguish between ESCC patients and healthy controls.Kaplan-Meier survival analysis and Cox proportional hazards regression analysis were performed to investigate the prognostic significance of the plasma metabolites.Finally,twelve differential plasma metabolites(six up-regulated and six down-regulated)were annotated.The predictive performance of the six most prevalent diagnostic metabolites through the diagnostic models in the test set were as follows:arachidonic acid(accuracy:0.887),sebacic acid(accuracy:0.867),indoxyl sulfate(accuracy:0.850),phosphatidylcholine(PC)(14:0/0:0)(accuracy:0.825),deoxycholic acid(accuracy:0.773),and trimethylamine N-oxide(accuracy:0.653).The prediction accuracies of the machine learning models in the test set were partial least-square(accuracy:0.947),random forest(accuracy:0.947),gradient boosting machine(accuracy:0.960),and support vector machine(accuracy:0.980).Additionally,survival analysis demonstrated that acetoacetic acid was an unfavorable prognostic factor(hazard ratio(HR):1.752),while PC(14:0/0:0)(HR:0.577)was a favorable prognostic factor for ESCC.This study devised an innovative strategy for ESCC diagnosis by combining plasma metabolomics with machine learning algorithms and revealed its potential to become a novel screening test for ESCC.

Effect of Trace Sn on Pitting Behaviors of High Voltage Anode Aluminum Foil

The effect of trace Sn on the pitting morphology of high voltage anode aluminum foils was investigated. The distributions of microelement Sn, Fe, Si, Cu and Mg in the surface layer of aluminum foils with different Sn content were determined by using a secondary ion mass spectrometer. It was found that the micro-alloyed Sn is enriched at the external surface. The mechanism of pitting behavior of trace Sn on aluminum surface is similar with that of lead. Enrichment of Sn in the surface layer provides large numbers of sites for initiation of pitting corrosion, while pitting sites appeared relatively inhomogenously in the foils without Sn. Sn, as an eco-friendly microelement, can be applied to replace Pb in improving the homogenous pitting behaviors of high voltage aluminum foils, in which the volume fraction of cube texture is not reduced.

Microstructure Evolution of Semi-solid Processed Hyper-eutectic Al-30%Si Alloy

An investigation was made on the influences of mechanical stirring on microstructure of hyper-eutectic Al-30%Si alloy (inmass fraction) during solidification. The primary Si crystals formed in the alloy melt were gradually changed from elongated platelets tonear-spherical shapes by mechanical stirring. The spheroidization of primary St crystals occurs by the mechanism of bending and fractureof Si platelets, wear and collision between Si crystals, and coalescence of small Si particles. The influence of under-cooling and coolingrate of the alloy melt on primary Si crystals of semi-solid processed alloys is investigated as well. The increase of under-cooling andcooling rate decreases the size of primary Si crystals.

Tensile behavior of AA3104 aluminum sheets at low deformation degree

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.

Temperature Field and Microstructural Formation of Semi-Solid AlSi_7Mg Alloy

The microstructural formation of the semi-solid AlSi7Mg alloy stirred by electromagnetic field is investigated together withthe tempeatre field of the stirred melt at continuously cooling. A impoat kinetic factor for primny a-Al nucleation is proposed. It isfound that a low temperatUre gradient exists in the electromagnetic stirred melt. This is why the first dendritic arms and secondary de-ndritic arms are refmed. Experimefltal results also show that the root remelting of secontw dendritic arms is an twortat mechanismfor the primary α-Al refmement. Strong electromagnetic stirring greatly reduces the composition supercooling in the melt and eliminatesprefedrig growth of the first dendritic arms. Therefore, many rosettes or spherical Primary α-Al phase particles form finally.

Preparation of Semisolid A356 Alloy Feedstock Cast via a Pipe Consisting of Partial Inclined and Partial Vertical Sections

In the present work, the microstructures of A356 feedstock cast via a pipe consisting of partial inclined and partial vertical sections were investigated. The experimental results indicate that semisolid feedstock with ideal microstructures can be obtained at higher temperatures 645℃ and above by the proposed process, and the solid shell inside the pipe can be avoided at the optimum pouring temperature. Thus the process is attractive for industrial applications. The slanted angle of inclined section has an influence on the optimum pouring temperature. That is, the bigger the slanted angle, the higher the optimum pouring temperature, but accordingly, the greater the possibility of solid shell occurring inside the pipe. Therefore, small slanted angle should be considered first on the premise of ensuring a certain nucleation. The formation of semisolid feedstock is owed to the coactions of wall nucleation and stirring resulting from fluid flow. The inclined section greatly affects nucleation, and the vertical section has an important effect on both nucleation and generating stirring.

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

到薄异构的电影盖住的 mediumsurface 的直螺丝钉脱臼平行的图象应力被分析并且推出，为了从螺丝钉脱臼计算在图象应力和距离之间的 imageshear stress.The 关系到盖住的纯铝和它的氧化物的 theinterface ，基于 analysis.It 被计算 shownquantitatively 图象应力的符号变换出现在薄 oxidecovering 的情况中，当脱臼将在 inte

Texture Evaluation of α_2 Phase in Ti-25Al-10Nb-3V-1Mo Alloy Sheet

The texture evaluation of α2 phase in Ti-25Al-10Nb-3V-1Mo sheet during rolling and annealing has been investigated by means of microstructure observation and ODF analysis. From the weak initial {1010} (1210) and {0001}(1210) textures a {1210}(1010) texture and a {0001}(uvtw)fibre texture are formed after cold rolling. The {0001} (1210) texture is also strengthened simultaneously. The activation process of slip systems is discussed concerning formation of the rolling texture. Because of the disappearance of {0001} (nvtw) fibre texture the primary recrystallization process should occur and the {1210}(1010) texture forms during annealing

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

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.

Relationship between texture and residual macro-strain in CVD diamond films based on phenomenological analysis

The relationship between texture and elastic properties of chemical vapor deposition （CVD） diamond films was analyzed based on the phenomenological theory, which reveals the influence of crystalline orientation and texture on the residual macro-strain and macro-stress. The phenomenological calculations indicated that the difference in Young＇s modulus could be 15% in single diamond crystals and 5% in diamond films with homogeneously distributed strong fiber texture. The experimentally measured residual strains of free-standing CVD diamond films were in good agreement with the correspondingly calculated Young＇s modulus in connection with the multi-fiber textures in the films, though the difference in Young＇s modulus induced by texture was only around 1%. It is believed that texture should be one of the important factors influencing the residual stress and strain of CVD diamond films.

Effect of the Solidification Conditions on the Microstructures of AlSi_7Mg Alloy during Semi-solid Remelting

The effect of the solidification conditions on the microstructures was studied during partial remelting of AlSi7Mg alloy with the help of an electrical pipe-type fumace. The results show that the eutectic is remelted above all and α phases are gradually evolved into spheroidal shape,if the AlSi7Mg alloys shrmd strongly by rotating electromagnetic field during the first solidification are heated again to 589 or 597℃ and have been held for a short time (for example, 5~10 min), and moreover, the higher the holding temperature,the faster the eutectic remelting process and α phase's evolution are. In contrast even though the AlSi7Mg alloy's samples non-stirred with fine dendritic microstructures are heated to the same temperatures as those stirred by rotating electromagnetic field and have been held for 60 min,it is not possible to change all the dendritic a phases to speroidal α phase.

Compressive Deformation of Semi-Solid AZ91D Magnesium Alloy

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^1.317.fn^-1.3511

Microstructral Evolution of the Dendritic AlSi7Mg Alloy during Semi-solid Remelting

The microstructural evolution during partial remelting of dendritic AlSi7Mg alloys was studied with the help of an electrical fumace. The results show that it is difficult to change all the primary a dendrites into the spheroidal a phases, when the dendritic samples of AlSi7Mg alloy are remelted under 589 or (597±1)℃ and held on mis condition for 5 to 120 min. The results also show that the samples remelted can be deformed under the heavy force, if the holding time is longer under higher temperature.

Analysis of Micro-texture during Secondary Recrystallization in a Hi-B Electrical Steel

The understanding of Goss texture in Hi-B electrical steels possesses significant industrial and academic value, thus attracts worldwide attention. The prevailing models for sharp Goss texture formation during secondary recrystallization are CSL （coincident site lattice） boundary theory and HE （high energy） boundary theory. These theories stress the key factor of preferred growth and the difference between them only lies in the specific selection manner. This work examined the texture gradient in primarily recrystallized sheet and demonstrated its possible influence on the formation of secondary grains, and then determined the micro- texture during different stages of secondary recrystallization using EI3SD （electron back-scattered diffraction） technique, finally analyzed a special type of secondary grains with near Brass orientation, which were detected in the later stage of secondary recrystallization, and discussed its origin and effect in terms of surface energy effect. The results indicate that texture gradient in primarily recrystallized sheet will lead to a multi-stage formation of Goss texture, namely, early stage of secondary grains with various orientations in subsurface region, intermediate stage of preferred growth of Goss grains into center layer and re-grow back to the surface and the final stage of Goss grain growth by swallowing slowly the island grains with the help of H2 atmosphere.

On the Taylor principles for plastic deformation of polycrystalline metals

Grain orientation evolutions and texture formation based on the Taylor principles offer important references to reveal crystallographic mechanisms of deforma- tion behaviors. Strain equilibrium between grains is achieved in Taylor theory, however, stress equilibrium has not yet been reached perfectly even in many modifications of the theory though the textures predicted become very close to those of experimental observations. A reaction stress model is proposed, in which mechanical interactions between grains are considered in details and grain deformation is conducted by penetrating and non-penetrating slips. The new model offers both of the stress and strain equilibria and predicts the same textures indicated by Taylor theory. The rolling texture simulated comes very close to the experimental observations if the relaxation effect of the non-penetrating slips on the up-limits of reaction stresses is included. The reaction stress principles open theoretically a new field of vision to consider deformation behaviors of poiycrystaliine materials, whereas the Taylor principles become unnecessary both theoretically and practically. Detailed engineering conditions have to be included in simulations if the deformation textures of industrial products should be predicted.

Analysis of the Transformation-induced Plasticity Effect during the Dynamic Deformation of High-manganese Steel

The transformation-induced plasticity(TRIP) effect and resistance characteristics to adiabatic shear failure at high strain rates of high-manganese steel were investigated by using scanning electron microscopy and electron backscattering diffraction. Results showed that the high-manganese steel exhibited excellent strain hardening effect and resistance to adiabatic shear failure because of the TRIP effect. The TRIP effect occurred during dynamic deformation and showed two distinct stages,namely,the smooth TRIP process before the formation of adiabatic shear band(ASB) and the inhibited TRIP process during further deformation. In the first stage,the martensitic transformation showed slight orientation dependence and weak variant selection,which promoted the TRIP effect. In the second stage,reverse martensitic transformation occurred. Adiabatic shear bands(ASBs) developed typical shear microtextures {111}<110>. In microtextures,two groups of fine grains are in a twin relationship and uniform distribution,which restrained the formation of holes and cracks within the ASBs and enhanced damage resistance after ASB formation.

Abnormal Growth of Goss Grains in Grain-oriented Electrical Steels

With the help of electron back scattering diffraction techniques and field emission microscope, the misorienta- tion and the precipitation environment of Goss grains in conventional grain-oriented steel were observed and investigated at the initial stage of secondary recrystallization. It reveals that the abnormal Goss grains have a high fraction of high angle boundaries ranging from 25 to 40 deg. The most important observation is that some of {110}〈001〉 grains in matrix indicated higher particle density than their neighbor grains during final annealing at 875℃ before secondary recrystallization, which could create a favorable environment for their abnormal grain growth. Based on misorientation and precipitation results, the abnormal growth mechanism of Goss grains was sketched.