Advanced Materials Research Vols. 146-147

Abstract: The microstructure and textures of oriented silicon steel produced by Thin Slab Casting and Rolling (TSCR) were studied in laboratory. The fractions of equiaxed grains and columnar grains are close to 35% and 65% respectively in as-quenched ingot after being pulled out from the mould. The equiaxed grains and no texture gradient from surface to center can be observed for the 3-pass hot-rolled strips, and the inhomogeneities of microstructure and texture in thickness are relatively clear for the 7-pass samples. The subsurface texture of the hot-rolled sample contains of e (TD// <110>) fibers. The texture of the cold-rolled samples mainly consists of a (<110>//RD) and g (<111>//ND) fibers, and Goss texture ({110}<001>) disappears. The strong a fiber, weak g fiber and minor {001}<110>can be found in all layers in the cold-rolled condition.

Abstract: Bisphenol A poly(carbonate) (PC) pellets used for production of 5 gallon drink water bottles were reprocessed in a twin-screw extruder for three processing cycles which simulated to those of PC bottle processing conditions. The reprocessed PC pellets were characterized by its mechanical, rheological, thermal, and optical properties. It was found that the mechanical properties of the reprocessed PC samples are slightly decreased after reprocessed. Whereas no further change was observed for the rheological and thermal properties and molecule weight of the PC samples after the second reprocessing cycles. Moreover, the melt flow index, color, and optical properties changed obviously after two reprocessing cycles.

Abstract: The compressive deformation experiments of 2124-T851 aluminum alloy were carried out over a wide range of temperature and strain rate. An artificial neural network (ANN) model is developed for the analysis and simulation of the correlation between the flow behaviors of hot compressed 2124-T851 aluminum alloy and working conditions. The input parameters of the model consist of strain rate, forming temperature and deformation degree whereas flow stress is the output. A three layer feed-forward network with 15 neurons in a single hidden layer and back propagation (BP) learning algorithm has been employed. Good performance of the ANN model is achieved. The predicted results are consistent with what is expected from fundamental theory of hot compression deformation, which indicates that the excellent capability of the developed ANN model to predict the flow stress level, the strain hardening and flow softening stages is well evidenced.

Abstract: Materials with different modulus in tension and compression have a wide application in engineering practice, especially the composite materials developed in recent years, which have properties of different tension-compression modulus. To exploring the general features of mechanical properties of structures with different modulus, the dimensionless equation of finite element was deduced for structure with different modulus, and corresponding finite element program was developed .the stresses of the cantilever beam by program of the theory with different modulus. The impacts on member stresses resulted from the change of structure size, external load and the ratio of different modulus are compared and analyzed. Finally, we have drawn a conclusion that the property of different modulus of the material is very important to its stress, and have given out suggestions on the optimization of state of structural stress.

Abstract: The microstructure evolution of Al-Cu alloys with different compositions is investigated in directional solidification. Two distinctly different microstructure evolution mechanisms are obtained in Al-0.85%Cu and Al-4%Cu systems, respectively. In Al-0.85%Cu alloy, it shows a peculiar phenomenon, the microstructure evolution is always cells and no dendrites are obtained. In other words, the cells undergo several transitions as the pulling velocity increasing from 15μm/s to 300μm/s, they follow the sequences: mixed microstructure of pox and banded cells →mixed microstructure of polygonal and banded cells →banded cells →elongated cells. Particularly, it is studied what caused the dendrites not appear in Al-0.85%Cu system. Finally, it comes to the conclusion that there are two aspects which lead to the phenomenon: a dilute alloy composition and a relatively higher temperature gradient.

Abstract: In this study, AZ91 and SiC particulates reinforced AZ91 (SiCp/AZ91) magnesium alloys were successfully fabricated using rapid solidification/powder metallurgy technique followed by hot extrusion. Microstructural evolution and mechanical properties of the monolithic AZ91 and SiCp/AZ91 magnesium alloys were evaluated. SiC particulates were well distributed with only few agglomerated particles. The porosity level and microhardness increased as SiCp content increased because the increased surface area of SiCp, harder ceramic phases and SiCp acted obstacles to the motion of dislocations. In addition, an increase in particulate reinforcement content was observed to decrease mechanical properties of the composite compared with the unreinforced counterpart due to increasing agglomerating regions and porosity, brittle interface debonding between matrix and SiCp.

Abstract: Discrete element method (DEM) is a powerful tool for the study of granular materials. Some issues in numerical modeling of DEM including parameter selection and mass/density scaling method are discussed. A new method to simulate the resin membrane in the laboratory which is more accurate and simpler is proposed. Using DEM, microscale behavior of soil including particle rotation and mesoscale void ratio distribution are analyzed. Failure modes and stain localization are revealed from the particle scale analysis. Configurations of the shear band are investigated. It shows that microstructure and micromechanics is the underlying mechanics of the macroscale behavior of the granular soil. Being a simpler, faster, and cheaper method compared with traditional experimental method, DEM can capture the discrete characteristics and provide deeper insight of the granular materials.

Abstract: The evolution of microstructure and texture due to recrystallization was investigated in cold rolled interstitial free (IF) steel. Samples taken from the cold band of a 0.07%Ti bearing IF steel with total cold rolling reduction of 75% were investigated by using optical microscopy, X-ray diffraction and electron back-scattered diffraction etc. The aim of this study was to obtain a real picture of the formation of the recrystallization texture of IF steel, which would contribute to proper texture control for improving deep drawability. The mechanism responsible for the evolution of texture is discussed experimentally from four aspects. First of all, the microstructure of partially annealed cold rolled specimen is obtained. The recrystallized grain form earlier in more darkly etched regions from the micrographs, which belong to the ND//<111> fiber components. In addition, the fractions of the {111}<110> and {111}<112> components increase slowly during the early stage of recrystallization, because the γ-fiber recrystallized texture is growing, while at the same time the γ-fiber deformed texture is being consumed. Moreover, The texture formation has been discussed taking into consideration of the stored energy and the misorientation between the orientation of the recrystallized grain and that of the surrounding deformed matrix. The work indicates that the recrystallized grains, which migrate into the deformed grains, are mainly with the high misorientation angles. The large percentage of the recrystallized grains, whose misorientation angles with deformed grains exceed 15°, are corresponding to the {111} transformation texture. Nucleation first starts at colonies that have the highest stored energy of deformation, which has the same orientation as the deformed grains. By analysis, the formation of recrystallization texture was well explained by oriented nucleation mechanism rather than by selective growth mechanism.

Abstract: The effect of composition on the Curie temperature of κ phase Fe3AlCx was investigated by thermomagnetometry analysis (TMA). Results reveal that increasing carbon content decreases the Curie temperature. Serrations in the magnetization vs. temperature curve in the Fe3AlCx found at about 100°C, may arise from the fluctuation of carbon atoms between Site I and II of κ phase unit cell.