Materials Science Forum Vols. 704-705

Abstract: Semi-solid forming technology is a short metal processing method between the liquid casting and solid forming. Many forming factors have been found concerning the quality of the forming part. In this study, the influences of slurry filling sequence were investigated in semi-solid forming one complex aluminum part. Two different slurry filling methods were designed. Method one is thixo-upsetting + compound extrusion, method two is thixo-upsetting + extrusion. The experimental results showed that the optimised method of thixo-upsetting + extrusion could be the best strategy in improving the part quality during thixo-forming of aluminum alloy A356.

Abstract: The finite element 3D model of heavy rail roller complex straightening is established by the finite element method in this paper.The straightening process is optimized by orthogonal experimentation and regression analysis. The formative mechanics and the regulation of the residual stress in the process of straightening are researched. The results of the simulation show that: whatever is on the basement of the residual stress or flatness, the new schedule is better than the real field one, residual stress is controlled within 250Mpa.

Abstract: Numerical simulation of connecting rod die forging processing was performed by finite element method (FEM) software Deform 3D. The changes of the temperature fields, stress fields of the billet and dies, and upper setting force-stroke curve during the die forging were obtained. The simulation results show that (1) the increase of the fillet radius of dies could effectively reduce the stress concentration so that to prevent the die crack arising at high level stress; (2) the optimum parameters of die forging process are 430°C for forging temperature, 200°C for preheat temperature of dies and 80mm/s for reduction rate by comparing both fields of the stress and temperature during different forging process..

Abstract: For reducing the mold manufacturing time as soon as possible, CAE technology is used to build work-piece three-dimensional draw, parting surface, gating system is designed, the mold’s moving process being simulated, especially liquid flowing system is emulated. If the parameters are set reasonable, the ideal mold can be made. Keywords:Injection mold; parting surface; gating system; liquid flowing system analysis.

Abstract: Chemical mechanical polishing (CMP) has become the most widely used planarization technology in the semiconductor manufacturing process. In this paper, the distinguish method of lubricating behavior in wafer CMP had been analyzed in theory firstly. Then, the tests of wafer CMP with silicon wafer and deposited copper wafer at different polishing pressure had been done. By the test results, the Stribeck curves obtained showed obvious smooth. But in normal wafer CMP conditions, the friction coefficient of polishing area was above 0.1. By analyzing the experimental results, it was concluded that the lubrication state in CMP interface is belong to the boundary lubrication and the material removal is the process of bringing and removed of the chemical reaction boundary lubricating film on wafer surface constantly. The contact form between the Wafer and the polishing pad is the solid-solid contact. These results will provide theoretical guide to further understand the material removal mechanism of in wafer CMP. Keywords: Chemical mechanical polishing, material removal mechanism, lubrication form, boundary lubrication.

Abstract: Grinding induces residual stresses, which can play an important role on the fatigue of the component. In general, residual stresses in a ground surface are primarily generated due to three effects: thermal expansion and contraction during grinding, plastic deformation caused by the abrasive grains of the wheel and phase transformations due to high grinding temperature. It was found that thermal expansion and plastic deformation in the grinding process were the major causes of residual stresses. In this paper, an analysis model for the calculation of residual stresses induced by a surface grinding process on an ultrahigh-strength steel (Aermet100) workpiece is presented. Firstly, the stress distribution induces by thermal expansion was obtained base on the transient heat conduction equation and the thermal properties of Aermet100. All the calculations were based on the moving heat source solution which was modeled as a uniformly distributed, 2D heat source moving across the surface of a half-space, found in Carslaw and Jaeger. The results show that the near surface residual stress is predominantly tensile and that the magnitude of this stress increases with increasing heat flux values. Secondly, the plastic deformation caused by the abrasive grains of the wheel was simulated base on the grain-workpiece interaction. The chip formation process and the material removal mechanisms can be examined using the micro-scale approach. The results show that the residual stress induced by the grinding force itself is generally compressive which is smaller than the residual tensile stress induced by thermal stress. Therefore, the residual stress brought about by grinding operation is generally a tensile stress. This paper offers an insight into the mechanism understanding of thermal and mechanical residual stresses induced by surface grinding. Key words: grinding, residual stress, grain

Abstract: The mechanical performance and corrosion resistance of Zr-Nb alloy (Zr705) treated in different ways is tested, and it is found that those properties of Zr-Nb alloy are significantly affected by heat treatment. The most important parameter of the heat treatment is quenching temperature. The Zr-Nb alloy, quenched below the critical quenching temperature Tcq (a temperature or a range of temperature between 850°C-870°C) presents good corrosion resistance performance, however, quenched above the Tcq gets a higher strength and a lower corrosion resistance. Through the study on the basis of the evidences gotten by means of metallographic, SEM, EPMA and TEM, the conclusion can be drawn as that the effect of heat treatment on the performances of Zr-Nb alloy is primarily because of the mechanism of the distribution change of Nb, the quantity of β-Zr, the morphology of grains. Keywords: Zr-Nb alloy, heat treatment, β-Zr, twins

Abstract: a necessary process, there are many volatile organic compounds of Chinese fir biomass during hot drying to pollute environment and affect the health of the people. Therefore, the chemical components from Chinese fir biomass in simulated hot drying environment were identified by TD-GC/MS to find the possible utilization of the resources and reduce environmental pollution. The main constituents at 90°С were cedrol (25.2%), 1,2-benzenedicarboxylic acid, buty l 2-methylpropyl ester (4.62%), 4-imidazolidinone, 5-(phenylmethyl)- 2-thioxo-(3.87%), acetic acid (3.85%), 1-naphthalenepropanol, .alpha.-eth enyldecahydro-.alpha.,5,5,8a-tetra (3.03%), etc. The main constituents at 120°С were cedrol (30.54%), phenol, 2,4-bis (1,1-dimethylethyl) (3.89%), globulol (2.76%), benzofuran, 2,3-dihydro-(2.71%), cyclohexasiloxane, dodecamethyl- (2.70%), .alpha.- cadinol (2.65%), taurolidine (2.33%), 2,4,6-octatrien-1-ol, 3,7-dimethyl-(E,E)- (2.31%), etc. So the volatile organic compounds of Chinese fir biomass during hot drying could be used as biomedicine, bioenergy, and so on.

Abstract: In this paper, an experiment model for the directional solidification of Lead/Tin alloy is built and the effects of different-shape seeds on the microstructures on the solidification microstructure are investigated. In a casting process, the temperature and concentration fields will affect the microstructures of materials and this influence is the key point of improving their mechanical and physical properties. It is not easy to control the morphology of solidifying microstructures. The scheme of directional solidification can make the microstructures grow along a fixed direction and it is also the base of single-crystal growth. In the experiment, a poly-grain seed with the same initial concentration of the solidifying casting is used to induce the columnar growth at the bottom portion of the casting, which could avoid the equiaxed growth due to the high undercooling or cooling rate there. In the experimental analysis, we studied the influences of different geometry seeds on the constrained growth, the preferential growth direction of dendrite, the grain size, the temperature gradient, the growth rate, the primary arm spacing and the secondary arm spacing. From the microstructure observation, the adding seed casting reduced the chill-affected and extended the directional solidification zone. This is expected to have the better or more complete structure of directional solidification. Keywords: Directional Solidification, Seed, Heat Transfer and Microstructure

Abstract: In conventional TIG welding, copper weld joint and its heat affected zone (HAZ) have the disadvantage of softening. In this paper, the new technology of softening control for copper weld joint using pretension method was studied. The results show that hardness of copper weld seam and its HAZ was increased by pretension. Moreover, the tensile strength and elongation of the welding joint were obviously improved. Keywords: pretension, weld joint, softening control, copper