Advanced Materials Research Vols. 189-193

Abstract: The hard spots and the hard part defects within the base body in the die-casting parts of aluminum alloy were observed and analyzed by means of photon microscope, electronic probe, micro hardness tester and other experimental methods. The causes led to the hard spots were discussed. The measures and solutions to control the raw materials of the alloy and to improve the smelting process were put forward.

Abstract: The self-prepared Cu-RE refining agents were used to refine impure-copper. The influences of RE elements on refinements and structures were studied and the mechanism of RE was discussed. The results show that by adding proper amounts of Cu-RE refining agents into impure-coppers, the refinements of RE on impure-coppers are perfect. Furthermore, the dendrites of the RE-refined ingot are refined and the structure becomes more homogeneous, leading that the electric conduction function and mechanics function of impure-copper have been improved.

Abstract: A three-dimensional mathematical model has been developed to study turbulent fluid flow, heat transfer and free surface profile in the initial stage of the twin-roll casting strip pool by a commercial software ProCAST. The coupled set of governing equations for mass, momentum and energy balance was solved with the finite element method. The free surface profile of the pool was treated with the Volume of Fluids (VOF) approach. A straight nozzle of metal delivery system has been chosen in the Twin-roll strip casting process. The filling sequences, flow patterns and corresponding temperature profiles in the metal pool of a vertical twin-roll strip casting process were simulated in this study. The calculated results provided a valuable basis for the optimization of process parameters and metal delivery system during the initial pouring stage of twin-roll strip casting.

Abstract: The microstructures and mechanical properties of a sector ductile iron casting with a wall thickness of 500 mm were investigated. Results show that spheroidal graphite is obtained in ductile iron, and chunky graphite is avoided because of chills used during solidification. Besides, the matrix structure is nearly a full ferrite structure at the edge of casting while some pearlite forms at the center of casting. The competing effect between graphite and matrix structure keeps the strength relatively inert to the change in solidification time or cooling rate, but these two parameters both impair elongation of ductile iron as well. The samples with full ferrite matrix exhibit a typical ductile fracture mode while those with some pearlite lead to a mixed ductile-brittle fracture mode. Graphite internal fracture or graphite/matrix interfacial cracking are two crack initiation sites.

Abstract: In this paper, the effect of superposition of rotating electromagnetic field and triangular pulse electric field on the microstructure of the cast Al-7wt％Si hypoeutectic alloy was investigated. The experimental results showed that solidification microstructure of Al-7wt％Si hypoeutectic alloy could be obviously improved from dendrites to nearly equiaxed grain with increasing the voltage of rotating electromagnetic field and α－Al dendrites were refined by superposed field. Moreover, refinement effects were further improved with increasing intensity of the superposed field.

Abstract: Aiming at large and thick automobile die casting as well as combining with production practice, the main factors which influence the strength of gray iron in electric furnace are investigated and the smelting technology of electric furnace for thick and large gray iron with high strength is proposed in this paper. The result shows that the tensile strength of attached test specimen or hardness of casting can meet the application requirements greatly. This smelting technology provides reference for large and thick castings smelting under similar conditions.

Abstract: In production,the Φ105 mm hole of rear oil seal bearing die castings often appear porosity, shrinkage and other defects , resulting in the parts to scrap. The existing gating system design of rear oil seal bearing die castings was improved , and the flow and temperature field of the two programs that before and after improvement were analyzed by ProCAST software. The simulation results predicted the casting defects, and the conclusion was consistent with the production. By using the improved process optimization, the rejection rate of die castings can be reduced effectively. Die casting is a chipless forming of casting with high casting dimensional accuracy, high surface quality and high production efficiency [1,2]. Therefore, it has developed rapidly in the automotive, communications and other industries. However, due to shrinkage, porosity and other reasons, leading to high rejection rate of castings. With the emergence of commercial casting simulation software, the casting production has been developed from semi empirical and semi theoretical onto theorization, quantification and controllable track[3-5]. In this paper, the casting defects of rear oil seal bearing is analyzed by using numerical simulation technology[6]. By optimizing the casting process, the casting quality is improved, and the rejection rate is reduced effectively.

Abstract: The tube-shaped parts of A356 alloy were deformed from 0% to 83% by spinning process. The microstructure and mechanical properties of A356 alloy were discussed. The results showed that as the wall thickness reduction increases, the dendrite cells of cast alloy are lengthened gradually and the average Secondary Dendrite Arm Spacing (SDAS) is reduced from 37.2μm to 23μm and eutectic silicon particles are distributed orderly along the spinning direction. The coarse acicular β-Al5FeSi is broken into many sections, and its length is reduced from 37.5μm to 12.5μm in the cross-section. The tensile strength and elongation exhibit a strong dependence upon the variation in wall thickness, with a parabolic relationship. The tensile fractured surface of parts with deformation ratio above 35% exhibits many equiaxial dimples, with intergranular ductile fracture mode.

Abstract: The roll-casting technology of 5000 series aluminum alloy is one of the difficulties at present. Roll-casting technology was employed in this paper and high quality 5005 aluminum alloy sheets were fabricated successfully under different conditions. The solidification of melt in roll-casting process is the rapid directional solidification. The effect of magnetostatic field on microstructure of 5005 aluminum alloy sheet by roll-casting has been investigated and analyzed. The results indicate that imposing magnetostatic field can refine the grains of 5005 aluminum alloy.

Abstract: This study used numerical simulation to investigate the growth conditions of yttrium aluminum garnet (YAG) single crystals by the vertical Bridgman method, and discusses the process performed with or without the installation of a submerged heater (SH). The maximum flow velocity of the melted material surrounding the melt/crystal interface can be decreased, and the deflection of the melt/crystal interface can be changed under various furnace temperature gradients and distances. The minimum of the maximized flow rate indicates that the natural convection can be decreased and controlled. In this manner, the growth rate of crystals increases in an identical environment.