Advanced Materials Research Vols. 264-265

Abstract: This paper presents the experimental investigation conducted on Al-Si cast alloy (LM6) cast using lost foam process. The main objective of the research is to investigate the effect of pouring temperature, section thickness and melt treatment on the microstructure of the lost foam casting of Al-Si alloy. Step pattern with five different sections was prepared from 20 kg/m³ density foam and poured at five different temperatures; 700, 720, 740, 760, and 780 with and without the addition of AlTiB as grain refiner. Analysis on microstructure, eutectic silicon spacing and porosity percentage were conducted to determine the effect of both parameters. The results show that pouring temperature has significant influence on the quality as well as microstructure of the lost foam casting of LM6 Al-Si alloy. Lower pouring temperature was found to produce finer microstructure casting. However, the addition of AlTiB as grain refiner did not affect the produced castings significantly whether in terms casting quality or microstructure.

Abstract: Average roughness is an increasingly important method in material sciences. The searching for a possible correlation between average roughness and impact energy are current interest. This paper present the results of an experimentally study made on the correlation between the average roughness and the impact energy in aluminum alloy by using scatted diagram. The impact energy of aluminum alloy was obtained by using Charpy Impact Test. The micrographs of fractured aluminum alloy were analyzed with the IFM (Infinite Focus Measurement) profile to determine the parameter of average roughness. The result shows the relationship maybe established between average roughness and impact energy.

Abstract: Compression tests of 7050 aluminum alloy have been conducted at different temperatures (340, 380, 420, and 460 °C) with strain rate of 0.1 s-1. The deformation behavior and service performance of the alloy are investigated using EBSD technique, TEM and hardness measurement. Results show that the volume fraction of recrystallized grains increases with the increase of deformation temperature. The primary softening mechanisms of the alloy deformed at 340, 380, and 420 °C are dynamic recovery, and dynamic recrystallization is the main softening mechanism of the alloy deformed at 460 °C. The hardness of the 7050 aluminum alloy deformed increases with increasing deformation temperature. Dynamic precipitation appears when the 7050 aluminum alloy was deformed at 340, 380, and 420 °C, and strengthening mechanisms include mechanical hardening and precipitation strengthening. When deformation temperature is 460 °C, solid solution strengthening and grain boundary strengthening are primary strengthening mechanisms.

Abstract: In continuous casting process, tundish operates as a refining finisher. Different flow modifiers can be used in order to optimize cleanliness of liquid steel. To study the effect of various flow modifiers such as dam, weir, inlet shroud and etc., a three dimensional mathematical model was developed to simulate turbulent flow inside the tundish. The computed flow field was further used to model the transient mass transfer in the melt flowing in the tundish. The residence time distribution (RTD) of particles was determined by mass transfer model. The performance of the model was evaluated by experimental data obtained by a physical model. The verified model was used to evaluate the effect of location and size of different flow modifiers on flow pattern and particles residence time and consequently on tundish performance.

Abstract: The effect of casting temperature, cooling rate in silica bound molding sand and modifier additions on tensile, ductility and hardness properties Al-Cu binary alloy is presented. The study revealed that casting at high cooling rate and low casting temperatures with sufficient addition of ferro-silicon not exceeding the limited concentration for solubility improve mechanical properties of castings. The study also indicated that casting temperature greater than 7000C expanded the liquidussolidus solidification line leading to multiple phase formation which in-turn affect the final microstructure. Casting temperature of 7000C, addition of modifier in amount up to 200g and rapid cooling rate optimized the mechanical properties. The microstructure in this condition consists of equiaxed grains with spot presence of CuAl2 intermetallics which probably is responsible for the increased tensile strength and marginal change in ductility.

Abstract: Metal Matrix Composite (MMC) is produced normally by melting the matrix material in a vessel and the molten metal is stirred systematically to form a vortex, and then the reinforcement particles are introduced through the side of vortex formed. However, this approach has disadvantages, mainly arising from the particle addition and the stirring method. There is certainly local solidification of the melt induced by the particles during particle addition. This condition increases the viscosity of the slurry and appears as air pockets between the particles. Moreover, the rate of particle addition needs to be slowed down particularly when the volume fraction of the particles to used increases. This study proposes the new methodology of producing cast MMC by investment casting. Deformations of the die-wax and shell alloy systems are considered in a coupled manner, but the coupled deformation of the wax-shell system is not included. Therefore, this study presents the tasks pertaining to metal matrix composites and their interactions. As a result, the work on wax and wax-die interactions is discussed. This study presents the use of computer programs for determining the wax pattern dimensions based on three-dimensional finite-element simulations. The model for coupled thermal and mechanical analysis is developed by ProCAST. The wax model is described. The following factors are considered in the analysis: (1) the restraint due to geometrical features in the metal die; and (2) process parameters such as dwell time, die/platen temperature, injection pressure, and injection temperature.

Abstract: In this study, a temperature distribution of 5083-O aluminum-magnesium (Al-Mg) alloy is analyzed at various die and blank initial temperature conditions using finite element analysis approach. Temperature distribution results of the blank reveal that the dies must be heated to predetermined temperatures for successful warm forming, even the blank is kept at room temperature.

Abstract: In this paper, a new technique to set up non-sinusoidal oscillations of the mold in continuous casting is presented. The waveform functions of this non-sinusoidal oscillation technique and operational parameters are analyzed and the design to realize the non-sinusoidal oscillation of mold is presented. It is anticipated that this technique will be widely applied as it has many advantages such as lower investment and maintenance cost, simple equipment which is easy to manufacture and maintain.

Abstract: In this work, the preliminary result on the effect of cryogenic cooling on grain growth in weld is reported. Ferritic stainless steel weld produced under TIG torch in argon environment is cooled in liquid nitrogen. The weld structure is characterized using LOM, SEM and EDX spectroscopy. The results suggest that cryogenic cooling reduced the weld width within 2% to 5% and HAZ to 39% relative to those cooled in normal condition. This ensures that the area of the base metal affected and exposed to the weld thermal cycle is reduced and hence probably generates less metallurgical distortion. The cryogenic cooling also generated 14% to 36% grain refinement compared to welds cooled in normal condition.

Abstract: In this research, the effects of two variables, pouring temperature and chemical composition, on residual stress/strain have been studied. The residual strain was experimentally measured using the cutting technique and compared for several alloys; carbon steel, stainless steel, Ni-base superalloy, and cast iron. The thermo-elasto-plastic model was used to model the thermal stress distribution during casting and to predict the residual stress from point to point in rectangularshaped steel castings. Simulation results show that stress distribution is related to the thermal gradients throughout the castings, and maximum residual stress is developed at location which solidifies at the later freezing stages. In addition, the results of experimental measurements are applied to evaluate the effect of pouring temperature and chemical composition on residual stress and distortions in shaped castings.