Faculty Publications
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Item Heat transfer and solidification behaviour of modified A357 alloy(2007) Kumar, G.; Hegde, S.; Prabhu, K.N.Al-Si alloys are subjected to melt treatment like modification to improve their mechanical properties. Non-destructive technique like thermal analysis is generally used to assess the effectiveness of melt treatment. In the present study, the behaviour of the melt treated Al-7Si-Mg alloy (A357) during solidification with or without chilling was investigated using thermal analysis. Thermal analysis and heat transfer parameters were determined. Thermal analysis parameters were affected significantly by modification and chilling. Modification treatment resulted in the increase of cooling rate, heat evolved, casting/mould interfacial heat flux and eutectic growth velocity. A theoretical model based on undercooling from the equilibrium temperature during eutectic solidification was used to predict growth velocities and eutectic grain size. The eutectic grain sizes estimated using the model and those measured from casting microstructures were found to be in good agreement. © 2006 Elsevier B.V. All rights reserved.Item Heat flux transients and casting surface macro-profile during downward solidification of Al-12% Si alloy against chills(American Foundry Society, 2011) Prabhu, K.N.; Sharath, K.; Ramesh, G.Heat flux transients were estimated during downward solidificationofAl- 12%Sialloy(A413)againstaluminumand graphite chills. The thermal plot of graphite chill indicated one-dimensional heat flow in the initial stages which then changes to two-dimensional heat transfer. The heat transfer becomes one-dimensional again during the final stages of solidification. In aluminum chill, heat flow was nearly one- dimensional. Experiments were designed to verify whether the peak heat flux is an artifact of the experiment. The results clearly showed that the occurrence of the peak in the heat flux transients is not an artifact of the inverse model or the experimental technique. The macro-profile of the casting surface in contact with the chill revealed the occurrence of crests and troughs. A mechanism based on the convection within the liquid metal below the solid shell was proposed to account for the formation of wavy casting surface. Copyright © 2011 American Foundry Society.Item Effect of Multiple Reflow Cycles and Al2O3 Nanoparticles Reinforcement on Performance of SAC305 Lead-Free Solder Alloy(Springer New York LLC barbara.b.bertram@gsk.com, 2018) Tikale, S.; Prabhu, K.N.The effect of Al2O3 nanoparticles reinforcement on melting behavior, microstructure evolution at the interface and joint shear strength of 96.5Sn3Ag0.5Cu (SAC305) lead-free solder alloy subjected to multiple reflow cycles was investigated. The reinforced SAC305 solder alloy compositions were prepared by adding Al2O3 nanoparticles in different weight fractions (0.05, 0.1, 0.3 and 0.5 wt.%) through mechanical dispersion. Cu/solder/Cu micro-lap-shear solder joint specimens were used to assess the shear strength of the solder joint. Differential scanning calorimetry was used to investigate the melting behavior of SAC305 solder nanocomposites. The solder joint interfacial microstructure was studied using scanning electron microscopy. The results showed that the increase in melting temperature (TL) and melting temperature range of the SAC305 solder alloy by addition of Al2O3 nanoparticles were not significant. In comparison with unreinforced SAC305 solder alloy, the reinforcement of 0.05-0.5 wt.% of Al2O3 nanoparticles improved the solder wettability. The addition of nanoparticles in minor quantity effectively suppressed the Cu6Sn5 IMC growth, improved the solder joint shear strength and ductility under multiple reflow cycles. However, the improvement in solder properties was less pronounced on increasing the nanoparticle content above 0.1 wt.% of the solder alloy. © 2018, ASM International.Item Thermal Analysis of Cerium-Treated Chill-Cast Al-23 Si Alloy(Springer New York LLC barbara.b.bertram@gsk.com, 2018) Vijayan, V.; Prabhu, K.N.The influence of elemental cerium addition on the cooling curve parameters and microstructure of hypereutectic Al-23Si alloy was investigated in this work. The cooling rate of the treated and untreated alloy samples was varied by solidifying the melt against chills of different materials in a stainless-steel tube. The cooling curve was recorded and nucleation temperatures of various phases in the alloy were measured. The results show that the chilling improves the effectiveness of the modifier. The two main phases of the alloy, primary silicon and eutectic silicon, were nucleated at temperatures of about 661.2 and 571.6 °C, respectively. The addition of Ce to slowly cooled alloys resulted in an increase in undercooling temperature of both the phases, with a decrease in its nucleation temperature, whereas the same additions increased the nucleation temperatures in chilled alloys. Based on the thermal analysis results, a relation between thermal analysis parameter (? TG) and silicon particle size of the alloy was proposed. © 2018, ASM International.Item Effect of Mold Contour on Interfacial Heat Transfer During Solidification of AlSi11Cu3Fe Alloy (ADC-12)(Springer Science and Business Media Deutschland GmbH, 2024) Kamala Nathan, D.K.; Prabhu, K.N.The present work investigated the effect of flat, concave, and convex mold contours on heat transfer during the solidification of an aluminum AlSi11Cu3Fe (ADC-12) alloy. Experiments were designed with copper/steel cylindrical and flat molds to study the effect of convex and flat casting/mold interface on heat transfer. To examine the effect of a concave and flat interfaces, an experimental setup consisting of a cylindrical and square bar chill was fabricated. Casting/mold (chill) interfacial heat flux was estimated by solving an inverse heat conduction problem (IHCP). The temperatures measured at locations inside the mold/chill were used as input to the inverse solver. It was observed that the flat contour yielded higher heat flux than a convex contour for both copper and steel molds. Although the volume to surface area (V/A) ratio for castings solidified against a flat and convex interface are the same, the larger mold volume associated with the flat interface yielded higher heat flux transients. Experiments involving chills suggested that the flat interface resulted in higher heat transfer when the (V/A) ratio for the chill was the same. To study and compare the combined effect of mold material and contour on heat transfer during casting solidification, the molds must have the same volumetric thermal effusivity per unit surface area available for heat transfer. © American Foundry Society 2023.Item Effects of Phosphorus Treatment on Cooling Behavior, Heat Transfer, Microstructure, and Mechanical Properties of Hypereutectic Al-23%Si Alloy(Springer, 2025) Vijayan, V.; Prabhu, K.N.The influence of phosphorus (P) treatment on the microstructure, cooling behavior, interfacial heat flux, and mechanical properties of hypereutectic Al-23 Si alloy is investigated in the present work. Computer-aided cooling curve analysis revealed that higher cooling rates suppressed silicon cluster agglomeration and promoted nucleation of primary silicon at lower undercooling. The addition of P increased the nucleation temperature of primary silicon and resulted in finer silicon crystals. Eutectic silicon nucleation was facilitated by P treatment, with refined primary silicon acting as nucleation sites. Interfacial heat flux analysis demonstrated that P addition decreased the heat flux, attributed to the presence of less conductive primary silicon, and unmodified eutectic silicon microstructure. Microstructural analysis revealed the refinement of primary silicon and transformation of its morphology to polyhedral shape with P treatment. Heat treatment improved tensile properties, with refined primary silicon and copper precipitation contributing to enhanced strength. The morphology and composition of copper intermetallic varied with P and Cu content, influencing mechanical properties. These findings provide insights into optimizing alloy compositions and processing conditions for hypereutectic Al-Si alloys in various industrial applications. © ASM International 2023.