Faculty Publications
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Item Review of microstructure evolution in hypereutectic Al-Si alloys and its effect on wear properties(2014) Vijayan, V.; Prabhu, K.Al-Si alloys with silicon content more than 13 % are termed as hypereutectic alloys. In recent years, these alloys have drawn the attention of researchers due to their ability to replace cast iron parts in the transportation industry. The properties of the hypereutectic alloy are greatly dependent on the morphology, size and distribution of primary silicon crystals in the alloy. Mechanical properties of the hypereutectic Al-Si alloy can be improved by the simultaneous refinement and modification of the primary and eutectic silicon and by controlling the solidification parameters. In this paper, the effect of solidification rate and melt treatment on the evolution of microstructure in hypereutectic Al-Si alloys are reviewed. Different types of primary silicon morphology and the conditions for its nucleation and growth are explained. The paper discusses the effect of refinement/modification treatments on the microstructure and properties of the hypereutectic Al-Si alloy. The importance and effect of processing variables and phosphorus refinement on the silicon morphology and wear properties of the alloy is highlighted. © 2013 Indian Institute of Metals.Item Modification of eutectic silicon in Al-Si alloys(2008) Hegde, S.; Prabhu, K.N.The mechanical properties of Al-Si alloys are strongly related to the size, shape and distribution of eutectic silicon present in the microstructure In order to improve mechanical properties, these alloys are generally subjected to modification melt treatment, which transforms the acicular silicon morphology to fibrous one resulting in a noticeable improvement in elongation and strength. Improper melt treatment procedures, fading and poisoning of modifiers often result in the structure which is far from the desired one. Hence it is essential to assess the effectiveness of melt treatment before pouring. A much investigated reliable thermal analysis technique is generally used for this purpose. The deviation from the standard curve in thermal analysis helps in assessing the level of refinement of the Si structure. In the present review an attempt is made to discuss various aspects of modification, including mechanism, interaction of defects and non-destructive assessment by thermal analysis. © 2008 Springer Science+Business Media, LLC.Item Influence of Ti, B and Sr on the microstructure and mechanical properties of A356 alloy(2011) Mallapur, D.G.; Kori, S.A.; Udupa, K.R.In the present investigation, the microstructural and mechanical properties study of A356 alloy have been discussed. The microstructural aspect of cast A356 alloy employed in the present study is strongly dependent on the grain refinement (Ti and B) and modification (Sr). The mechanical properties such as PS, UTS, %E, %R, YM and VHN have been investigated. This paper deals with the combined effect of grain refinement and modification, which improves the overall mechanical properties of the alloy. It is also a well-known fact that the mechanical properties of cast A356 alloy were improved by subjecting suitable melt treatment such as grain refinement, modification and mould vibration, etc. The quality of castings and their properties can be achieved by refining of ?-Al dendrites in A356 alloy by means of the addition of elements such as Ti and B which reduces the size of a-Al dendrites, which otherwise solidifies with coarse columnar a-Al dendritic structure. In addition, modification is normally adopted to achieve improved mechanical properties. Metallographic studies reveal that the structure changes from coarse columnar dendrites to fine equiaxed ones on the addition of grain refiner and further, plate like eutectic silicon to fine particles on addition of 0.20% of Al-10Sr modifier. The present result shows that a reduction in the size of a-Al dendrites, modification of eutectic Si and improvement in the mechanical properties were observed with the addition of grain refiner Al-3Ti, Al-3B and modifier Al-10Sr either individual addition or in combination. The change in the microstructure from coarse columnar ?-Al dendrites to fine equiaxed dendrites and plate like eutectic silicon to rounded particles leads to improved mechanical properties. © Springer Science+Business Media, LLC 2010.Item Influence of Ti, B and Sr on tribological properties of A356 alloy(2011) Mallapur, D.G.; Udupa, K.R.; Kori, S.A.The wear behaviour of an A356 alloy has been investigated in this paper. To understand the wear behaviour of the materials, the experiments were carried out using a pin on disc testing machine at various combinations of normal pressure, sliding speed and sliding distances. Tribological results reveal that weight loss of A356 alloy increases with increasing normal pressure and decreases with increasing sliding speed. Also, the results at microlevel revealed a structural change from coarse columnar dendrites to fine equiaxed ones on the addition of grain refiner (Al and B) and furthermore, plate-like eutectic silicon to fine particles on addition of modifier (Sr). It is further noted in the present study that addition of modifier does not disturb the influence of grain refiner and vice versa. Abrasive wear mechanism was interrupted by the formation of microwelds and later by oxidation of the Al matrix. © 2011 W. S. Maney & Son Ltd.Item The effect of the addition of strontium and cerium modifiers on microstructure and mechanical properties of hypereutectic Al-Si (LM30) alloy(ASTM International, 2013) Vijayan, V.; Ravi, M.; Prabhu, K.The present work deals with the melt treatment of LM30 hypereutectic Al-Si alloy using cerium and strontium and the assessment of its effect on microstructure and properties of the alloy. The addition of cerium simultaneously modified both primary and eutectic silicon, leading to an increase in ultimate tensile strength, as well as the wear resistance of the alloy. It was found that the coefficient of thermal expansion of the alloy decreased on modification of the microstructure. © 2013 by ASTM International.Item Effect of chilling and cerium addition on microstructure and cooling curve parameters of Al-14%Si alloy(Maney Publishing maney@maney.co.uk, 2015) Vijayan, V.; Prabhu, K.Al-14%Si alloys, with and without cerium, were cast at varying cooling rates by solidifying them in a crucible and against chills. The effect of melt treatment and chilling on microstructure and cooling curve parameters of the alloy was assessed. Ce treated alloys solidified in clay graphite crucible at a slow cooling rate showed refinement of primary silicon and the formation of Al-Si-Ce ternary intermetallic compound. The addition of Ce to the alloy solidified against chills resulted in simultaneous refinement and modification of primary and eutectic silicon. Nucleation temperatures of both primary and eutectic silicon decreased on addition of cerium. The formation of the intermetallic compound decreased with increase in cooling rate, leading to the modification of the eutectic silicon. The increase in the degree of modification of the eutectic Si was associated with the decrease in the volume fraction of the intermetallic compound formed. © 2015 Canadian Institute of Mining, Metallurgy and Petroleum Published by Maney on behalf of the Institute.Item The Effect of Chilling and Ce Addition on the Microstructure and Mechanical Properties of Al-23Si Alloy(Springer New York LLC barbara.b.bertram@gsk.com, 2017) Vijayan, V.; Prabhu, K.The present work involves the study of the effect of varying concentration of Ce addition on microstructure and mechanical properties of Al-23%Si alloys. Melt-treated alloys were solidified in copper, brass, stainless steel molds to assess the effect of cooling rate. The effect on microstructure was assessed by measuring the fineness of primary silicon and eutectic silicon particle characteristics. The Ce melt treatment transformed the coarse and irregular primary silicon into refined polyhedral silicon crystals, and the effect was more significant at higher cooling rates. Although the melt treatment had refined the eutectic silicon at lower cooling rates, it did not show any considerable effect on the eutectic silicon at higher cooling rates. The mechanical properties of the alloy increased significantly with increase in cooling rates and cerium concentration. Analysis of the results and literature reveals that the refined primary silicon was formed as a result of an invariant reaction between Ce compounds and primary silicon at higher temperatures. © 2016, ASM International.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.