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1

Parametric Optimization for Producing Semi-Solid A383 Alloy using Cooling Slope Casting Process

Rao M. S., Khandelwal Himandshu, Kumar M., Kumar A.

Archives of Foundry Engineering

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2023

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Vol. 23, iss. 1

43--52

EN

Cooling slope casting is a simple technique to produce semi-solid feedstock with a non-dendritic structure. The cooling slope technique depends on various parameters like slope length, slope angle, pouring temperature etc, that has been investigated in the present study. This work presents an extensive study to comprehend the combined effect of slope angle, slope length, pouring temperature, on hardness and microstructure of A383 alloy. Response Surface Methodology was adopted for design of experiments with varying process parameters i.e. slope angle between 15o to 60o, slope length between 400 to 700 mm, and pouring temperature between 560 oC to 600 oC. The response factor hardness was analysed using ANOVA to understand the effect of input parameters and their interactions. The hardness was found to be increasing with increased slope length and pouring temperature; and decreased with slope angle. The empirical relation for response with parameters were established using the regression analysis and are incorporated in an optimization model. The optimum hardness with non-dendritic structure of A383 alloy was obtained at 27o slope angle, 596.5 mm slope length and 596 oC pouring temperature. The results were successfully verified by confirmation experiment, which shows around 2% deviation from the predicted hardness (87.11 BHN).

2

Investigations on the suitability of some ferrous alloys for semi-solid processing

Robert M. H., Galdino A. G. S.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 34, nr 2

188-195

EN

Purpose: the work analyses the thixoability of SAE 1070, SAE 1548 and SAE 4340 steels; the possibility of producing thixotropic semi-solid by partial melting of these alloys and the phase transformations taking place during the process. Design/methodology/approach: thixoability was characterized by differential scanning calorimetry (DSC) to determine transformation temperatures involving liquid formation and dfl/dT within the solidification range. Thixotropic slurries were produced by heat treatments at different temperatures above Ts, and distinct holding times. Microstructures were analysed by RX diffractometry, optical and electronic microscopy and EDS microanalysis. Findings: results show that the three alloys investigated present high thixoability, given by wide solidification ranges associated with affordable sensitivity of liquid fraction with temperature within these ranges. Higher thixoability is presented by SAE 1070, followed by SAE 1548 and SAE 4340. Results show also that is perfectly feasible the production of thixotropic slurries of all investigated alloys, by simply heating to temperatures where a liquid phase can be present. Spheroidisation of solid primary phase is fast and increasing holding time at the semi-solid temperature leads to excessive growth of the globules in the thixocast material. Research limitations/implications: thixoability prediction models rely on sensitive experiments as thermoanalysis, with results strongly dependent on experimental conditions; and on thermodynamic data, sometimes not available or reliable for a specific alloy composition. Practical implications: the prediction of the thixoability of a certain alloy can make it more effective its thixoprocessing, allows better control of processing parameters and of the quality of final product. The viability of producing thixotropic semi-solid of ferrous alloys by simple partial melting can definitively insert these families of metallic alloys in the semi-solid processing field. Originality/value: ferrous alloys have become part of the thixoforming scenario more recently, when compared to aluminium and magnesium alloys. Therefore, the study of the thixoability of three commercial steels can bring important information as far as their utilization in thixoforming processing is concerned.

3

Analysis of the thixoability of ASTM A536 ductile iron

Robert M. H., Cristofolini R.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 28, nr 2

115-122

EN

Purpose: Thixoability of the ASTM A536 nodular cast iron is analyzed, it meaning its ability to hold a thixotropic semi-solid state and to be formed as such. Thixoability can be characterized by the solidification range, fraction of primary phase and sensitiveness of liquid fraction with temperature (df1/dT) within the solidification range. It is also investigated the effect of thixocasting in the microstructure of the considered alloy. Design/methodology/approach: Differential thermal analysis, differential scanning calorimetry and thermodynamic calculation package THERMOCALC were used to predict transformations temperatures involving liquid formation and df1/dT within the solidification range. Microstructures of thixotropic slurries produced by partial melting were observed. Findings: Thixoforming of ASTM A536 nodular iron can be considered in a narrow window of about 28° C, were some dissolution of graphite nodules can still be afforded; this window meaning the range of temperatures of co-existence of austenite + graphite + liquid were the eutectic transformation is taking place. At higher temperatures the dissolution of graphite nodules in liquid can be significant. Research limitations/implications: Thixoability prediction models rely on sensitive experiments as thermoanalysis, with results strongly dependent on experimental conditions; and on thermodynamic data, sometimes not available or reliable for a specific alloy composition. Practical implications: The prediction of the thixoability of a certain alloy can make it more effective its thixoprocessing, allows better control of processing parameters and quality of final product; can also subsidize modifications in the alloy to make it more suitable to semi-solid processing. Originality/value: The study of the thixoability of a nodular hypereutectic cast iron is an original subject, not available in the specialized literature, however absolutely necessary if thixoprocessing of this family of alloys is to be considered.

4

Producing thixotropic semi-solid A356 alloy: microstructure formation x forming behaviour

Robert M. H., Zoqui E. J., Tanabe F., Motegi T.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 20, nr 1-2

19-26

EN

Purpose: The work discuss the phenomena involved in the formation of the microstructure of semi-solid thixotropic alloy A356 produced by different techniques and the relation between microstructure and forming behaviour of the material. Design/methodology/approach: Thixotropic slurries of A356 alloy were produced from liquid and from solid conditions; in the first case either by stimulating nucleation rate or crystal multiplication during solid growth; in the second case by recrystallization and partial melting of deformed structures. Flow behaviour was analysed by viscosity measurements or by flow ability in forging operations. Findings: Results show that different production techniques activate different mechanisms, leading to distinct structure features in the semi-solid slurry, and, as consequence, in its forming characteristics. Techniques which promote formation of isolate globules of primary phase, like those involving nucleation stimulation and recrystallization, result in a semi-solid with better flowing behaviour. On the other hand, techniques based on crystal multiplication during growth lead to more interconnected globules in the slurry and poorer forming behaviour. Research limitations/implications: Semi-solid processing is suitable only for alloys with appropriate liquid fraction x temperature relation. Practical implications: the konowledge of the phenomena involved in the formation of thixotropic metallic slurries produced by different techniques, and their consequences in the material structure and flow behaviour, allow the decision of the adequate slurry production method for a specific application, in order to take the best advantage of the semi-solid technology. Originality/value: The analysis of the relation between production process x flow behaviour of semi-solid thixotropic A 356 is original.

5

Innovative induction heating installation for re-heating thixocasting billets up to 5" diameter: thermal and metallurgic results

Bonollo F., Forzan M., Lupi S., Schiavon M.

Archives of Electrical Engineering

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2005

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Vol. 54, nr 4

397-404

EN

The pressure casting of aluminium alloy A356 is a metallurgical technique that provides a very high quality of the final product, because it avoids defects in the filling of the mould and consequent solidification, typical for the traditional casting process. The semi-solid metal shows excellent injection characteristics, if the required uniform temperature distribution is assured. The paper presents the last results achieved at the Padua University and ATE srl in the domain of research activity aimed at development of an induction system for re-heating thixocasting billets and maximisation of its performance. The system allows significant reduction of the heating times and higher production rates.

PL

Odlewanie ciśnieniowe stopu aluminium A356 to technologia metalurgiczna pozwalająca na uzyskanie bardzo wysokiej jakości produktu finalnego dzięki uniknięciu wad wypełnienia formy i w uzyskanie krzepnięcia typowego dla tradycyjnego procesu odlewania. Jeśli zapewniony jest równomierny rozkład temperatury to metal w stanie półciekłym wykazuje znakomite charakterystyki wtrysku. W pracy przedstawiono najnowsze wyniki badań uzyskane w Uniwersytecie Padwa i firmie ATE ukierunkowane na optymalizację nagrzewnicy indukcyjnej do przegrzewania wlewków w stanie półciekłym. Zastosowany układ pozwala na zmniejszenie czasu nagrzewania i zwiększenie wydajności procesu.