Ali Kalkanli

Microstructure characteristics in Al-C system after mechanical alloying and high temperature treatment

Abstract In this work elemental powders of Al and 2 wt-% graphite were mechanically alloyed in a high energy horizontal attritor under purified argon atmosphere for 0·5-2 h. Powder mixes were then cold pressed at 1200 MPa and sintered at 550°C for between 2-32 h under the same protective atmosphere. Structural evolution was characterised by X-ray diffraction, scanning electron microscopy and transmission electron microscopy techniques. Results revealed that mechanical alloying was very effective in pulverising the powder mix, where after 2 h, the mix was fine enough to oxidise rigorously when exposed to open air. In general however, mechanical alloying was found to be inefficient to synthesise Al with C. But after sintering, Al4C3 phase nanosized particles were formed in the microstructure. When the duration of sintering was prolonged, the particle population multiplied in number. Hence because of improvement in dispersion strengthening, the room temperature hardness of the material increased gradually.

Evaluation of latent heat of solidification of grey cast iron from cooling curves

Abstract The temperature history in the casting obtained from cooling curves can be used to determine some information related to latent heat release during alloy solidification. This work presents a procedure for the evaluation of latent heat of primary and eutectic solidification of grey cast iron from cooling curves based upon the Newtonian cooling principle. The thermal data obtained from quik-cups are processed with the Mathcad code in order to obtain the cooling curve, its first and second derivatives and the first derivative of the fictitious neutral body generated according to the principles of Newtonian cooling assumption. The cooling curves of seven different alloys of hypoeutectic, eutectic and hypereutectic compositions were investigated with special emphasis on the amounts of latent heat released during primary and eutectic solidification. The values obtained are consistent with the statement that the latent heat of eutectic solidification should increase as the composition of the cast iron comes closer to the eutectic point, but the methodology is found to be unreliable for the estimation of latent heat of primary solidification. On peut utiliser l’histoire thermique dans le moulage, obtenue à partir des courbes de refroidissement, pour déterminer l’information reliée au relâchement de chaleur latente lors de la solidification de l’alliage. Ce travail présente une procédure d’évaluation de la chaleur latente de solidification primaire et eutectique de la fonte grise, à partir des courbes de refroidissement, basée sur le principe de refroidissement newtonien. Les données thermiques obtenues de coupelles sont traitées avec le code Mathcad afin d’obtenir la courbe de refroidissement, sa première et sa seconde dérivées ainsi que la première dérivée du corps neutre fictif, engendré d’après les principes de l’hypothèse de refroidissement newtonien. On a étudié les courbes de refroidissement de sept alliages différents de compositions hypoeutectiques, eutectiques et hypereutectiques, avec emphase particulière sur les quantités de chaleur latente relâchées lors de la solidification primaire et eutectique. Les valeurs obtenues sont consistantes avec l’énoncé disant que la chaleur latente de solidification de l’eutectique devrait augmenter à mesure que la composition de la fonte s’approche du point eutectique, mais on trouve que la méthodologie n’est pas fiable pour l’estimation de la chaleur latente de solidification primaire.

Effect of cooling rate on microstructure and high temperature stability of rapidly solidified Al–Fe–V–Si alloys

AbstractRecently, Al–Fe–V–Si alloys have received more attention owing to their high temperature stability associated with vanadium rich precipitates and silicides. In this work, a series of alloys was prepared and processed by melt spinning and gas atomisation to observe the effect of solidification rate on crystal structures existing in both as cast and heat treated conditions. This study covers their microstructural examination and crystallography. The composition of these alloys was Al–(6·8–7·8)Fe–(1·0–3)V–(1·6–2 ·2)Si and the ribbons and powders produced were examined by SEM and TEM. Investigations revealed that most of the rapidly solidified ribbons and powders consisted of a cellular structure with cubic spherical dispersoids and quasicrystalline i phase spheroids. The proportions of these phases were found to be dependent on section thickness and cooling rate of the products. More i phase spheroids were observed in sections of melt spun ribbons and coarse powders. After heat treatment at 300, 400,...

Effect of spraying rate on microstructure of spray deposited Al-Fe-V-Si alloy

Abstract In this study gas atomisation and spray deposition of a series of AlFeVSi alloys were carried out. Traces of transient liquid were observed as lamellar structure in the middle of the specimen. The heat transfer conditions of this structure were modelled by finite difference calculation. Metallographic specimens for optical microscopy were prepared from the preforms formed in these processes. Optical microscopy showed the presence of dispersoids in the specimens. The dispersoids were characterised as AlFeVSi cubic phase by X-ray diffraction analysis. SEM was used to examine the morphology of phases and quantitative element analysis to reveal the chemical composition of the dispersoids present. The one-dimensional mathematical model, which describes the heat diffusion during spray deposition, was solved using the finite difference method.

Production and assessment of direct cast soft magnetic alloy strips

Abstract The melt overflow process has been developed as a technique to produce tonnage quantities of strip and fibre in a wide range of materials. Typical thicknesses vary from 150–700 μm depending on liquid alloy surface tension and process parameters. Here a number of crystalline alloys considered for their soft magnetic properties have been cast in air and an enclosed atmosphere. The surface tensions measured by a modified oscillating droplet technique indicate that small impurity concentrations can markedly affect strip properties. As yet no strong reduction annealing effect on coercivity has been established.

Investigation of microporosity formation mechanisms in A356 aluminium alloy castings

The problem of microporosity formation during solidification of aluminum alloy castings has great commercial importance and engineering interest due to its detrimental effects on mechanical properties. The present study concentrates on the mechanisms of microporosity formation in aluminium alloy castings. The microstructural characterisation of the produced samples was carried out with image analysis and SEM. It was observed that formation of shrinkage induced interdendritic porosity depends on solidification mode of the sample. The precipitation of intermetallic s-Al5FeSi platelets in the interdendritic liquid were also found to promote the interdendritic porosity formation by blocking interdendritic feeding. The results reveal that the oxide inclusions have a significant effect on formation of hydrogen precipitation induced regular micropores.

The Effect of Magnesium to Sulfur Ratio on the Graphite Morphology of Graphite Cast Iron Produced at Differrent Section Thicknesses

This paper is concerned with the investigation of the effect of magnesium to sulfur ratio on the graphite morphology and estimation of the ranges of this ratio use to produce graphite cast iron at different section sections. The main factors affecting shape of graphite cast iron are the metallurgical structures and the section thicknesses. Cast iron of different shapes of graphite particles directly affect its thermo-mechanical properties. The nodular shape of these graphite particles such as in ductile cast iron improve its mechanical properties, on the other hand, when the shape of these graphite particles become elongated such as in flake graphite cast iron results in improving its thermal conductivity. In between, the worm-like shape of these graphite particles such as in compacted graphite cast iron, make this type of cast iron to have thermo-mechanical properties in between those of ductile and flake graphite cast iron. The different types of ductile , compacted and flake graphite cast iron were produced by means of plunger method at different section thicknesses and the effect of Mg/S ratio on these types of graphite particles was investigated and its range was established.

Application of cooling curve analysis as a process control tool to produce compacted graphite cast iron

Compacted graphite cast iron is becoming an alternative to lightweight alloys, especially in production of automotive engine blocks due to its high strength and its high thermal conductivity. However, the successful casting process to produce compacted graphite cast iron depends on the quality of the control procedures that are utilised during production. The aim of the present study is to investigate the relations between the thermal analysis parameters and the graphite morphologies of the cast irons that were produced over a suitable range of Mg/S ratios and to attempt to present a methodology that can supply information during production.

OXYGEN POTENTIAL VALUES TO PRODUCE COMPACTED GRAPHITE CAST IRON

Abstract Compacted graphite cast iron (CGI) is a potential alternative to lightweight alloys. It is accepted that CGI can effectively reduce the automobile total weight by virtue of its high strength and its high thermal conductivity giving an opportunity to designers to design components with thinner sections. However, the successful casting process to produce this material requires detailed information for the prediction of microstructure and accurate casting process knowledge. In this paper, compacted graphite with four different cooling rates and with different Mg/S ratios ranging from 2/3 to 7/1 has been produced by using a plunger technique. The oxygen potential of all ranges has been measured by using a special oxygen potential measuring device equipped with a vibrating oxygen measurement sensor. The relationship between the oxygen potential and the graphite shape was investigated and the oxygen potential range to produce compacted graphite iron was established. It has been demonstrated that the oxygen potential measurement is a valuable method to evaluate the potential of cast iron melts to produce compacted graphite iron. La fonte à graphite compact (CGI) est une substitution possible des alliages légers. On accepte que la CGI puisse effectivement réduire le poids total de l’automobile en raison de sa grande résistance et de sa conductivité thermique élevée, donnant ainsi la chance aux concepteurs de créer des éléments à profilés plus minces. Cependant, le procédé de moulage efficace pour la production de ce matériau nécessite une information détaillée pour la prédiction de la microstructure et une connaissance précise du procédé de moulage. Dans cet article, on décrit la production de graphite compact à quatre vitesses différentes de refroidissement et à rapports différents de Mg/S variant de 2/3 à 7/1, en utilisant une technique de piston d’injection. On a mesuré le potentiel-oxygène de toute la gamme en utilisant un appareil particulier pour mesurer le potentiel-oxygène, équipé d’un capteur à vibration pour la mesure d’oxygène. On a étudié la relation entre le potentiel-oxygène et la forme de graphite et l’on a établi la gamme de potentiel-oxygène pour produire de la fonte à graphite compact. On a démontré que la mesure du potentiel-oxygène était une méthode valable pour évaluer le potentiel des bains de fonte pour produire de la fonte à graphite compact.

Effect of Heat-Treatment and Reinforcement With Silicon Carbide on the Microstructure and Mechanical Properties of AlFeVSi Alloy

The aging response of Al-Fe-V-Si composite was compared with the un-reinforced alloy. The effects of solutionizing time, alloying element and SiC reinforcement on the age hardening response, microstructure and mechanical properties of these alloy and its composites was also investigated. The study was performed by T6 heat treatment at three different solutionizing times. Room temperature tensile testing was conducted for peak aged specimens to determine the effect of this heat treatment on the strength of squeezed cast un-reinforced and reinforced Al-Fe-V-Si alloy with SiC particles. The presence of SiC particles accelerated the aging kinetics of the composites compared to the unreinforced alloys. The time to reach peak age hardness was decreased by addition of SiCp. Mainly two different Fe-intermetallics; small α-Al7 (Fe, V)3 Si and large β-Al18 Fe11 Si phases were present in the system studied. The fracture surfaces of composites revealed decohesion of SiC particles from the matrix and cracking of needle like-β intermetallics was observed.Copyright