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H. K. Jung - One of the best experts on this subject based on the ideXlab platform.
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A study on quantitative formability assessment of rheological materials based on the microstructural characterization with a moderate control of the process
Journal of Materials Processing Technology, 2006Co-Authors: H. K. Jung, Han-goo Kim, Chung Gil KangAbstract:Abstract The Semisolid forming (cleaner rheological forming) of aluminum alloys is a new net shape manufacturing method that incorporates elements of both forging and casting. It is characterized by the use of induction heating to reheat billets to the highest possible solid fraction in order to maximize the mechanical properties such as strength, wear resistance and elongation. It is necessary to develop tailored alloys specifically for cleaner rheological forming (CRF). The selection is basically from the entire range of cast and wrought aluminum alloys, although most of these alloys were optimized either for the casting or for the forging process. Nowadays, their formability evaluation in the Semisolid State has rarely been investigated, and more essentially, it lacks a systematic theoretical base for dealing with unexpected behavior under the new and possibly extreme conditions encountered as we expand the limits of this criterion. So, the present article uniquely focused on an advanced description (advanced JK criteria) to evaluate the formability and castability of next-generation nonferrous materials such as cast and wrought aluminum alloys in the Semisolid State based on the microstructural characteristics with an appropriate control of the process. Using the proposed criteria (advanced JK criteria) to evaluate the quantitative formability of cleaner rheological materials in the Semisolid State shows that a nine-point alloy represents an optimal Semisolid formability while a zero-point alloy is extremely unsuitable for CRF, confirming the validity of the proposed criteria.
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A study on a thixoforming process using the thixotropic behavior of an aluminum alloy with an equiaxed microstructure
Journal of Materials Engineering and Performance, 2000Co-Authors: H. K. Jung, Chung Gil KangAbstract:Alloys with an equiaxed microstructure exhibit significantly lower flow resistance in the Semisolid State than alloys with a dendritic microstructure. Their thixotropic behavior (solidlike in the unperturbed State and liquidlike during shearing) has been the basis for a thixoforming process. It is accepted today that thixoforming is a new net-shaped manufacturing technology in which the billet is heated to the Semisolid State with coexisting solid-liquid phases.
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A study on a thixoforming process using the thixotropic behavior of an aluminum alloy with an equiaxed microstructure
Journal of Materials Engineering and Performance, 2000Co-Authors: H. K. Jung, C.g. KangAbstract:Alloys with an equiaxed microstructure exhibit significantly lower flow resistance in the Semisolid State than alloys with a dendritic microstructure. Their thixotropic behavior (solidlike in the unperturbed State and liquidlike during shearing) has been the basis for a thixoforming process. It is accepted today that thixoforming is a new net-shaped manufacturing technology in which the billet is heated to the Semisolid State with coexisting solid-liquid phases. The thixoforming process has some industrial advantages, such as the successful fabrication of high-quality components with fewer inner defects, suitable for less machining, high productivity comparable to high-pressure die casting, and being an energy-saving system without the conventional melting process. It consists of inductive coil design, a billet reheating process, billet handling, filling into the die cavity, and solidification of the thixoformed part. This work presents an overview of all the detailed stages in the thixoforming process to manufacture the net-shaped product with good mechanical properties. An air compressor part with high strength has been fabricated by the thixoforming process.
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induction heating of Semisolid billet and control of globular microstructure to prevent coarsening phenomena
Journal of Materials Engineering and Performance, 2000Co-Authors: H. K. Jung, C.g. Kang, Y H MoonAbstract:An important step in the thixoforming process is the induction heating of the raw materials to the Semisolid State. Using this technology, the process behavior is satisfactory from the point of view of reproducibility and temperature control. Therefore, the objectives of this study are to define the correct relationship between coil length and billet length for uniform induction heating and to present the optimal reheating conditions suitable for the thixoforming process (or to secure a fine globular microstructure without liquid segregation).
Chung Gil Kang - One of the best experts on this subject based on the ideXlab platform.
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Coarsening of equiaxed microstructure in the Semisolid State of aluminum 7075 alloy through SIMA processing
Journal of Materials Science, 2012Co-Authors: Amir Bolouri, Mohammad Shahmiri, Chung Gil KangAbstract:In the present study, the coarsening mechanism of equiaxed grains in the Semisolid State of aluminum 7075 alloy, treated via strain induced melting activation process, was investigated. The kinetics of equiaxed grain growth in the Semisolid State of the experimental alloy was determined. The results revealed that when the holding temperature increased, the coarsening rate constant ( K ) showed a precipitously increasing character in the range of 590–610 °C. This was attributed to the extensive effect of the coalescence mechanism on the grain growth at the high solid fractions. By further increasing the holding temperature to 620 and 625 °C (increasing the liquid fraction), the effect of coalescence on the grain growth appeared to be weakened, that is, although there was a slight decrease at 620 °C, a gently increasing character could be generally supposed. Severe segregation of Zn and Cu alloying elements at grain boundaries and intragranular droplets was detected at 620 and 625 °C after 15 and 10 min, respectively.
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A study on quantitative formability assessment of rheological materials based on the microstructural characterization with a moderate control of the process
Journal of Materials Processing Technology, 2006Co-Authors: H. K. Jung, Han-goo Kim, Chung Gil KangAbstract:Abstract The Semisolid forming (cleaner rheological forming) of aluminum alloys is a new net shape manufacturing method that incorporates elements of both forging and casting. It is characterized by the use of induction heating to reheat billets to the highest possible solid fraction in order to maximize the mechanical properties such as strength, wear resistance and elongation. It is necessary to develop tailored alloys specifically for cleaner rheological forming (CRF). The selection is basically from the entire range of cast and wrought aluminum alloys, although most of these alloys were optimized either for the casting or for the forging process. Nowadays, their formability evaluation in the Semisolid State has rarely been investigated, and more essentially, it lacks a systematic theoretical base for dealing with unexpected behavior under the new and possibly extreme conditions encountered as we expand the limits of this criterion. So, the present article uniquely focused on an advanced description (advanced JK criteria) to evaluate the formability and castability of next-generation nonferrous materials such as cast and wrought aluminum alloys in the Semisolid State based on the microstructural characteristics with an appropriate control of the process. Using the proposed criteria (advanced JK criteria) to evaluate the quantitative formability of cleaner rheological materials in the Semisolid State shows that a nine-point alloy represents an optimal Semisolid formability while a zero-point alloy is extremely unsuitable for CRF, confirming the validity of the proposed criteria.
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A study on a thixoforming process using the thixotropic behavior of an aluminum alloy with an equiaxed microstructure
Journal of Materials Engineering and Performance, 2000Co-Authors: H. K. Jung, Chung Gil KangAbstract:Alloys with an equiaxed microstructure exhibit significantly lower flow resistance in the Semisolid State than alloys with a dendritic microstructure. Their thixotropic behavior (solidlike in the unperturbed State and liquidlike during shearing) has been the basis for a thixoforming process. It is accepted today that thixoforming is a new net-shaped manufacturing technology in which the billet is heated to the Semisolid State with coexisting solid-liquid phases.
Antonios Zavaliangos - One of the best experts on this subject based on the ideXlab platform.
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Evolution of near-equiaxed microstructure in the Semisolid State
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2000Co-Authors: Evangelos Tzimas, Antonios ZavaliangosAbstract:The microstructure of alloys with a near-equiaxed microstructure, produced by spray casting, magnetohydrodynamic (MHD) casting and the stress induced, melt activated (SIMA) process, as it evolves within short times in the Semisolid State, is examined by rapid quenching and isothermal soaking experiments. Quenching experiments reveal the morphology and distribution of solid phase at high and medium volume fractions of liquid. At medium liquid content, the microstructure of spray-cast and SIMA alloys consists of discrete equiaxed grains uniformly dispersed in the liquid phase, while the corresponding microstructure of MHD-cast alloys exhibits extensive agglomerates consisting of incompletely spheroidized grains. The connectivity of solid phase and the formation of a solid skeleton in the Semisolid State are discussed in terms of grain misorientation. Isothermal soaking experiments investigated grain growth and degree of spheroidization as a function of soaking time and liquid content in the Semisolid State. Results demonstrated that MHD-cast microstructures are less equiaxed compared with SIMA and spray-cast alloys even after 5 min of soaking in the Semisolid State. It is also shown that the grain growth rate is smaller in spray-cast alloys than in SIMA alloys. The role of coalescence and the effects of alloying elements are also discussed.
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Evaluation of volume fraction of solid in alloys formed by Semisolid processing
Journal of Materials Science, 2000Co-Authors: Evangelos Tzimas, Antonios ZavaliangosAbstract:Three of the methods used to determine the volume fraction of solid as a function of temperature in alloys in the Semisolid State, namely utilization of thermodynamic data, thermal analysis, and quantitative metallography on quenched microstructures, are studied. The accuracy of each method is evaluated and the advantages and limitations are recognized. It is demonstrated that, while all methods are approximate, they offer distinct and different advantages.
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Materials Selection for Semisolid Processing
Materials and Manufacturing Processes, 1999Co-Authors: Evangelos Tzimas, Antonios ZavaliangosAbstract:Abstract The mechanical behavior of alloys in the Semisolid State is very sensitive to the volume fraction of solid. In this paper, a simple criterion for processability in the Semisolid range is introduced, based on the sensitivity of the volume fraction of solid with respect to minor temperature variations. In addition it is proposed that the processability in the Semisolid State can be enhanced using microsegregated material.
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Mechanical behavior of alloys with equiaxed microstructure in the Semisolid State at high solid content
Acta Materialia, 1999Co-Authors: Evangelos Tzimas, Antonios ZavaliangosAbstract:Abstract The mechanical response in compression of A2014 and Al–4 wt% Cu alloys with equiaxed microstructure in the Semisolid State at high volume fraction of solid (>0.6) is studied. When the amount of liquid is low, deformation in compression is highly non-uniform due to strain localization. In the range of conditions examined no phase segregation was detected. The stress–strain curve exhibits a peak at low strain, around 5–10%, and then decreases to a plateau value. Secondary phase particles in A2014 that remain solid in the Semisolid range of the alloy are responsible for the lower peak and higher plateau stress compared to Al–4 wt% Cu alloy. The effect of the grain size for the alloys tested was small. Strain rate jump experiments show that the instantaneous strain rate sensitivity in the Semisolid State is similar to that of the solid phase. As the volume fraction of solid decreases, the plateau stress becomes rate insensitive to the strain rate jump. The results allow the relative importance to be assessed of various mechanisms responsible for resistance to flow of Semisolid alloys with equiaxed microstructure in compression.
Michel Suéry - One of the best experts on this subject based on the ideXlab platform.
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Mechanical Behavior of AA6061 Aluminum in the Semisolid State Obtained by Partial Melting and Partial Solidification
Metallurgical and Materials Transactions A, 2010Co-Authors: Eliane Giraud, Michel Suéry, Michel CoretAbstract:The tensile properties of a 6061 aluminum alloy have been studied in the Semisolid State at large solid fractions. The tests have been carried out either after a partial melting treatment or after partial solidification. Results show the following: (1) the mechanical behavior depends on the liquid-phase distribution and, therefore, on the way the Semisolid State has been achieved (melting or solidification); (2) there is a critical solid fraction range where the Semisolid alloy is relatively brittle; and (3) the mushy alloy exhibits viscoplastic behavior with the occurrence of micro-superplasticity at low strain rate. Modeling of this behavior is carried out by considering either the area fraction of grain boundaries wetted by the liquid or a cohesion parameter of the solid phase, which depends on solid fraction and thermal treatment.
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Microstructural and mechanical characterisation of an Al-21.8 wt.% Ge brazing alloy with a globular morphology of the primary Al-rich phase
Materials Science and Engineering: A, 1999Co-Authors: Juana Valer, Péricles Ménéses, François Saint-antonin, Michel SuéryAbstract:This paper is concerned with the microstructural and mechanical characterisation of a hypoeutectic Al-Ge alloy designed to join the plasma facing components of thermonuclear fusion reactors to permanently cooled substrates. The alloy was prepared from pure aluminium and germanium by casting, hot rolling and heat treatment above the eutectic temperature. This treatment leads to a globular morphology of the primary Al-rich phase provided that the thickness reduction during rolling is sufficient, about 20%. Increasing the rolling reduction, however, leads to liquid entrapment in the globules, the amount of which depends on the temperature in the Semisolid range. The mechanical behaviour of the material was determined in tensile tests at room and elevated temperature after various heat treatments in the Semisolid State and compared with the mechanical properties after hot rolling. In addition, compression tests were also carried out in the Semisolid State. These tests show that the globular materials deform under very low stresses without segregation of the liquid. A comparison is made with non-globular materials obtained simply by partial remelting of the as-cast alloy.
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Microstructure and compression behaviour in the Semisolid State of short-fibre-reinforced A356 aluminium alloys
Materials Science and Engineering: A, 1995Co-Authors: L. Nguyen Thanh, Michel SuéryAbstract:Abstract This paper is concerned with the microstructural characterization and compressive behaviour of partially remelted A356 aluminium alloys reinforced with 10 vol.% chopped SiC Nicalon fibres. The composites were fabricated by the compocasting technique and subsequently solidified under pressure, some materials being also extruded at high temperature. It is shown that compocasting leads to breakage of the fibres, which are further fragmented by extrusion and aligned along the extrusion direction. Isothermal holding of the extruded composites in the Semisolid State leads to rapid globularization of the structure of the solid phase, with globules coarsening as the holding time increases. The globularization is associated with a decrease in the compression stress at constant strain rate, this stress increasing with increasing strain rate according to a classical power low σ = K e m with values of m close to 0.3. Comparison with the unreinforced alloy and with as-cast composites clearly demonstrates the influence of the presence of the reinforcing elements on the compressive stress of the material together with that of extrusion before partial remelting.
Plato Kapranos - One of the best experts on this subject based on the ideXlab platform.
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Microstructural Evolution of Solid-solution-treated Zn-22Al in the Semisolid State
Journal of Materials Science & Technology, 2013Co-Authors: M. A M Arif, Mohd. Zaidi Omar, Norhamidi Muhamad, Junaidi Syarif, Plato KapranosAbstract:The effect of solid-solution-treatment on the Semisolid microstructure of Zn–22Al with developed dendrites was investigated. Forming Zn–22Al products by Semisolid metal processing offers significant advantages, such as reductions in macro-segregation, porosity and forming costs. Thermal and microstructural analyses of the formed Zn–22Al alloy were performed by differential scanning calorimetry, scanning electron microscopy and optical microscopy. The changes in the microstructures and phase transformation in response to various solid-solution-treatments were analysed. In this study, as-cast samples were held isothermally at 330 °C for 0.5–5 h and then partially remelted at a Semisolid temperature of 438 °C for 1 h to produce a solid-globular grain structure in a liquid matrix. A non-dendritic Semisolid microstructure could not be obtained when the traditionally cast Zn–22Al alloy with developed dendrites was subjected directly to partial remelting. After solid-solution-treatment at 330 °C, the black interdendritic eutectics were dissolved, and the dendritic structures gradually transformed into uniform β structures when the treatment time was increased. The coarsened and merged dendrites were separated as a result of penetration by the liquid phase and melting of the residual eutectic at sites along the former grain boundaries. The microstructure of the solid-solution-treated sample transformed into a small globular structure; the best shape factor of 0.9, corresponding to a particle size of 40 ± 16 μm, is achieved when the sample was treated for 3 h followed by direct partial remelting into its Semisolid zone.
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Multistep induction heating regimes for thixoforming 7075 aluminium alloy
Materials Science and Technology, 2004Co-Authors: S. Chayong, Helen V. Atkinson, Plato KapranosAbstract:Thixoforming involves processing alloys with a spheroidal microstructure in the Semisolid State. Commercially it is applied to conventional casting alloys, and one of the scientic challenges is to extend its application to high performance aluminium alloys such as 7075.Aluminium alloy 7075 is readily available in extruded form, and one route to a spheroidal microstructure is to reheat extruded material into the Semisolid State to obtain recrystallisation, with the liquid penetrating the recrystallised boundaries. Here this route has been followed, but it has been found that the presence of pinning particles in the microstructure inhibits recrystallisation. To overcome this, a multistep induction heating regime has been developedconsisting of a 1 min hold at 475– 500°C, a 1 min hold at 575– 600°C and a shorter 20 s hold for the final step at 620°C.
