Started in 1985 Semimonthly
ISSN 1005-0302
CN 21-1315/TG
Impact factor:6.155

The journal has been awarded the excellent periodical in China, and its articles are covered by SCI, EI, CA, SA, JST, RJ, CSA, MA, EMA, AIA etc., PASCAL web. ISI web of Science,SCOPUS.

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      28 January 2008, Volume 24 Issue 01 Previous Issue    Next Issue
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    Research Articles
    Heat Transfer and Acoustic Properties of Open Cell Aluminum Foams
    Bokhyun KANG, Kiyoung KIM, Byungmin LEE, Jaesoo NOH
    J. Mater. Sci. Technol., 2008, 24 (01): 1-6. 
    Abstract   HTML   PDF (1052KB)
    The aluminum open cell foams have been prepared by the conventional precision casting method to investigate the thermal and acoustic properties. A water heating system and silencers were organized as a first step for its applications. The temperature increase between the top and bottom of the foam became larger as the cell size increased in the heat transfer measurement. Sound absorption ratio of the close cell foams was 60%–100%, whereas the open cell aluminum foam showed only 10%–20% of sound absorption at low frequency. When the prototype electric water heater manufactured by combining aluminum open cell foam with a heater was heated to 100–400℃, the highest temperature of water was in the range of 16–46℃. This suggests that there could be potential for this type of heater to be used as a commercial electric water heater. Sound silencer made with the aluminum open cell foam was applied to exit of exhaustion side at air pressure line. Sound silencing effect of open-celled aluminum foam showed that the noise level went down by introducing smaller cell size foam.
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    Effect of Squeeze Cast Process Parameters on Fluidity of Hypereutectic Al-Si Alloy
    Jong-Kyu Baek, Hae-Wook Kwon
    J. Mater. Sci. Technol., 2008, 24 (01): 7-11. 
    Abstract   HTML   PDF (1780KB)
    The effects of processing variables on the fluidity of hypereutectic Al-Si alloy melt during squeeze casting were investigated. The maximum fluidity of Al-16.0%Si alloy during squeeze casting was obtained under the applied pressure of 30 MPa. The fluidity increased with superheat. The fluidity increased with silicon content in the range from 12.0% to 20.0%. That was decreased respectively by eutectic modification and primary silicon refinement.
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    Development of Deformation-Semisolid-Casting (D-SSC) Process and Applications to Some Aluminum Alloys
    Tatsuo Sato
    J. Mater. Sci. Technol., 2008, 24 (01): 12-16. 
    Abstract   HTML   PDF (2130KB)
    Recent advances in the semisolid casting technologies are introduced for aluminum alloys. The advantages of the rheocast and thixocast methods to fabricate alloys with refined spheroidized α-Al particles are described. The deformation-semisolid-casting (D-SSC) process developed by the author’s group is presented. The D-SSC process is extremely effective to produce microstructures of refined intermetallic compound particles as well as the spheroidized α-Al particles in the Al-Si based alloys containing highly concentrated Fe. In the D-SSC processed Al-Si-Cu alloy high elongation of about 20% was achieved even contained concentrated impurity of Fe. The D-SSC process is also useful to produce wrought aluminum alloys with microstructures of refined α-Al particles.
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    Effect of Sc on Precipitation Hardening of AlSi6Mg Alloy
    Wattanachai Prukkanon, Satit Chanpum, Chaowalit Limmaneevichitr
    J. Mater. Sci. Technol., 2008, 24 (01): 17-20. 
    Abstract   HTML   PDF (3395KB)
    The effect of Sc on precipitation hardening of AlSi6Mg was studied. Zr was previously reported that it increased the effectiveness of Sc in wrought aluminum in many areas so Zr was also used together with Sc in this study. Different levels of Sc and Zr additions were added to AlSi6Mg before casting in the permanent mold. The samples were precipitation hardened at different aging temperatures and for various aging time before testing for tensile strength and hardness. It was found that Sc addition into Al6SiMg can change its response to age hardening. Additions of Sc and Sc with Zr increased both yield strength and hardness for both aging temperatures. In addition, Sc was found to modify eutectic Si to obtain fibrous morphology. This effect of Sc on eutectic silicon modification has never been reported before.
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    Effects of Cr and Cr/Mn Combined Additions on Semi-Solid Microstructures of Al-Mg-Si Alloys Produced by D-SSF Process
    Witthaya Eidhed, Hiroyasu Tezuka, Tatsuo Sato
    J. Mater. Sci. Technol., 2008, 24 (01): 21-24. 
    Abstract   HTML   PDF (6552KB)
    The effects of Cr and Cr/Mn combined additions on the semi-solid microstructure of wrought Al-Mg-Si alloys are investigated. In the Cr-added alloy, the Al7Cr compound is formed with homogeneously distributed in the α-Al matrix after homogenization. Both of the Al7Cr and α-Al12Mn3Si2 dispersiod particles are found in the homogenized microstructure of the Cr/Mn-added alloy. In the semi-solid microstructures, the smallest α-Al grains are obtained in the 60% cold-rolled alloys. After prolonged holding time, the α-Al grain size of the Cr/Mn-added alloy is smaller than that of the Cr-added alloy. Heavy deformation by cold-rolling accelerates spheroidization of the α-Al grains. The D-SSF process is found to be useful to modify the microstructures of both the Cr-added and Cr/Mn-added Al-Mg-Si alloys.
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    Effect of Alloying Element Antimony on Macrostructural and Microstructural Development in A356 Alloy Directionally Solidified under Unsteady-state Conditions
    Supparerk Boontein, Julathep Kajornchaiyakul, Chaowalit Limmaneevichitr
    J. Mater. Sci. Technol., 2008, 24 (01): 25-28. 
    Abstract   HTML   PDF (3179KB)
    Microstructure development is well accepted to have a major effect on mechanical properties during its services. One of the most interesting ways to improve mechanical properties is to reduce secondary dendrite arm spacing (SDAS). SDAS also plays an important role in controlling and providing the well distributed and fine microstructure resulting in better tensile strength and elongation. To reduce SDAS, it is commonly known by increasing cooling rate and increasing interface instability by limited-soluble alloy addition. It is, however, unclear that how both cooling rate and limited-soluble alloy, e.g. Sb, relate to each other. This may be the reason that the limited-soluble alloy may not effectively reduce SDAS. To better understand this phenomenon, influences of Sb on solid/liquid interface instability using columnar to equiaxed transition (CET) were studied in the directionally solidification experiment. From macrographs and micrographs, it was observed that at 0.06–0.18 wt pct Sb the CET min, CET max, CET zone and %CET area gradually increased. The increases of CET max and CET zone in samples with 0.06 to 0.18 wt pct Sb addition results from recalesced zone. On the other hand, the variations of CET max and CET zone in samples with 0.24 to 0.30 wt pct Sb results from equiaxed grain formations that prohibit the growth of columnar grain and latent heat from intermetallic phase solidified.
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    Effects of Solution Treatment Time and Sr-Modification on Microstructure and Mechanical Property of Al-Si Piston Alloy
    Witthaya Eidhed
    J. Mater. Sci. Technol., 2008, 24 (01): 29-32. 
    Abstract   HTML   PDF (7454KB)
    The purpose of this paper was to investigate the effects of solution treatment time and Sr-modification on the microstructure and property of the Al-Si piston alloy. It was found that as-cast microstructures of unmodified and Sr-modified Al-Si alloys consisted of a coarse acicular plate of eutectic Si, Cu3NiAl6 and Mg2Si phases in the α-Al matrix but different in size and morphology. Both size and inter-particle spacing of Si particles were significantly changed by increasing the solution treatment time. After a short solution treatment, the coarse acicular plate of the eutectic Si appears to be fragmented. Fully modified microstructure of Sr-modified alloy can reduce the solution treatment time compared to unmodified alloy. The maximum of a peak hardness value is found in the very short solution treatment of both Al-Si piston alloys. Compared to 10 h solution treatment, the solution treatment of 2–4 h is sufficient to achieve appropriate microstructures and hardness. The short solution treatment is very useful to increase the productivity and to reduce the manufacturing cost of the Al-Si piston alloys.
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    Microstructure, Elastic Modulus and Tensile Properties of Ti-Nb-O Alloy System
    H.S.Kim, T.Y.Ra, I.D.Yeo, H.J.Bang, Y.G.Yoo, W.Y.Kim
    J. Mater. Sci. Technol., 2008, 24 (01): 33-36. 
    Abstract   HTML   PDF (1316KB)
    In the present study Ti-Nb binary alloy system was chosen because it has excellent biocompatibility as well as reasonable mechanical properties, aiming at understanding oxygen content on microstructural formation, elastic modulus and tensile properties in Ti-Nb alloy system. Small alloy buttons of 50 mm in diameter were prepared by arc melting on a water-cooled copper hearth under an argon gas atmosphere with a non-consumable tungsten electrode. The button ingots were then heat treated in a vacuum atmosphere at 1273 K for 0.5 h followed by water quenching in a specially designed heat treatment furnace. Microstructure, elastic modulus and tensile properties were investigated in order to understand the effect of oxygen content in quenched Ti- Nb alloy system. The orthorhombic structured α00 martensite was changed to bcc structured β-phase with increasing Nb content. Interestingly, it was found that oxygen makes β-phase stable in quenched Ti-Nb alloy system. Elastic modulus values were sensitive to phase stability of constituent phases. Yield strength increased with increasing oxygen content. Details will be explained by phase formation and stability behavior.
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    Effect of Aging Treatment on Microstructural and Mechanical Characteristics of PEO Coatings on Mg-Al Alloy
    S.Y.Chang, Y.L.Kim
    J. Mater. Sci. Technol., 2008, 24 (01): 37-40. 
    Abstract   HTML   PDF (708KB)
    Cast Mg-6 wt pct Al alloy solution-treated at 683 K for 16 h and aged at 498 K was coated by plasma electrolytic oxidation (PEO) method. The Mg-6 wt pct Al alloy aged for 16 h exhibited the highest microhardness and wear resistance. After PEO coating, however, the microhardness and wear resistance of coatings on Mg-6 wt pct Al alloy showed a tendency to decrease with increasing aging time, which was in aggrement with the change of thickness with aging time. In addition, the coatings on solution-treated Mg-6 wt pct Al alloy had better microhardness and wear resistance than those on aged Mg-6 wt pct Al alloys. Consequently, it can be understood that the aging treatment has a deleterious influence on the mechanical properties of coatings on Mg-6 wt pct Al alloy.
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    Hot-Dip Coating of Lead-free Aluminum on Steel Substrates with Ultrasonic Vibration
    Y.Tsunekawa, S.Tamura, M.Okumiya, N.Ishihara
    J. Mater. Sci. Technol., 2008, 24 (01): 41-44. 
    Abstract   HTML   PDF (1217KB)
    Hot-dip coating has been practically employed in manufacturing zinc alloy coated steel sheets. However, it is difficult to coat aluminum alloy on a bulky steel substrate without sufficient preheating, because a rapidly solidified layer containing gas babbles is formed on a substrate surface. A variety of iron-aluminides are also formed at the interface of a steel and aluminum hot-dip coating system, which is the main difficulty in joining of steel with aluminum. Ultrasonic vibration was applied to a steel substrate during hot-dip coating of aluminum alloy to control a rapidly solidified layer and a brittle reaction layer. Hot dipping of columnar steel substrates into molten aluminum alloy (Al-2.7 mass fraction Si-4.6 mass fraction Sn) was carried out through the use of a Langevin oscillator with resonant frequency of 19.5 kHz. The application of ultrasonic vibration is quite effective to control a rapidly solidified layer and a surface oxide layer from a substrate surface by the sonocapillary effect based on a cavitation phenomenon, so that the intimate contact is achieved at the beginning of hot-dip coating. The application of ultrasonic vibration to hot-dipping is effective to control a reaction layer with less than 5 μm in thickness. An impact test exhibits that the good adhesive strength is approved in hot-dipped aluminum coatings with a thin reaction layer of approximately 5 μm.
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    Modification of β-Al5FeSi Compound in Recycled Al-Si-Fe Cast Alloy by Using Sr, Mg and Cr Additions
    Witthaya Eidhed
    J. Mater. Sci. Technol., 2008, 24 (01): 45-47. 
    Abstract   HTML   PDF (4048KB)
    The effects of Sr, Mg, Cr, Sr/Mg and Sr/Cr combined additions on the Fe-containing intermetallic phase in a recycled Al-Si-Fe cast alloy are investigated. The experimental results show that the additions of Cr and Sr/Cr successfully modified the platelet and flake-like β-Al5FeSi phases (β-compound) into the fibrous α-Al8Fe2Si (α-compound). The additions of Sr and Sr/Mg were less effective to modify the β-compound into the α-compound, while the eutectic Si was fully modified into the fibrous morphology. A small secondary dendrite arm spacing (DAS) was found in the Sr-added, Cr-added and Sr/Cr-added alloys, especially in a steel mold. The Sr, Sr/Cr and Sr/Mg combined additions modify the eutectic Si simultaneously. A sludge phase was found in the addition of Cr-added, Sr/Cr-added and Mg-added alloys, especially in the graphite mold casting. The volume fraction of β-compounds was decreased by the addition of various modifying elements. The Cr and Sr/Cr combined additions are very effective to modify the β-compound for the recycled Al-Si-Fe based alloys.
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    Microstructure and Mechanical Properties of Hyper-eutectic Al-Si Alloys Fabricated by Spray Casting
    Min Ryou, Chul-Hyun Kim, Myung-Ho Kim
    J. Mater. Sci. Technol., 2008, 24 (01): 48-50. 
    Abstract   HTML   PDF (2919KB)
    Microstructure and mechanical properties of hyper-eutectic Al-Si alloy fabricated by spray casting were investigated and then these results were compared with those by squeeze cast. The spray-cast specimen was found to have finer Si particles (~5 μm) compared to the squeeze-cast specimen (10–25 μm). The tensile strength and elongation of the spray-cast specimen are also higher than those of the squeeze cast one. It was considered that the increased mechanical properties of the spray-cast specimen were mainly due to finer size of the Si particles distributed in Al matrix.
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    Ageing Behavior of Mg-xAl-Zn with Variation of Al Content
    Byoungho Kim, Jongjin Jeon, Yeongdo Park, Yongho Park, Ikmin Park
    J. Mater. Sci. Technol., 2008, 24 (01): 51-53. 
    Abstract   HTML   PDF (1421KB)
    The ageing behavior of Mg-xAl-Zn alloys with a variation of Al contents (x=3, 5, 7, 9 and 11 wt pct) were investigated. Solid solution treatment and artificial ageing were carried out at 693 and 493 K, respectively. After the solid solution treatment, β-Mg17Al12 was resolved to the α-Mg matrix in the specimens which contained Al up to 9 wt pct and partially resolved in the specimen of 11 wt pct Al. During ageing, the β-Mg17Al12 phase was precipitated at the grain boundary in the form of discontinuous precipitation and grown into the matrix. The volume fraction of β-phase was increased with the Al contents. Tensile strength increased with the volume fraction of precipitated β-phase, which was believed to strengthen the matrix.
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    Effect of Process Parameters on Morphology and Grain Refinement Efficiency of TiAl3 and TiB2 in Alumimum Casting
    Prapas Kunnam, Chaowalit Limmaneevichitr
    J. Mater. Sci. Technol., 2008, 24 (01): 54-56. 
    Abstract   HTML   PDF (694KB)
    This paper presents the effects of different process parameters in producing Al-5Ti-1B grain refiner, i.e. various sequences and reaction time, on grain refinement efficiency of aluminum castings. It was found that different process parameters resulted in different morphology and size distribution of TiAl3 and TiB2 in grain refiner. The experiment was carried out by adding KBF4 and K2TiF6 to molten aluminum. The melting temperature was controlled at 800℃ in an electric resistance furnace. Three different sequences of KBF4 and K2TiF6 additions were applied, i.e., adding KBF4 before K2TiF6, adding K2TiF4 before KBF4 and mixing both KBF4 and K2TiF6 before adding to molten aluminum. Three different holding time at 1 min, 30 min and 60 min were applied. The results showed that no significant difference of morphology and size distribution was found by varying three different sequences. Whereas, the different holding time provided major differences in both morphology and size distribution, which are technically expectable from diffusion and agglomeration between particles resulting in larger particle size and wider range of size distribution of TiAl3 and TiB2. If the reaction time was longer than 30 min, morphology of both TiAl3 and TiB2 became too large. If the reaction time was too short, less reaction between TiAl3 and TiB2 to form would be obtained. For grain refinement efficiency, it was found that mixing KBF4 and K2TiF6 before adding to molten aluminum with a holding time of 30 min resulted in best grain refinement efficiency.
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    Properties of Dispersion Casting of Y2O3 Particles in Hypo, Hyper and Eutectic Binary Al-Cu Alloys
    J.J.Park, G.H.Kim, S.M.Hong, S.H.Lee, M.K.Lee, C.K.Rhee
    J. Mater. Sci. Technol., 2008, 24 (01): 57-59. 
    Abstract   HTML   PDF (1300KB)
    In the present work, the dispersion casting of Y2O3 particles in aluminum-copper alloy was investigated in terms of microstructural changes with respect to Cu contents of 20 (hypo), 33 (eutectic) and 40 (hyper) wt pct by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). For the fabrication of Al-Cu alloy dispersed Y2O3 ceramic particles, stir casting method was employed. In case of Al-20 wt pct Cu alloy (hypoeutectic), SEM images revealed that primary Al was grown up in the beginning. After that, eutectic phase with well dispersed ceramic particles was formed. In case of eutectic composition, Y2O3 particles were uniformly dispersed in the matrix. When the Cu is added into Al up to 40 wt pct (hypereutectic), primary θ phase was grown up without any Y2O3 ceramic particles in the early stage of solidification. Thereafter, eutectic phase was formed with well dispersed ceramic particles. It can be concluded that Y2O3 ceramic particles is mostly dispersed in case of eutectic composition in Al-Cu alloy.
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    Study of the Interface between Steel Insert and Aluminum Casting in EPC
    K.H.Choe, K.S.Park, B.H.Kang, G.S.Cho, K.Y.Kim, K.W.Lee, M.H.Kim, A.Ikenaga, S.Koroyasu
    J. Mater. Sci. Technol., 2008, 24 (01): 60-64. 
    Abstract   HTML   PDF (1421KB)
    The effective surface treatment method for steel insert composited with Al base metal by expendable pattern casting (EPC) process and the bonding interface between steel insert and Al base metal were investigated. It was found that Zn plating on steel insert was effective on improving the bonding property between steel insert and Al base metal in EPC process. Zn is thought to promote the formation of diffusion layer. But almost none content of Zn was observed in the boundary which had been plated on the steel insert. A diffusion layer consisting of Al, Si and Fe was formed at the insert/alloy interface and its hardness was higher than the steel insert as matter of course Al base metal. This layer turned out to be intermetallic compounds of Al-Si-Fe system. Higher pouring temperature promoted the diffusion of Fe into Al alloy, so Fe content in intermetallic layers increased at higher pouring temperature. The layer nearest to steel disappeared due to applied pressure.
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    Thin-Wall Aluminum Die-Casting Technology for Development of Notebook Computer Housing
    Chang-Seog Kang, Jae-Ik Cho, Chang-Yeol Jeong, Se-Weon Choi, Young-Chan Kim
    J. Mater. Sci. Technol., 2008, 24 (01): 65-69. 
    Abstract   HTML   PDF (2311KB)
    Silicon-based aluminum casting alloys are known to be one of the most widely used alloy systems mainly due to their superior casting characteristics and unique combination of mechanical and physical properties. However, manufacturing of thin-walled aluminum die-casting components, less than 1.0 mm in thickness, is generally known to be very difficult task to achieve aluminum casting alloys with high fluidity. Therefore, in this study, the optimal die-casting conditions for producing 297 mm×210 mm×0.7 mm thin-walled aluminum component was examined experimentally by using 2 different gating systems, tangential and split type, and vent design. Furthermore, computational solidification simulation was also conducted. The results showed that split type gating system was preferable gating design than tangential type gating system at the point of view of soundness of casting and distortion generated after solidification. It was also found that proper vent design was one of the most important factors for producing thin-wall casting components because it was important for the fulfillment of the thin-wall cavity and the minimization of the casting distortion.
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    Evaluation of Alpha-case in Titanium Castings
    Si-Young Sung, Bong-Jae Choi, Beom-Suck Han, Han-Jun Oh, Young-Jig Kim
    J. Mater. Sci. Technol., 2008, 24 (01): 70-74. 
    Abstract   HTML   PDF (2382KB)
    The alpha-case formation reactions between Ti and investment molds (Al2O3, ZrSiO4, ZrO2, CaO stabilized ZrO2) were evaluated in a plasma arc melting furnace. Regardless of thermodynamic approaches, there were distinct alpha-case formations. The reaction products were characterized by electron probe micro-analysis and transmission electron microscopy. The α-case generation between Ti and Al2O3 mold was not able to be explained by the conventional α-case formation mechanism, which is known to be formed by the interstitials, especially oxygen dissolved from mold materials. However, from our experimental results and thermodynamic calculations, it was confirmed that the α-case is formed not only by an interstitial element but also by substitutional metallic elements dissolved from mold materials. Our newly established α-case formation mechanism will surely lead to a variety of significant applications of the α-case controlled Ti casting.
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    Effect of Injection Velocity on Structure Part Characteristic in AZ50 Die Casting Process with High Vacuum System
    S.M.Lee, P.K.Seo, C.G.Kang
    J. Mater. Sci. Technol., 2008, 24 (01): 75-79. 
    Abstract   HTML   PDF (1524KB)
    When diecasting large and thin Mg alloy parts, material defects occur, which include porosity, nonuniform mechanical properties, irregular surfaces, and incomplete filling. To resolve these problems, it is necessary to have uniform injection velocities and temperatures as well as control the melt. This study investigated the feasibility of producing large and thin components using a die caster by attaching a high vacuum system. In particular, the effects of injection velocity on surface quality and the mechanical properties of the products were investigated. Hence, an injection velocity scheme and a die structure capable of casting in a vacuum were proposed. As a result, it was found that the critical low injection velocity was 0.2 m/s to produce large thin Mg alloy structures having good mechanical properties.
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    Aging Behavior of Mg-Y-Zr and Mg-Nd-Zr Cast Alloys
    Yang-Do Kim, Nam-Hyun Kang, Il-Guk Jo, Kyung-Hyun Kim, In-Bae Kim
    J. Mater. Sci. Technol., 2008, 24 (01): 80-84. 
    Abstract   HTML   PDF (708KB)
    Aging behavior of Mg-3.6Y-0.5Zr and Mg-2.7Nd-0.5Zr alloys was investigated by microhardness measurement and transmission electron microscopy. In the case of Mg-Y-Zr alloy, the presence of β″ phase, a major strengthener, having base centered orthorhombic structure with its lattice constants of aβ″=0.64 nm, bβ″=2.22 nm, and cβ″=0.52 nm was identified. In the case of Mg-Nd-Zr alloy aged at 250℃, the presence of β″ and β′ phases was identified. The crystal structure of β″ phase was found to be DO19 and its orientation relationships with Mg matrix were [0001] β″//[0001]Mg and [01 0] β″//[01 0]Mg. The β′ phase had face centered cubic structure and its orientation relationships with Mg matrix were [011] β′//[0001]Mg and [ 1 ]β′//[ 110]Mg. The Mg-2.7Nd-0.5Zr alloy showed higher hardness compared with Mg-3.6Y-0.5Zr alloy.
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    Microstructure and Mechanical Properties of Mg-Al-Ca-Nd Alloys Fabricated by Gravity Casting
    Hyeon-Taek Son, Jae-Seol Lee, Ik-Hyun Oh, Chang-Seog Kang
    J. Mater. Sci. Technol., 2008, 24 (01): 85-88. 
    Abstract   HTML   PDF (1361KB)
    The aims of this study are to investigate the effects of Nd addition in the Mg-Al-Ca alloys on microstructure and mechanical properties. Microstructure of as-cast Mg-5Al-3Ca alloy containing Nd consists of α-Mg matrix, eutectic phase and Al-Nd rich intermetallic compound. As Nd addition was increased, α-Mg matrix morphology was changed from dendritic to equiaxed grains and average value of grain size was decreased. Nd addition to Mg-5Al-3Ca based alloys resulted in the formation of Al-Nd rich intermetallic compounds at grain boundary and α-Mg matrix grains. And these Al-Nd rich intermetallic compounds were dispersed homogeneously. In these alloys, two kinds of eutectic phases were observed, i.e. coarse irregular-shape structure at grain boundary and fine needle-shape structure in the α-Mg matrix grain. It is found that the ultimate strength showed the maximum value of 271 MPa at Mg-5Al-3Ca-2Nd alloy and elongation was decreased as the addition of Nd was increased.
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    Microstructures and Mechanical Properties of Rapidly Solidified Mg-Al-Zn-MM Alloys
    Yeon-Wook Kim
    J. Mater. Sci. Technol., 2008, 24 (01): 89-92. 
    Abstract   HTML   PDF (893KB)
    Mg-Al-Zn-MM (misch metal) alloy powders were manufactured by inert gas atomization and the characteristics of alloy powders were investigated. In spite of the low fluidity and easy oxidation of the magnesium melt, the spherical powder was made successfully with the improved three piece nozzle systems of gas atomization unit. It was found that most of the solidified powders with particles size of less than 50 μm in diameter were single crystal and the solidification structure of rapidly solidified powders showed a typical dendritic morphology because of supercooling prior to nucleation. The spacing of secondary denrite arms was deceasing as the size of powders was decreasing. The rapidly solidified powders were consolidated by vacuum hot extrusion and the effects of misch metal addition to AZ91 on mechanical properties of extruded bars were also examined. During extrusion of the rapidly solidified powders, their dendritic structure was broken into fragments and remained as grains of about 3 μm in size. The Mg-Al-Ce intermetallic compounds formed in the interdendritic regions of powders were finely broken, too. The tensile strength and ductility obtained in as-extruded Mg-9 wt pct Al-1 wt pct Zn-3 wt pct MM alloy were σT.S.=383 MPa and ε=10.6%, respectively. All of these improvements on mechanical properties were resulted from the refined microstructure and second-phase dispersions.
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    Gating System Design for a Magnesium Alloy Casting
    Zhizhong SUN, Henry HU, Xiang CHEN, Qigui WANG, Wenying YANG
    J. Mater. Sci. Technol., 2008, 24 (01): 93-95. 
    Abstract   HTML   PDF (1558KB)
    The gating system of a cylindrical magnesium casting has been designed by using multiple objective optimization and Taguchi method. Mold filling and solidification processes were simulated by using MAGMASOFT®. The simulation results indicate that the gating system design has a significant effect on the quality of magnesium castings. In an effort to obtain the optimal design of gating system, the signal-to-noise (S/N) ratio was used to analyze the effect of various gating designs on cavity filling and casting quality by using a weighting method based on the design of an orthogonal array. Four gating system parameters, namely, ingate height, ingate width, runner height, runner width, were optimized with a consideration of multiple objective criteria including filling velocity, shrinkage porosity and product yield.
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    Mg-Al Alloys Manufactured by Casting and Hot Working Process
    J.M.Kim, J.H.Jun, W.J.Jung
    J. Mater. Sci. Technol., 2008, 24 (01): 96-98. 
    Abstract   HTML   PDF (1089KB)
    Mechanical properties of Mg-Al based alloys at different fabrication state, namely as-cast, hot rolled, and annealed, were investigated to develop the alloys that are suitable for the casting/hot working process. Experimental results indicated that the castability such as hot cracking resistance tends to improve with increasing the aluminum content. However, the elongation at elevated temperatures was observed to decrease as the Al content increases, implying difficulties in hot forming. A small amount of Zr additions could significantly enhance the room temperature mechanical properties of hot-rolled Mg-6%Al-1%Zn alloy. The tendency of remarkable grain coarsening at high temperatures was effectively reduced by the Zr additions. TEM analyses suggested that very fine Al3Zr precipitates formed in the Zr-added alloy are responsible for the obtained results.
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    Effect of Sb Addition on Microstructure and Mechanical Properties of Al18B4O33/AS52 Magnesium Matrix Composites
    Wookjin Lee, Ikmin Park, Yongho Park
    J. Mater. Sci. Technol., 2008, 24 (01): 99-101. 
    Abstract   HTML   PDF (1774KB)
    The effect of antimony addition on the microstructure of Mg-Al-Si magnesium matrix composite was investigated. The addition of Sb can modify the morphology of Mg2Si particles which have Chinese script shape to fine polygonal one. Magnesium matrix composite with Alborex whisker was successfully fabricated by using a squeeze infiltration method. Tensile strength and elongation were increased in the Sb modified alloy and the composite at both room and high temperatures.
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    Fabrication and Properties of SiB6-B4C with Phenolic Resin as a Carbon Source
    G.C.Hwang, J.Matsushita
    J. Mater. Sci. Technol., 2008, 24 (01): 102-104. 
    Abstract   HTML   PDF (1488KB)
    Si-B-C ceramic composites were synthesized using SiB6, B4C, and phenolic resin as a carbon source by pressureless sintering in an Ar atmosphere. Then, the Si-B-C ceramic composites were fabricated to determine their potential for applications as high hardness and high temperature composites. The X-ray diffraction patterns of sintered bodies of SiB6-B4C with carbonized phenolic resin can be seen that SiB6 and C changed to B4C and SiC. In this study, it is obtained that carbonized phenolic resin is good addition material as a reaction material comparing to carbon powder at 1683 K for 1 h by pressureless sintering in an Ar atmosphere.
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    Evaluation the Properties of Titanium Matrix Composites by Melting Route Synthesis
    Bong-Jae Choi, Si-Young Sung, Myoung-Gyun Kim, Young-Jig Kim
    J. Mater. Sci. Technol., 2008, 24 (01): 105-109. 
    Abstract   HTML   PDF (2284KB)
    The main purpose of this study is an in-situ synthesis of (TiB+TiC) hybrid titanium matrix composites (TMCs) by vacuum induction melting method and to verify its mechanical properties. The melting route was adopted to synthesize the commercial pure titanium (cp Ti) and granular boron carbide (B4C). The reinforcements, the fraction of 10 vol. pct, were formed by adding 1.88 wt pct B4C to cp Ti. After in-situ synthesis of TMCs, electron probe micro-analysis elemental mapping was carried out to confirm the distribution and shape of reinforcements. The cone-on-disk type sliding wear test was also done for the identification of TMCs. It is concluded that (TiB+TiC) hybrid TMCs can be in-situ synthesized and has better wear properties than H13.
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    Microstructural Evolution in Directionally Solidified Ni-Base Superalloy IN792+Hf
    S.M.Seo, I.S.Kim, J.H.Lee, C.Y.Jo, H.Miyahara, K.Ogi
    J. Mater. Sci. Technol., 2008, 24 (01): 110-114. 
    Abstract   HTML   PDF (3827KB)
    Microstructural evolution during directional solidification (DS) of Ni-base superalloy IN792+Hf has been investigated with an emphasis on the γ′ precipitates and MC-type carbides. The quantitative image analyses revealed that the increase in the solidification rate up to 100 μm/s at constant thermal gradient of 178 K/cm resulted in a fine and uniform distribution of γ′ precipitates. The relationship between the as-cast γ′ size and cooling rate was also determined for DS IN792+Hf. In the mean time, the MC carbide size was found to be dependent both on the solidification rate and the S/L interface morphology while the area fraction of MC carbide was significantly influenced by the S/L interface morphology.
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    Effect of Annealing Atmosphere on the Mechanical Property of Free-cutting Phosphor Bronze Alloy
    Byoung-Soo Lee, Hoon Cho, Hyung-Ho Jo
    J. Mater. Sci. Technol., 2008, 24 (01): 115-119. 
    Abstract   HTML   PDF (5581KB)
    The present work is focused on the influence of annealing atmosphere on the microstructure and mechanical property of free-cutting phosphor bronze alloy. The annealing of the alloy was conducted in the three kinds of annealing atmosphere such as air, vacuum and nitrogen. After annealing, a discernable difference in recystallized grain size and lead particle size was not appeared with different annealing atmosphere. The tensile strength of the alloy annealed in air or nitrogen atmosphere was higher than that of those annealed in vacuum atmosphere. In the case of the alloy annealed in vacuum atmosphere, the mechanical strength was reduced by vaporization of zinc. In the case of annealing in nitrogen and in air atmosphere, the sweating of lead was occurred. However, the inverse segregation of lead was suppressed by copper oxide layer on the surface annealed in air. This copper oxide layer leads to a decrease of the yield during fabrication process. Therefore, annealing of the alloy in nitrogen atmosphere is favorable in terms of the mechanical strength and yield.
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    Influence of Aging Treatment on the Mechanical and Electrical Properties of Cu-0.5%Be Alloy
    Min Ryou, Byoung-Soo Lee, Myung-Ho Kim
    J. Mater. Sci. Technol., 2008, 24 (01): 120-122. 
    Abstract   HTML   PDF (9088KB)
    The influence of aging treatment on the microstructure, mechanical properties and electrical conductivity of Cu-0.5 wt pct Be alloy for connector material applications was investigated. The properties of mechanical strength and electrical conductivity increase with increasing aging temperature and time. Microstructure of the aged Cu-Be alloy revealed that grain size and fraction of low angle and high angle grain boundary were not greatly changed; however, transmission electron microscopy (TEM) analysis exhibited that beryllides precipitation (CoBe and NiBe) with a size of 50 nm were distributed in grains. It was, therefore concluded that these beryllide precipitates improved the mechanical strength and also it was favor in improvement of electrical conductivity.
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    Effect of Applied Pressure on the Joining of Combustion Synthesized Ni3Al Intermetallics with Al Alloy
    G.S.Cho, J.H.Yang, K.H.Choe, K.W.Lee, A.Ikenaga
    J. Mater. Sci. Technol., 2008, 24 (01): 123-126. 
    Abstract   HTML   PDF (1000KB)
    We focused on the surface reinforcement of ligth weight casting alloys with Ni-Al intermetallic compounds by in-situ combustion reaction to improve the surface properties of non-ferrous casting components. In our previous works, green compact of elemental Ni and Al powders were reacted to form Ni3Al intermetallic compound by SHS (Self-propagating high temperature synthesis) reaction with the heat of molten Al alloy and simultaneously bonded with Al casting alloy. But some defects such as tiny cracks and porosities were remained in the reacted compact. So we applied pressure to prevent thermal cracks and fill up the pores with liquid Al alloy by squeeze casting process. The compressed Al alloy bonded with the Ni3Al intermetallic compound was sectioned and observed by optical microscopy and scanning electron microscopy (SEM). The stoichiometric compositions of the intermetallics formed around the bonded interface and in the reacted compact were identified by energy dispersive spectroscopy (EDS) and electron probe micro analysis (EPMA). Si rich layer was formed on the Al alloy side near the bonded interface by the sequential solidification of Al alloy. The porosities observed in the reacted Ni3Al compact were filled up with the liquid Al alloy. The Si particles from the molten Al alloy were detected in the pores of reacted Ni3Al intermetallic compact. The Al casting alloy and Ni3Al intermetallic compound were joined very soundly by applying pressure to the liquid Al alloy.
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    Microstructural Stability of a Single Crystal Superalloy DD8 during Thermal Exposure
    K.Y.Cheng, D.H.Kim, Y.S.Yoo, C.Y.Jo, T.Jin, Z.Q.Hu
    J. Mater. Sci. Technol., 2008, 24 (01): 127-130. 
    Abstract   HTML   PDF (1326KB)
    Microstructural stability of a nickel base single crystal alloy DD8 has been investigated. Standard heat treated specimen showed good microstructural stability at 950℃. While under the as-cast condition, a kind of rod-like phase precipitated in the interdendritic region of as-cast specimen during thermal exposure. The phase, which has bcc structure, was enriched with Cr. Thermo-calc also predicted precipitation of a bcc phase at around 950℃. The Cr-rich bcc phase was considered as α-Cr and formed due to the segregation of Cr under the as-cast condition.
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    Heat Transfer between Casting and Die during High Pressure Die Casting Process of AM50 Alloy-Modeling and Experimental Results
    Zhipeng GUO, Shoumei XIONG, Sang-Hyun Cho, Jeong-Kil Choi
    J. Mater. Sci. Technol., 2008, 24 (01): 131-135. 
    Abstract   HTML   PDF (5786KB)
    A method based on die casting experiments and mathematic modeling is presented for the determination of the heat flow density (HFD) and interfacial heat transfer coefficient (IHTC) during the high pressure die casting (HPDC) process. Experiments were carried out using step shape casting and a commercial magnesium alloy, AM50. Temperature profiles were measured and recorded using thermocouples embedded inside the die. Based on these temperature readings, the HFD and IHTC were successfully determined and the calculation results show that the HFD and IHTC at the metal-die interface increases sharply right after the fast phase injection process until approaching their maximum values, after which their values decrease to a much lower level until the dies are opened. Different patterns of heat transfer behavior were found between the die and the casting at different thicknesses. The thinner the casting was, the more quickly the HFD and IHTC reached their steady states. Also, the values for both the HFD and IHTC values were different between die and casting at different thicknesses.
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    Plasma Post Oxidation of Plasma Nitrocarburized SKD 61 Steel
    Insup Lee, Kwang-Ho Jeong
    J. Mater. Sci. Technol., 2008, 24 (01): 136-138. 
    Abstract   HTML   PDF (640KB)
    Plasma nitrocarburizing and plasma oxidizing treatments were performed to improve the wear and corrosion resistance of SKD 61 steel. Plasma nitrocarburizing was conducted for 12 h at 540℃ in the nitrogen, hydrogen and methane atmosphere to produce the ε-Fe2–3 (N,C) phase. The compound layer produced by plasma nitrocarburising was predominantly composed of ε-phase, with a small proportion of γ′-Fe4(N,C) phase. The thickness of the compound layer and the diffusion layer are about 10 μm and about 200 μm, respectively. Plasma post oxidation was performed on the nitrocarburized samples with various oxygen/hydrogen ratio at constant temperature of 500℃ for 1 h. The very thin magnetite (Fe3O4) layer of 1–2 μm in thickness on top of the compound layer was obtained. Anodic polarization test revealed that plasma nitrocarburizing process contributed a significant improvement of corrosion resistance of SKD 61 steel. However, the corrosion characteristics of the nitrocarburized compound layer was deteriorated by oxidation treatment.
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    Mold Filling and Prevention of Gas Entrapment in High-pressure Die-casting
    Itsuo Ohnaka, Akira Sugiyama, Takashi Ikeda, Hideyuki Yasuda
    J. Mater. Sci. Technol., 2008, 24 (01): 139-140. 
    Abstract   HTML   PDF (478KB)
    This paper presents some results of direct observation of mold filling in a specially designed die-casting by X-ray diffraction, including comparison with numerical simulation. Based on such work the authors discuss how to prevent gas entrapment and propose new methods.
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    Preparation of Pure Copper Powder from Acidic Copper Chloride Waste Etchant
    H.S.Hong, M.S.Kong, J.K.Ghu, J.K.Lee, H.G.Suk
    J. Mater. Sci. Technol., 2008, 24 (01): 141-142. 
    Abstract   HTML   PDF (1426KB)
    The method for the recycling of copper from copper chloride solution was developed. This process consists of extraction of copper, purification and particle size reduction. In the first step, reductive metal scraps were added to acidic copper chloride waste enchants produced in the PCB industry to obtain copper powder. Composition analysis showed that this powder contained impurities such as Fe, Ni, and water. So, drying and purification were carried out by using microwave and a centrifugal separator. Thereby the copper powder had a purity of higher than 99% and spherical form in morphology. The copper powder size was decreased by ball milling.
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    Effect of Cristobalite and Quartz on the Properties of Gypsum Bonded Investment
    Yun-Jong Kim, Sang-Bae Kim, Hyun-Hye Park, Myeong-Deok Seo, Byoung-Cheon Lee, Man-So Han, Taik-Nam Kim, Sung-Baek Cho
    J. Mater. Sci. Technol., 2008, 24 (01): 143-144. 
    Abstract   HTML   PDF (706KB)
    Generally the gold investment material consists of cristobalite, quartz and plaster. The physical property of gold investment materials depends on its thermal expansion coefficients, compressive strength, and particles size distribution. Since the thermal expansion coefficient of cristobalite and quartz are 2.6×10-6/℃ and 2.32×10-6/℃ respectively, the composition ratio of each components influence the thermal and physical properties of gold investment materials. For the clinical applications, it is necessary to improve the properties of gold investment materials such as homogeneous size distribution and thermal expansion coefficients. In the present study, effect of inorganic fillers such as cristobalite and quartz on gold alloy investment was investigated to improve the properties of it. The compressive strength and thermal expansion coefficients of the specimens were evaluated. The results showed that cristobalite and quartz were homogeneously distributed by milling. The optimum compressive strength was obtained at the ratio of 42:22 cristobalite and quartz, respectively.
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CN: 21-1315/TG
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