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We here introduced a simple, but efficient, sulfur-doping method applying delta-function-like doping profiles by using near-infrared chemical-vapor deposition. The thermally decomposed sulfur was found to play the role of the n-type dopant, and hydrogen in hydrosulfide gas acted as the reducing agent corresponding to the oxygen functional groups during the growth of the graphene sheet. The doping mechanism by sulfur atoms as a substitutional impurity requires further study due to the increase in the number of unintentional defects in the crystalline graphene.

Condenser tubes are mainly produced by precision extrusion with a porthole die and are used to allow flow in refrigerant cooling systems in automobiles. To produce condenser tubes, the recent goal has been to develop a tube that has high strength to allow for multi-cellizing and flattening, and to minimize the wall thickness, and to increase the heat transfer area and heat efficiency. This study was designed to produce Al3003 condenser tube for industrial production, including extrusion die design, inspection of die design through the results of FE simulation and performance of trial extrusion. Chamber shape dimension and initial temperatures of tool and die were variables and the possibility of extrusion was estimated from the forming load, welding pressure, and stress analysis of die in this paper. The validity of the simulated results was verified by extrusion experiments on the condenser tubes.

The objective of this study is to develop an optimal drawing process for clad wire. Steel wires with copper clad are widely used, e.g. in telecommunication, power engineering, electronics as a replacement of traditional applied copper wire. The reason is that the properties of these bimetal wires combine the good strength of steel with the good conductivity and corrosion resistance of copper. The main aspect of producing clad wires is to ensure the uniform thickness of the sleeves, i.e. the coating ratio. This study investigates the effect of the process variables such as semi-die angle and reduction in area on the maximum damage value and the coating ratio through FE-analysis. FE-analysis and an experiment verified that the final coating ratio depends on the initial coating ratio. To produce a clad wire with a single or variety of coating ratios, the wire with the required coating ratio should be produced in a continuous casting process.

Graphene was coated on STS 316L by electro spray coating method to improve its properties of corrosion resistance and contact resistance. Exfoliated graphite (graphene) was made of the graphite by chemical treatment. Graphene is distributed using dispersing agent, and STS 316L was coated with diffuse graphene solution by electro spray coating method. The structure of the exfoliated graphite was analyzed using XRD and the coating layer of surface was analyzed by using SEM. Analysis showed that multi-layered graphite structure was destroyed and it was transformed into fine layers graphene structure. And the result of SEM analysis on the surface and the cross section, graphene layer was uniformly formed with 3~5 thickness on the surface of substrate. Corrosion resistance test was applied in the corrosive solution which is similar to the PEM fuel cell stack inside. And interfacial contact resistance test was measured to simulate the internal operating conditions of PEM fuel cell stack. The results of measurements show that stainless steel coated with graphene was improved in corrosion resistance and surface contact resistance than stainless steel without graphene coating layer.

In this study, the mechanical properties of boronized 316L austenitic stainless steel have been investigated. Boronizing was carried out in solid medium consisting of Ekabor powder at 900 C and 1000 C for 2, 4 and 8 hours, respectively. The properties of sample were analyzed by field emission scanning electron microscope, X-ray diffractometer, Glow discharge spectrometer, micro-hardness tester and ball-on-disk wear tester. Increasing the boronizing time and temperature, the hardness of boronized samples were shown over Hv 2000 and the thickness of boride layers were also increased linearly. XRD patterns of samples were revealed the presence of borides such as FeB, Fe B, CrB, Cr B and Ni B. Friction coefficient of boronized STS 316L was shown the low value at 900 C for 8 hours and 1000 C for 4 hours, respectively.

The rotor is a key determinant of the performance of a compressor and many attempts have been made to improve the efficiency of compressors by optimising rotor design. Rotors are usually made of several layers of steel sheets with thin cavities through the steel sheets, and aluminium alloys are used to fill the cavities by high pressure die casting process, and so bind the steel sheets together. Because of their high fluidity and good damping ability, magnesium alloys can be a good alternative for a high efficiency rotor. In this study, magnesium alloys were used for manufacturing rotors by high pressure die casting process using pin-point gate mold. By adopting a pin-point gate system, additional machining was eliminated and casting defects were reduced due to good castability of magnesium alloys.

The effect of thermal heat treatment on the mechanical and electrical properties of Cu–Ag alloys was investigated. The homogenization heat treatment leads to an increase in tensile strength and a decrease in electrical conductivity due to dissolution of Ag into copper matrix. Also, it is shown that electrical conductivity of as-cast Cu–Ag alloys decreases with increasing Ag content. In contrast, the aging heat treatment gives rise to increase both the tensile strength and electrical conductivity because the Ag solute diffuses out from copper matrix during aging heat treatment. Therefore, it can be mentioned that the electrical conductivity of Cu–Ag alloys depends on Ag solute in copper matrix. Also, aging treatment is favorable to acquire high strength and high electrical conductivity.

The effect of thermal heat treatment on the mechanical and electrical properties of Cu–Ag alloys was investigated. The homogenization heat treatment leads to an increase in tensile strength and a decrease in electrical conductivity due to dissolution of Ag into copper matrix. Also, it is shown that electrical conductivity of as-cast Cu–Ag alloys decreases with increasing Ag content. In contrast, the aging heat treatment gives rise to increase both the tensile strength and electrical conductivity because the Ag solute diffuses out from copper matrix during aging heat treatment. Therefore, it can be mentioned that the electrical conductivity of Cu–Ag alloys depends on Ag solute in copper matrix. Also, aging treatment is favorable to acquire high strength and high electrical conductivity.

Diamond-like carbon(DLC) films were deposited by linear ion source(LIS)-physical vapor deposition method changing the anode voltages from 800 V to 1800 V, and characteristics of the films were investigated using residual stress tester, nano-indentation, micro raman spectroscopy, scratch tester and Field Emission Scanning Electron Microscope(FE-SEM). The results showed that the residual stress and hardness increased with increasing the ion energy up to anode voltage of 1400 V. It was also found that the content of carbon increased with increasing the anode voltage ratio through investigation of ratio by the micro-raman analysis. From these results, it can be concluded that the physical properties of DLC films such as residual stress and hardness are increased with increasing the anode voltage. These results can be explained that 3-dimensional cross-links between carbon atoms and Dangling bond are enhanced and the internal compressive stress also increased with increasing the anode voltage. The optimal anode voltage is considered to be around 1400 V in these experimental conditions.

Energy requirement and yield for production of aluminum wirerods manufactured by continuous casting process were investigated to enhance yield of aluminum wiredrods. Also, it was compared with conventional process including extrusion process. The enhancement of yield more than 30% could be accomplished through the continuous casting process. The conventional process including extrusion process for production of wirerods consumes more energy compared to continuous casting. In addition, a number of intermediate annealing may be introduced during wiredrawing process of wirerods manufactured by conventional process including extrusion process. It can be mentioned that continuous casting process is suitable process for wiredrawing process because it can save energy requirement not only during manufacturing process of wirerods but also during following wiredrawing process.

The anisotropy in mechanical strength and electrical conductivity in Cu-Ag alloy during cold rolling were investigated. The anisotropy in tensile strength and electrical conductivity was significant with increasing Ag content in Cu-Ag alloy. The cold rolled Cu-Ag alloys with higher Ag content have filamentary structure, which is composed of elongated eutectic phase and Cu matrix. In addition, the eutectic phase in Cu-Ag alloys with higher Ag content has a strong α-fiber texture. It can be mentioned that the eutectic phase in filamentary structure is promotes the anisotropy of electrical conductivity of Cu-Ag alloys. This strong a-fiber texture of eutectic phase was decreased by annealing process (300 OC for 1h), and the anisotropy in strength and conductivity was decreased.

The influence of extrusion temperature and Ti content was investigated by observing the microstructure and determining the mechanical strength of A3003 alloy tube. The A3003 alloy was modified by inoculation in terms of addition of Ti and then extruded at the various extrusion temperatures. In case of A3003 alloy tube without addition of Ti, the yield strength was slightly improved with decreasing extrusion temperature. On the other hand, the yield strength was improved markedly in A3003 alloy tube with small addition of Ti, and also ductility was slightly reduced. Grain size distribution from observing the microstructure was different with addition of Ti. Coarse grains were formed on the outer and inner parts of the alloy tube without addition of Ti, whereas the finer grains were uniformly distributed in the alloy tube with addition of Ti. Thus the microstructure and mechanical strength of A3003 alloy tube could be controlled by addition of Ti. Threefore, optimum Ti content and extrusion temperature to fabricate high yield strength and ductility A3003 alloy tube (σy=60 MPa, ε=30%) for eco-friendly refrigerant application are above 0.05wt.Ti and below 480 °C, respectively. Introduction

The influence of annealing atmosphere on mechanical and wear properties of free-cutting phosphor bronze alloy was investigated. After annealing in vacuum, the mechanical properties of the alloy decreases due to vaporization of alloying element. In addition, the softening of matrix induces decreasing the wear resistance dramatically. In contrast, high mechanical properties were observed in the alloy annealed in air and in nitrogen atmosphere. In particular, a large smearing of lead in the alloy annealed in air atmosphere was observed and was affected on the enhancement of wear resistance. Consequently, annealing in vacuum atmosphere is not suitable for high mechanical properties and wear resistance.

In accordance with environmental regulations on refrigeration technology, the commercial A1100 alloy condenser tube that has widely been used in CFC and HCFC refrigerant systems and operated at a low working pressure (10–30 bar) was inappropriate to the eco-friendly CO 2 refrigerant systems which possess a high working pressure (60–80 bar) due to the low mechanical properties. As a result, the stiffness of the conventional 1000 series alloys might not be appropriate in this requirement. The present study is mainly aimed at developing condenser tube material such as A3003 alloy for the application of eco-friendly refrigerants with higher working pressure rather than for conventional CFC and HCFC refrigerants. The mechanical properties and pressurized strength of condenser tube are greatly affected by the coarse grains, which grow during the brazing process. According to the pressurized testing, A3003 alloy is more suitable than A1100 alloy when the condenser tube is applied to eco-friendly refrigerants usage because A3003 alloy can be durable in a heat exchanger which requires high working pressure.

Magnesium alloys are attractive for structural components in transportation industries. At present, magnesium components for structural applications are mainly produced by die casting process. It is, however, commonly acknowledged that structural components made from wrought alloys through metal forming processes have great advantage in terms of obtainable strength and toughness. In addition, most of wrought magnesium alloys are heat treatable and thus allow their strengths to be further improved or their mechanical performance to be tailored by adjusting the parameters of heat treatment. However, wrought process route of melting, ingot casting/continuous casting, forming and heat treatment for magnesium alloys should be carried out under protective cover gas to prevent oxidation and ignition. The purpose of this study was to eliminate cover gas during whole wrought process route. This paper discussed effect of CaO on ignition and oxidation behaviors of AZ31 Mg alloy as well as on surface roughness and mechanical properties AZ31 Mg alloy extruded parts.

The aim of this study is to develop novel thixoextrusion process for hard-to-form Al wrought alloys. Thixoextrusion for 7003 Al alloy of Al–Zn–Mg system and 7075 Al alloy of Al–Zn–Mg–Cu system were investigated as functions of isothermal holding temperature and time in the partially remelted semisolid state. The interesting point of the results was that the thixotropic structures of 7003 and 7075 Al alloys could be obtained without additional pretreatment only through simple partial remelting. More than that, the thixoextrusion pressure of 7075 Al alloy was lower than the thixoextrusion pressure of 7003 Al alloy at the same liquid fraction of 10%, despite the big difference of extrudability index between 7075 and 7003 Al alloys. The microstructures of thixoextruded specimens did not show any dendrites or rosette-like structures.

Gas atomized amorphous Ni 59 Ti 16 Zr 20 Si 2 Sn 3 feedstock particles were fed into warm gas dynamics and they were successfully overlaid onto the mild steel substrate. Through the X-ray diffractometry and differential scanning calorimetry, it could be confirmed that thermally activated processes such as crystallization and in-flight particle oxidation were effectively suppressed during the modified kinetic spraying process. In order to evaluate the tribological behavior of the kinetic sprayed Ni 59 Ti 16 Zr 20 Si 2 Sn 3 BMG coating, a partially crystallized coating and a fully crystallized coating were prepared by isothermal heat treatments.

Free-cutting phosphor bronze alloy (ASTM C54400) was used as a material for automotive parts and industrial valve parts for its high strength, machinability and excellent corrosion resistance. To obtain desired mechanical strength of the alloy, the process parameters including continuous casting speed, reduction in area and annealing temperature have to be controlled. In this study, we investigated the effect of annealing on the mechanical property and machinability of free-cutting phosphor bronze alloy fabricated by continuous casting with different casting speeds of 80, 100, and 120 m/min, respectively. After annealing, the tensile strength of the alloy decreased with increasing annealing time owing to the occurrence of recrystallization and grain growth. In the cast and swaged alloy produced at casting speed of 120 m/min, the grain growth occurred rapidly. In contrast, in the alloy produced at the casting speed of 80 m/min, the grains growth rate was low. Furthermore, the effect of Pb particle in the alloy on machinability was also investigated by using a tool dynamometer installed force sensor.

The proper control of total impurities and oxygen contents of oxygen-free high conductivity (OFHC) copper prepared by vacuum high-frequency melting technique was studied using Mahalanobis-Distance (MD) outlier detection method as functions of raw material purities, vacuum pressure, melting temperature and holding time. The properties of vacuum-melted OFHC copper was examined by thermo-gravimetric analysis, differential scanning calorimetry, hardness test, macro and optical microstructure analyses and ultimate tensile test. In multivariate systems, the existence of outlier makes it difficult to analyze the system and oultier detection belongs to the most important tasks in experimental data analysis. Mahalanobis Distance is most commonly used as a diagnosis of existance of outlier in multivariate system. The relationship between experiment conditions and total impurities and oxygen contents can be defined with the regression analysis results. At this research, our desirable manufacturing conditions is to obtain the total impurities under 40 ppm and oxygen contents under 5 ppm. After this statistical approach, the suggested minimum maufacturing conditions are the purity of raw material was 4N, vacuum pressure was 10-1 torr, melting temperature was 1150°C and melt holding time was 20 minutes.

The present study discussed extrudability improvement for 7000 series Al wrought alloys by thixoextrusion, with emphasis on controlling thixoextrusion parameters, such as initial ram speed, die bearing length and extrusion temperature of billet in semisolid state. The results of thixoextrusion experiments about microstructures and extrusion pressures were compared with conventional hot extrusion results. The maximum extrusion pressure for thixoextrusion was greatly decreased than that of conventional hot extrusion. This will contribute to extrudability in terms of extrusion pressure, which in turn means that shorter process time is required and smaller extrusion machine can be applied for the same operation. It is also possible to make complex shape components of 7000 series Al wrought alloys, which is not possible by conventional hot extrusion processes. The elongated grains to extrusion direction were generally observed during conventional hot extrusion, while the thixoextruded microstructures were isotropic.

Thixoextrusion, one of the thixoforming processes, has advantages of high productivity, reduction of the extrusion pressure and cost saving because of the low energy consumption compared with the conventional extrusion processes. For the thixoextrusion, the low liquid fraction (fL

The strength of aluminum alloys was improved by a severe deformation process while the decrease of elongation leads to the defect. Modification of A3003 alloy was attempted in order to develop a high strength and high formability Al alloy tube for the application of air-conditioning systems in transportation, such as passenger planes and automobiles. An A3003 alloy was modified by Ti addition, grain refiner. As a result of modification, the modified A3003 alloy was able to suitably satisfy the mechanical strength requirements, including elongation. Grain size and secondary dendrite arm spacing of A3003 alloy decreased by as much as 50 % by Ti addition. The finer grains were uniformly distributed in the modified A3003 alloy billet. The yield strength of the modified A3003 alloy was improved by 30 % without decreasing elongation.

It is generally known that Ag-CdO electric contact material excels others in characteristics. Thus, the contact material has been widely used, regardless of current strength. However, in a view point of environment, the advanced electric contact material without environmental load element such as cadmium has to be developed. Extensive studies have been carried out on Ag-SnO2 electric contact material as a substitute of Ag-CdO contact materials. In the manufacturing process of Ag-SnO2 electric contact material, it can be mentioned that typical internal oxidation process is not suitable to produce Ag-SnO2 electric contact material because the Sn located around surface may interrupt oxidation of Sn in the middle of material. Therefore, in the present study, powder metallurgy including compaction and sintering is introduced to solve the incomplete oxidation problems in manufacturing process of Ag-SnO2 electrical contact material. The formation of the blends was manufactured by wet blending of powders of Ag and SnO2. The quantity of SnO2 powder was 15wt.%, with intent to optimize the powdering process for the minute powder of which diameter is less than 5μ m. Particle size and grain distribution of Ag powder and SnO2 powder by powder metallurgy were measured by image analyzer. In order to estimate the properties of specimen tested with a variation of mixed time, the micro-hardness measurement was carried out. The Ag-SnO2-based contact material, which was produced through this study, was actually set in an electric switchgear of which working voltage is 462V and current is between 25 and 40A, for the purpose of testing its performance. As the result, it excelled the existing Ag-CdO-based contact materials in terminal-temperature ascent and main contact resistance.

Effects of isothermal oxidation on the chemical instability which triggers crystallization of Cu54Zr22Ti18Ni6 (numbers indicate at.%) bulk metallic glass were investigated. Comparing the isothermal heat flux of Cu54Zr22Ti18Ni6 bulk metallic glass within the supercooled liquid region in differential scanning calorimetry, it could be observed that the isothermal oxidation did decrease the incubation time for crystallization. What is further, this amorphous phase instability was enhanced with the decrease of particle size. Through this study, chemical instability due to preferential oxidation of alloying element and resulting deviation of chemical composition in intact metallic region needs to be considered in phase evolution of bulk metallic glass during material processing.

In this study, vacuum plasma spraying (VPS) was chosen for making Ni–Ti–Zr–Si–Sn bulk metallic glass (BMG) coating and the process parameters were optimized in view of phase composition of as-sprayed BMG overlay. When it comes to the phase evolution of BMG particle in thermal spraying process, the crystallization does occur by chemical instability and/or thermal instability. For the VPS process, the chemical instability such as in-flight particle oxidation can be neglected and thus the crystallization of BMG feedstock can be considered to result from the thermal instability. Actually, the crystalline phase fraction of the as-sprayed coatings was largely affected by the plasma gas composition which determines the plasma jet characteristics and also in-flight particle melting state. As the gas enthalpy is increased with the increase of hydrogen gas flow rate, number density of unmelted particle within the coating and crystalline phase fraction were consistently decreased. It implied that the phase composition of VPS BMG coating was largely dependent on the melting state of the impacting BMG particle.

In order to enhance understandings of the coating formation in the plasma spraying, an empirical method known as the spot spraying bead formation, was designed. This study is focused on the applicability of the proposed empirical method to explain the microstructural inhomogeneity during the process. Based on the in-flight particle diagnostics using DPV-2000, two different plasma gas compositions were chosen to evaluate the plasma gas effect on the microstructural evolution of Al2O3-TiO2 composite feedstock. A blended NiCr-Cr2O3-Ag-Ca/BaF2 feedstock was sprayed in order to examine the effects of particle parameters on the particle trajectory and the coating microstructures. Through the empirical approach, impacting particle properties and particle trajectory depending on process parameters could be directly shown and coating microstructures could be deduced from the characteristics of the spot spraying bead.

Fine and coarse alumina-titania composite particles were overlaid by allowing the particles to be deposited for a short time without moving a plasmatron [spot spraying bead]. Both the deposition efficiency and maximum deposition rate were measured at the different plasma gas composition. Considering the normalized maximum deposition rate [(maximum deposition rate)x(deposition efficiency)-1], effects of particle size and plasma gas composition on the particle segregation within a cross-section of mass flux could be estimated. Also, particle melting state according to the position within a mass flux at the moment of impact could be also estimated through the investigations of microstructure and phase composition of the spot spraying bead.

The processing of high strength Al wrought alloys does lead either to restrictions for geometrical complexity or to high production costs due to low productivity and multiple-step processes. Thixoextrusion process to overcome these difficulties has been under investigation. In the present study, the effect of thixoextrusion parameters was investigated on mechanical properties of 7003 Al wrought alloy. The maximum extrusion pressure of the thixoextrusion process is three times lower than that of the hot extrusion process. The elongated grains which have the axisymmetry with extrusion direction are generally observed during hot extrusion process, while the microstructures of the thixoextruded are isotropic. The tensile and yield strengthes of the thixoextruded bar are lower than those of the hot extruded bar, while the elongation value of the thixoextruded bar is higher than that of the hot extruded bar.

Mg alloys exhibit a number of good properties such as low density, good castability and high specific strength. However, molten Mg and Mg alloys are ignited without the melt protective gases during melting and casting process due to their high reactivity. The purpose of this study is to investigate effects of Ca and CaO on pure Mg through microstructure observation, ignition test and phase analysis. With increasing Ca and CaO contents, the ignition resistance of Ca or CaO added pure Mg is increased and the grains are refined. As results of XRD and EDS, CaO is reduced to Ca in CaO added pure Mg. Mg2Ca phase is formed even in 0.1 wt.% CaO added pure Mg by reduction mechanism, while Mg2Ca phase is formed over 1.35 wt.% Ca added pure Mg.

Mg alloys have been widely used in automobile and electronic industries because of high specific strength, good castability, etc. However, molten Mg alloys will burn rapidly in air if not protected. To solve this problem, the molten metal should be protected from oxidation by blanketing the surface with flux or protective gases. SF6 gas is widely used for Mg alloys as a cover gas and has proved to be a successful inhibitor. However, the use of SF6 gas is limited because of its high cost and its significant impact on non-global warming potential. Therefore, SF6 gas is being replaced by alternative protection gases. Recent studies show that there has been another attempt by adding CaO into Mg alloys. The aim of this study is to evaluate the effect of CaO on the minimum amount of protective gas, which is necessary not to make ignition in the molten AZ31 and AZ91 Mg alloys.

In recent year, various rheocasting methods, other than stirring in the semisolid state, have been developed to produce a fine globular primary phase in cast alloys. These new methods, called as slurry-on-demand, involve the controlled nucleation and growth/ripening of primary phase during partial solidification. In-Ladle direct thermal control (DTC) rheocasting has been competitively and successfully developed. It requires no processing equipment outside of the casting machine, no grain refinement procedure and no additional cycling time except for cooling down to the desired casting temperature. Process concept of In-Ladle DTC rheocasting is simply based on the fact that there is slurry and mush transition in the range of liquid fraction of 0.1 to 0.6 and the fact that the transition could be controlled by controlling the shape of solid and the relative energy. This study is mainly concerned about the feasibility to achieve semisolid slurry during partial solidification only through thermal and time control, this is, by In-Ladle DTC rheocasting. Based on the optimum conditions obtained by thermal modeling, microstructural evolution of Al alloys was carried out by In-Ladle DTC rheocasting. The fluidity was also investigated by In-Ladle DTC rheocasting for Al alloys.

Thixoextrusion for 7003 and 7075 Al wrought alloys with different content of Cu was carried out with respect to isothermal holding temperature in the partially remelted semisolid state. Especially, despite higher extrudability index of 7075 Al wrought alloy compared with the extrudability index of 7003 Al wrought alloy, the maximum extrusion pressures of 7075 Al wrought alloy were about the same as the maximum extrusion pressures of 7003 Al wrought alloy at temperature with the liquid fraction 10% (7003-624, 7075-609). The hardness values of thixoextruded specimens were higher than that of as-quenched specimens only after partial remelting. The microstructures of thixoextruded specimens did not show any dendrites or rosette-like structures. The average grain sizes of thixoextruded specimens were smaller than average grain sizes of homogenized specimens.

The feasibility study for thixoextrusion of 7075 Al wrought alloys was carried out with respect to reheating profile, isothermal holding temperature and time during the partial remelting through simple partial remelting. The reheating rates were 40/min and 60/min. The isothermal holding temperatures were controlled at 609, 622, 628 and 632 for 0, 2, 5, 10 and 30 min. The interesting point of this study was that the thixotropic structures of 7075 Al wrought alloy without additional pretreatment could be obtained through simple partial remelting. The average grain size was significantly smaller in the quickly heated specimen. The liquid fraction was increased with increasing isothermal holding temperature and time while the average grain size was inversely proportional to isothermal holding temperature and time. However, there was no big change of liquid fraction and average grain size with respect to isothermal holding time. The important fact that the liquid fraction and average grain size were almost uniform after 5 min is considered very useful for thixoextrusion in terms of actual extrusion time.

Melt extrusion is a new fabrication process with the characteristics of both casting and extrusion. In this process, a metallic melt which is poured and solidified up to semisolid state in the container can be directly extruded through the die exit to form a product of bar shape without other intermediate processes. The aging behavior of Al-Cu alloys in the semisolid state was investigated. And the microstructure and mechanical properties of the melt extruded Al-Cu alloy bar were measured and its characteristics are compared with those of a hot extruded Al-Cu alloy bar. Al-Cu alloys were successfully extruded after squeezing out of liquid during melt extrusion with smaller force compared to the solid extrusion. Al-Cu alloys bar with the mean grain size of up to 200 μm was fabricated by melt extrusion process. And the mechanical properties of the melt extruded Al-Cu alloy bar were improved after the T6 treatment.

Porthole die extrusion has a great advantage in the forming of hollow sections of Al alloy tubes that are difficult to produce by conventional extrusion with a mandrel fixed at the stem. In general, the porthole die extrusion process consists of three stages (dividing, welding, and forming stage) through the complex die structure composed of container, porthole, mandrel, welding chamber and bearing part. Thus, in order to obtain the detailed mechanics, to assist in the design of proper die shapes and sizes, and to improve the quality of products with high welding strength, porthole die extrusion should be analyzed in as non-steady state as possible. This paper analyzed porthole die extrusion processes through 3D FE simulation in the non-steady state during the entire process for following process variables: initial billet temperature, bearing length, tube thickness, and extrusion ratio. The extrusion load for each stage, the welding pressure, and the dead metal zone in the welding chamber were examined through a numerical analysis. Extrusion loads found by FE simulation were compared with experimental results. The surface state of extruded products was also examined. Whole investigations were made for Al7003.

There are two primary semisolid processing (S2P) routes, thixocasting and rheocasting. Especially, the rheocasting process has become a new focus in the field of semisolid process because of its many advantages such as increased shot size flexibility, no special SSM billet, inhouse recycling of scrap and smaller investment, compared with the thixoforming process. In-Ladle direct thermal control (DTC) rheocasting was developed, based on the fact that there is slurry and mush transition in molten metal, which is controlled by solid shape and relative interfacial energy. Fluidity is investigated by applying pressure casting for optimizing conditions of in-ladle DTC rheocasting of A356 Al alloy based on research results of simulation and actual microstructure control.

Thixoextrusion, one of the thixoforming processes, has advantages of high productivity, reduction of the extrusion pressure, extension of the die life, and cost saving owing to its low energy consumption compared with the conventional extrusion processes. Especially, thixoextrusion process is expected to be very effective for hard-to-form materials with high strength. The present study focuses on 7075 Al wrought alloy to investigate the potential industrial applications of the thixoextrusion process. The microstructural evolution of 7075 Al wrought alloy for thixoextrusion was investigated with respect to isothermal holding temperature and time in the partially remelted semisolid state. The results showed that the liquid fraction increased with increasing isothermal holding temperature and time while the average grain size was inversely proportional to isothermal holding temperature and time up to 5min. However, there was no big change of liquid fraction and average grain size with respect to isothermal holding temperature and time. The important fact that the liquid fraction and average grain size were almost uniform after 5 min holding time is considered very useful for thixoextrusion in terms of process control.

Environmental regulations in the refrigeration technology make the harmful refrigerants such as CFCs (chlorofluorocarbons) and HCFCs (hydro-chlorofluorocarbons) replaced by eco-refrigerants such as CO2 , and the substitution of CO2 increases the pressure of multi-void condenser tube. As a result, the stiffness of the conventional 1000 series Al alloys can be open to question. The present study is mainly aimed at developing a direct extrusion process and neocondenser tube material for the application of eco-friendly refrigerants with higher working pressure than the conventional CFC and HCFCs refrigerants. The mechanical properties and burst strength for condenser tube were greatly affected by the large grains formed by brazing condition. As a result of the burst testing, 3003 Al alloy proved to be more suitable than 1100 Al alloy for the application of condenser tube to eco-friendly refrigerant usage because 3003 Al alloy can be durable in the heat exchanger required high pressure of working. Furthermore, optimum dies design has to be introduced for control metal flow and metal welding during direct extrusion process.

The environmentally friendly manufacturing process, continuous casting process with small cross sections, is the near net-shaped manufacturing technology used to fabricate copper alloy wires and plates with the required final tolerance and sound quality. Furthermore, the process consumes less energy and discharges less environmental loads because the process can eliminate the need for hot extrusion, hot rolling and heat treatment for production copper alloy wires and plate. In the present study, the effects of a continuous casting speed on the mechanical properties and the microstructure of the nickel-silver (Cu-Ni-Zn) alloy were studied and energy requirements, atmospheric CO2 emission and yield for the production of the Cu-Ni-Zn alloy was investigated quantitatively with respect to continuous casting with small cross sections and conventional material processing including casting, extrusion and heat treatment. The yield for production of Cu-Ni-Zn alloy can be improved above 30% with the application of continuous casting with small cross sections when the productivity is similar. Twice the amount of energy required and CO2 were consumed and emitted in the conventional manufacturing process when the yield of the processes was considered.

A magnesium alloy was adopted to an evaporative pattern casting (EPC) process to combine advantages of each. In the present study, foam patterns were cast at a top gating system under atmospheric and reduced pressure to evaluate casting characteristics of AZ91D to develop a complete EPC process for high productivity of magnesium alloy castings. Filling time and temperature of molten metal were measured during mold filling. It was recognized that the average filling velocity was affected by the difference of the coating material and the degree of reduced pressure. The grain size of the magnesium alloy was slightly dependent on the degree of reduced pressure. It was considered that the application of the high reduced pressure, which changed the shape of melt surface from convex to concave, was related to the occurrence of internal defects such as cold shut laps or folds in the casting.

It has been generally known that the refining efficiency in zone refining process depends on travel rate, number of pass and distribution coefficient of impurity. In the present study, the effect of distribution coefficient on copper purification was investigated by zone refining process. A numerical model capable of predicting the solute redistribution at any stage of zone refining was proposed. The composition profiles of each segment at the given condition were compared with the results of micro hardness profiles. After zone refining, metallic elements were analyzed by GDOS (Glow Discharge Optical Spectroscopy) and GDMS (Glow Discharge Mass Spectrometry). The impurities Ag, Pb, S and Ti, whose distribution coefficients are below 0.5, were concentrated at the finishing position. Cr, Mn, Si and Zn, whose distribution coefficients are between 0.5 and 1, were distributed irregularly. Fe and Ni, whose distribution coefficients are greater than 1, moved to the starting position. It was found that zone refining process was actually effective to remove impurities whose distribution coefficients are below 0.5. The experimental results agreed well with the simulation result.

Porthole die extrusion has a great advantage in the forming of hollow section tubes that are difficult to produce by conventional extrusion with a mandrel on the stem. Because of the complicated structure of the die assembly, the extrusion of hollow section tubes has been investigated experimentally. Analytic approaches that are useful in profitable die design and in the improvement of productivity are inevitably demanded. In porthole die extrusion the welding strength promises the possibility of producing sound hollow section tubes. Welding strength is affected by many parameters, such as extrusion ratio, extrusion speed, die shape, porthole number, bearing length, billet temperature and mandrel shape. In this paper, parameters such as billet temperature, bearing length and product thickness, are examined. The welding pressures are examined through 3D simulation of the non-steady state and compared with experimental results. The objective of this study is to analyze the metal flow and to predict the welding pressure of product by FE simulations and experiments. These results will be applied to porthole die design in the future.

In a view point of mechanical property of medium strength alloy such as A7003 aluminum alloy, it is necessary to increase Mg content in the alloy however an increment in Mg content has an adverse effect on the extrudability. Furthermore, it has been generally practiced to reduce the Mg content for enhanced recovery efficiency during Al scrap recycling in the aluminum industry. Therefore, it is important to select the amounts of alloy elements for mechanical property and extrudability in medium strength A7003 alloy. To examine the effect of Mg content on extrudability in A7003, hot extrusion experiments and then microstructure examination by XRD, SEM and EPMA have been performed. The quantitative analysis of energy consumption and CO2 emission for production of A7003 extruded bar are estimated with different process variables such as Mg content, extrusion process (direct or indirect extrusion) and billet pre-heating process (heating by light oil or LPG). The estimation of energy consumption is performed in a stage except mining and extraction (from shipping to gate) to investigate an influence of the parameters on energy consumption and CO2 emission in detail. As Mg content is increased, the flow stress and the extrusion pressure for A7003 alloy are increased. It has been thought that an increment in extrusion pressure with increasing Mg content is caused by the solid solution hardening of Mg atoms in the matrix and an increment in volume fraction of intermetallic compound, Mg2Si. The energy consumptions can be reduced when lower content of Mg in A7003 alloy and indirect extrusion process are used. It has been found that CO2 emission in billet heating process can be reduced when induction heating process is introduced.