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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.

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 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

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.

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.

The precipitation kinetics of Al 3 Sc phases in Al-0.090at.%Sc and Al-0.15at.%Sc alloys were investigated in the aging temperature range from 533 to 733 K mainly by electrical resistivity measurements. The average Sc concentration c Sc of the Al-rich matrix was calculated from the value of the resistivity. The results of aging time dependence of c Sc and fraction of solute transformed were analysed from the viewpoint of time scaling, the Johnson-Mehl-Avrami equation and the Ostwald ripening theory. The rapid growth stage of the Al 3 Sc phases was successfully scaled and nearly characterized by the model of diffusion-controlled growth of a fixed number of particles. The solid solubilities of Sc in aluminium from 733 K down to 643 K were estimated by the analysis of c Sc of the Al-rich matrix during the Ostwald ripening of the Al 3 Sc precipitates.