• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.227-230
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• 2009

The aim of this study was to improve extrudability limit, eliminate welding line and obtain optimum thixoextrusion conditions for manufacturing tubes of 7075 Al wrought alloy. By thixoextrusion, it was possible to improve deformability, control isotropy with extrusion direction, eliminate welding line (seamless) and save cost due to low energy consumption compared with conventional extrusion processes. The welded part was not observed at the welding line area. The grains of thixoextruded tube were homogeneously distributed and equiaxed grains were observed. Therefore, thixoextrusion is the most effective variable for the control of the magnitude of the welding line.

• 한국주조공학회지
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• 제30권6호
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• pp.210-216
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• 2010

The aim of this study is to characterize a thixoextruded 7075 Al wrought alloy bar in terms of its isotropic behavior through the optical microscope, mechanical test and electron back scattered diffraction. It is also discussed of the extrudability improvement for 7075 Al wrought alloy by thixoextrusion, with emphasis on controlling thixoextrusion parameters. Hot extrusion shows that the maximum extrusion pressure depends on their characteristics in terms of flow stress and hot workability. In the contrary, thixoextrusion demonstrates that the maximum extrusion pressure is almost uniform regardless of the experimental parameters, such as initial ram speed, die bearing length and thixoextrusion temperature. The hot extruded microstructures become elongated to extrusion direction, while the thixoextruded microstructures are isotropic and homogeneously distributed due to the existence of liquid phase between solid grains during the process. The grain refinement due to dynamic recrystallization during thixoextrusion has been also occurred. Subsequent recrystallization would lead to the strengthening of mechanical properties, as observed in the study. The important point is that the values of tensile, yield strength and elongation of the thixoextruded bar without plastic deformation are similar to those of the hot extruded bar with severe plastic deformation.

• 한국주조공학회지
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• 제26권5호
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• pp.211-216
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• 2006

The study for thixoextrusion process of 7075, 7003 Al wrought alloys and AZ31 Mg wrought alloy was carried out with respect to reheating rate, isothermal holding temperature and time with an emphasis to the effect of homogenization on thixotropic micro-structures during the partial remelting, especially in the low liquid fraction ($f_L<0.2$). The liquid fraction and average grain size with respect to reheating profile such as reheating rate, isothermal holding temperature and time were almost uniform. It is considered very useful for thixoextrusion in terms of process control such as billet temperature control and actual extrusion time. Micro-structural controls of 7075, 7003 Al wrought alloys and AZ31 Mg wrought alloy before and after homogenization were available and thixotropic microstructures were obtained in both specimens.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2012년도 추계총회 및 학술대회 논문집
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• pp.179-180
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• 2012

Aluminum alloys are widely known as non-ferrous metal with light weight and high strength. Consequently, these materials take center stage in the aircraft and automobile industry. The Al7075 aluminum alloy is based on the Al-Zn-Mg-Cu and one of the strongest wrought aluminum alloys. Aluminum nitride has ten times higher thermal conductivity($319W/m{\cdot}K$) than Al2O3 and also has outstanding electric insulation($1{\times}1014{\Omega}{\cdot}cm$). Furthermore, it has high mechanical property (430 MPa) even though its co-efficient of thermal expansion is less than alumina For these reasons, it has great possibilities to be used for not only the field which needs high strength lightweight but also electronic material field because of its suitability to be applied to the insulator film of PCB or wafer of ceramic with high heat conduction. This paper investigates the mechanical properties and corrosion behavior of aluminum alloy Al7075 deposited with aluminum nitride thin films To improve the surface properties of Al7075 with respect to hardness, and resistance to corrosion, aluminum nitride thin films have been deposited by pulsed DC reactive magnetron sputtering. The pulsed DC power provides arc-free deposition of insulating films.

• 한국주조공학회지
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• 제26권5호
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• pp.217-221
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• 2006

The main emphasis of this study was to utilize thixoextrusion process for improving extrudability of 7075, 7003 Al wrought alloys and AZ31 Mg wrought alloy. The results of thixbextrusion experiments about microstructures and extrusion pressures were compared with conventional hot extrusion results. The maximum extrusion pressure of thixoextrusion was greatly decreased compared with that of conventional hot extrusion. It was pointed out that the extrusion temperature dependence of the maximum extrusion pressure was large and the influence of extrusion temperature on the improvement of extrudability was remarkable in thixoextrusion. 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. The elongated grains to extrusion direction were generally observed during conventional hot extrusion, while the thixoextruded microstructures were isotropic.