A study was made to investigate the microstructure and the mechanical properties of low-carbon steel, Al-Mg alloy and Ti-6Al-4V alloy each representing bcc, fcc and hcp crystal structures, respectively fabricated by equal-channel angular(ECA) pressing. After a series of ECA pressings was performed, most grains were significantly refined below ${\mu}m$ in diameter with high mis-orientation of grain boundaries irrespective of different crystal structure used. Regarding the strain hardening capability, tensile tests of ultrafine grain (UFG) dual-phase (ferrite/martensite) steel which was different from UFG ferrite-pearlite steel were carried out at ambient temperature, and corresponding mechanical properties were discussed in relation to modified C-J analysis. Low-temperature and/or high strain-rate superplasticity of the UFG Al-Mg alloy and UFG Ti-6Al-4V alloy were also studied. Based on the analysis used in this study, it was concluded that UFG alloys exhibited the enhanced mechanical properties as compared to coarse-grained (CG) counterparts.

Sliding wear mechanism of a high nitrogen austenitic 18Cr-18Mn-2Mo-0.9N steel has been investigated. Dry sliding wear tests of the steel were carried out at various loads of IN-10N under a constant sliding speed condition of 0.15m/s against AISI 52100 bearing steel balls. Solution ($1050^{\circ}C$) and isothermal aging ($900^{\circ}C$) heat treatments were performed on the steel and the effect of the heat treatments on the wear was investigated. Wear rates of the solution-treated steel specimen remained low until 5N load, and then increased abruptly at loads above 5N. The rates of isothermally aged specimens were low and increased gradually with the applied load. Worn surfaces, their cross sections, and wear debris of the steel specimens were examined with a scanning electron microscopy. Phases of the heat-treated specimen and the wear debris were identified using XRD. The transformed phase underneath a sliding track was investigated and analyzed using a TEM. Effects of the phase transformation during the wear and $Cr_{2}N$ precipitates formed during the isothermal aging on the wear of the austenitic steel were discussed.

API steel is used for line-pipe to transport the oil and natural gas. As the recent trends in the development of API steel are towards the use of larger diameter and thicker plate, many researches have been studied to achieve higher strength, higher toughness and lower yield ratio in API steel. However, the strength of API steel after pipe forming is changed depending on the competition of the Bauschinger effect and work hardening which are affected by the strain history during pipe forming process. So, the purpose of this study is to investigate the influence of microstructure on the Bauschinger effect for API steel. To change the microstructure of API steel we have changed the hot rolling condition and the amounts of V and Cu addition. The compression-tensile test and the microstructure observation by OM and TEM were conducted to investigate the yield strength drop and the correlation between the Bauschinger effect and microstructure of API steel. The experimental results show that the increase of polygonal ferrites volume fraction increases the Baushcinger effect due to the back stress which comes from the increase of mobile dislocation density at polygonal ferrite interior during the compressive deformation. The hot rolling condition was more effective on the Bauschinger effect in API steel than the small amount of V and Cu addition.

Metallic sandwich plates are ultra-light materials not only with high strength and stiffness but also with other multifunctional physical properties. Inner dimpled shell structure can be fabricated by a piecewise sectional forming process, and then bonded with face sheets of the same material by resistance welding. Possible region for bending and limit radius of curvature are defined to compare the formability of sandwich plates. Tests have shown that sandwich plates with inner dimpled shell structure subject to bending have longer possible region for bending and smaller limit radius of curvature than other types of sandwich plates. The proposed inner dimpled shell structure is shown to have better formability of sandwich plates for bending than other types inner structures.

This paper is concerned with the thermo-mechanical behavior including temperature dependent strain-rate sensitivity of steel sheet for an auto-body. In order to identify the temperature dependent strain-rate sensitivity of SPRC35R and SPRC45E, uniaxial tension tests are performed with the variation of the strain-rates from 0.001 /sec to 200 /sec at environmental temperatures varied from $-40^{\circ}C\;to\;200^{\circ}C$. The thermo-mechanical response at the quasi-static state is obtained with the static tensile test and at the intermediate strain-rate is from the high speed tensile test. Experimental results show that the strain-rate sensitivity increases at low temperature. It represents that as the strain-rate increases, the variation of flow stress becomes sensitive on the temperature. The results indicate that the flow stress of SPRC35R is more dependent on the changes of strain-rate and temperature than those of SPRC45E.

A tube hydroformability testing system was designed and manufactured to observe the forming steps and to provide arbitrary combination of internal pressure and axial fred. The forming limit diagram of an aluminum tube was obtained from the free bulge test and the T-shape forming test using this system, giving the criteria for predicting failure in the hydroforming process. The hydroformability of aluminum tube according to different conditions of a prebending process was discussed, based on the finite element analysis and the forming limit test. The effects of 2D and 3D pretending on the tube hydroforming process of an automotive trailing arm were evaluated and compared with each other.

Effect of processing condition on the hot extrusion of Al-Zn-Mg-Sc alloy was investigated. For this purpose, hot compression test and FE-simulation were conducted via Thermecmaster-Z and DEFORM-3D, respectively. The microstructure evolution during hot extrusion and post heat-treatment was investigated and deformation mechanisms were analyzed by constructing processing map. FE-simulation results show that the temperature difference between container and billet has considerable influence on the final shape of extruded T-shape bar. The relation between applied load and processing time was predicted by the FE-analysis as well as punch speed vs. stroke chart.

In this study, the experiments of warm deep drawing were done with heated die, and with heated die, and blankholder, and cooled punch in order to investigate the formability of AZ31 magnesium alloy sheet in warm deep drawing. For this, warm deep drawing experiments were executed under various temperatures and punch velocities. The results of warm deep drawing with heated die showed that fracture occurred around the punch part at punch velocity of 75mm/min and punch stroke of 10mm under temperature range of 373-523K, but did not occur under temperature range of 548-673K even punch stroke of 25mm. And fracture at the punch stroke of 25mm and the temperature of 523K did not occur under the punch velocity of 30mm/min, but occurred under punch velocity of 75 and 125mm/min. Also warm deep drawing with heated die and blankholder, and cooled punch showed that the temperature range happening maximum height under punch velocity of 10-100mm/min was around 498-523K. Finally, with heating and cooling technique necking of AZ31 magnesium alloy occurred at punch shoulder part under the temperature range of 293-423K, but at die wall part under the temperature range of 473-573K.

In this study, the die design and die series on the surface residual stress of cold drawn eutectoid steel wire have been investigated. Test pieces were fabricated using die series with different mean and final reduction ratios. Surface residual stresses in the axial direction were measured by X-ray diffraction, Bruker's 2-dimensional GADDS system. The results were compared with stress profiles that were calculated by 3D and 2D finite element simulations, ABAQUS 6.4 program in finite element analysis(FEA). By means of the FEA method, optimal die shape considering delta-parameter were induced and applied in order to determine die sequence designs. Balance of the drawing stresses was also introduced to optimize die sequence.

The demand for the miniaturization and high-precision of machine part has recently increased in new technology like biotechnology(BT) and nanotechnology(NT). The purpose of this study is to analyze the molding characteristics according to injection conditions by measuring the filling height in micro injection molding of the polypropylene(PP) and cyclic olefin copolymer(COC). The result shows that the filling effect of COC is better than that of PP in micro rib structure with injection molding process.

The die development of the high-strength steel sheet is very different with that of the common steel sheet. Especially, the springback problem of the high-strength steel is serious in the stamping process. This paper showed the optimized die development of the high-strength steel sheet which was based on the experimental measured and simulated springback auto panel stamping process.