Search

The present work describes the development and characterization of mechanical properties of an Al-Mg based die-cast alloy (ALDC6-10Si) for spider arm components in washers. The effect of the addition of silicon (10 wt.%) and magnesium (2.7 wt.%) on the microstructure and mechanical properties of the developed ALDC6-10Si alloy was evaluated. The optical microscopy images and energy dispersive x-ray spectroscopy profiles reveal that the presence of Mg2Si in the ALDC6-10Si alloy is higher than that of commercial ALDC3 alloy. The hardness and tensile strength of the ALDC6-Si10 alloy were found to be improved due to the presence of intermetallic phases such as Mg2Si and π-Al8Si6Mg3Fe. Moreover, the formation of spheroidal primary α-Al and the refinement of the fine eutectic Si structure also enhanced the mechanical properties. In addition, a spider arm component was fabricated using the developed ALDC6-Si10 alloy and evaluated its microstructure and mechanical properties. The results indicated that ALDC6-Si10 alloy can be a better alternative for fabricating the spider arm component in washers.

Hot press formed parts in a fully martensitic structure limit its application in the centre pillar, which requires high collision resistance. In this study, the combined effect of the patchwork and...

Carbon fabric-reinforced thermoplastic (CFRP) composites, fortified with carbon fiber prepreg and epoxy base materials, have been mainly used for body parts for weight lightening, advanced high strength, and impact absorption In the current automotive industry However, as recycling of the composite material is required, attempts have been made to manufacture body parts using a thermoplastic polymeric material as a base substance. In order to produce various types of body parts by impregnating a liquid thermoplastic material into carbon fabric preform in methods of manufacturing a carbon fiber-reinforced thermoplastic composite material (CFRTP), it is important to understand the effect of the impregnation process parameters (time, temperature, pressing force) on the mechanical properties of the composite material. Therefore, in this study, the influence of impregnation process parameters on the mechanical properties of CFRTP is proposed. In addition, this paper presents the problems and solutions when polymeric materials are impregnated in carbon fabric.

In this article, the tribological properties of aluminum/MWCNTs/Al2O3sf hybrid composites with varying volume fraction of 10 vol%, 15 vol% and 20 vol% was investigated under dry sliding conditions. The experiments were performed according to design of experiments approach using Taguchi method to predict the wear properties of composites. The results indicated that the composites of 15 vol% had lower wear loss, whereas the coefficient of friction (COF) decreased significantly at 20 vol%. Taguchi based ANOVA analysis showed that the sliding distance was found to be the prominent factor controlling the wear loss; applied load influenced COF most significantly. It could also be noticed that the COF and wear loss increases with an increase in sliding load and sliding distance. The decrease in wear loss and the COF can be attributed to the self-lubrication effect of MWCNTs, and the combined effect of reinforcements in the composites. In addition, nanoscratch test was performed to determine the COF and the effect of the reinforcements on local regions of the composites. The results revealed that higher friction force was obtained near the regions of MWCNTs and Al2O3sf while nanoscratching. The COF of composites of 20 vol% was found to slightly higher compared to that of 10 vol% and 15 vol%. This is attributed to the presence of MWCNTs cluster within the Al2O3sf network results prevent the micro-plastic deformation of Al matrix, and the formation of tribofilms with nanoscaled thickness in the scratch region. These friction and wear results indicate that the presence of a limited amount and size of MWCNTs clusters are beneficial to the tribological properties of the hybrid composites.

Recently, researchers and engineers have been interested in the development of hybrid metal matrix composites (HMMCs) for the applications of automotive and aerospace industries owing to their superior properties due to the usage a wide range of material combinations in its manufacturing. The present study focuses on the machining of magnesium based hybrid composites reinforced with CNT (1vol.%) and SiC (2vol.%).The influence of machining parameters such as spindle speed, feed rate, drill diameter and point angle on burr formation and surface roughness on drilling the composites were investigated using Taguchi method. The drilling parameters were optimized by using ANOVA experimental design and also find out the percentage of contribution of each factor. Based on the results, the most influential factor for the burr thickness was spindle speed and point angle. While spindle speed and feed rate were the influencing factors for surface roughness. The analysis revealed that burr height, burr thickness, and surface roughness decreases significantly with an increase in spindle speed.

In this paper, hot and cold deep drawing processes are determined with direct deep drawing process and indirect deep drawing process. To predict the friction coefficient, the finite-element method, which can predict deformation behavior until the fracture of a blank sheet, was proposed using the forming limit diagram (FLD) curve. The effect of fracturing of the coating layer on the friction coefficient during the hot and cold deep drawing processes was investigated. The deformation behavior of the coating layer of the boron steel sheet that affects the friction coefficient in the hot and cold deep drawing processes was also proposed. A forming method that can control the surface condition of the formed product is further proposed by explaining the fracture of the coating due to the forming process.

Recently, automobile components such as center pillars and impact beams have been fabricated using materials that satisfy both high strength and impact absorption. In this study, the forming process of CR340 (cold rolled steel)/CFRP hybrid composites was investigated. Initially, hybrid composites were fabricated by stacking carbon fibre reinforced plastic (CFRP) prepreg on CR340 steel with Zn coating. An adhesive agent developed by the research team was applied for bonding between the cold rolled steel and CFRP to enable the blank fabrication of hybrid composites. The mechanical properties of the developed hybrid composites were investigated by tensile, bending and lap shear adhesion test. The results showed that the tensile strength and shear strength of composites increases with the increase in the number of laminations but the bending strength decreases.

In this study, the closed die forging of aluminium based compoistes reinfoced with CNTs (1vol% and 3vol%) were investigated. Initially, the composites were fabricated using high energy ball milling followed by compaction and sintering. The microstructural results showed that finer grain size and homogeneous dispersion of CNTs were obtained. Composites with up to 97% densification were produced when fine open porosities were removed by closed die forging. The results imply that the hardness and compressive strength of composites with 3vol.% of CNTs has improved without any deterioration. In addition, workability behaviors of composites were investigated by cold upsetting test. For that pore reopening test was performed to confirm the closure of micro-pores after the closed die forged, and to further analyze the densification of the composites. Typical cases, as the pores were not re-opened even after increasing the strain, additional forming is possible up to large deformations.

In this study, the microstructure and mechanical properties of extruded aluminium (Al6061) based composites reinforced with multiwall carbon nanotubes (MWCNTs) were investigated. Composites with varying volume fractions of MWCNTs (1 vol% and 3 vol%) were fabricated initially using high energy ball milling, followed by compaction and sintering. Hot extrusion was carried out for the developed composites at different extrusion temperatures, extrusion ratios and die angles. SEM analysis of the extruded composites showed good dispersion of the MWCNTs within the Al matrix alloy. Improvements in micro-hardness and compressive strength were observed in the extruded composites with 3 vol.% MWCNTs without any deterioration in elongation. In addition, the workability behaviors of the composites were investigated by a cold upsetting test. The pore reopening tests were performed to confirm the closure of pores after the extrusion and to further analyze the densification of the composites. The results for the densification process based on extrusion confirmed that the pores turned into spherically closed pores. For typical cases, the pores did not reopen even after increasing the strain therefore, additional forming was possible up to large deformations.

In coal-fired power plants, approximately 5% of sewage sludge solid fuel mixed with coal is used as power generation fuel for environmental protection and global warming prevention. The co-firing method needs a sewage sludge solid fuel crusher that can crush sewage sludge solid fuel to generate a fine powder. This study aims to determine the size of the rotor perpendicular plate hole that can minimize accumulation of the crushed fuel in the roller type sewage sludge solid fuel crusher to be used in the co-firing method. The range of the design parameters for optimization of the rotor perpendicular plate hole is selected and make an orthogonal array table according to design of experiments. The CFD is performed to analyze effect of design parameters according to an orthogonal array table. In addition, the dimension of the rotor perpendicular plate hole that can minimize accumulation of the fuel inside the crusher is drawn using the Multi-objective optimization method.

Owing to environmental problems generated in the course of economie growth, the industry is implementing renewable portfolio stan-dards (RPS) for companies that own power generation facilities with capacities equal to or in excess of 500 MW. In coal-fired electrical power plants, renewable portfolio standards are implemented using sewage sludge organic solid fuels to address environmental problems. Currently, sewage sludge organic solid fuels are crushed using a hammer mill operated in the co-firing mode. However, the hammer mill has low operation efficiency owing to the fast wear and tear and frequent breakdowns of the hammer and grate that constitute two of its key components. Therefore, the development of a crusher with increased durability and high-operation efficiency is necessary. In this study, a roller-type crusher was designed for the organic solid fuels of the sewage sludge that was operated with the use of compression and friction forces. The effect of the crushing condition of the designed roller type sewage-sludge organic solid-fuel crusher was analyzed. In addition, fuel crushing analysis was carried out using the discrete element method (DEM). Based on the DEM analysis results, the effect of process parameters (rotation speed of the rotor, roller size) of the roller type sewage-sludge solid-fuel crusher on the crushing rate was analyzed. A fuel crushing experiment was conducted using the roller-type crusher used for sewage-sludge organic solid fuels. In addition, the crushing rates against the amount of fuel discharge according to the DEM results and fuel crushing experiments were compared.

Recently, vehicle parts such as center pillars and impact beams used in automobiles have been requiring materials that satisfy both high strength and impact absorption. Therefore, in this study, the applicability of the forming process of CR340 (cold rolled steel sheet)/carbon fiber reinforced plastic (CFRP) hybrid composites which are a bonded material of cold rolled steel sheet having excellent formability and carbon fiber prepreg having high strength and high collision absorption in the vehicle parts was investigated. Hybrid composites are fabricated by stacking CFRP prepreg on a cold rolled steel sheet (CR340) with Zn coating. Bonding materials were used at the interface between the CFRP prepreg and steel sheet. This study investigated the formability and fiber orientation of CR340/CFRP hybrid composite after deep drawing. Square cup deep drawing tests were conducted with various process parameters to evaluate the formability of CR340/CFRP hybrid composite. The square deep drawing process parameters and the thinning rate at each position of the drawing product were measured, and the various problems encountered during the deep drawing process were reviewed with the thermal flow of epoxy. Experimental data between the forming depth and blank holding force was introduced with CFRP/CR340 with Zn coating sheet hybrid composite. The thickness variations of the materials and the fiber orientations were observed using cross sections at each position. Void and delamination defects were observed at the die round and were discussed in detail.

Development of environment-friendly materials to improve the safety and fuel efficiency of automobiles has attracted great research attention with regards to the automobile industry in recent years. With increase in demand for technological developments to improve performance and efficiency, an increased number of researches are being performed concerning the use of advanced high-strength steel in parts manufactured by means of the hot-press forming process. Furthermore, research concerning the improvement in fuel efficiency through additional weight reduction using tailor-welded blanks (TWBs) and partial quenching (PQ) has gained popularity in the automobile industry in recent times. Many car components are, nowadays, being fabricated using different materials to improve collision toughness and safety in the event of a car crash. However, no standard has yet been established to evaluate the replacement of automobile parts, and such a standard must account for mechanical properties of the material under tensile and flexural loadings. A car crash test was conducted at the Insurance Institute for Highway Safety (IIHS) to evaluate automobile safety. However, collision-toughness evaluation of each car component is expensive and difficult to realize. In this study, drop tests were simulated, and collision characteristics of the center-pillar were correspondingly evaluated. Values of fracture toughness were compared in accordance with center-pillar types for evaluating collision-test conditions.

The aim of present wor is, therfore, to investigated the effect of the damage value prediction equation on the formability of compression specimen and find the optimize forming condition.Although Inconel 625 alloys are excellent materials, Ni-base alloy cannot be formed at room temperature owing to limitation of formability. To improve the formability of Inconel 625, it is necessary to investigate the formability at a high temperature range.A high temperature compression test is performed with a Gleeble 3500 testing machine at various temperatures (approximately 900 1200°C) and strain rates (10/s and 30/s) to obtain high temperature deformation characteristics of Inconel 625. Furthermore, high temperature tensile tests results are used to measure elongations and reductions in the area of Inconel 625.A rigid-plastic finite element simulation is applied to the high temperature compression process to obtain the damage valueThe results of the hot deformation experiment and analysis are presented for various conditions of temperatures and strain rates, and it is expected that damage value will be used in hot forming processes such as hot extrusion and rolling process.

In this study, vehicle center-pillar reinforcements were formed from steel tailor welded blanks (TWBs) and CR420 steel/carbon-fiber-reinforced plastic (CR420/CFRP) hybrid composite materials. After forming, collision tests were conducted to evaluate the fracture toughness of the center-pillar reinforcements made of TWB and of CR420/CFRP hybrid composite materials. The center-pillar reinforcement with the CR420/CFRP hybrid composite materials was lighter than the one with TWB, and the CR420/CFRP fracture toughness was also improved. The experimental collision results were compared with a computer-aided engineering simulation to provide a second verification. The detailed results were analyzed using the Abaqus/explicit software. Because the elastic modulus of the TWB is higher than that of the CR420/CFRP hybrid composite materials, the impact time for the CR420/CFRP hybrid composite materials is longer than for the TWB. Accordingly, when conducting the collision test of the CR420/CFRP hybrid composite materials, the impulse that the impactor received was greater. When the TWB was replaced with the next generation CR420/CFRP composite material, the body weight of the car became lighter by approximately 44%, while the impulse improved by approximately 10.0%. In this simulation, the impact time, fracture toughness and velocity change of the impactor were evaluated and were in close agreement with the experimental results.

Hybrid composites in which a CR980 metal plate was bonded on carbon-fiber-reinforced plastic (CFRP) were prepared. Hybrid composites were two types of CFRP/CR980 hybrid composites and CR980/CFRP hybrid composites. The properties of the hybrid composites according to surface roughness on CR980 plate and the laminating number of CFRP prepregs were analyzed. The spring-back or spring-go angles were also measured through the V-bending test of hybrid composites. In addition, a three-point bending test for the hybrid composites was conducted to measure the flexural strength. Spring-back occurred in the CFRP/CR980 hybrid composites, while spring-go was observed in the CR980/CFRP hybrid composites. Voids were not found at the bonding area of the CFRP and CR980. As the roughness at the bonding area increased, the flexural strength slightly increased. The higher the laminating number of the CFRP prepregs, the lower the deformation value. CFRP/CR980 was deformed more easily than CR980/CFRP.

Inconel 625 alloys are widely applied for high-corrosion resistance and as high-efficiency materials in aeronautical, aerospace, chemical, nuclear, petrochemical, and marine industries. Although Inconel 625 alloys are excellent materials, they cannot be formed at room temperature owing to difficulties in processing. To improve the formability of Inconel 625, it is necessary to investigate its formability at a high-temperature range and its strain rate variation. In this study, high-temperature deformation behavior after forming was investigated. A high-temperature compression test was performed with a Gleeble 3500 testing machine at various temperatures (approximately 900&ndash, 1200 &deg, C) and strain rates (10 and 30 s&minus, 1) to obtain the high-temperature deformation characteristics of Inconel 625. Furthermore, high-temperature tensile tests were performed to measure elongations and reductions in the area of the Inconel 625 alloy. The tests focused on obtaining the flow stress data and optimal hot forging conditions under various strain rates and temperatures. The results of this research are expected to contribute to hot forming processes and to formability in hot extrusion and pilger processes.

In this study, a hybrid composite material was fabricated by stacking carbon fiber-reinforced plastic onto CR420 plates to increase the specific strength and stiffness relative to those of thick boron steel plates and dual-phase steels. Simulations were first used to compare and evaluate the abilities of two forming processes to manufacture appropriate center-pillar reinforcements. After determining the best process, a die was prepared using computer aided engineering (CAE), and a center-pillar reinforcement was formed with a carbon fiber-reinforced plastic (CFRP)/CR420 hybrid composite. The differences in the mechanical properties of the specimens were investigated according to their position using simulations. The specimen thicknesses in the experiment and simulation were compared. Positions where the contact pressure was low could be found in the simulation. Further, the reasons for the deterioration of the mechanical properties were elucidated by observing the micro-structure. Large quantities of voids with a size greater than 50 μm were found in those specimens that had a contact pressure lower than 0.5 MPa. The results obtained confirm that large quantities of voids cause the mechanical properties of CFRP composites to deteriorate.

In this study, a hybrid composite material was fabricated by stacking carbon fiber-reinforced plastic on CR340 plates to increase the specific strength and specific stiffness, compared to thick boron steel plates or dual-phase steels. A deep drawing test was conducted for this hybrid composite material, using various blank holding force, to assess its formability and potential use in vehicle parts. After experiment, the results of formability were compared with analysis data by using ABAQUS explicit. The formability was then assessed according to the blank holding force and friction coefficient. The friction coefficient decreased with increasing Bf. After deep drawing, the epoxy flow behavior was examined. Problems with the metal/CFRP hybrid composites were investigated through macroscopic and microscopic observations.

To manufacture automotive clutch housing parts in application of high pressure die casting, the following three gating system designs were taken into account. Since adopting these gating system designs in actual experiment would require too much cost and time, a casting simulation program was used instead: Analyzed were flow behaviors as elements filled the mould. Based on the air pressure and air pocket after the melt was completely filled in mould, the final gating system design was selected. The third gating system design with 5 gates was expected to involve less defects than others was even and uniform. A cooling channel and a chill vent were designed. In a real casting test, five products in total were produced. All of them were sound and involved neither any spot of insufficient filling nor defect on the surface. The real test expected to involve shrinkage porosities based on the analysis and those of the manufactured products that actually involved shrinkage porosities did not exactly correspond to each other but were similar. The hardness was about 84 HV regardless of location.

In this study, Cold Rolled 340 (CR340)/Carbon Fiber Reinforced Plastic (CFRP) composites were fabricated, and experiments and simulation were performed to compare their flexural properties from three-point bending tests. The mechanical properties of CR340 and CFRP were input by dividing the material regime into elastic, plastic, and fracture regions in order to improve the simulation reliability. A forming limit diagram was determined through a stretch test for the CR340 steel plate and used as data input in the simulation. For CFRP, simulation was carried out using the Hashin damage theory and damage evolution obtained from references. Results showed that the maximum bending stress, fracture displacement, and gradient in the experiments closely matched those obtained from the simulation.

Nano-microhybrid reinforced metal matrix composites are the novel combination of composite system which enhanced the mechanical properties of the metal matrix composites. The aim of this study is to determine the nano- and macromechanical properties of aluminium (A356)-based hybrid composites reinforced with multiwall carbon nanotubes and alumina short fibers (Al2O3sf). Hybrid preforms were developed initially, by a combination of multiwall carbon nanotubes and Al2O3sf with total volume fractions of 10%, 15% and 20% and by varying the weight percentage of multiwall carbon nanotubes such as 1%, 2% and 3%. The fabricated hybrid preforms were then infiltrated with aluminium alloy (A356), and the microstructure and mechanical properties of the composites were evaluated. The distribution of multiwall carbon nanotubes within the array of the Al2O3sf network which exists in clusters was found to be relatively good. The mechanical properties such as the hardness and tensile strength of Al-based hybrid metal matrix composites were found to be improved by up to 2 wt% of multiwall carbon nanotubes. The causative reason for this is attributed to a combined effect of both multiwall carbon nanotubes and Al2O3sf, which contributed to better load sharing between the fibers and the Al matrix, and also accounted for the resistance of dislocation movements caused by the presence of the multiwall carbon nanotubes. In addition, the continuous stiffness measurement method was also used to evaluate the nanomechanical properties of the composites. The results showed that the influence of multiwall carbon nanotubes highlighted the properties on a nanoscale.

The variables of die temperature, pressure, time, lamination method, and forming count are applied to fabricate thermosoftening CFRP (CFRTP) with compression molding method. The mechanical properties of CFRTP are compared with those of thermosetting CFRP (CFRTS). The first lamination method is that one hotmelt is inserted into carbon fiber (five carbon fibers and four hotmelts). The optimal lamination conditions are the die temperature of 220°C, pressure of 6 MPa, and pressurization time for 10 min. The tensile strength of CFRTP of this lamination method is 400 MPa. For higher tensile strength value, the second lamination method was applied. CFRTP prepreg was prepared with one hotmelt and one carbon fiber by applying die temperature at optimal lamination conditions. Five CFRTP prepregs were laminated under the same conditions. When the CFRTP sheet was three formings, the tensile strength of 494 MPa could be obtained. CFRTS are prepared by laminating the epoxy prepregs at 140°C with the compressive pressure of 0.5 MPa for 30 min. CFRTP sheet has the lower tensile strength than CFRTS sheet by 223 MPa, but the flexural strength was higher by 61 MPa and by 1.0 J/cm2 for Charpy impact test.

Carbon fiber-reinforced plastic (CFRP), which is a light and composite material, has a higher specific strength and stiffness than metal materials. However, owing to its low elongation, it is vulnerable to local impacts such as collision. Therefore, hybrid composite materials that can overcome the disadvantages of homogeneous materials by bonding CFRP and metal materials are increasingly popular. In this study, a physical surface treatment sandblast process was applied on a high tensile steel plate (CR980) manufactured by cold rolling to form another surface condition, and the bonding strength with CFRP was measured. In addition, spring-back due to the manufacturing process of the CFRP and CR980 hybrid composite material bonded with different surface roughness was observed. The bonding strength and the spring-back angle of the CFRP/CR980 hybrid composite material tended to increase with the increase in the surface roughness.

The optimum gating system for manufacturing turbine housing is designed in this study, and a heater as heat source is provided to the riser, attempting to reduce its size. In the case where the runner is divided into two branches, a symmetrical gating system is adopted so that the two products could be produced in one process. Furthermore, cross-sectional shapes of the sprue, runner, and gate are designed by setting the sprue:runner:gate ratio at 1:0.9:0.6. A casting analysis is then conducted to investigate the effects of shape of the riser, sleeve material, temperature of the heater, and provision of insulation material at the top of the riser. The conditions obtained from the analysis are applied to the experiment. Hot spot defects calculated by casting simulation are reduced when sand sleeve material, straight type riser, open top sleeve, and more than 600°C of heater temperature are used. It is possible to produce a casting with almost no surface defects by adopting a riser with a size of 10–20 mm and a heater of 600°C–700°C. A casting recovery rate of 80% is achieved and, regarding mechanical properties, its tensile strength is 534 MPa, its elongation rate is 9%, and its Brinell hardness is 170 HB.

This study involves performing direct and indirect hot press forming on ultra-high-strength steel (UHSS) boron steel sheets to determine formability. The indirect hot press process is performed as a cold deep drawing process, while the direct hot press process is performed as a hot deep drawing process. The initial blank temperature and the blank holding force are set as parameters to evaluate the performance of the direct and indirect deep drawing processes. The values of punch load and forming depth curve were obtained in the experiment. In addition, the hardness and microstructure of the boron steel sheets are examined to evaluate the mechanical properties of the material. The forming depth, maximum punch load, thickness, and thinning rate according to blank holding force were examined. The result shows that a larger blank holding force has a more significant effect on the variation of the thickness and thinning rate of the samples during the drawing process. Furthermore, the thinning rate of the deep drawing part in with and without fracture boundary was respectively examined.

This study is dedicated to overcome the poor formability problem of thin stainless steel sheets used as bipolar plates of proton exchange membrane fuel cells (PEMFCs). Different parameters such as the sheet type (SUS 304 and SUS 316), sheet direction (rolling and transverse), load condition (static and dynamic), and heat treatment can be varied to adjust the channel depth in the bipolar plate. The channel of a bipolar plate is formed using static and dynamic loads and along different directions (rolling and transverse). The depth of the formed channel is about 0.18 mm, and the difference in channel depth from static and dynamic loads is small regardless of the sheet direction. The forming limitations due to the stainless steel hardening during the process can be solved through heat treatment. The channel of a bipolar plate formed with a heat-treated sheet is more than twice as deep as the one formed from a sheet without heat treatment and is more uniform. The formed channel is deeper with a dynamic load than a static load and in the transverse to rolling direction than in the rolling direction of sheet.

Hybrid composites material was fabricated by stacking carbon fiber reinforced plastic on CR340 (cold rolled) steel sheet to increase the specific strength and specific stiffness, compared to thick high strength steel or dual-phase steels. Among mechanical properties of hybrid composites, spring-back of CFRP/Steel composites is one of the most important issues. V-bending was conducted to measure spring-back of CFRP/CR340 composites according to process parameters such as punch pressure, punch radius, CFRP layers and steel’s rolling direction. In this study, effect of these parameters on spring-back of CFRP/CR340 composites was investigated and discussed.

Spheroidizing annealing cycle was applied on the SNCM 220, which is an alloy steel for mechanical structures to improve warm forgeability. Heat treatment was given on the specimen, filled with Ar gas to prevent oxidization. Spheroidizing microstructure was examined in the specimens received the intercritical cycle, measured the largest elongation rate during mechanical properties evaluation. And, carbides cracked more as retaining time at the intercritical annealing was extended. Formability of the SNCM 220 was investigated by changing temperature and compression speed at high temperature under heat treatment condition, set as per the preliminary experiment result. As compression speed was increased, the stress on the specimen was also increased, while the stress was decreased as the temperature was increased. Flow curve by treating the specimen at 600°C - 900°C was also drawn. From the zone at 900°C, pinning appeared due to precipitation hardening. Structure of the specimen was examined, which was changed by deformation speed of flow stress and temperature, confirmed with the compression experiment. The highest hardening value was achieved at 900°C. However, it would be the most beneficial to carry out a forming at 600°C with deformation speed at 0.01 mm/s, at the economic as well as mechanical view point.

Thin plates with a thickness of 1.2 mm are fabricated from semi-solid A356 alloy through an indirect rheo-casting process both with and without an electromagnetic stirrer (EMS). The thin die cavity for forming is designed with the fluid analysis software MAGMA. A semi-solid slurry with a solid fraction of 40% is prepared and then injected into the die of a 200 t hydraulic press. Forming tests are performed on the thin plates at two punch speeds (30 and 300 mm/s) and two cavity friction conditions (mf = 0.4 and mf = 0.9). The formability, mechanical properties, and microstructure are then evaluated. The semi-solid slurry obtained with an EMS contains fine and globular solid particles; the semi-solid slurry produced without an EMS reveals rosette particles and coarser globular solid particles. At high friction (mf = 0.9), the cavity is mainly filled with the liquid phase. At a higher punch rate, the thin plates show better formability and a microstructure with fine and even solid particles. The tensile strength and elongation of the thin plate formed with a punch speed of 300 mm/s in the cavity with graphite lubrication (mf = 0.9) are 216 MPa and 10%, respectively. These values are 57 MPa and 5.5% higher, respectively, than those of the thin plate formed at a punch speed of 30 mm/s.

The aim of this study is to fabricate SUS304 bipolar plates through a rubber forming process and investigate the characteristics of these bipolar plates with TiN, CrN and CrN/TiN coating layers. SUS304 bipolar plates with a channel depth of more than 0.3 mm are manufactured through a rubber forming process. TiN, CrN and CrN/TiN coating layers are deposited directly on the surface of the bipolar plates. The surface hardness and roughness of the TiN, CrN and CrN/TiN coating layers on the SUS304 bipolar plates are estimated using a nanoindenter and an atomic force microscope (AFM), respectively. The interfacial contact resistance (ICR) is measured on three samples and is found to be 10.2, 26.4 and 23.5 mΩ cm 2 for TiN, CrN and CrN/TiN coating layers, respectively, under a 140 N cm −2 compaction force. The corrosion properties are investigated in a proton exchange membrane fuel cell (PEMFC). The TiN coating layer showed a higher corrosion potential and lower corrosion current density than the two other coating layers in both anode and cathode environments. The current densities of a single cell with TiN/SUS304, CrN/SUS304 and CrN/TiN/SUS304 bipolar plates are 0.670, 0.623 and 0.656 mA cm −2 , respectively.

In this study, a fuel cell bipolar plate is formed using indirect squeeze casting which uses liquid materials and stamping process which uses solid state materials. The formability of these two types of processes is discussed. The shapes of die cavity in the indirect squeeze casting and that in the stamping are same. The materials filling rate during indirect squeeze casting was increased as punch pressure that pushes molten aluminum into cavity of die is increased. A breakage occurs when load of upper die which presses aluminum plate 0.1mm thick is at 20 kN. When load of upper die is at 15 kN, the maximum channel depth is achieved. Though precise channel shape can be achieved by the indirect squeeze casting, the thickness of bipolar plate is larger by around three times than that formed by stamping. An irregular-shaped channel is obtained in the bipolar plate formed by stamping due to problems of wrinkle, springback, and flatness. The current density of unit cell with casted aluminum bipolar plate with TiN layer and stamped aluminum bipolar plate are 421 and 410 mA cm−2 at 0.6 V, respectively.

A full annealing cycle and two types of spheroidizing annealing cycle were implemented to improve poor forgeability for alloy-steel SNCM220 which is used for mechanical structures. Initial micro-structure was normalized ferrite+pearlite and all the heat treatment was carried out with tube furnace filled with Ar gas to prevent oxidization. Critical temperature was investigated through a thermodynamics calculation of Thermo-calc soft. Among three types of heat treatment cycles, spheroidized structure was observed from the alloy-steel sample treated with intercritical annealing with the largest elongation rate while evaluating mechanical properties. Also, the effect of intercritical annealing holding time on the alloy-steel was investigated. The results showed that as holding time was increased, carbide was more decomposed. Further, hardness test results showed that hardness value did not change significantly between 5–10 hours of intercritical annealing cycle. When intercritical annealing cycle was repeated to investigate the effect of repeated frequency heat treatment cycle, the best micro-structure and mechanical property were achieved by repeating the intercritical annealing cycles three times.

Because of the growing importance of passenger safety and fuel efficiency in the auto industry, efforts continue to apply higherstrength and lighter-weight steel to automotive parts. Because hot press forming (HPF) can potentially satisfy both the strength and weight requirements, the number of HPF parts has increased in recent years. Although bare or Al–Si-coated steel has been widely used for HPF, steel companies are trying to develop Zn-coated press-hardened steel because of its advantage of cathodic corrosion protection. However, there are hurdles that must be overcome to use Zn-coated steel in a direct HPF process, including liquid metal embrittlement, cracks, and micro-cracks. In this study, a direct HPF process was implemented through deep drawing, with experiment variables that included the heating temperature (850°C, 900°C, 950°C) and heating time (3, 5, 10 min). After the experiment, the Zncoating surface, layer, and transition of the specimen were investigated. In addition, the optimum conditions for using Zn-coated boron steel in direct HPF were studied. The Al–Si coating surface and layer were also observed under the experimental conditions for the direct hot deep drawing.

In casting steel for offshore construction, integral casted structures are superior to welded structures in terms of preventing fatigue cracks in the stress raisers. In this study, mold design and casting analysis were conducted for integral carrier housing. Casting simulation was used for predicting molten metal flow and solidification during carrier housing casting, as well as the hot spots and porosity of the designed runner, risers, riser laggings, and the chiller. These predictions were used for deriving the final carrier housing casting plan, and a prototype was fabricated accordingly. A chemical composition analysis was conducted using a specimen sampled from a section of the prototype; the analytically obtained chemical composition agreed with the chemical composition of the existing carrier housing. Tensile and Charpy impact tests were conducted for determining the mechanical material properties. Carrier housing product after normalizing (920 degrees C/4.5 h, air-cooling) has 371 MPa of yield strength, 582 MPa of tensile strength, 33.4% of elongation as well as 64 J (0 degrees C) of impact energy.

For carbon nanotube (CNT)/Al composites, compaction forming is conducted for densification processing, and then sintering and secondary processes are conducted. This general process has problems such as the complexity of the processing procedures, and high manufacturing costs. This study presents a hot extrusion process without sintering for fabrication of CNTs/Al6061 composites. Before hot extrusion, preforms are fabricated by the compaction process for the mixture of Al6061 power and CNTs. Several hot extrusion experiments were performed under six types of CNT content; three extrusion ratios and three extrusion temperatures. The formability increased as the extrusion temperature increased for low CNT content. At 620 °C, the forming of all materials except for 10 vol % CNTs/Al6061 was possible at extrusion ratios R = 4, R = 8, and R = 16. As CNT content increases, extrusion pressure almost linearly increases. As the extrusion ratio increases, the extrusion pressure increases. The amount of CNT content increases as Vickers hardness increases. The Vicker’s hardness of 1 vol % CNTs/Al6061 billet is about 100 HV while that of 10 vol % CNTs/Al6061 billet is about 230 HV. There are no significant differences of compression stress according to extrusion ratio as observed in terms of pure Al6061, 1 vol % CNT/Al6061, and 3 vol % CNTs/Al6061.

Recently, vehicle parts such as center pillars and impact beams used in automobiles have been requiring materials that satisfy both high strength and impact absorption. Therefore, in this study, the applicability of the forming process of CR340 (cold rolled steel sheet)/CFRP Hybrid Composites which are a bonded material of cold rolled steel sheet having excellent formability and carbon fiber prepreg having high strength and high collision absorption in the vehicle parts was investigated. Hybrid composites are fabricated by stacking carbon fiber reinforced plastic (CFRP) prepreg on a cold rolled steel sheet (CR340) with Zn coating. Bonding materials were used at the interface between the CFRP prepreg and steel sheet. In addition, in the case of CR340/CFRP Hybrid composites which are made by bonding CFRP prepreg to the surface of press-formed CR340 material, it is impossible to manufacture complicated shapes due to an interfacial bonding separation phenomenon between the reinforcement and steel sheet. An adhesive agent developed by this research team was applied on the cold rolled sheet between CFRP and CR340 materials to enable the blank production of CR340/CFRP Hybrid composites. The heating time and temperature required for bending test were set similar to the curing curve of the CFRP prepreg. The surface roughness of steel materials is important in terms of their tensile strength and bending strength In this study, the steel sheet used was cold rolled 340 with Zn coating without surface roughness treatment for application to mass production in industry. This study investigates the properties of a CFRP/metal hybrid composite material. The hybrid was fabricated after spreading a developed binder on high-strength steel sheets (CR980) prepared by cold rolling and pressing. During the preparation of the CR980/CFRP hybrid composite, and its mechanical characteristics were investigated through bending, tensile, and lap shear adhesion test experiments.

In the conventional sand casting process, the size of the riser is made larger than that of the cavity (product part) in order for the molten metal in the riser to solidify at a later stage than the molten metal in the cavity. In this study, a continuous heating method is developed and applied to the riser, using a cylindrical heater, to minimize the size of the riser. A mold having four cavities is designed for casting turbine housings. The height and diameter of the riser are chosen to be 80 mm and 20 mm, respectively. Solidification analysis results, using the analysis program MAGMA soft for casting simulation, showed that when the heater is implemented, the riser is the last to solidify. However, without the heater, the riser solidifies before the cavity, thus causing the riser to function improperly. Moreover, misruns are generated in the casted product if the heater is not implemented, as opposed to the case of a solid product without any defects, with the heater attached in the riser.

This study aims at a mold design based on the casting simulation and mold structural simulation in order to manufacture automotive clutch housing aluminum parts in a high-pressure die casting process. For melt to flow into the mold and fill to the product section evenly, a gating system with five gates was designed. MAGMAsoft, a casting simulation program, was used to predict or prevent the possibility of casting defects that may occur in the filling process and solidification process. The way to select proper casting devices for the clutch housing product is also presented. A structural simulation of the mold base was conducted by means of ANSYS Workbench to predict possible damage to the vulnerable part of the mold right from the step of mold design. In the actual shot test, five clutch housing products in total were manufactured. All of them were fully filled and involved no defect on the surface. The spot of shrinkage porosity predicted in the casting simulation and the spot of actual occurrence were not exactly the same but quite close. The degree of hardness of these products was about 84 HV regardless of location.

In this paper, aluminium-based (Al6061) composites with 1, 3, 5, 7, and 10 vol % of multi-walled carbon nanotubes (MWCNTs) are investigated. The composites are fabricated by high-energy ball milling, cold-compacting at room temperature under compacting pressures of 400–1600 MPa, and sintering at 620 °C in an argon gas atmosphere. Thereafter, the hardness and microstructure of MWCNTs/Al6061 composites are examined. Further, to improve the relative density and hardness level of the complex material, open-die forging is performed after cold-compacting under 1 GPa pressure at room temperature and sintering at 620 °C. The open-die forging parameters include 1, 3, 5, 7, and 10 vol % MWCNTs/Al6061, and Al6061. The experimental results show that the mechanical properties of the composites are significantly superior to that of the Al6061 alloy after undergoing cold-compacting, sintering, and open-die forging.