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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.

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.

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.

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.

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.

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.

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.

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 this study, a dynamic load (square wave) is applied to bipolar plates in order to reduce forming defects from the stamping process. Four round (R) sizes of die (R 0.05, 0.1, 0.2, 0.3 mm) are applied to edges that ran from the channel to the rib of the stamping die. Fuel cell performance tests are carried out to analyse the depth and shape of bipolar plate channels formed according to the load conditions, and the effect of the die size on the fuel cell performance is evaluated. The depth of the bipolar plate channel increase with the round size of die regardless of the load type. The shape of the channel formed with a die of R 0.05 mm is trapezoidal, while that formed with a die of R 0.3 mm is triangular. Triangular channels have a higher current density than trapezoidal channels. A higher current density can be obtained with a square load than with a conventional straight load because the former produces a deeper and more uniform bipolar plate channel. The current density of a bipolar plate with a triangular channel formed by a square load with a die of R 0.3 mm is 531 mA cm−2. After TiN coating, the current density is 784 mA cm−2, which is about 58% of that of a graphite bipolar plate.

Metallic bipolar plates for polymer exchange membrane (PEM) fuel cells are currently manufactured by stamping of thin sheets. However, there are dimensional and shape errors of microchannels because of forming limitation such as spring back of thin sheets after stamping. On the other hand, stamping process is limited to commercially available sheet alloys, which restricts the development of a high corrosion resistant substrate aluminum alloy. Here, thixoforming (a commercial semisolid route) that is applicable to a wide range of aluminum alloys is proposed for net-shape micromanufacturing of aluminum bipolar plates with high dimensional stability. High corrosion resistance cast A356 (Cu-free) and wrought AA7075 (∼2% Cu) aluminum billets are used for this study. Initial billets are heated at different semisolid temperatures. Subsequently, the semisolid slurries are injected into the die cavity. A356 and AA7075 aluminum bipolar plates are successfully fabricated by thixoforming with very small deviation of 0.7% and 1.5% from the nominal value of 0.300 mm in the microchannel depth, respectively. A multilayer coating of TiN/CrN is deposited on the surface of thixoformed bipolar plates through a commercially available magnetron sputtering technique. Electrochemical corrosion tests show that coated-thixoformed A356 (Cu-free) bipolar plates have significantly lower corrosion current densities than coated-thixoformed AA7075 (∼2% Cu) bipolar plates. This seems to be due to the deleterious effect of Cu alloying element on the corrosion resistance of aluminum alloys that clearly confirms the importance of substrate material development for corrosive PEM fuel cell environment. It is suggested that specific high corrosion resistance aluminum alloy for PEM fuel cell application can be simply designed and then thixoforming can be efficiently and cost effectively employed to fabricate net-shape aluminum bipolar plates.

A titanium alloy is selected as an ideal material for a fuel-cell bipolar plate because it has a low density and, like aluminium, exhibits excellent corrosion resistance due to an insulating oxide film. Microchannelled bipolar plates are fabricated using a 25-ton material-testing machine by varying the parameters of the static and dynamic loads (type of load wave, punch load, number of cycles) and the die curvature in order to evaluate the formability. The bipolar plate formed by dynamic-load stamping (square wave of 0.5 Hz, 32 load cycles, punch load of 90 kN) with die curvature of 0.3 mm resulted in 13.0% deeper channels compared to static-load stamping of 90 kN. Moreover, in the case of 0.1 mm die curvature, the bipolar plate formed by square-wave dynamic-load stamping had 22.7% deeper channels, compared to static-load stamping. Dynamic-load stamping with die curvatures of 0.1 and 0.3 mm shows a channel depth of 0.251 and 0.353 mm, respectively. Compared to die curvature of 0.1 mm, 0.3 mm die curvature resulted in channels that are deeper by 28.9%.

The global price of oil, which is both finite and limited in quantity, has been rising steadily because of the increasing requirements for energy in both developing and developed countries. Furthermore, regulations have been strengthened across all industries to address global warming. Many studies of hull resistance, propulsion and operation of ships have been performed to reduce fuel consumption and emissions. This study examined the design parameters of the propeller boss cap fin (PBCF) and hub cap for 6,000TEU container ships to improve the propulsion efficiency. The design parameters of PBCF have been selected based on the geometrical shape. Computational fluid dynamics (CFD) analysis with a propeller open water (POW) test was performed to check the validity of CFD analysis. The design of experiment (DOE) case was selected as a full factorial design, and the experiment was analyzed by POW and CFD analysis. Analysis of variance (ANOVA) was performed to determine the correlation among design parameters. Four design alternatives of PBCF were selected from the DOE. The shape of a propeller hub cap was selected as a divergent shape, and the divergent angle was determined by the DOE. Four design alternatives of PBCF were attached to the divergent hub cap, and the POW was estimated by CFD. As a result, the divergent hub cap with PBCF has a negative effect on the POW, which is induced by an increase in torque coefficient. A POW test and cavitation test were performed with a divergent hub cap with PBCF to verify the CFD result. The POW test result showed that the open water efficiency was increased approximately 2% with a divergent hub cap compared to a normal cap. The POW test result was similar to the CFD result, and the divergent hub cap with the PBCF models showed lower open water efficiency. This was attributed to an increase in the torque coefficient just like the CFD results. A cavitation test was performed using the 2 models selected. The test result showed that the hub vortex is increased downstream of the propeller.

Aluminum bipolar plates that can replace graphite bipolar plates for PEM fuel cells are made by applying a semi-solid forging process. A semi-solid slurry is made using electromagnetic stirring (EMS), and the resulting slurry is injected into a forging die attached to a 200 ton hydraulic press. The slurry is then compressed with a punch, flowed into a die cavity, and solidified into the bipolar plate form. A356 (cast Al alloy), A6061 (wrought Al alloy), and A1100 (pure Al) are used to make the plates. Titanium nitride (TiN) coating is deposited on the aluminum bipolar plates. An atomic force microscope (AFM) is used to measure the surface roughness of the plates. TiN coated A356 and A1100 plates have a surface roughness of Ra

Rheoforming is a near net-shape manufacturing technology for fabricating components from light alloys in their semisolid states with improved mechanical properties. In this work, a feasibility study on the fabrication of Silafont 36 aluminum thin plates via rheoforming was conducted. The thin plates were fabricated under different experimental conditions, such as different solid fractions and punch pressures. Electromagnetic stirring was used to prepare a semisolid slurry of Silafont 36 aluminum alloy. Subsequently, the slurry was transferred to die sleeve and injected into the die cavity of the thin plate. The thin plates were successfully fabricated under the optimal conditions of 50% solid fraction and a rheoforming pressure of 130 MPa.

Thin plates (150 × 150 × 1.2mm) with embedded corrugation are fabricated using semisolid forming. The die cavity used in the forming is designed using fluid analysis. A semisolid slurry is prepared by a cooling with EMS and heating process. The slurry is then injected into a forging die attached to a 200 tonf hydraulic press. Subsequently, the slurry is compressed by a punch, flown into the die cavity, and then solidified. A356 (cast Al alloy) and AA6061, AA2024, and AA7075 (wrought Al alloys) are used.

We propose the possibility of fabricating A6061 thin plates using the rheology forging process. Electromagnetic stirring (EMS) is used to fabricate a semi-solid slurry. A thin plate is formed by injecting the slurry into the forging die. When the punch speed used to compress the slurry is low, turbulent flow occurs. When the punch speed is high, laminar flow occurs, and the solid and liquid phases move simultaneously. For a pressure of 150 MPa or below, incomplete filling behavior and cracks occur. For a pressure of 200 MPa or above, a durable formed product can be obtained. However, the differences between the mechanical properties according to the application of EMS and pressure are slight. The microstructure of the slurry without EMS has an unclear distinction between the liquid phase and solid phase. However, the microstructure of the thin plates formed by using this slurry has a clear distinction between the liquid and solid with respect to the spheroid shapes. The tensile strength and elongation for a thin plate formed with a punch speed of 300 mm/s and pressure of 250 MPa with EMS slurry are 169 MPa and 11.0 pct, respectively. After T6 heat treatment, the tensile strength improves to 305 MPa.

In this study, A356 aluminum billets in different extruded states are used as feedstock for the thixoforming. The extrusion billets were fabricated by a hot extrusion process through a flat-face and a curved die. After the induction reheating of the extrusion billets into a semisolid state, the microstructural evolution was thoroughly investigated. For the extrusion alloy by the flat-face die, there was a large variation in the average grain size (20 %) and the mean roundness (17 %) of equiaxed α-Al grains. This, together with evidence of elongated grains in the interior regions of the billet, indicated that a noticeably nonuniform globular microstructure had been obtained. In contrast, for the extrusion alloy through the curved die, the obtained globular microstructure was more uniform. There were slight variations of 5 % and 7 % in the average grain size and the mean roundness, respectively. By using the extrusion billets, some parts fabricated via the thixoforming process those underwent T6 heat treatment. The tensile test results for the fabricated parts showed that when the extrusion billet through the conventional flat-face die was used as the feedstock, there was a large scattering in the tensile properties throughout the part. In contrast, when the extruded billet through the curved die was used as the feedstock, limited variation was observed in the tensile properties.

Cast steels with carbon contents of approximately 0.05%, 0.1%, and 0.2% (low-carbon steels) were processed. The investigated steels were first cast. Fully lath martensite was obtained after austenitization and water quenching of the cast steels. The mechanical properties of ∼0.05% carbon steel did not significantly change after tempering at 500°C, 540°C, and 580°C. The strength of ∼0.1% carbon content steel decreased after tempering for 2 h to 3 h at 580°C, and then stabilized at longer tempering times of 6 h. The ductility remained almost constant through the processes. The Charpy impact energy increased when the tempering time was increased from 2 h to 4 h, but decreased remarkably after tempering for 6 h. By increasing the tempering temperature from 450°C to 550°C, the ductility of the ∼0.2% carbon content steel increased, followed by a drop at 600°C. The strength of this steel was the highest at 450°C, but decreased and stabilized at tempering temperatures of 500°C to 600°C. The Charpy impact energy i...

In this study, we investigated the effects of TiN/Ti and TiO2/Ti double layer coatings, with a metal buffer layer, on the corrosion resistance, and electrical properties of Al1050 substrates for using them as bipolar plates in PEMFCs. TiN/Ti and TiO2/Ti double layers were deposited using the electromagnetic-field-superpositioned DC and RF magnetron sputtering method. The surface resistivity and contact resistance of the specimens were measured using the van der Pauw method and a previously reported interfacial contact resistance (ICR) measurement method, respectively. Further, the corrosion resistance of the specimens was characterized using electrochemical tests such as potentiodynamic and potentiostatic polarization tests. The results obtained in this study indicated that coating of the Al1050 substrates significantly increased the corrosion resistance of bipolar plates in the operating environment of a fuel cell when compared to uncoated substrates. In particular, the substrate coated with a TiN/Ti double layer exhibited the best performance: its corrosion current density was 30 times lower than that of an uncoated substrate under anodic conditions. Further, the Al1050 bipolar plate coated with a TiN/Ti double layer showed performance enhancement over an uncoated bipolar plate in an actual fuel cell test.

Currently, the automobile industry is focusing all its attention to creating high-strength, ultra low-weight car bodies. Many techniques can be used to decrease the thickness of a steel plate in a car body but increase the strength. Among these, the hot stamping process makes use of boron steel to produce ultra high-strength components. On the contrary, this process has a low elongation that causes a decrease in collision absorptiveness. Therefore, this study examined the material and weldability of components with high collision absorptiveness using boron steel plates welded at different thicknesses, where the thinner steel sheet can absorb the collision, whereas the thicker steel sheet can endure it. This study was conducted using boron steel coated with either Al–Si or Zn. The results showed that satisfactory tensile strength and elongation could be obtained when both sides of the coating layer were removed by the laser. The hardness in the welded area of Zn-coated boron steel was greater than 450 Hv, even when the specimen was welded without laser ablation of the coating layer, but the coating layer peeled off when heated for 5 min at 950 °C.

Brackets in ships and offshore structures are added structures that can endure stress concentrations. In this study, a concurrent engineering solution was proposed, and a high strength low carbon cast steel alloy applicable to offshore structures was designed and developed. The yield strength and ultimate tensile strength of the designed steel were 480 and 600 MPa, respectively. The carbon equivalent of the steel was 0.446 with a weld crack susceptibility index of 0.219. The optimal structural design of the brackets for offshore structures was evaluated using ANSYS commercial software. The possibility of replacing an assembly of conventional built-up brackets with a single casting bulb bracket was verified. The casting process was simulated using MAGMAsoft commercial software, and a casting fabrication process was designed. For the proposed bulb bracket, it was possible to reduce the size and weight by approximately 30% and 50%, respectively, compared to the conventional type of bracket.

A thin plate like a bipolar plate for a proton exchange membrane fuel cell is one of the core parts for improving the power density in a fuel cell. Stainless steel has excellent characteristics in terms of electrical resistivity, density, and thermal conductivity. Furthermore, stainless steel, instead of graphite, is used as a bipolar plate because it is cheaper and easier to machine. Therefore, in this study, a stainless steel alloy is selected as the ideal material for a bipolar plate. In this article, the results of feasibility experiments are presented; these experiments are performed with the aim of developing fuel cells using stainless steel bipolar plates with multiple channels. In this investigation, a dynamic load was applied, and the formability of microchannels was estimated with different punch pressures and die roundness, using a thin sheet metal of SUS304 with thicknesses of 0.3 and 0.1 mm. In the case of the die roundness of 0.1 mm, the formability is optimized with a sine wave dynamic load that has 90 kN of maximum pressure and five cycles of punch movement. The experimental results demonstrate the feasibility of the proposed manufacturing technique for fabricating bipolar plates.

Thixoforming investigations have been developed primarily for the manufacturing of bulk components, and the current knowledge is very limited with respect to the fabrication of thin cross sections of alloys. We studied the effectiveness of thixoforming process for the fabrication of A356 aluminum alloy bipolar plates with microchannels on both sides. Feedstock semisolid slurries, with different solid contents of ~55, 50, and 45 pct, were prepared at 858 K, 863 K, and 868 K (585 °C, 590 °C, and 595 °C), respectively, and were used to thixoform 1.20-mm-thick bipolar thin plates. The microstructures of the thixoformed thin plates consisted of (i) large primary α-Al globular grains, (ii) a quenched liquid phase, and (iii) fine secondary α-Al particles. The fraction and size of the primary α-Al globular grains decreased, and the primary α-Al globular grains became more spherical with the increasing thixoforming temperature. It seemed that these changes in the microstructural features led to the reduction in the agglomeration and interaction among the primary α-Al globular grains surrounded by the liquid matrix during thixoforming. This enabled the semisolid slurry to effectively flow and fill in the sharp corners (such as the microchannels) of the die cavity at higher thixoforming temperatures. The thin plates thixoformed at 868 K (595 °C), consequently, exhibited the highest dimensional stability and the fewest internal defects. The liquid matrix surrounding the primary α-Al grains solidified inside the die cavity after thixoforming. Either the liquid phase was instantly quenched or fine secondary α-Al particles were formed inside the die cavity. The fraction and size of the latter increased with increasing thixoforming temperature. The surface hardness of the thixoformed plates was measured, and the hardness values were correlated with the microstructural features of the thixoformed plates.

Due to the demand for reduced weight, improved safety, and crashworthiness in vehicles, the need to manufacture automobile structural components from ultrahigh-strength steels is apparent. Indirect hot press forming process is a process developed from hot press forming because of steel’s high resistance to trimming after hot press forming. From the researches about indirect hot press forming, considerable springback in the indirect hot press forming is accrued after preforming. After this trimming, the material is calibrated by hot press forming process. In this article, the springback is accrued at preforming and the final shape of u-bending with varying cooling rates is predicted using ABAQUS software. To find the characteristics and effects of temperature changes during the hot press forming process, high-temperature tensile test with simultaneous cooling is conducted and the results are applied to the analysis. The shape deviations after the indirect hot press forming process are compared according to cooling rate conditions.

The effects of rheoforming parameters such as the rheoforming temperature and pressure on the tensile properties of H-shaped components were examined. An H-shaped component is useful for practical investigation into the influence of different wall thicknesses on the microstructural and mechanical properties. A simulation study on the effect of forming pressure on the die filling was conducted using the DEFORM-3D package, and the results were compared with that obtained using the actual rheoforming. The semisolid slurries were prepared by employing the electromagnetic stirring (EMS) technique. The components were rheoformed at different forming conditions and their tensile properties in the center and side positions were evaluated and linked to the corresponding microstructure. The tensile properties remained approximately constant when the rheoforming temperature was increased from 580 °C to 590 °C, but was followed by a substantial reduction at 600 °C. Moreover, the tensile properties in the center and side positions were distinct. Increasing the rheoforming pressure from 200 MPa to 250 MPa had a harmful effect on the elongation values, whereas the effect on the ultimate tensile strength values was limited. This trend could be linked to the increase in prevalence of internal defects such as the liquid segregation.

The automobile industry has recently produced vehicle bodies using advanced high strength steel with the aim of reducing carbon emissions and developing green products. Among various processes for body manufacturing, hot stamping has been gained a remarkable consideration. In this study boron sheet steel with the initial tensile strength of 600 MPa and 22% elongation was used. The sheets were heated at 950°C for 5 min before die quenching through hot stamp forming process. After hot stamping, the tensile strength of the boron sheet steel improved and reached 1.5 GPa while the elongation markedly deceased to 7%. A very low elongation value, is not favourable in safety of automobiles since it deteriorates the shock absorption capacity upon a car accident. In order to overcome this problem, it is suggested to weld boron sheet steel with different thicknesses and make an assembly of sheets. This assembly acts as a buttress in which the lower sheet absorbs shocks. Furthermore, Al-Si coating layer has a deleterious effect on the mechanical properties of weld joints. Thus the effect of laser ablation of the coating has been thoroughly studied and discussed.

Recently, the demand for energy is growing at a very high rate all over the world. The fossil fuels eventually lead to the foreseeable depletion of limited fossil energy resources. Hydrogen is considered a promising candidate to remedy the depletion of fossil fuels. The bipolar plate is the second most important component of a proton exchange membrance (PEM) fuel cell stack after the membrance electrode assembly (MEA). Its primary roles are to supply reactant gases to the fuel cell electrodes and provide electrical connection between adjacent cells in the stack while removing product water from the cell and transferring away the heat of reaction. Historically, machined graphite had been chosen as a good compromise between all of these requirements, but alternatives are emerging. New materials are light metals. In this study, rubber pad forming process was employed as the manufacturing method for metallic bipolar plates. The rubber pad and the sheet metal plate were pressed together by the punch, and the repulsive force of the deformed rubber is loaded at the plate, and can contribute to improving formability. And then, its surface was coated with TiN. After coating process, the performance characteristics of single stack in the condition of PEMFC using the metal bipolar plate have been investigated.

Recently, the demand for energy is growing at a very high rate all over the world. The fossil fuels eventually lead to the foreseeable depletion of limited fossil energy resources. Hydrogen is considered a promising candidate to remedy the depletion of fossil fuels. The bipolar plate is the second most important component of a proton exchange membrance (PEM) fuel cell stack after the membrance electrode assembly (MEA). Its primary roles are to supply reactant gases to the fuel cell electrodes and provide electrical connection between adjacent cells in the stack while removing product water from the cell and transferring away the heat of reaction. Historically, machined graphite had been chosen as a good compromise between all of these requirements, but alternatives are emerging. New materials are light metals. In this study, rubber pad forming process was employed as the manufacturing method for metallic bipolar plates. The rubber pad and the sheet metal plate were pressed together by the punch, and the repulsive force of the deformed rubber is loaded at the plate, and can contribute to improving formability. And then, its surface was coated with TiN. After coating process, the performance characteristics of single stack in the condition of PEMFC using the metal bipolar plate have been investigated.

The utilization of high-strength steel for automotive structural parts has increased since the oil crisis in the 1970s owing to its high strength and potential for weight reduction. Because of the limited formability of high-strength steels, automotive components are increasingly produced through hot press forming. In some instances, high-strength steel sheets are coated with an Al–Si layer in order to prevent scaling of components during hot press forming, and this can increase their reliability with a view to the dimensional accuracy and stress distribution when they are in service. In this contribution, the coating degradation mechanisms of Al–Si-coated boron steel after the hot bending process are reported. The issues related to coating degradation during hot press forming are critically reviewed at different positions on a part that was subject to hot bending. In addition, the hardness and friction coefficient were tested by a nano-indenter at various positions. The relationship between the experimental parameters and coating layer properties is also reported. It is concluded that the bending deformation affected the coating layer behavior the most.

HSS (high-strength steel) is now commonly employed in various automobile structural reinforcements and crash protection systems. Although HSS has high strength, it has various disadvantages such as springback at room temperature and cracks; also, it is difficult to form HSS into complicated structures. The HPF process is a forming method that offers various advantages such as superior mechanical properties, good formability, and very small springback. However, relatively large-sized parts such as center pillars exhibit poor formability in the HPF process due to the limited material flow and thickness reduction in the process. Also, reduction in thickness leads to cracks. One of the reasons is the relatively high friction between the sheet and the die. In this study, in order to obtain the optimal conditions in the HPF process for center pillars, various process parameters were studied and analyzed by using the sheet forming software, J-STAMP. The effects of various parameters such as the heating temperature, blank holding force, punch speed, clearance (upper and lower dies), distance block, blank shape, and forming type were analyzed and compared.

In this paper, we present the results of our studies on optimal die design towards development of a vacuum die casting process to fabricate fuel cell bipolar plate with micro-channel array. Cavity and overflow shape is designed by computational filling analysis of MAGMA soft. Optimal die design consists of seven overflows at the end of cavity and three overflows at each side wall of cavity. The molten metal that passed the gate and reached the side wall flowed into the side overflow, no turbulent flow occurred, and the filling behavior and velocity distribution were uniform. In addition, partially solidified molten metal passing through the channel was perfectly eliminated by overflow without back-flow. When vacuum pressure, injection speed of low and high region was 300 mbar, 0.3 m/s and 2.5 m/s respectively with Silafont 36 die casting alloy, sound sample without casting defects was obtained. The experimental results are nearly consistent with simulation results.

In this study, a low carbon cast steel (0.1% C) alloy designed for offshore structures, and the mechanical properties of the alloy under different heat treatment cycles have been evaluated. The effect of austenitizing time on the austenite grain size was studied. Subsequently, the quenched samples with minimum austenite grain size subjected to tempering experiments at different tempering temperatures (450 °C, 550 °C, and 650 °C) and cooling rates (0.23, 36, and 50 °C/s) from the temperature. The results showed that by increasing the austenitizing time, the austenite grain size initially decreased and reached the minimum value with ASTM number of 6.35 and then followed by an increase. When the tempering temperature increased, yield and tensile strengths decreased, whereas the ductility properties improved. In addition, yield and tensile strengths were not affected by cooling rate from tempering temperature, whereas the ductility properties were slightly affected. The increase in tempering temperature significantly led to improvement in the toughness to fracture of the alloy. The effect of cooling rate on impact energy for the samples tempered at 450 °C and 550 °C was negligible. By the contrast, impact energy for the samples tempered at 650 °C was markedly affected by cooling rate, in which the highest value was achieved for a cooling rate of 50 °C/s.

Recrystallization and remelting (RAP), a promising route for thixoforming process, was used to process three aluminum alloys, AA2024, AA6061, and A356, under experimental conditions designed to yield various solid fractions (liquid fractions) within the microstructure. The thixotropic microstructures obtained were characterized in detail and linked to the corresponding tensile properties. When the liquid fraction increased (the solid fraction decreased), an initial reduction in the tensile properties was perceived. The lowest tensile properties were obtained at liquid fractions of 35% (610 °C), 25% (623 °C), and 40% (585 °C) for AA2024, AA6061, and A356 alloys, respectively. For the AA6061 and A356 alloys, a further increase in the liquid fraction resulted in improvement of the tensile properties. However, for the AA2024 alloy, the samples could not withstand their own weight at higher liquid fractions that further tensile tests were rendered. It was concluded that for alloys below the liquid fraction corresponding to the minimum tensile properties, the structural properties of interconnected grains (skeletons), and the quenched liquid eutectic phase located at the grain boundaries (liquid film) controlled the fracture behavior. Nevertheless, the nature of the cohesion between the grains and the liquid film was the determining factor in the improvement in the tensile properties that resulted when the liquid fraction was increased to 46% and 60% for the AA6061 and A356 alloys, respectively.

In this study, semi-solid thin plate of A 356 aluminum alloy was fabricated by using slope plate apparatus and vacuum pressurization. Slope plate was used to produce semi-solid material with spheroidal microstructures. After molten metal was poured into the slope plate connected to the pouring hole of die, semi-solid material flowed into the die cavity by vacuum degree. The primary crystals of the cast metal became spheroidal. In order to increase the working pressure, gas pressurization of U shape was designed for fabrication of thin plate. For 3 bar of gas pressure and 60 mmHg of vacuum degree, thin plate was fabricated without defects on surface.

In this study, we develop the lower pressure die casting with rheo-forming process of A356 aluminum alloy and vacuum system which can control the crystal size and obtain the high strengthened-light material. Using this process, we fabricate the thin plate for bipolar plate through the low pressure die casting with electromagnetic stirring and vacuum-evacuation which can control the crystal grain by electromagnetic stirring. Thin plate () is fabricated by this process. The average Vickers hardness of thin plate is about 77 HV.

Great strides made in the industries manufacturing components for IT devices have facilitated the development of cellular phones that are either similar in size or smaller than previously existing phones. In addition, the functions carried out by devices such as MP3 players, digital cameras, and GPS devices are now being incorporated into cellular phone, the quintessential IT device. However, there are limitations on the extent to which the sizes of the components can be reduced due to technical reasons pertaining to mechanical and/or electrical properties, the manufacturing process, and the structure of the assembly. In addition, more emphasis than ever is being placed on the design of a cellular phone as it has come to be regarded as a necessity; thus, like an accessory, it needs to be stylish, highly mobile, and portable, regardless of advances in technology. To develop phones that meet these requirements, the thickness and degree of design freedom have to be reduced and improved, respectively. With this in mind, we propose a novel spring unit for the slide mechanism of a cellular phone as a practical alternative not only for maintaining the mobility and portability of the phone, but also for increasing competitiveness as this component helps to reduce the thickness of the phone. In addition, it provides a degree of freedom that allows other hardware components in the phone to be placed and adjusted more freely than conventional spring units built for the same purpose. Experiments conducted indicate that the life cycles and sliding forces of our proposed spring can be easily set by merely controlling the thickness and hardness of the sheet metal plate used for fabricating the spring. Furthermore, our proposed spring can be used to further reduce the thickness of the existing IT devices while preserving their performance and reliability. We believe that our etching process using heat-treated sheet metal can be widely applied to fabricate springs for various applications that require minimized thickness.

The size and design of a slider phone, which is one of the most important IT applications, are strongly affected by the deformation of the spring unit and the interface for PCB-to-PCB connection located in the same drive space. This implies that the components contribute to the enhancement of the degree of freedom in the design. Past technical developments have focused on thickness and cost reduction, but no fundamental research has been performed on the design. We propose a spring unit in which the interface is integrated with the spring unit in order to share the drive space. Finally, the degree of freedom of the H/W PCB artwork can be enhanced on the basis of the disposition of parts that have major functions. Therefore, a simplified spring that is capable of unifying the interface with the spring unit is proposed, and the type of interface appropriate for this study is identified. Finally, five spring unit samples are evaluated by testing the mechanical performance on the basis of the sliding force; further, reliability tests are performed to examine the life cycle, and environmental tests such as the thermal shock and salt-spray tests are performed after assembling the spring unit of the mock-up phone.

The rubber pad forming process has been used to fabricate metallic bipolar plates from aluminum 1050 alloy for use in a proton-exchange membrane fuel cell. The plates were fabricated using a 200 ton hydraulic press and the effects of the process parameters of the rubber pad forming process (plate thickness, punch speed, press pressure, rubber thickness and rubber hardness) on the forming depth and thinning were evaluated.

This study has evaluated the formability of thin boron alloy sheets, 0.6 mm thick, which can be bent through heating and torn easily during hot press forming. The punch velocity was used as the parameter for the contact time, and the initial blank temperature and blank holding force parameters were controlled. The temperature of the dies and punch was fixed at 300 °C to improve the formability. Microstructural observations and the hardness were examined at different parts of the formed boron steel sheets after die quenching. After the forming process, relationships between the process parameters were found. The punch load and forming depth decreased with increasing punch velocity. On the other hand, the punch load increased with increasing blank holding force, but the forming depth decreased. An increase in the initial blank temperature resulted in an increase in forming depth, but a decrease in punch load.

Various portable applications such as a mobile phone, MP3 player, PMP player and so on, have been continuously developing with influencing on each other. In this environment, functions of IT applications have been built in the mobile phone, and consequently, the additions of them increase the size of the phone. However, the sizes of present phones have changed less than those of the past, and this trend is expected to be continued in the future because of the inherent characteristics mobility and portability of the phone. Great strides made in the industries manufacturing cellular phone components have facilitated the development of phones having similar size to the existing phone. However, in common, there are limitations on the extent to which the sizes of the parts can be reduced because of the technical reasons pertaining to mechanical or electrical properties, the forming process and assembly structure. In such a scenario, the use of a slide mechanism is the practical alternative for maintaining the mobility and portability. Reduction of the sliding space has a decisive effect on the decrease of the phone size. Therefore, a study of a novel spring to be manufactured by the etching process was performed to minimize the thickness. Meanwhile, the use of the slide mechanism is advantageous for maximizing visibility and increasing functionality with the limited space which are of utmost importance for the design of a contemporary cellular phone. In addition, various extra function keys including the main keypad buttons are required to maximize the visibility. However, the sliding stroke must increase to have them, and the existing spring units cannot be satisfied with the requirements under the limited space. Therefore, the study of a long-stroke spring unit and its manufacturing process to minimize the thickness with the stroke of 60 mm was performed.

Recently, aluminium usage in the automobile industry has been increased cause of its lightweight. The aluminium has a melting-solidification process in producing line and another melting process was needed in manufacturing process. Two times of meltingprocess for making ingot and casting not only makes the loss of time and money but contaminates the air with Sox, Nox. For thisreason, the holding furnace with laminated adiabatic material was developed. This holding furnace can deliver the molten alu-minium directly to the industry needing molten aluminium. Recent holding furnace has above 15 o C/h of cooling rate and that causessolidification of molten aluminium. The ANSYS software was used to analysis the heat transfer. The adiabatic materials were lam-inated with optimized arrangement and holding furnace shape was changed with optimized modelling by ANSYS analysis forreducing the cooling rate of molten aluminium in holding furnace.Key word : Holding furnace, Laminated adiabatic structure, Thermal insulation, Temperature reduction.(Received July 11, 2011 ; Accepted October 21, 2011)

In the present study, the coarsening mechanism of equiaxed grains in the semisolid state of aluminum 7075 alloy, treated via strain induced melting activation process, was investigated. The kinetics of equiaxed grain growth in the semisolid state of the experimental alloy was determined. The results revealed that when the holding temperature increased, the coarsening rate constant (K) showed a precipitously increasing character in the range of 590–610 °C. This was attributed to the extensive effect of the coalescence mechanism on the grain growth at the high solid fractions. By further increasing the holding temperature to 620 and 625 °C (increasing the liquid fraction), the effect of coalescence on the grain growth appeared to be weakened, that is, although there was a slight decrease at 620 °C, a gently increasing character could be generally supposed. Severe segregation of Zn and Cu alloying elements at grain boundaries and intragranular droplets was detected at 620 and 625 °C after 15 and 10 min, respectively.

The hot stamping process has been used in the automotive industry to reduce the weight of the body-in-white and to increase passenger safety via improved crashworthiness. However, defects such as fracture and wrinkle occur when hot stamping is performed using a conventional drawing or forming method. In this study, a channel-type indirect blank holder (CIBH) is proposed to develop a high-strength center pillar in form-type hot stamping, so that the aforementioned drawbacks are overcome. This type of blank holder plays an important role in reducing severe wrinkling at the flange; such wrinkling leads to folding after the completion of form-type hot-stamping. First, we investigated the effect of the channel shape on the indirect blank holding force by using a simplified two-dimensional plane-strain stamping process. Second, we selected the slope angle and corner radius of the channel as the main shape parameters by finite element analysis and artificial neural network (ANN). It is known that fracture at the hot formed wall and wrinkle at the flange are significantly affected by the slope angle of the channel, and the appropriate value for eliminating fracture and wrinkle is determined to be 99°. By performing hot stamping using a form die with the selected channel, we can manufacture a high-strength center pillar without wrinkle and fracture.

In this study, a vacuum-assisted electromagnetic stirring system was designed and manufactured in order to minimize the defects such as porosities in the semisolid processing A356 aluminum alloy by electromagnetic stirring (EMS). A sleeve cooling system was manufactured and two different cooling media (air and water) were tested for the stirred and unstirred slurries. For the stirred slurry, the obtained cooling rates were lower than the values for the unstirred slurry in both cooling media. Also the effects of the different cooling types and the thickness of the slurry cup on the microstructural evolution were thoroughly studied. The maximum cooling rate with the least evidence of the liquid segregation for the stirred slurry was achieved in water-cooling condition when the slurry cup of 2 mm thickness was used. At the pouring temperature of 620 o , the optimum EMS stirring current and time were obtained 30 A and 60 s, respectively. The vacuum level with the least presence of the porosity was determined at 50 kPa, while further increase in the vacuum level (decrease in the applied pressure) resulted in increase in the presence of the porosity. The last trend could be attributed to the possible effect of the stirring during the EMS process on the entrainment of bifilms into the semisolid slurry, which is discussed in details. Keywords Electromagnetic stirring (EMS).A356 aluminum alloys.Microstructure.Porosity.Vacuum

The effects of compression ratios on the microstructure evolution of semisolid Al7075 alloy produced by the strain induced melt activation (SIMA) process were investigated. The samples were cold deformed by compression into the different heights up to 40% reduction. The isothermal holding treatments within mushy zone of the alloy were carried out at 610, 620 and 625 °C for predetermined time intervals. The results revealed that the average grain size gradually reduced with the increase in the compressive ratio. While the compressive ratio surpassed 30%, the descending trend above was not as evident as that of below 30% reduction. The optimum condition presenting the minimum grain size and the maximum shape factor with the highest uniformity is discussed. During the subsequent mushy zone heating, the recrystallization was induced in the deformed samples by the increasingly accumulated strain energy.