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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.

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.

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 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.

In this study, a rubber forming method is used to fabricate titanium bipolar plates for proton exchange membrane fuel cells. A titanium blank with a thickness of 0.1 mm is compressed using a stamping mold equipped with a 200-ton hydraulic press to fabricate bipolar plates. A forming experiment is carried out by changing different parameters such as the punch velocity, punch pressure, rubber thickness, rubber hardness, and draft angle of the channel. The optimum forming conditions are found to be a rubber thickness of 10 mm, rubber hardness equivalent to that of Shore A 20, punch velocity of 30 mm s−1, punch pressure of 55 MPa, and punch draft angle of 30°. The fabricated titanium bipolar plate is coated with a TiN layer. A single cell with a TiN-coated titanium bipolar plate is examined and compared to those with uncoated titanium and graphite bipolar plates. The initial performances (in terms of current densities) of the single cells with the uncoated titanium, TiN-coated titanium, and graphite bipolar plates are 396, 799, and 1160 mA cm−2, respectively, at a cell voltage of 0.6 V.

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.

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.

Hybrid composite material was fabricated by stacking CFRP (carbon fiber–reinforced plastic) on CR340 plates to increase the specific strength and specific stiffness, compared to stacked composites by different laminating method. A deep drawing test was conducted for this hybrid composite material by using various process parameters, to assess its formability and potential use in vehicle parts. The experimental results showed that with low blank holding force, the forming depth of the CR340/CFRPR* composites was higher than the forming depth of CR340/CFRP. On the other hand, when the blank holding forces were increased to 30 and 90 kN, the forming depth of CR340/CFRP and CR340/CFRPR* composites were almost same. As the punch velocity increased, CFRP flowed abruptly toward the round part of the die. The thinning rate in each position of the drawing product and the problems encountered during the deep drawing process were reviewed by a comparison of the experiment results.

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.

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.

A356 aluminum thin plates with a thickness of 1.2 mm were produced via thixoforming process under different temperatures ranging from 585 °C to 610 °C. In addition to large primary α-Al grains, unique fine secondary α-Al grains (equivalent diameter below ~ 8 μm) were revealed through microstructural examinations. These secondary α-Al particles exhibited irregular morphology at 590 °C, which gradually transformed into equiaxed/globular grains at higher thixoforming temperatures of 605 °C and 610 °C. On the other hand, their size (the equivalent diameter of the grains) continuously increased from 3.2 ± 0.16 μm at 590 °C to 8.1 ± 0.4 μm at 610 °C. Energy dispersive X-ray spectroscopic analyses showed that the Si concentration gradually increased within these secondary α-Al grains. A quenched modified morphology consisting of angular and finely branched eutectic silicon was observed at the thixoforming temperature of 590 °C, which seemed that it changed to a fibrous morphology at 605 °C and 610 °C. By increasing the thixoforming temperature, the elongation of the thixoformed plates monotonically increased to 12.6 ± 0.4% at 610 °C, whereas the ultimate tensile strength reached its highest value of 280 ± 12 MPa at 600 °C then experienced the sharp reductions at 605 °C and 610 °C.

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.

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.

There are various methods for the fabrication of bipolar plates, but these are still limited to machining and stamping processes. High-pressure die casting (HPDC) is an ideal process for the manufacture of bipolar plates This study aims to investigate the formability of bipolar plates for polymer electrolyte membrane fuel cells (PEMFCs) fabricated by vacuum HPDC of an Al–Mg alloy (ALDC6). The cavity of the mold consisted of a thin-walled plate (200 mm × 200 mm × 0.8 mm) with a layer of serpentine channel (50 mm × 50 mm). The location and direction of the channel in the final mold design was determined by computational simulation (MAGMA soft). In addition, simulation results for different conditions of plunger stroke control were compared to those from actual die-casting experiments. Under a vacuum pressure of 35 kPa and for injection speeds of 0.3 and 2.5 m s−1 in the low and high speed regions, respectively, the samples had few casting defects. In addition, the hardness was higher and porosity in microstructure was less than those of the samples made under other injection speed conditions. In case of thin-walled plates, vacuum die casting is beneficial in terms of formability compared to conventional die casting.

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.

In recent years, various rheo-forming methods have been developed to produce products with improved mechanical properties. To this end, rheo-forging of metal offers not only superior mechanical strength but also requires much lower machine loads than solid forming processes. However, there are many problems, such as air indraft during the stirring of the molten metal as well as the expense of the starting materials. As a result, the commercial availability of products formed through semi-solid processes is still limited. Semi-solid materials with a desired microstructure are produced by stirring during solidification from their molten state. Occasionally, indraft of air has degrades the resultant mechanical properties. This paper presents the results of the influence of air control during stirring and forging. A356 aluminum alloys were prepared by electromagnetic stirring under vacuum in order to prevent the indraft of air and sample parts were subsequently fabricated with hydraulic press machinery. To compare the influence of air control, two type samples were fabricated (1) samples fabricated under vacuum and (2) samples fabricated while open to the free atmosphere. An H-shaped product was formed in order to select and observe the deformation behavior.

This study investigated nano/microsturcture and mechanical/tribological properties in the thixo/rheoformed A356 alloy parts using nano/microindentation and nanoscratch, incorporated with optical microscopy and atomic force microscopy (AFM). As a result, thixo-cast sample exhibited higher mechanical properties than rheo-cast, irrespective of grain size. The reason that mechanical properties of thixo-cast part was higher than that of rheo-cast, was interpreted by the effect of the eutectic region surrounded by the primary α phase on the hardness. It was also observed that shape and distribution of Si particles in the adjacent eutectic region to the primary α-Al phase of the thixo/rheo-cast products were different. By scratching surface of thixo/rheo-cast parts using a nanoindentor, friction forces and coefficients for the primary α-Al and eutectic phases in thixo-cast products were resulted to be higher than those in the rheo-cast. Nanoscratch for the thixo-cast product also revealed a rough and irregular surface compared to that for the rheo-cast, providing the evidence for the effect of eutectic entrapped by primary α-Al phase on mechanical properties.

In this paper, the effects of gate shape and solid fraction on filling behavior during semi-solid processing of A356 alloys have been demonstrated by experimental and computer simulation. Effects of solid fractions and gate shapes on material properties have been investigated through experiment and computer simulation. Although the cross-section areas of the gates were identical, the filling behavior of the semi-solid material differed due to differences between the widths and heights of the gates. Furthermore, when the cross-section area of the gate is held constant, the increase in height plays a key role in improving mechanical properties. Because the pressure applied by the plunger transfers easily to the material during injection when the cross-section area of the cavity is large, the mechanical properties improved. Therefore, the optimization of die design and the experimental conditions that enhance material properties are proposed in this paper.

Using nano/micro-indentation and nanoscratch techniques incorporating optical microscopy and atomic force microscopy (AFM), mechanical/tribological properties of a rheo-formed Al 6061 wrought alloys have been investigated. The results have been compared to those obtained by using a Vickers hardness test. For the Al 6061 alloy, peak hardness and surface roughness in specimens aged for 10 h after solution-treatment at 530 °C have been obtained. By using the constant load scratch (CLS) method, tribological characteristics of rheo-formed material was investigated. By using this technique, the heat treatment condition for rheo-formed wrought alloys was optimized.

This paper demonstrates a methodology for thermal and flow analysis when forging solid- and liquid-phased rheology material. A mixture rule representing solid and liquid phases was used in the thermal analysis, and the numerical analysis was compared with simulation results by commercial software MAGMAsoft. Methods for predicting defects in rheology material and die life based on the thermal analysis have been proposed.

Rheology forming is a novel semi-solid processing method, which is different from traditional mold forging and conventional casting processes. The rheological behavior of metallic alloys containing both solid and liquid phases investigated the low and high solid fraction ranges. Rheology forming has several obvious advantages including its excellent forming ability resulting in the easier production of complex work pieces, more flexibility in shaping pieces, and more compact inner quality because of its high pressure. This research paper presents the theory of the rheology forming process and the results of a finite element simulation of rheology forming for aluminum alloys. The algorithms for both a single- and two-phase flow model, developed for this study, gives the die filling patterns, velocities, temperatures and solid fractions of the rheology material during the rheology process. To calculate the velocity and temperature fields, the respective governing equations corresponding to the liquid and solid regions were used. Therefore, the respective numerical models that take the co-existing solid and liquid phases within the rheology material into consideration have been developed to predict the defects of parts manufactured by the rheology process. This study compares of the velocity, temperature, and solid fraction between the single- and two-phase flow models. And, to predict the liquid segregation in the parts, the deviation of velocity between the liquid and solid regions in the two-phase flow model was analyzed.

Compression tests were performed in order to observe and investigate the rheological behavior of wrought aluminum alloy while varying the processing parameters such as liquid fraction, strain rate. The results of an experimental investigation using Al 6061 with a closed die are presented here. Specimens of wrought aluminum alloy were characterized with their rheological behavior during partial melting and holding in the semi-solid state. The characteristics of flow between solid and liquid phases by considering liquid segregation are examined by restricting material (100% of packing rate in a closed die) during compression. Also, the strain–stress curves and microstructures of the rheological materials were investigated. Moreover, the tests allow the apparent viscosity of the alloys to be determined as a function of the liquid fraction and shear rate together with the densification behavior of the solid phase. Finally, the experimental results should be used in flow and solidification analyses and useful for manufacturing good SSM products through observing the microstructures according to changes of the solid fraction and compression rate.

In this paper, an electromagnetic stirring system (EMS) was adapted to the forming process for manufacturing knuckles. After producing knuckles with EMS, the microstructures of the parts were investigated by image analysis and mechanical properties and then compared to parts fabricated by without using EMS. According to this comparison, the parts formed using EMS have better mechanical properties by over 30% and have globular microstructures.

A computer program has been developed to analyze the two-dimensional unsteady conservation equations for transport phenomena in the pool region of a twin roll strip casting in order to predict a velocity, temperature distributions of fields and a solidification process of molten magnesium. The energy equation of cooling roll is solved simultaneously with the conservation equations of molten magnesium in order to consider the heat transfer through the cooling roll. In this paper, it is examined the quantitative relationships of the important control parameters such as the roll speed, height of pool region, outlet size of nozzle, solidification profile and the final point of solidification in a twin roll strip casting. The finite difference method (2-D) and the finite element method (2-D) are used in the analysis of pool region and cooling roll to reduce computing time and to improve the accuracy of calculation, respectively.

In this paper, the morphology of the change of primary Al phase in A356 alloy by a self-designed horizontal electromagnetic stirrer was used to determine the rheological behavior of A356 aluminum alloy. Electromagnetic stirring has been recognized as the most efficient way to produce globulitic structured pre-material for forming. The globularity of the structure is the key to the low apparent viscosity and also to good rheological properties. The stirring promotes the coarsening of primary particles by the formation and melting of grain boundaries produced either by deformation or by sintering of the primary particles. The initial dendritic structure is fragmented by the stirring of the partially solidified alloy, so that the melting of the grain boundaries is the predominant mechanism during the initial stage of stirring. The effects of the stirring current, the stirring time, the pouring temperature and the holding time were determined. The greater stirring current and longer stirring time were to get the finer Al phase. However, over a certain stirring current and stirring time, the primary-Al was merged together and was increased. The optimum conditions of horizontal electromagnetic stirrer have been investigated for rheology forging with controlled solid fraction.

In this study, the effect of the temperature on a magnesium slurry was investigated by mechanical stirring method. The slurry temperature of the solid fraction was measured by differential scanning calorimeter (DSC). The slurry had been melted, and was cooled and heated at solid fraction temperature by induction coils. The apparent viscosity tests show that the semi-solid state temperature in the two-phase region was in the range 620–597 °, fs 0.3–0.7, for AM50A magnesium alloy. The rheological behaviors of AM50A magnesium alloy were investigated by measuring its viscosity and microstructures in the semi-solid state. The apparent viscosity was investigated at a continuous cooling rate using a concentric cylinder viscometer. The measurement of viscosity was expressed by torque using a torque meter to assess the rotation caused by a stirrer as the metal continuously cooled. The results are expressed by power law. Microstructures after mechanical stirring were observed with temperature correspond to the solid fraction and various shear rate.

In recent years in the automobile industry, it has been necessary to reduce the weight of automobile parts. To solve this problem, lower arm parts have been fabricated with the aluminum alloy metal by semi-solid die casting as substitutes for steel arm parts. Aluminum alloy parts can reduce the weight of automobiles, but the mechanical properties of aluminum alloy parts are inferior to those of steel parts. In order to substitute aluminum alloys parts for steel arm parts, simulations of strength and fatigue have to be performed, before changing to new model designs. The die design for the semi-solid die casting of the arm part has to be considered according to defects from air porosities, impurities and filling errors. In this study, the filling and solidification processes were simulated in order to propose the optimal die design.

Semi-solid forming is an attractive process for fabricating sound, weight-reduced automotive parts. Therefore, in this work, die systems of varied gate shape, gate width, and gate thickness were designed to investigate the filling characteristics of semi-solid material with a controlled solid fraction. When semi-solid materials with controlled solid fraction of 50% filled inside die cavity, the causes of liquid segregation according to the separation phenomena of solid particles and liquid materials were investigated. The parts were characterized for eutectic segregation, a segregation band, cracks and shrinkage hole on the part surface. It was found that all these defects could be solved by the selection of the optimal casting speed and selection of gate shape when the semi-solid material with a controlled solid fraction completely filled the die cavity. The correlation between liquid segregation and a gate system has been synthetically investigated with experimental results and theoretical results. The hardness in the primary α zone and the eutectics microstructural zone were measured by nano indentation. The relationship between liquid segregation and hardness was also investigated.

Compression tests were performed in order to observe and investigate the rheological behavior of wrought aluminum alloys while varying the processing parameters such as liquid fraction, strain rate and materials. The results of an experimental investigation using Al2024, Al6061, Al7075 with a closed die are presented here. Specimens of each wrought aluminum alloy were characterized with their rheological behavior during partial melting and holding in the semi-solid state. The characteristics of flow between solid and liquid phases by considering liquid segregation are examined by restricting material (100% of packing rate in a closed die) during compression. The grain size was compared before and after the compression. Also, the strain–stress curves and microstructures of the rheological materials were investigated. Moreover, the tests allow the apparent viscosity of the alloys to be determined as a function of the liquid fraction and shear rate together with the densification behavior of the solid phase. Finally, the experimental results should be used in flow and solidification analyses and useful for manufacturing good SSM products through observing the microstructures according to changes solid fraction and compression rate.

The semisolid forming (cleaner rheological forming) of aluminum alloys is a new net shape manufacturing method that incorporates elements of both forging and casting. It is characterized by the use of induction heating to reheat billets to the highest possible solid fraction in order to maximize the mechanical properties such as strength, wear resistance and elongation. It is necessary to develop tailored alloys specifically for cleaner rheological forming (CRF). The selection is basically from the entire range of cast and wrought aluminum alloys, although most of these alloys were optimized either for the casting or for the forging process. Nowadays, their formability evaluation in the semisolid state has rarely been investigated, and more essentially, it lacks a systematic theoretical base for dealing with unexpected behavior under the new and possibly extreme conditions encountered as we expand the limits of this criterion. So, the present article uniquely focused on an advanced description (advanced JK criteria) to evaluate the formability and castability of next-generation nonferrous materials such as cast and wrought aluminum alloys in the semisolid state based on the microstructural characteristics with an appropriate control of the process. Using the proposed criteria (advanced JK criteria) to evaluate the quantitative formability of cleaner rheological materials in the semisolid state shows that a nine-point alloy represents an optimal semisolid formability while a zero-point alloy is extremely unsuitable for CRF, confirming the validity of the proposed criteria.

This paper investigates the effect of single-point diamond machining conditions, such as the Berkovich tip orientation (0°, 45°, and 90°) and the normal load (0.1, 0.3, 0.5, 1, 2, 3, 4, 5 mN and 0.1 μN), on the both deformation behavior and the chemical properties of single-crystal silicon through nanoscratch with 20 wt.% KOH-etching tests. The tip orientation had a significant influence on the coefficient of friction, which varied from 0.16 to 0.38, the material removal mode, and the KOH-etching property of silicon. In normal load ranges from 0.1 to 1 mN, the friction coefficient remarkably increased with decreasing normal. KOH-etching results showed that, as a whole, the size of etch-hillock structures increased with an increasing normal load, indicating that that the higher the load that is applied to the material surface, the more the etch-mask effect of the mechanically affected layer increases. Contrarily, the groove surface machined under a very low load (0.1 μN) showed only the etch-promotion effect. The evolution of the morphology of a scratched Si(1 0 0) surface during the etching process was visualized by 20 wt.% KOH-etching tests under dipping times ranging from 0 to 30 min. The initial size of the etch-hillock structure was closely related to that of the contact zone between the diamond tip and materials.

Semi-solid die casting of Al alloy is suitable for complicated large parts of near net shape without defect and excellent mechanical properties in comparison with conventional casting process. Die design for the product with high quality in semi-solid die casting is required to prevent micro porosity, inflow of oxidized substances, and liquid segregation. Therefore, shape and size of runner, position and size of overflow and air vent, and arrangement of heating line are very important. Micro porosity, unfilled phenomena, turbulent flow, and liquid segregation occurs during semi-solid die casting. To prevent these phenomena, defect analysis of product according to the change of injection velocity is carried out and optimal injection velocity for high quality product is proposed and simulated. Also, the measurement of mechanical properties according to various injection velocity and heat treatment condition is performed.

The nano/microstructure, the aging response (in T5 heat treatment), and the mechanical/tribological properties of the eutectic regions in squeeze-cast A356 alloy parts were investigated using nano/micro-indentation and mechanical scratching, combined with optical microscopy and atomic force microscope (AFM). Most eutectic Si crystals in the A356 alloy showed a modified morphology as fine-fibers. The loading curve for the eutectic region was more irregular than that of the primary Al region due to the presence of various particles of varying strength. In addition, the eutectic region showed lower pile-up and higher elastic recovery than the primary Al region. The aging responses of the eutectic regions in the squeeze-cast A356 alloys aged at 150 °C for different times (0, 2, 4, 8, 10, 16, 24, 36, and 72 h) were investigated. As the aging time increased, acicular Si particles in the eutectic regions gradually came to a fine structure. Both Vickers hardness (HV) and indentation (HIT) test results showed almost the same trend of aging curves, and the peak was obtained at the same aging time of 10 h. A remarkable size-dependence of the tests was found. The friction coefficient for the eutectic region was lower than that for the primary Al region.

This paper describes a 3D FE simulation of the cold ironing process for forming the drum clutch, the main part component of the automatic transmission. The process of the drum clutch with inner gears that was employed in this study consists of 12 steps associated with nine deep drawing processes and three ironing processes to form the inner gear shape. The ironing processes were focused on this study in order to estimate the dimensional accuracy of the inner gear shape according to the process variables such as the punch shape, the approach angle of the punch, and the thickness reduction ratio. A rigid-plastic finite element simulation was applied to analyze the deformation characteristics of the ironing processes and to determine the optimum parameter for selected conditions. Finally, an experiment on the whole drum clutch forming process was carried out to examine the validity of the analytical results and the chosen parameters.

Two estimating methods are proposed for predicting the die life due to wear or plastic deformation during hot forging considering the deviation of the preheating temperature of the billet. The characteristics of the billet during electroplating or induction heating are very complex in the preheating process. Therefore, an induction heating of billet has become increasingly important as a means of reducing the heating time and an effective control of heating temperature. In this paper, to calculate the temperature distribution of the billet in the preheating process according to the parameters such as heating time, frequency and current density in high-frequency induction heating, an induction heating program has been developed. Then, FE-simulation with the proposed wear and the plastic deformation models has been carried out for the hot forging sequence of a spindle part widely used in the present continuous hot forging die. The results showed that die life is greatly affected by the wear under the conditions that exist in a given deformation process and the maximum wear occurs at the corner of the finisher die. These proposed methods of the die life could be used effectively for quantitative prediction of the die life in the hot forging process. These results might also be extended further for the study of optimization of the die change schedule to grind the die.

This paper describes a 3D FEM simulation of porthole die extrusion process for producing condenser tubes used for a cooling system of automobiles. In general, condenser tube is mainly manufactured by the conform extrusion method, but this process is less effective as compared with the direct extrusion method in productivity per unit time and in the equipment investment. Therefore, it is essential for the conversion to the direct extrusion with porthole die that can produce condenser tube with competitiveness in costs and qualities compared with the existing conform extrusion. However, an experimental method to quantify the deformation behavior of porthole die for condenser tube extrusion has not been established yet, due to its complicated die assembly and complexity of metal flow. FEM is a good alternative to evaluate the three-dimensional deformation behavior of metals in condenser tube extrusion. Especially, an understanding of metal flow in porthole die extrusion is important, because it provides necessary information in die design for high performance extrusion. This study was designed to evaluate material flow, welding pressure, extrusion load, and the tendency of mandrel deflection that is affected by variation of chamber shape on porthole die. An estimation was carried out using FE analysis in non-steady state. Also, this study examined into the mandrel fracture behavior through investigating elastic deformation of mandrel during the extrusion.

In mass production of thixo die casting, there are many disadvantages such as high raw material cost, billet reheating cost, non-destructive control cost, the difficulty of scrap recycling and billet loss during reheating process. On the contrary, in rheo die casting, on-demand slurry like not only cast alloy but also structural alloy can be used and the recycling of scrap is comparatively easy. However, metal composition may be varied and treatment of liquid metal is difficult. Two processes have been adapted to the production of automobile suspension parts. In order to investigate advantages of rheo and thixo die casting process, both processes were compared with optimal process parameters. Microstructure by image analysis and the mechanical properties of produced automobile suspension part are compared between thixo and rheo die casting process. Particularly, the effect of injection conditions on liquid segregation has been investigated for thixo and rheo die casting. The interrelation of microstructure, injection condition and mechanical properties was discussed.

In this paper, the reheating process in the A356 alloy, by electromagnetic stirring (EMS) and extrusion, is discussed. The EMS method is used mainly to manufacture raw materials of a globular microstructure. If relevant reheating is carried out, products with excellent mechanical properties can be manufactured by EMS. However, the cost of raw material for EMS is very high. Contrarily, extruded material has a fine dendrite microstructure and has rarely been assumed to be suitable for the semi-solid forming process. It was found in this study that the microstructure of extruded material could be globularized and applied to the semi-solid forming process only with the relevant reheating parameters. This applicability was estimated by investigating, through image analysis properties such as the solid fraction, the mean equivalent diameter and roundness under various reheating conditions. Under the same reheating conditions, the microstructure of the material by EMS and that of the material by extrusion was compared. Also, the variation of the globular morphology and the coarsening of the primary α-Al phase were investigated according to the final isothermal holding time in the reheating process using a billet diameter 4 in.

Crystal orientation etching of the rheocasting structure of A356 alloy was carried out. The precise measurement of the grain size of the rheocasting structure showed that longer stirring time correlated with finer grains. It was concluded that secondary nucleation directly led to the grain refinement of the rheocasting structure.

The purpose of this work is to construct the database on mechanical properties and microstructures of thixoforged hypereutectic and hypoeutectic aluminum parts. Mechanical properties of the semi-solid components can be improved by controlling process parameters such as solid fraction of the material, punch velocity, applied pressure, die temperature, and heat treatments condition, etc. In this study, the characteristics of the microstructures and mechanical properties of thixoforged 357, 319, and 390 Al alloy parts with an arbitrary shape were studied for variation of applied pressure (110, 140, and 170 MPa) and aging time (4, 6, and 10 h) followed by solution treatment.

Line patterns were machined on borosilicate (Pyrex 7740 glass) surface using the combination of mechanical machining by Nanoindenter® XP and HF wet etching, and a etch-mask effect of the affected layer of the nano-scratched Pyrex 7740 glass surface was investigated.

Actual trends in the automotive industry lead to an increasing use of lightweight structures imposing the need for high strength aluminium alloys combined with complex shape. In this study, for the development of aluminium upper arm part with semi-solid die casting, series of studies have been performed. In semi-solid casting process, various defects are strongly affected by die shape than fabrication parameters because the semi-solid materials have to travel relatively long distance to fill the die cavity through a gate during filling time. To reduce the time and cost in part and die design, die filling and solidification simulation were carried out with Ostwald–de Waele rheological model. In order to propose the proper overflow position, two cavity geometry models were proposed for the variation of the overflow number and position considered in the die design by the numerical simulation. Their filling and solidification characteristics were calculated in order to propose the proper overflow position. On the basis of the computer simulation results, upper arm parts were fabricated, and defects were analysed by observing the microstructures.

Die design by computer simulation has some advantages compared to the conventional method that was performed by designer’s experience and trial and error. The die filling and solidification phenomenon in semi-solid injection forging process were simulated by MAGMAsoft/thixo module. Furthermore, the die design for semi-solid injection forging was performed with the two kinds of geometric shapes. The effect of designed gate dimension on filling phenomenon was estimated by filling simulation. The calculated results were compared with experimental data. The free surface phenomenon obtained by experiment has good agreement with computer simulation results. The solidification affect much as porosity and shrinkage for designed semi-solid forging die had been predicted by computer simulation. The designed die for semi-solid injection forging had been applied to the production of the frame part used in air conditions system.

The squeeze casting process of molten metal is very attractive for producing near net shape components with an arbitrary complicated shape. It is particularly attractive for processing engine mounting brackets with high strength at desired elongation and hardness, since the porosity of dispersed defects under the action of the pressure is remarkably reduced during squeeze casting. Therefore, to develop suspension parts, such as the knuckle, arm, and structure parts to support the automobile engine, the squeeze casting process was developed with die design and process parameter control.

Numerical simulations for industrial net shape forming application by the finite element method (FEM) are based on the integral form of the mechanical equations governing the physical process. However, current commercial packages cannot analyze the die filling and solidification for materials in the semi-solid state because they lack material models for liquid and solid materials and do not address segregation of the liquid and solid phases. Thus, this work presents an overview of the development of a new finite element program entitled SEMI-FORM S/W to predict the solid-phase deformation of semi-solid materials, filling defects and liquid segregation. The automatic mesh generation scheme by the modified looping algorithm using quadrilateral elements is proposed in this present study by a new loop splitting method and a local finite element control. An automatic quadrilateral mesh generator with automatic mesh refinement is developed in order to meet special demands found in the thixoforming process analysis with arbitrarily shaped dies by the node renumbering and modifications of the nodal position. Applying the remeshing criterion carries out the remeshing due to B-spline form. The SEMI-FORM S/W developed in this present study would be recognized as efficient and economical tool for designing and optimizing thixoformed products with arbitrarily shaped dies.

A semi-solid casting will have a higher internal integrity, mechanical properties and dimensional accuracy than a conventional castings. This process can reduce the manufacturing costs and finished weight for critical components. Semi-solid castings are capable of greater dimensional repeatability, this affording considerable savings when extensive machining, salvage and scrap are key variables in the current automotive product. The most important factors regarding the semi-solid die casting process are the reheating method of the raw materials to the semi-solid state, the specifications of the semi-solid die casting machine, the optimal injection conditions and die design. Thus, in the present work, a horizontal-type induction heating system to obtain the optimal reheating conditions for the semi-solid die casting process was designed and manufactured. The mechanical properties of semi-solid die castings for varying die temperatures, injection velocity and applied pressure were investigated, and the relationship between applied pressure and stroke to assess semi-solid die castability was proposed. Semi-solid die casting experiments to replace heavier cast iron compressor products with lightweight aluminum castings were also carried out. The possibility of their use for compressor parts was verified.

To obtain high quality components with the semi-solid forging process, it is important to obtain a homogeneous distribution of solid particles without liquid segregation. In the closed-die semi-solid forging process, liquid segregation is strongly affected by injection velocity than process parameters such as the pressure and the solid fraction, because the material has to travel a relatively long distance to fill the cavity through a narrow gate before solidification begins. To investigate the effect of gate shape on the filling phenomenon in the semi-solid forging process, two kinds of gate shape system are proposed. A filling test for the two kinds of gate systems was carried out. Therefore, in this study, the optimal injection velocity and die temperature were investigated to fabricate a near-net-shape compressor component called an Al frame. For uniformity of the solid particles, the injection velocity has to be higher than 160 and 370 mm/s to produce sound part without filling defects, in the range of die temperature of from 200 to 300 °C. In addition, the mechanical properties for a forged semi-solid component with a good filling situation were tested with the specimen before and after heat treatment. The forming limits and mechanical properties were discussed in terms of chemical composition and microstructure of the materials used.

For optimization of net shape forging process with semi-solid materials (SSMs), it is important to predict the deformation behavior of material. In this study, compression experiments have been performed to investigate the deformation behavior of SSM with variation in processing parameters such as test specimen size and strain-rate. Stress–strain curves and microstructures of SSM were investigated. The characteristics of flow between solid and liquid phase considering liquid segregation is examined through the above experiments. Moreover, porosities were measured to evaluate the effects of experiment parameters on liquid segregation quantitatively.

Clad composite materials consist of stacks of different materials. During the extrusion process of clad composites, fracture of the sheath or core materials frequently occurs because of the discontinuity of deformation caused due to the differences in the flow stress of the sheath material and core material. In order to predict fracture of the sheath material with oxygen-free high conductivity copper, the theory of ductile fracture has been applied. The effect of lubrication behavior on fracture of core material has been investigated. A technique to predict the fracture strain rate has been proposed. The calculated interface bonding force between the core material and the sheath material has been used to assist in die design for the indirect and direct extrusion processes.