The measurement of the hardened depth of surface-hardening spheroidal graphite cast iron is important in the maintenance of various mechanical parts etc. Electromagnetic properties differ between layers that have been hardened and those that have been not. This enables evaluation of the hardened depth by detecting the difference in electromagnetic characteristics. In this paper, the electromagnetic method for measuring the depth of a hardened layer using an alternating magnetic field is proposed. The flux density in the surface hardening spheroidal graphite cast iron is estimated by 3-D nonlinear electromagnetic FEM taking into account the electromagnetic properties of hardened and unhardened layers. In addition, experimental verifications were also carried out.

  The effect of coat permeability on mold filling for thin wall aluminum alloy castings in the expendable pattern casting (EPC) process was investigated experimentally. Thin wall aluminum alloy plates were cast by the EPC process, using eight kinds of coats with different permeabilities. The fluidity length and melt velocity were measured. The use of thin expendable polystyrene (EPS) pattern led to shorter fluidity length of melt. When the coat permeability was less than approximately 2, the fluidity length of the melt and melt velocity increased with increasing coat permeability. When the coat permeability was greater than approximately 2, even when the coat permeability increased, the fluidity length of the melt and melt velocity did not increase so much. The application of high expansion ratio of EPS pattern or high pouring temperature, led to long fluidity length of the melt. The distances of melt flow stop were predicted based on the heat transfer from the molten metal to the mold through the coat using measurement melt velocity values. The predicted values more or less agreed with experimental values for fluidity length.

  The Si content of α-Al and aggregation substance of P at the product surface of AC4CH (Al-7%Si-0.45%Mg) alloy castings which were cast with different semi-solid die casting conditions (Sleeve filling ratio : SFR and Shot time lag : STL) were investigated to determine the generation mechanism of very-fine globular α-Al (diameter : under 15μm). In the case of SFR of 10% with STL of 10 seconds, a number of very-fine globular α-Al (diameter : under 10μm) containing over 2at.% Si were observed at the product surface than with SFR of 30% and 50% and STL of 10 seconds. AlP which could be the nucleus of eutectic Si was eliminated when P was aggregated as AlP in the melt. Therefore, it was difficult to form eutectic Si even if the melt temperature reached the eutectic temperature. Consequently, eutectic undercooling occurred easily. Moreover, the degree of undercooling was greater because of the die-cast product. Furthermore, eutectic structures did not form easily due to the high content of Si in crystallized α-Al, suggesting that considerable ultrafine α-Al had occurred.

  Vertical-type tandem twin-roll casting is a highly effective method for thin clad strip fabrication. In addition, precipitation refinement and high solubility can be achieved by rapidly cooling the roll casting, so property improvement can also be expected. The aim of this study is to clarify the advantage of vertical-type tandem twin-roll casting by considering the property of brazing sheet fabricated by the present method. Six mm thick clad sheets consisting of 4045/3003/4045 were fabricated by both hot-roll bonding (HRB) and vertical-type tandem twin-roll casting (TRC). The clad sheets were cold-rolled to 0.17mm in thickness, subjected to intermediate annealing at several temperatures, cold-rolled to 0.10mm in thickness, and finally brazed at 600℃ for 3min. The microstructure and brazing characteristics of clad sheets were compared. After intermediate annealing, the HRB sheets fully recrystallized at 350℃. On the other hand, fibrous structures still remained in the TRC sheets at 400℃. Fine dispersoid particles with 0.1μm diameter were observed at all intermediate annealing conditions of HRB and 400 and 500℃ of TRC. The recrystallization behavior during brazing heat treatment was affected by each initial condition. In the HRB sheets, strain energy was dominant at no/250℃ intermediate annealing. In the TRC sheets, the precipitation behavior of super saturated Mn was the key factor regardless of the intermediate annealing condition. After the brazing heat treatment, TRC recrystallized grain was elongated in the rolling direction. This elongated grain reduced the grain boundary area vertical to the interface and erosion amount. From the sagging test, the TRC sheets showed higher sagging resistance than the HRB sheets. It was confirmed that the TRC process is more advantageous for brazing sheet fabrication although it is a simple process compared to HRB.

  Graphite shapes in gray cast iron are determined by the course of solidification. Therefore, it is important to study the causal factors of graphite shapes. Traditionally, it has been reported that D-type graphite readily appears on the surface or thin walled portion of a casting. This phenomenon can be explained by thermal undercooling. On the other hand, there are cases in which D-type graphite appears in the center region of a casting. Such cases can not be fully explained only by thermal undercooling. In this research, we considered constitutional undercooling as one of the mechanism of D-type graphite formation in the center region. We conducted thermal analysis of iron melt equivalent to FC250 in the shell mold to obtain cooling curves for the surface and center region, respectively. We also observed microstructures in each of the regions.

  We found that A-type graphite was formed in the middle of the surface and the center while D-type graphite was formed along with A-type graphite in the center region. We also noticed that the temperature gradient became milder as the measured point got closer to the center. Therefore, we assumed that a certain range of the center region of a casting has an inclination for constitutional undercooling. We also assumed that the growth speed of a eutectic cell is accelerated during the constitutional undercooling of the iron melt. Hence, we concluded that the graphite shapes in the center region tend to become D-type by the effect of constitutional undercooling.

  In order to reduce weight in automobile parts, the use of hypereutectic Al-Si system alloys with high fluidity is considered. For these alloys, the presence or absence of coarse Si phase makes a large difference in the abrasion resistance. In this study, Al-17% Si alloy with no P was cast in sand mold and permanent mold, and investigations were conducted on the presence/absence of coarse Si phase in the obtained ingot.

  Primary Si phase crystallized on the contact site of the mold in the sand mold and permanent mold. In the permanent mold, eutectic cells with dendritic-coupled growth were observed. The coarse Si phase had a tendency to crystallize at the top and around it. We were able to clarify the formation of the coarse Si phase based on undercooling due to concentration of solute.