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Low pressure die casting is defined as a net shape casting technology in which the molten metal is injected at high speeds and pressure into a metallic die. The low pressure die casting process plays an increasingly important role in the foundry industry as a low-cost and high-efficiency precision forming technique. In the low pressure die casting process is that the permanent die and filling systems are placed over the furnace containing the molten alloy. The filling of the cavity is obtained by forcing the molten metal, by means of a pressurized gas, to rise into a ceramic tube having protuberance, which connects the die to the furnace. The ceramics tube, called stalk, has high temperature resistance and high corrosion resistance. However, attention should be paid to the thermal stress when the stalk having protuberance is dipped into the molten aluminum. It is important to reduce the risk of fracture that may happen due to the thermal stresses. In this paper, thermo-fluid analysis is performed to calculate surface heat transfer coefficient. The finite element method is applied to calculate the thermal stresses when the stalk having protuberance is dipped into the crucible with varying dipping speeds. It is found that the stalk with or without protuberance should be dipped into the crucible slowly to reduce the thermal stress.

An empirical prediction method for the fatigue strength considering the effect of porosity was proposed. We prepared six types of specimen of ADC12 high pressure die cast aluminum alloy, where the casting condition was different to each other, and obtained the S-N curve for each specimen type from the fatigue test. The porosity volume fraction for all specimens was calculated using the X-ray CT images. The image-based finite element analysis was also carried out for all specimens to evaluate the maximum first principal stress corresponding to the nominal stress amplitude in the fatigue test. The maximum stress was referred to as the local stress amplitude, and its ratio to the nominal stress amplitude was defined as the local stress concentration factor. We modified the S-N data by using the local stress amplitude instead of the nominal stress amplitude, and obtained a single master S-N curve. From the statistical investigation, the local stress concentration factor was found to be determined empirically by the porosity volume fraction. The relationship was identified by the least-square approximation. Consequently, we found that the fatigue strength was predicted from the porosity volume fraction via the local stress amplitude and the master S-N curve.

A roll caster for making the five layers clad strip was devised. In this process, three twin roll casters were set at the vertical tandem position. This vertical type tandem twin roll caster was assembled. Five layers clad strip can be cast directly from the molten metals by the vertical type tandem twin roll caster. First layer was cast by the first caster (upper caster). Second layers were cast by the second caster (mid caster). Third layers were cast by the third caster (lower caster). Procedure of casting to make five layers clad strip is as below. First layer was cast by first caster. This layer was drawn into second caster. When first layer went into the roll-bite of the second caster, the molten metal of second layers was poured to second caster. This three layers clad strip was drawn into third caster. When this three layers clad strip went into the roll-bite of the second caster, the melting of third layers was poured to third caster. In this study, two kinds of five layers clad strips were tried by this caster. One of 3003 aluminum alloy was used for first and second layers, and 4045 aluminum alloy was used for third layers. The other of 3003 aluminum alloy was used for first layer, and AC4C aluminum alloy was used for second layers, and 4045 aluminum alloy was used for third layers. Two kinds of five layers clad strips could be cast by this caster. The interfaces of five layers clad strips were clear and flat.

Magnesium has the smallest specific gravity in the structural metallic material applied to automotive parts. It is expected to be suitable light material to meet the needs of a vehicle weight reduction in recent years. However, as magnesium alloy has low forgeability due to its crystal structure, forged magnesium application is quite few in automotive parts. Therefore, if the cast- forge method can be applied for magnesium alloy, it is expected to reduce the process number and improve the yield of the material. In this research, semi solid magnesium injection molding process has been studied as a method to obtain the perform with refined grain size of the crystal which is smaller than that of the method of gravity casting. In addition, the influence of various factors on the mechanical property has been examined. Moreover, this new cast -forge process which was combined with semi solid metal injection and forging was applied for actual automotive part. As a result, it was proved that the preform fabricated by semi solid injection had high forgeability and the studied new process had high potential as manufacturing process applied for actual structural member.

Magnesium has the smallest specific gravity in the structural metallic material applied to automotive parts. It is expected to be suitable light material to meet the increasing requirements of a vehicle weight reduction in recent years. However, as magnesium alloy has low forgeability due to its crystal structure, the forged magnesium application is quite few in automotive parts. In this research, the effect of forging rate for the aluminum-zinc system magnesium alloy casting on the crystal grain size, the strength characteristic etc. have been investigated in order to clarify the possibility of the cast- forge method of the magnesium and apply this method to an actual parts in automotive car. As a result, it is proved that the cast- forge method has high possibility as the manufacturing process to be applied for magnesium parts. By using this developed process and designing preform with proper shape with CAE, the final dimension of part and higher strength can be attained at only one stage forging.

In order to evaluate a casting material which had a variable tensile strength, a strength evaluation method was proposed. Tensile tests were carried out on a specimen with a particular artificial defect as the fracture origin. The fracture origin size could be controlled using the proposed evaluation method. Therefore, the tensile test results, which had slight scatter, were obtained. However, the shape of the artificial defect was different from the casting defect, thus the effects of each defect on the tensile strength might be different. Both the critical stress intensity factors at the beginning of the unstable fracture were then compared, and it was clarified that the artificial defect and the casting defect had the same effect on the tensile strength. By this method, a non-combustible Mg alloy with added-Si, which contained large casting defects, could be evaluated. It was clarified that there was no difference of tensile strength between the noncombustible Mg alloys with 1% and 2% Si, and the relationship between the tensile strength and temperature was obtained.

This study was aimed at investigating of Casting of hypereutectic Al-Si alloy strip by a vertical type twin roll caster. Hypereutectic Al-Si alloy has some useful advantages i.e., low thermal expansion, better thermal conductivity and wear registrant. Recently, the plate of hypereutectic Al-Si alloy which thickness is thinner than 1mm, is demanded. The hypereutectic Al-Si is hard and brittle. Therefore, only the many times of hot rolling was useful process to make thin plate. In the present study, the roll casting of Al-25%Si strip was tried by a vertical type high speed twin roll caster from the point of energy saving. The twin roll size of the roll was φ300×W100. Roll-load was set low enough to prevent the sticking of the strip. The roll speed was operated at 20m/min and 40m/min. The solidification length was 100mm. The Al-25%Si strip, which thickness was about 1.7mm, was cast directly from the molten metal. The primary Si was not dispersed uniformly. The eutectic Si became fine and globular. The roll cast Al-25%Si was expected superior ductility.

In hydraulic turbine runner, accidents due to fatigue often occur. In this study, tension-compression and bending fatigue tests were carried out for the stainless cast steel cut out from the turbine runner crown, in order to clarify fatigue properties and mechanism of fractures on stainless cast steel SCS6 used as hydraulic turbine runner aged 27 years. The test results are summarized as follows:(1)The S-N curve of aged SCS6 used in this study has wide scatter and the tension-compression fatigue strength was lower than bending test data. (2)From SEM observation of the fracture surfaces, crack initiation sites were found to be the casting defect which consist of dendritic phase and pore. (3)It is possible to evaluate the fatigue life of aged SCS6 by using the casting defect size √area and the initial stress intensity factor calculated by defect size. The value of the threshold stress intensity factor obtained in this study were 2.6 MPa·m1/2. (4)It was proposed that a critical volume of tension-compression test specimen where uniform stress was applied should be 20% of the region from the surface, because stress intensity factor of surface crack is larger than that of interior crack of the same size.

Effect of casting defects on the fatigue strength of die cast aluminum alloy was addressed through the tension-compression fatigue test and the X-ray CT inspection, which revealed the amount of porosity included in the specimen. Six types of casting condition were employed to examine the effect of different porosity. Most of fatigue crack sources were the pores. The porosity volume fraction was calculated for all specimens from the three-dimensional X-ray CT images. The fatigue limit of each specimen type was estimated from the fatigue test results. The correlations among fatigue limit, porosity volume fraction, Vickers hardness, and dendrite arm spacing were evaluated, and the result showed that the porosity volume fraction most dominantly affected the fatigue limit in the averaged sense.

In hydraulic turbine runner, unexpected accidents due to fatigue often occur. In this study, in order to clarify fatigue crack growth and closure properties on SCS6 and SC49 used as hydraulic turbine runner over 27 years, fatigue crack growth test under the stress ratio R-constant were carried out using compact tension specimens of both materials. Fatigue crack growth rate and crack closure were measured by means of an unloading elastic compliance method. The results are summarized as follows:(1) Although the stress ratio dependency on the fatigue crack growth rate is found in both materials, the influence is recognized remarkably in SCS6 except for threshold value. (2) Although the threshold stress intensity factor ΔKth of SCS6 is almost same as that of SC49 when R

Mechanical properties of cast irons strongly depend on the graphite morphology and the matrix structure, thus both of them should be evaluated for their characterization. The former can be evaluated by ultrasonic testing (UT), and the latter can be evaluated by eddy current testing (ECT). Considering the background above, this study proposes a novel method for the material characterization of cast irons with an EMAT/EC dual probe. For this purpose, we conducted UT and ECT for cast irons with different graphite morphology and matrix structures with the present probe. As a result, correlations betwe en the nodularity of graphite and ultrasonic velocity, and between one the pearlite ratio and EC signals were obtained. These results imply that the EMAT/EC dual probe is effective for the material characterization of cast irons. Cast iron is an Fe-C base alloy that contains iron as the princ ipal ingredient and carbon more than 2%. It is useful engineering material due to its excellent mecha nical properties, such as strength, ductility, free cutting, and productivity. Accordingly, it is widely used f or the parts of automobiles, industrial machinery and so forth. However, the manufacturing process of casting is complex, and the microstructure control is difficult. Therefore, nondestructive characterization of mechanical properties of cast irons is necessary and one of key issues in the foundry industry. The structure of cast irons consists of graphite and a steel matrix. Mechanical properties of cast irons depend on the graphite morphology and the matrix structure, thus both of them should be evaluated for their characterization. The nodularity of cast irons is estimated by measuring the ultrasonic velocity, and the method is established (1). The matrix structure and hardness of cast iron are estimated by measuring the EC signals of ductile cast irons (2). Therefore, the graphite morphology and matrix structure can be evaluated by ultrasonic testing (UT) and eddy current testing (ECT), respectively. We have proposed an EMAT/EC dual probe (3) that can obtain ultrasonic and EC signals with a single probe structure. This probe was applied to the evaluation of wall thinning of pipes, and the feasibility of the nondestructive evaluation based on the complementarity between ECT and UT was verified. This paper proposes a new method for the material characterization of cast irons with an EMAT/EC dual probe. The material properties of cast irons are not uniform and should be characterized with respect to each point. The dual probe with a single and compact structure can acquire UT and EC signals