The test of fatigue crack growth was achieved using CT specimens of aluminum alloy die casting ADC12 which were varied in thickness from 2.9mm to 25.4mm And the relation between the rate of fatigue crack growth da/dN and the stress intensity factor range ΔK was obtaind. From the result, the fatigue fracture toughness K_fc and the threshold stress intensity factor range ΔK_th in each specimen were calculated. The same test was carried out in heat-treated die castings ADC12, B390, and aluminum cast alloy AC4A specimens. The results were as follows.
  (1) In ADC12, both K_fc and ΔK_th were independent of the thickness of CT specimens.
  (2) Heat-treamant in ADC12 and B390 caused increase of K_fc. but little change in ΔK_th.
  (3) K_fc in ADC12, was as same as in aluminum alloy AC4A cast using a sand mold, but was smaller than cast using a metal mold. In ΔK_th there were very little difference between AD12 and all AC4A specimens.

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  The local squeezing method with pin was adopted to prevent internal defects such as gas blowholes and shrinkage porosities in the local area of ADC12 die-castings. This treatment remarkably improved the fatigue strength of the die-castings. The smaller the size and density of defects, the higher is the fatigue strength is.

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In order to determine the grain-size of tea, the sieve analysis of tea was examined with J. I. S. standard sieves. The test sieves used had openings of 500-5, 660μ in √2 magnifi-cation series. On measuring the grain-size distribution of tea, 50g. of tea were sieved for 5min. with Ro-Tap shaker, and the residue on each sieve was weighed.

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Causes for scattering of the tensile strength values were investigated on specimens which were cut from various parts of aluminum castings (ADC10, 12) made by die casting machines (5-20MN). The strengths of non-defect specimens are 200-350MPa. In the case where the distance along the flow of molten metal from the gate is less than 150-200mm, the strength is almost constant. But this value varies with the kinds of castings or their thickness, corresponding to the size of dendrite arm spacing. The strengths at locations beyond the above-mentioned distance are lower, and the apparent specific gravities are also lower. The strengths of specimens containing defects are under 200MPa. These casting defects are classified into lump, thin and scatter structure defect. While the lump defect reduces both apparent specific gravity and tensile strength, the thin and scatter structure defects reduce the tensile strength but hardly affect the apparent specific gravity. The tensile strength varies almost linearly with the fraction of defect area on the fracture surface. The scatter of the strength of aluminum die castings can be reduced, when they are cast under the conditions that produce defects within a certain small quantity.

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  The cooling rate and solidification time of aluminum die castings were estimated by their dendrite arm spacing (DAS II). DAS II of the die castings is the smallest in their surface layer, increasing toward the center of section thickness. The cooling rate is about 1000°C/s in the surface layer, whereas it is only 20-30°C/s in 2mm inner from the surface. Namely, the aluminum die castings are solidified toward their center at a remakably large temperature gradient. Furthermore, the solidification time of the die castings was estimated to be 1 sec in the surface layer, and 2-6 sec in the center of 3-7mm section thickness. The cooling rate and solidification time are more strongly influenced by shooting conditions rather than the section thickness of the castings.

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Heat Checking is a very important problem limiting the service life of aluminum die casting dies. In this paper, the relationship between the surface residual stress, which varies with die casting operation, and the initiation and propagation of heat checking is described.
Measurement of residual stress and observation of heat checking were carried out on a cover and an ejector production die made by SKD61 (AISI H13). The surface residual stress was measured by X-ray and the heat checking was observed in detail by SEM after every prescribed shots from the beginning to the end of the die service life. The mechanism of residual stress variation and the effects of the position and the cavity shape of dies on the residual stress variation and the initiation and propagation of heat checking were clarified.
The following conclusions were drawn from this investigation.
(1) The surface residual stress, which was compressive before die casting operation, changed immediately toward tensile side and saturated in the early stage of operation, say at only 50 shots. This fact is considered to result from the following process; the surface layer of dies is rapidly heated by molten aluminum. The thermal expansion due to this rapid heating is restrainted by the substratum and thus the surface layer is subjected plastically to compressive strain. After cooling, the surface residual stress changes toward tensile side and saturates at some tensile value in the early stage of die casting operation.
(2) The value of saturated tensile residual stress depended on the position and the shape of die cavity. This experimental result is caused by the magnitude of thermal load and restraint.
(3) On the gate side of die cavity, in which the saturated tensile residual stress is large because of large thermal load, microcracks initiated in the saturated period. But on the position apart from the gate, in which the saturated tensile residual stress is small because of small thermal load, the residual stress did not decrease and microcracks did not initiate even at the end of die service life.
(4) In the later stage of crack propagation on the gate side of die cavity, heat checking was observed by the naked eye and the residual stress decreased to zero.

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  The temperature change and the heat flow in a die were analytically calculated using a simple one-dimensional model to obtain the basic knowledge about the thermal behavior of a die during casting cycles. According to the characteristic of the heat flow field, three regions were defined in the die : the reverse heat flow region, the variable heat flow region and the constant heat flow region. In the constant heat flow region, temperature and heat flow were steady and calculations thus simple. The reverse heat flow ratio was defined as the ratio of the heat flowing to the cavity side to the total heat absorbed by the die. This concept should prove useful for evaluating the relative importance of cavity side spray. The general relation between the thermal behavior of a die and the casting conditions was studied based on the results of this study.

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Effects of a surface layer with chill structure, specimen thickness, shape of mold and powder lubrication in a sleeve on fracture mechanic characteristics were investigated for aluminum alloy die castings ADC12 with two different types of molds (flat and staircase shapes). The results are as follows. In the case of a flat mold, a decrease of thickness improves mechanical properties. A surface layer with chill structure has a substantial influence on mechanical properties, but little influence on fracture toughness. In the case of the staircase mold, the mechanical properties are the same as for the flat mold. On the other hand, the powder lubrication in the sleeve improves the fracture toughness and reduces the scatter in fracture toughness. There is little influence of both the surface layer with chill structure and the specimen orientation on the fatigue crack growth resistance, but with decrease of specimen thickness, the fatigue crack growth resistance decreases, especially in the region of near-threshold fatigue crack growth rate. In addition, the lubricating method has no effect on the fatigue crack growth resistance for the staircase-shapes die castings.

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  The die cast process is useful for producing parts with smooth surface, high dimensional precision, and complicated shapes. However, with increasing importance placed on energy-saving in recent years, energy-saving has also become an important theme in the die casting process. During the die casting process, molten metal is injected at high velocity and pressure into a mold die cavity to prevent casting defects such as porosity, cold shut, flow line, etc. For this reason, die casting machines require considerable energy using several hydraulic pressure pumps and accumulators. On the other hand, melting furnaces have poor energy efficiency of about 20% due to large energy loss through radiant heat from the furnace surface and exhaust fumes.
  To promote energy-saving in the die casting process, we developed the “hybrid die casting machine with servo and hydraulic mechanism” to enhance energy efficiency. By using this technology, we have successfully reduced energy consumption to 1/6 of that of our previous die casting process.

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  In a previous article, rapid solution treatment until five minutes with the temperature rising rate of 50℃/sec using high frequency induction heating was applied to JIS ADC12 high pressure die castings. This heat treatment leads to the moderate increase in solid solution amount, preventing pores, and eutectic silicon refining, and spheroidizing. Especially, changing the eutectic silicon shape improves fracture toughness. In this article, the effect of rapid solution treatment on toughness improvement was evaluated from tensile strength and ductility. The results were as follows. It was found that elongation to fracture increased about 67% by solution treatment, moreover tensile strength increased by around 10% with aging treatment for four hours at 200℃, compared with as-cast specimens. Under-aging treatment was more effective than peak aging for toughness improvement in rapid solution treatment. The one hour aging treatment resulted in about 20% increase in elongation to fracture, while significant decrease was not found in tensile strength, in comparison to specimens treated by peak aging (200℃, 4hrs). In addition, it was assumed that the microstructure of as-cast specimens contained considerable solid solution amounts due to rapid cooling of castings, and also included fine precipitation formed during natural aging for a long-term period.

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This paper aims to clarify the relationship between Japan's ODA Policy and the Diet, analyzing the trend and content of the Diet discussions in the past 10 years.

The findings are as follows: 1) there are high correlation between the news of mass media and diet discussions, 2) special committee for ODA does not exist in Japanese Diet, 3) the budget and annual plan of Japan's ODA are not discussed substantially. It seemed that the role of the Diet is affected deeply by the institutional and administrative circumstances where Japan' ODA is located.

On the other hand, mature arguments have been developed recently. The discussions tends to more concentrated to “What is our strategy”, “Where and What we allocate ODA”, “How we reform ODA system”. In addition, it is clear that the Diet has given important role to policy making, especially in the case of aid policy to China and reform of ODA administration.

It seems that participation to the ODA policy by the Diet will increase still more in the future.

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The effect of microstructure, especially DAS II (Secondary Dendrite Arm Spacing) and chill layer in ADC10 aluminum alloy die castings on the tensile properties, the fracture toughness and the crack propergation is examined by preparing the die castings which have different DAS II and different thickness of chill layer cast under several casting conditions by cold chamber die casting machine. The results are as follows. (1) The tensile strength increases with the decrease in DAS II and there is the Hall-Petch relation between DAS II and 0.2% proof stress. While DAS II doesn't affect the fracture strain. (2) As a crack propagates through the boundary between α-phase and eutectic Si crystal, the increase in DAS II makes the fracture surface be rougher and it causes the increase in the fracture toughness. (3) The tensile strength and the surface hardness of chill layer are higher than substrate. It is possible for the reason to be not only relaxation of stress concentration due to small DAS II but also strengthening by solid solution due to the larger amount of occluded copper and magnesium.

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