In the die casting process, it is difficult to prevent porosity in products. Porosity has undesirable influence on mechanical properties such as strength of components and resistance to air leakage of pressure vessels. Recently, the PRPC (Porosity Reducing Post Compression) method is adopted as a secondary process to deal with porosity. The PRPC process has the potential for improving productivity because it allows the impregnation process to be eliminated or reduced. In this study, the improvement of tensile strength by applying the PRPC process was investigated. The porosity inside die cast specimens was observed nondestructively by X-ray computed tomography (CT) to examine the reduction efficiency of porosity by applying the PRPC process. It was shown that PRPC with permanent strain of about 10% at the temperature of 300 degrees reduces porosity by approximately half. In addition, the tensile strength could be improved by optimizing the compression direction.

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  In the automobile industry, both lightweight solution for improvement of fuel efficiency and operating characteristics, and installation of new equipment for collision safety, are required. To address this requirement, porous aluminum, which has good lightweight properties and high energy absorption properties, has been considered for application to automotive components, but this application has been delayed because of the high production costs of porous aluminum. We propose a new fabrication method of porous aluminum utilizing friction stir processing (FSP). With this method, it is expected that, ① inexpensive common aluminum rolled material can be used, ② productivity is good because FSP is a simple process, and ③ energy conservation can be realized because FSP does not require inconvenient heating processes with high energy consumption. In this study, the applicability of the FSP method for fabricating porous aluminum by using inexpensive aluminum alloy die casting was investigated. It was shown that porous aluminum with porosity of about 50% can be realized and FSP has a high potential for fabricating porous aluminum using inexpensive die castings.

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  A cold crack criterion for JIS ADC12 aluminum alloy die casting is proposed. Through investigations on the temperature dependence of the fracture strain of JIS ADC12 aluminum alloy die casting, it was found that the fracture strain features a turning point at a temperature Tc (we call “critical temperature to ductility”, about 573K for the present composition), where the strain stays smallwhile below Tc and increases rapidly to a high level beyond Tc. Focusing on this character of the fracture strain, we analyzed the equivalent plastic strain (ε_c) of castings introduced below Tc in casting processes by thermal stress simulation and compared with the occurrence of cold cracks in die casting experiments. It was found that ε_c of the cracking positions in castings exceeded the fracture strain of JIS ADC12 aluminum alloy die casting below Tc, while ε_c of castings without cracks were much lower than the fracture strain. That is to say, the occurrence of cold cracks in die casting can be estimated by comparing ε_c with the fracture strain below Tc. Based on this proposed criterion, it is possible to predict the appearance of cold cracks in die casting by thermal stress simulation.

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  Effects of mold temperature and injection pressure on mechanical properties and surface defects of Na₂CO₃-20mol%NaCl-30mol%KCl salt-mixtures made by high pressure die-casting machine were investigated. The bending strength of the salt-mixture was increased with increasing mold temperature, while the injection pressure in the temperature range from 39MPa to 78MPa was not influenced by the bending strength. Results of the Weibull statistics analysis suggest that increasing the mold temperature is effective for increasing the reliability of the strength as well as the bending strength, because the surface crack decreases with increasing mold temperature. In addition, we succeeded in making a salt core for single closed deck type cylinder blocks. These results suggest that the Na₂C0₃-NaCl-KCl salt-mixtures made by die-casting machine are promising core material for aluminum alloy high pressure die-castings.

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  Magnesium alloys have been used in applications for various large car components such as an instrument panel cylinder block and oil pan due to light weight, high specific strength and recycle ability. Several types of creep resistant alloys have been developed for the purpose of utilization for the power-train parts, transmission case. However, many of those alloys suffer from inferior diecastability. We have developed the creep resistant alloy in order to be utilized for the automobile components, for example, the transmission case, the converter housing and the crank case. This paper summarized the mechanical, high temperature properties and die castability of new die cast creep resistant alloy.

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