Solidification cracking is one of the defects of casting. In order to increase productivity of DC casting and various shape casting processes, predicting the occurrence of solidification cracking by using CAE (Computer Aided Engineering) should be essential. Therefore, it is necessary to obtain mechanical properties of solid-liquid coexistence alloys. However, in the previous reports, flat distribution of temperature in the gage length was not ensured. In this study, tensile test device for a semi-liquid Al–Mg alloy with 2°C of the temperature distribution in the gage length (Max. 10 mm) was developed. Tensile strain was measured by using in-situ observation of marker on the surface of the specimen. As the result, stress-strain curves and fracture strain in various temperatures on the semi-liquid Al–4.3mass%Mg alloy were measured. It is also found that tensile strain tends to be higher at neighborhood of the crack. Thus, strain depends on the gage length. From the observation of the fracture surface and estimation of Scheil-Gulliver micro-segregation, microstructure of the specimen were supposed to change due to the heating process.

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Color, texture and the tactile senses are recognized as the evaluation factors for a metal surface. In the present, though those factors are widely used as the popular comprehensive indexes to characterize a metal surface, evaluation of these factors are mainly referred to the terms of touch or visual look. From a customer point of view, particular factors to characterize a metal surface and its numerical expression may not only be helpful to judge its commercial value, but also to avoid unnecessary trouble on judging its appearance. Moreover, these quantitative evaluations are able to improve reproducible accuracy. This paper describes the quantitative evaluation method of a surface texture for metals. As the specimens, aluminum alloy that is one of the popular metals of the exterior material for industrial products are used. The surface textures have been measured by a non-contact 3D surface profiler and the results have been compared with nickel silver alloy and stainless steel. First, the surface textures are measured by stylus method and optical interferometer method to find the relationship between those two measurement methods. Then, as x surface property parameters to express transcriptive property of shot blasted, upper material ratio Sr1 and lower material ratio Sr2 were concluded to be effective.

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Ti-x HAp (x=0, 10, 20 and 30 mass%) composite powders were synthesised by mechanical alloying (MA) using a vibrational ball mill, and MAed composite powders were consolidated into bulk composite materials by spark plasma sintering (SPS). The hardness and constituent phase of the MAed powder and SPS materials were investigated by hardness measurements and X-ray diffraction (XRD) , respectively. Mean particle size of the MAed powders and microstructure of the SPSed materials were characterised by scanning electron microscopy (SEM) and optical microscopy, respectively. No decomposition of HAp in the MAed Ti-10 and 20 HAp composite powders occurred. However, decomposition of HAp in the MAed Ti-30 HAp composite powders occurred to form both CaO and CaTiO₃. Formation of both TiC and CaO was observed in the all SPSed materials. In addition, formation of both CaO and CaTiO₃ was also observed in the Ti-30 HAp SPSed materials. The hardness of the SPSed materials increased by both an increase in the amount of HAp and in the MA time. The results thus imply that the Ti-HAp composite materials exhibiting the high hardness can be obtained by a controlling of the amount of HAp powder and MA time.

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Phase transformation of solid solution decomposition occurring in a 96 at%Mg–4 at%Dy alloy, which was solution-treated at 540°C and subsequently aged at 250°C for various lengths of time, has been investigated by conventional transmission electron microscopy (TEM)in combination with high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM). The atomic-scaled observations based on both techniques provide the evidence that the first appreciable change in microstructure caused by aging is the occurrence of a short-range ordered state in Dy-segregated regions and that the short-range ordered state allows full of the nuclei of β′ phase associated with an Mg₇Dy-type structure to occur in the domains, just as in cases of Mg–Gd and Mg–Y systems. With an increase of age-hardening effect, the β′ precipitates become larger and increasingly anisotropic in morphology, accompanying three orientation variants in coherent with the Mg-matrix. When reaching at the stage of hardness maximum (as-aged at 250°C for 100 h), the β′ precipitates, which have an orthorhombic structure with lattice parameters of a=0.659 nm, b=2.231 nm, c=0.523 nm, take the form of a thin disk-shape with a thickness of 20~100 nm and a diameter of 200~400 nm. With an advance of over-aging effect, the β′ precipitates are gradually reduced in volumes and replaced by β precipitates of cubic structure.

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Cylindrical 2024-T3 aluminum alloy studs were welded to 5052-H34 aluminum alloy plates by using an advanced high-speed solid-state joining method. Double cylindrical copper tubes, an assembly consisting of an inner tube and an outer tube, were used as electrodes. A stud having a circular ridge projection at its bottom was mounted at the end of the inner tube. The stud was then pressed against the plate surface. A discharge current was next introduced to the stud through the inner tube, whereupon the current flowed through the plate surface to the outer tube, which acts as a ground. The welding was completed within a few milliseconds without a notable increase in temperature of the joint. Subsequent examination revealed that the circular ridge projection had crushed and spread along the plate surface. Asymmetrical deformation occurred on both the inner side and outer side of the projection. The deformed area on the inner side of the projection consisted of a compacted grain structure. In contrast, the deformed area on the outer side exhibited a refined grain structure. These results indicate that the outside region was subjected to a higher temperature than the inside region. The joint was next investigated by tensile testing to evaluate its strength. The fracture surface of the joint region on the inner side of the projection exhibited a relatively flat surface with a limited number of dimples. On the other hand, that on the outer side was entirely covered with small dimples. Fracture stress was calculated by dividing the measured tensile fracture load by the dimple fracture area. The fracture stress thus obtained was found to be equivalent to the UTS of 5052-H34 alloy.

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A356 alloy was cast into permanent molds and subjected to T6 heat treatment. Two solutionizing (solution heat treatment) temperatures (540°C and 560°C) were used, with the holding time for each varied between 0 min and 240 min. Tear test specimens of 4 mm in thickness were machined from the castings. Tear toughness (UEp: unit crack propagation energy) was obtained from load-displacement curves. With increasing solutionizing holding time, eutectic silicon particles were found to become larger and mean interparticle distance was found to increase. The UEp of specimens solutionized at the higher temperature (560°C) increased with holding time until 120 min but decreased with longer holding times. SEM observation of fracture surfaces after tear testing revealed dimples originating from dispersed silicon particles within the eutectic phase. Fine dimples were also observed in the eutectic aluminum region in specimens with reduced UEp. These fine dimples were different from the dimples found to originate from the eutectic silicon particles.

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