Squeeze die casting with a composition similar to JIS ADC12 aluminum alloy was aged at 453 K with or without prior solution treatment. Aging following solution treatment, which is termed T6-treatment, increased the hardness of this alloy. Using transmission electron microscopy, we investigated precipitates responsible for the age-hardening. Concentration of solute silicon, copper and magnesium during aging led to the formation of several types of precipitates in the matrix face-centered cubic (fcc) Al-phase. Precipitates exhibiting equiaxed shape and possessing copper-enriched faces at the interface with the Al-phase were observed. We suggest that these precipitates have fcc structure containing silicon, copper and magnesium atoms substituting for aluminum. Prolonged aging caused the formation of another type of precipitates with elongated shape, and they were identified to be the S″-phase. Some regions within the precipitates of the S″-phase transformed into the Q-phase with increasing silicon content in the precipitates. Precipitates of the S-phase and θ′-phase also formed by over-aging.

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The effect of solid solution and precipitation on recrystallization of Al–Mg–Si alloys was investigated. Hot-rolled sheets were heated at 823 K, and then they were treated with or without intermediate annealing (IA) at 623 K. Both samples were rolled at room temperature up to 87.5% and annealed finally at 623 K. The sheets with IA (IA sample) showed recrystallized grains elongated to rolling direction. The sheets without IA (non-IA sample) consisted of small equiaxial recrystallized grains. Cube (｛001｝〈100〉) texture density of the IA sample was higher than that of the non-IA sample. In the IA sample, β-phase precipitates and the precipitate free zone (PFZ) were formed by IA. The PFZ was likely to be elongated with rolling and become a preferential recrystallization zone. Therefore, recrystallized grains grew along the elongated PFZ and formation of long cube orientation grains caused high density of cube texture. On the other hand, in the non-IA sample, shear bands were formed by rolling. They were speculated to work as recrystallization sites. Because of origination of randomly oriented grains from shear bands, it was assumed that small equiaxial recrystallized grains were formed and the density of cube texture decreased.

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The high-temperature oxidation behavior of Ti–6 mass%Al–4 mass%V alloys have been investigated in temperature ranges of 773 to 973 K, and 1123 to 1273 K, in air. A kinetic study of the oxidation has been also carried out in Ti–6 mass%Al–4 mass%V alloy. The oxidation products have been examined by X-ray diffraction (XRD), electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS). The banded Al₂O₃ layer is probably formed in the oxides of the Ti–6 mass%Al–4 mass%V alloy by means of EPMA, although the rutile TiO₂ is mostly detected by means of XRD in the oxides of surface layer in the alloy at 1273 K. Furthermore, the TiO₂ and Al₂O₃ are observed by XPS in surface of the above alloy at 1123 K for 3.6 ks, but the V₂O₅ is not observed. It is found that the apparent activation energy for the isothermal oxidation in the Ti–6 mass%Al–4 mass%V alloys is Q_i=223 kJ/mol, and the activation energy for the non-isothermal oxidation (TG experiment) at a constant heating rate is Q_a=209 kJ/mol in the present alloys.

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Today, stent is employed to expand the narrowed tubular organ such as blood vessel, esophagus and bile duct. The major of materials used for the stent is stainless steel or Ni–Ti alloy which remains in the body permanently and prevents the second application. Accordingly, this research targets on developing the biodegradable magnesium stent. Magnesium is, however, inferior to the conventional materials in mechanical properties. Therefore, it is required to improve the mechanical properties of magnesium and design the stent considering poverty of strength and ductility. To improve the mechanical properties, strengthening by solid solution due to adding Zn and Ca and by grain refining due to doubly hot extrusion were conducted. As a result, the extruded Mg–Ca–Zn alloy showed the superior mechanical properties compared with the conventional magnesium alloys. Furthermore, finite element analysis (FEA) based on the material data was conducted to investigate mechanical performance of a stent model. As a result of the FEA, it was indicated that Mg alloy stent has sufficient ductility for expansion and strength for restenosis. Examination for expanding a fabricated stent revealed that the FEA was reasonable and the present alloy was a good candidate for the stent application.

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The magnesium composites containing hydroxyapatite (HA) particles were synthesized. Unreacted Mg/HA composites were successfully fabricated by extruding the two component powders. The Young’s modulus and strength of the extruded composites were lower than that of extruded magnesium, whereas the damping capacity of the composite was superior to that of extruded magnesium over the entire strain range examined. Microstructural observation of the composite containing 10 vol%HA revealed that HA agglomerates with the size of 10–15 µm were formed during the fabrication. The mechanical properties of the composites were closely associated with the HA agglomeration.

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