The microstructural changes in 99.999mass% aluminum were investigated during deformation at elevated temperatures by the constant-speed-compression tests. The stress vs. strain curves of poly-crystals showed multipeak stress oscillations at temperatures from 511K to 820K at an initial strain rate of 1.67 × 10^-3/s. An in-situ observation of diffraction patterns for a single-crystal was carried out during a compression test at an initial strain rate of 1.67 × 10^-4/s at 533K. Asterism patterns appeared in the work hardening stages, while spot patterns appeared in the work softening stages. An anodized single-crystal compressed up to 0.6 at an initial strain rate of 1.67 × 10^-4/s at 583K showed dynamically recrystallized grains containing subgrains. These observations prove that the recrystallization is caused by the discontinuous dynamic recrystallization mechanism.

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The composite which was prepared by squeeze casting process had a high Young's modulus (470GPa) and a low coefficient of thermal expansion (0.4 × 10^-6K^-1) in the longitudinal direction. Thermal cycling between 300 and 620K caused residual expansion in the transverse direction and cracks in the interface between fibers and matrix. However, these damages were scarcely observed after thermal cycling either between 150 and 390K or between 300 and 540K. The residual expansion increased with the temperature difference of thermal cycling, namely, with increasing plastic strain of the matrix. These thermal fatigue damages were observed under the condition of thermal strain higher than 5×10^-3. This critical strain is much higher than 2×10^-3, which is the critical strain for the PAN-based carbon fiber composites. Therefore, it is considered that the pitch-based carbon fiber composite is superior in thermal fatigue resistance. The calculation on the basis of anisotropic properties of the pitch-based carbon fiber indicates that the inter- facial stress is as low as a tenth of the bonding strength.

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Heat-treated aluminum alloys are strengthened by aging following solution treatment and quenching. Low cooling rate after solution treatment causes precipitates to occur intergranularly along the grain boundaries. The grain-boundary precipitation results in intergranular corrosion and lowers mechanical properties of alloys. In this study, effect of cooling rate after solution treatment on structures and mechanical properties of as quenched and as aged 2090 aluminum alloy, Al-3mass%Cu-2mass%Li-0.12mass%Zr alloy, one of Al-Li alloys which have been developed as new aluminum alloy for aircraft was investigated. Tensile strength of both as solution-treated and as aged alloys was constant at cooling rate over 1.4K/s, while it decreased with decreasing cooling rate at cooling rate below 1.4K/s.0.2% proof stress showed the same tendency as the tensile strength. Elongation of aged alloy decreased with decreasing cooling rate. Precipitates such as T₁ and θ-Al₂Cu were formed at the grain boundaries and T₁ in the grains as cooling rate was lowered. It is likely that T₁ precipitate formed at the grain boundaries mainly lowers mechanical properties, especially elongation of aged alloy. T₁ precipitated on δ'-Al₃Li when cooling rate was slower. Heterogeneous precipitation of T_B. on β'-Al₃Zr.was observed in aged alloy.

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Possibility of making laminate, which is made directly from molten metal and the rapidly solidified aluminum alloy foils were laminated, was investigated. To laminate foils into multi-layer laminate from molten metal, rotating disk process was devised. Sticking of the first foil and laminate to the surface of the disk is most important to make the laminate. Fundamental factors which affect sticking length of the foil are disk temperature, disk speed, disk material, number of slit. Disk was heated up to 100°C. Disk was made from SUS304 and rotating speed was up to 47m/s. Nozzle which has 1-7 slits was used to eject molten metal. Al-12mass%Si alloy was melted in air and ejected onto the disk. Laminate consisting of more than 50 layers of foils can be cast by rotating disk method. Cooling rate of laminate in the range of 10³-10⁴°C/s is attained. There is not much difference in cooling rate of each layer. Tensile strength of laminate is about 300Pa. Each layer of the laminate is not torn along interface by bending.

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The cold deformability of 2218 aluminum alloy cast bars was evaluated by constant speed compression tests. The cold deformability increased with decreasing in Al₉NiFe constituents controlled by the amount of Ni, and with decreasing in the constituentsize controlled by solidification rate. Similar result was obtained when the formation of micro-cavity acted as stress concentration sites was suppressed by the decrease in the hydrogen gas content. The deformability increased when the stress concentration at the grain boundary was reduced by refining in the grain size. And the deformability increased with decreasing in the deformation resistance controlled by the precipitation of S (Al₂CuMg)-phase.

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Japanese Industrial Specification recommends Al-Zn-Mg alloys are annealed at 688K followed by furnace cooling. However sometimes the cold working (drawing or rolling) of annealed material in the above condition becomes more difficult because of natural age hardening. In this study, the effect of annealing temperature (493-683K) on both mechanical property and cold workability in annealed Al-Zn-Mg extruded bars was investigated from the view point of precipitation of second-phase particles. In the case of annealing at 573K or less, high elongation, low tensile and yield strength were obtained compared with annealing at 683K, and furthermore the hardness was not changed during room temperature aging. The material annealed at 548K can be rolled up to 95% reduction without edge cracking. However, edge cracking with shearing was occurred at 80-85% reduction in the material annealed at 683K. A lot of particles with a diameter of about 0.1μm, which are estimated as MgZn₂-phase precipitates having no coherency with matrix, were observed in annealing at low temperature. While, these particles were reduced at annealing at 683K and solute atoms increased. The reason why cold workability of materials annealed at low temperature was improved is that homogeneous deformation occurs and shearing fracture is inhibited because of dynamic recovery around particles.

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