The microstructure of the aluminum borate whisker reinforced AC8A matrix composite fabricated by squeeze casting was examined with high resolution electron microscopy. Fine reaction products were observed on the whisker surface, which were identified to be MgAl₂O₄ (partly γ-Al₂O₃). Those reaction products introduced large strain inside to accomodate the lattice mismatch with a whisker and showed the crystallographic orientation relationship as follows:
{010} Al₁₈B₄O₃₃//{111} MgAl₂O₄
[001] Al₁₈B₄O₃₃//[110] MgAl₂O₄
No further reaction took place at the area covered with the reaction products. Steps were formed on the whisker with the reaction products on them. A thin amorphous-like layer was observed on the interface between the whisker and the matrix.

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XPS spectra of Al (110) plane polarized in HCl solutions added aliphatic carboxylic acids and ATR IR spectra of film on Al specimen polarized in the same solutions were measured. The magnitudes of chemical shifts of the XPS spectra are proportional to both decrease in i_corr and the magnitude of E, and the shifts are proportional to strengths of the carboxylic acids. The ATR IR spectra show that weak hydrous oxide films form on the Al surface and RCOO^- is adsorbed on the surface. The Al₂O₃ film is made on the Al surface and H₂O, RCOO^- form a hydrogen bonding with the Al₂O₃ film, and this becomes the hydrous oxide films. The strength and holding of the films are the same as the degree of the decrease of i_corr and the order of the strengths is CH₂=CHCOO^->HCOO^->MeCOO^->EtCOO^-.

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Rotating bending fatigue tests of modified Al-Si-Cu-Ni-Mg eutectic casting alloys (AC8A) and hypereutectic casting alloys (AC9A and AC9B) were carried out in a temperature range between room temperature and 400°C. The fatigue strength of sodium modified AC8A is superior to that of phosphorus modified AC8A. The fatigue strength of AC9B with lower content of silicon is greater than that of AC9A. The decrease in fatigue strength is due to a coarse primary silicon. It is concluded that the fatigue properties of Al-Si-Cu-Ni-Mg casting alloys are influenced by the primary silicon grains.

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The effect of prior warm-working on superplasticity was studied by means of tensile tests as well as metallographic observations for a cold-rolled 7075 aluminum alloy. Superplasticity appeares in the warm-worked samples above a critical strain ε_c within the range of temperatures of 570K to 620K and at strain rates from 10^-4s^-1 to 10^-2s^-1. Metallographic observations show that static discontinuous recrystallization occurrs in materials warm-worked below ε_c at high temperatures, but it does not occur at all above ε_c. In the latter case unrecrystallized and recovered substructures containing fine precipitates exist stably at high temperatures, then the evolution of fine grained matrices with an average grain size of 4.7μm follows during further hot deformation. Continuous recrystallization takes place dynamically, leading to superplasticity. The following results are obtained from the optimum warm-worked samples: (i) the apparent activation energy for plastic flow is 90kJ/mol, which is about the same as that for grain boundary diffusion, (ii) the minimum stress exponent is 1.6, and (iii) the grain size dependence of flow stress is large. It is concluded, therefore, that the plastic flow is controlled by grain boundary sliding.

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It is true that wettability plays an important role in fabrication of metal matrix composites: it decides an applied pressure in molten metal infiltration into fiber preforms. Infiltration occurs when the work done by the applied pressure balances the interfacial energy change due to the replacement of the solid/vapor interface by the solid/liquid interface. It has been experimentally and theoretically approved that fiber arrangement greatly influences the threshold pressure of infiltration in the alumina fiber/molten aluminum system. The threshold pressure of the uni-directional fiber array preforms is experimentally determined to be 425kPa, which is a little less than that calculated theoretically because of slight disarray in the fiber alignment. By contrast the experimentally observed threshold pressure of the quasi-planar random array is 245kPa. If the whole fiber surface is wetted, the wettability, γ_la cosθ, where γ_la: the molten aluminum/atmosphere interfacial energy and θ: the contact angle, is calculated to be-0.592Pa•m. The relation between the threshold pressure and wettability is derived for infiltration with non-infiltrated defects at the intersection of non-wetted two fibers. According to this relationship, the threshold pressure of alumina fiber/molten aluminum system with defects is smaller than that without defects, and it decreases with decrease in intersection angle of two fibers because of increasing defects.

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It has been known that fine grain in a 7475 alloy sheet was obtained by the precipitation of large second phase particles with about 0.75μm in diameter followed by warm rolling. In this study, the roles of the large particles and dissolyed solute atoms in the grain refinement were investigated. Cold rolling was carried out instead of warm rolling. The results show that the large particles, which are Mg₃ (Al, Cu, Zn)₅ phase, contribute to homogeneous deformation during cold rolling, and the solute atoms, which are Zn, Mg, and Cu, precipitate on dislocations and retard the restoration of substructures during cold rolling and heating at lower temperature. At higher temperatue, it is supposed that the growth of recrystallized grain is inhibited by precipitaion of Cr on grain boundaries during rapid heating. While, in case of no large particles, heterogeneous deformation with shear bands occurres during cold rolling. Large recrystallized grains are formed at these bands during heating.

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It has been well known that superplasticity occurs when grain size is fine. Rockwell International (RI)'s thermomechanical treatment is one of the grain refining methods. However, the RI's process has several difficulties in a commercical production. Therefore a new process was investigated in this study. As a result, the process which has an intermediate heat treatment of a plate, cold rolling and rapid heating has been developed. To obtain fine grains with less than 20μm, it is neccesary to precipitate large particles during slow cooling which rate is less than 25K/h from more than 673K, then, to cold-roll the plate in the reduction of more than 70% and finally to recrystallize the cold-rolled sheet at 753K in a heating rate of 10K/s or over. By the reduction of 90%, very fine grain with less than 10μm is obtained without the occurrence of edge cracks during cold rolling. In the superplasticity, the finer the grain is, the higher the elongation becomes. This result is related to the formation and growth of cavity.

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