Aluminum alloy matrix composite materials are expected to be used for various applications because of the low density and superior properties at high temperatures. However, the composite materials give problems in the tool wear because of their difficulty in cutting. In this work the turning test for SiC particle reinforced aluminum alloy composite materials was performed and the effects of SiC particle size and content on the tool wear and surface roughness were discussed. The tool wear increased with increasing SiC particle size and content. Only the diamond tool was useful to cut the SiC particle reinforced aluminum alloy composite material. In the case of using a carbide tool, the cutting condition should be low cutting speed as well as high feed rate. To suck the chips during cutting was effective to decrease the tool wear. In the wet cutting, however, to suck the chips resulted in the increased tool wear. While the increased SiC particle size resulted in the worsened surface roughness, the increased SiC content improved the surface roughness.

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Microstructures and hardness of an Al-1.63%Cr-1.64%Zr alloy prepared by hot-extrusion of rapidly solidified powder were investigated. Vickers microhardness of the as-extruded alloy ranges from 115 to 135. Transmission electron microscopy observation shows that the dislocation density of the as-extruded alloy is high and that a number of granular Al7Cr preipitates and fine metastable L1₂-type Al₃Zr prepitates are formed on grain boundaries and in grains. After annealing at 573K for 3.6×10³ks, the hardness of the alloy remains un-changed and recrystallized grains are not observed in the alloy. It is concluded from TEM observation that the Al₃Zr and Al₇Cr precipitates in the grains and the Al₇Cr precipitates on the grain boundaries suppress the recrystallization and softening.

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Effects of Zn addition, stretching prior to aging and aging condition on the corrosion behavior of 2090 and 2091 alloy sheets have been studied using electrochemical measurements and total immersion-corrosion tests. The stretching prior to the peak-aging, which results in a uniform precipitation of Cu rich phases within grains, reduces the susceptibility to intergranular corrosion, having a more marked effect in 2090 alloy. The combination of stretching and Zn addition of 0.7% or over facilitates pitting dissolution within grains and enhances well general corrosion. The corrosion rates obtained from the total immersion test increase with the progress of aging. 2090 alloy has a lower corrosion rate and a higher resistance to localized pit than 2091 alloy. The results of the immersion test show a good correlation with the polarization properties.

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The built-up edge in machining of an aluminum alloy is an important problem, and its shape affects the cutting state of the alloy. The aim of this study is to elucidate the main cause of the shape change of the built-up edge. The effect of the shape of the built-up edge on the cutting process was also investigated. The shape of the built-up edge can be roughly classified into two types: the wedge type and nose type. The machining of Al-Mg alloys results in the formation of the wedge type built-up edge which remains on the tool face. The addition of Si or Bi to a work material of an aluminum results in the formation of the nose type built-up edge. The wedge type built-up edge was observed in machining of alloys with high hardness and high work hardenability. While the cutting force, surface roughness and affected-layer depth decrease in the case of the wedge type built-up edge, these values increase in the case of the nose type built-up edge.

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The powder-liquid-forging (PLF) process was employed to make SiC or Al₂O₃ particle/6061 aluminum alloy metal- matrix-composite (MMC). Since the aluminum alloy powder is enveloped by oxide layer, usual sintering is difficult. It becomes, however, possible to break the oxide film to sinter, when a powder compact is pressed above the melting point. This unique PLF technique has been found to be applicable to produce MMCs containing up to 30% of the reinforcement with high density. The Young's modulus and hardness of solution treated MMCs are monotoneously increased with an increase in the volume fraction of reinforcement of either SiC or Al₂O₃. The age-hardening decreases drastically in Al₂O₃/6061 MMC but a little in SiC/6061 one. This is because the spinel (MgAl₂O₄) formes in Al₂O₃/6061 MMCs during the PLF process, i. e., the loss of magnesium in the 6061 matrix is considered to lower age-hardening. Even in a SiC/6061 MMC in which such a reaction at the interface was not detected, the precipitation by the aging is suspected to occur very inhomogeneously. The tensile strength at room temperature is increased by adding the rein forcement particles. However, the tensile strengths of MMCs above 450K become to be approximately the same as those of the 6061 alloy prepared by the conventional ingot metallurgy.

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Tensile strength at temperatures between room temperature and 773K of the unidirectional Si-Ti-C-O fiber (Tyranno fiber) reinforced aluminum matrix composite produced by a squeeze casting method was investigated. The longitudinal strength decreased gradually with increasing temperature up to 673K, but then a rapid decrease was observed at the higher temperature. The transverse strength decreased larger than longitudinal one with increasing temperature. A drop of strength was observed at about 500 and also at 673K. In order to understand the temperature dependence of composite strength, temperature-dependence of matrix yield stress in the composite was deduced from thermal expansion curve. Using thus deduced matrix yield stress and temperature dependence of shear modulus of matrix taken from a literature, the stress concentration factor in the fibers adjacent to broken fibers and the critical length of broken fibers in the composite, which are representative strength-determining factors, were calculated for various temperatures by means of the shear lag analysis. The stress concentration factor decreased slightly, while the critical length increased much with increasing temperature. From the calculation, the decrease in longitudinal strength with increasing temperature could be attributed to the increase in critical length due to the softening of matrix. The reduction in transverse strength was caused directly by the softening of matrix.

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In order to reveal the small electrical discharge machining (EDM) characteristics of Ti-6Al-4V alloy with rotating electrode, a series EDM tests are carried out. Attaching importance to surface roughness, the discharge current must be small, but when it under the range of 0.2A, even though it is more smaller, the surface roughness can not be in expectation of improvement. When the electrode is negative polarity, the work surface will be stuck with carbon to make a clear-out crater profile of discharge point. Machining the Ti-6Al-4V alloy in the small discharge current, the material removal rate increases with the increasing of pulse duration, but there is no effect on the work surface.

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