Powders of metal silicides: CrSi₂, FeSi₂ and ZrSi₂ were mechanically alloyed with pure aluminum powder by a high energy ball mill under an argon atmosphere. P/M materials were fabricated from mechanically alloyed powders by cold pressing, vacuum degassing and hot extrusion. The obtained P/M materials exhibit high strength at both room and elevated temperatures. The solid state reaction of Al-silicide systems was studied by X-ray diffraction. No change of constituent phases is observed during mechanical alloying and subsequent consolidation processes. However, decomposition of metal silicides occurs during heating at 873K of the P/M materials.

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CVD-SiC fibers of SCS-6 and SCS-2 were dipped into liquid pure aluminum for a certain time at dipping fiber length of 1 or 3mm. The melt was solidified, leaving dipped fiber as it was, and the interfacial shear strength was measured by pull out method. The mean interfacial shear strength was determined as 63MPa for SCS-6 fiber having 3μm carbon rich layer on the surface, though it could not be measured for the dipping length of 3mm due to the increase in interfacial area. For SCS-2 fiber having 1μm carbon rich layer the interfacial shear strength could not be measured for the dipping length of both 1 and 3mm, because of fiber degradation by SiC baring and its reaction with melt following disappearance of carbon coating layer. Critical fiber length for reinforcing of composite was estimated from the measured interfacial shear strength.

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The effects of alloying elements on the interfacial shear strength were measured by pull-out method, and the critical fiber length for reinforcing composite was evaluated. The interfacial shear strength was high for SCS-6 fiber which was dipped into liquid aluminum alloy containing silicon or titanium with high affinity to carbon. The critical fiber length was estimated as 3.3 to 3.5mm. Aluminum alloys containing such surface active element as magnesium or lithium, the interfacial shear strength for SCS-6 fiber was low and its critical fiber length was longer than 20mm. This is because magnesium atoms adsorbed on the carbon rich layer and disturbed the binding reaction between aluminum and carbon. It was also found at both dipping lengths, especially at 1mm of SCS-6 fiber in Al-5%Mg alloy, that, after middle stage of dipping time, the interfacial shear strength increased, due to the formation of crater like erosion on the surface of carbon rich layer, resulting in decrease in critical fiber length as 6.5mm. These craters may act not as a notch but as an anchor.

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Changes in microstructure and viscosity with both stirring conditions and a fraction of solid have been investigated in order to obtain fundamental aspects of various poroperties of a semi-solid stir-cast AZ91D magnesium alloy. Mechanical stirring was conducted during cooling of a liquid phase into mushy zone at a given temperature. Tensile test was performed for as-cast and T6-treated specimens. The primary α phase in specimens changed from the rosettelike α phase, whose dendrite arms were bent by stirring, to spheroid during the isothermal stirring. The spheroidization of the primary α phase and the decrease in their size were accelerated with the increase in stirring speed, stirrer width and the fraction of liquid. The stirring torque during the isothermal holding decreased in accordance with the spheroidization of the α phase. 0.2% proof stress of as-cast specimens was higher than the minimum value specified in JIS because of a fine eutectic phase crystallized by rapid cooling. Tensile properties of both as-cast and T6-treated samples had a tendency to decrease with increasing the fraction of solid. Tensile stress increased with the T6 heat treatment and the increment became higher with the fraction of solid being lower during isothermal stirring.

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The effect of surface roughness on the diffusion weldability of Al, Al-Sn and Al-Sn-Mg alloys in the atmosphere and in a vacuum (about 0.1Pa) have been investigated. Welding surfaces were polished either with #800 grinding paper, or with 3μm diamond powder, or electrolytically. The welding was carried out at 773K for 3.6ks under a pressure of 2MPa. Results obtained are summarized as follows:
1) Magnesium reduces a part of the oxidation film at the interface during welding, being contained in liquid tin phase. The degree of reduction is high and the best weldability is obtained when Mg distributes homogeneously at the welding interface.
2) Grinding of surface with 3μm diamond powder is best for the homogeneous distribution of Mg.
3) Weldability is better in the atmosphere than in the vacuum. This behavior is prominent in A1-0.5Sn-lMg/Al-0.5Sn-1Mg couple polished with diamond powder.
4) When the couple mentioned above is welded under the applied experimental condition where the temperature is much lower than melting point of Al, nearly complete weldability is obtained even in the atmosphere.

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The cutting resistance, cutting ratio, surface roughness and chips disposal of Mg-1-20%Li alloy castings were examined. The factors crucial to precision, such as the coefficient of thermal expansion and elastic modulus, were also examined. The tangential force, radial force and cutting ratio were almost constant regardless of the cutting speed. At a cutting depth of 1mm, the cutting ratio and surface roughness of Mg-5%Li alloy was 0.65 and 4.0-5.0μm, respectively. The surface roughness decreased slightly with increasing the cutting speed. The cutting chips of Mg-8% Li alloy were bandspane and classified as unsuitable. The cutting forms of other alloys were classified as good or suitable. The coefficient of thermal expansion showed a steep rise when 3% or more Li was added to Mg. The elastic modulus showed a steep drop when Li was 5% or more. The turning machinability of Mg-1-5%Li alloys were verified as suitable. However, when Li was 8% or more, the alloys were unsuitable and increased oxidization was observed.

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