Molten metal flow behavior during fast shot injection with 500 to 1650 ton commercial die casting machines was studied in the filling portion of the die cavity in the shape of disc, box and plate. The velocity of the molten metal is as high as 15 to 20m/s at the gate of a die cavity, but it decreases abruptly within a passage of 20 to 25cm and reaches 2 to 3m/s at the final filling portion, irrespectively of the tested cavity shapes. The gas pressure in the cavity shows a maximum value when the flow reaches the probe. The gage pressure increases from 0.1 to 0.2kgf/cm² at the gate to 1 to 2kgf/cm² at the final filling portion. The velocity of metal decreases with increase in the gas pressure at the final filling portion. Its abrupt decrease in practical aluminum casting is attributable to the pressure rise in the cavity. Provision of an appropriate gas vent in the final filling portion increases the velocity of the molten metal.

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Liquid cooling rate (V_LC), average cooling rate of solidification range (V_SC), temperature gradient (G), moving rate of solid-liquid interface (R) and G/R were changed as solidification conditions. Structures of ingots are all equiaxed by presence of grain refining zirconium. The grain size is primarily affected by V_LC and decreases exponentially with its increase. With increasing R and decreasing G, the amount of Mg-RE-Zn eutectic compound increases. It crystallized along grain boundaries nucleating at boundary triple junctions. The morphology of the eutectic compound remains unchanged after a heat treatment for 5h at 215°C.

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Tensile strength, 0.2% proof stress and elongation in tensile test, Brinell hardness, and maximum load, crack initiation energy, crack propagation energy and total absorbed energy in instrumented Charpy impact test were measured as a function of solidification conditions. In both as cast and T5 conditions, the mechanical properties are improved by increasing temperature gradient and by decreasing moving velocity of solid-liquid interface. They are upgraded by decrease in equiaxed grain size and in amount of Mg-RE-Zn eutectic compound. Crystallization of the compound along grain boundaries expanding from boundary triple points degrades the properties.

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Microstuctures of Al-Cr alloys containing Cr up to 10% solidified by various cooling methods and precipitation behavior during aging at 200-600°C of a melt spun Al-2.75%Cr alloy were investigated. No precipitates can be observed in splat quenched Al-10%Cr nor in melt spun Al-2.75% alloys. The hardness of chill cast alloys increases with Cr content up to about 4%. Electrical resistivity of the melt spun 2.75% Cr alloy shows a two stage sigmoidal recovery during isothermal aging at 200-600°C. Electron microscopy observation of aged samples concludes that the first and the second stages of electrical resistivity change correspond to preferred precipitaion at grain boundaries and within grains, respectively. The size R, half of the length, and S, thickness of the grain boundary precipitated particles during isothermal aging are proportional to tⁿ, where t is isothermal aging time. The time dependent exponent n for R and S are 0.077-0.083 and 0.11-0.17, respectively.

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The flow stress and ductility of an aluminum P/M alloy prepared by hot extrusion from rapidly solidified powders of an Al-20Si-5Fe-2Cu-1Mg-1Mn alloy were investigated by compression and tensile tests to clarify its workability. Flow stress decreases and critical amount of strain for deformation without cracking increases with deformation temperature. The increase in strain rates increases flow stress at a higher temperature than 180°C. In compression test, the relation between flow stress σ and strain rate ε is described as σ=Kε^m. The strain sensitivity exponent, m increases with deformation temperature and becomes about 0.3 at 480°C. A nomograph useful to predict the flow stress at a certain ram speed and temperature has been made.

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Al-(50-60) Zn alloys of lower density than the eutectoid alloy were successfully processed to superplastic sheets. The superplasticity is observed in a wide range of temperature above and below the eutectoid temperature. It is pronounced at a strain rate of about 10^-3s^-1 in the region of α/β phases below the eutectoid temperature, and at a strain rate of about 10^-2s^-1 in the region of α/α' phases above the eutectoid temperature. The Al-(50-60) Zn alloys are strengthened by solution treatment at 400°C followed by quenching and show a higher specific strength at room temperature with better hardenability than the eutectoid alloy. Addition of Cu and Mg to the alloys reduces superplastic elongation, but doubles the strength at room temperature without heat treatment. The γ values simply obtained by dynamic indentation tests can be used to replace strain rate sensitivity index m obtained by tensile test, in order to predict superplastic elongation of the sheets.

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Pure aluminum and iron powders were processed by mechanical alloying to composite powders, and consolidated by strained powder rolling (SPR). Iron particles are dispersed finely in aluminum powders after long mechanical alloying time. Their size is about 200nm after 130ks and the number increases with increasing iron content. The composite powders processed less than 172ks are well consolidated by the SPR method. The formability goes, however, worse with longer processing time. In the case of the specimens powder-processed for 130ks and consolidated at 673K by the SPR method, tensile strength increases almost linearly but elongation decreases hardly with iron content increasing up to 8%. The increase of tensile strength is thought to be due to the fine particles of iron. The tensile strength of Al-8%Fe is about 550MPa and its elongation is about 1.6%.

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Measurement of a median cooling time τ was carried out for various cooling rates between 2100K/s to 0.25K/s and the concept suggested by Maitland et al. was adopted in the analysis. Obtained relationship between τ and tensile strength as well as 0.2% proof stress shows that the quench sensitivity of Al-Cu alloys becomes dull with addition of Sn, but it remains unchanged by addition of Mn. The dullness is attributed to acceleration of the growth rate of θ' precipitating on the Sn-rich phase particles which formed during quenching.

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