Al-4%Zn-4%Mg-1%Cu and Al-2.5%Zn-3.5%Mg-1%Cu alloys were cast in alumina-base water soluble molds, silica-base CO₂ process molds and iron molds having columnar and cylindrical mold cavities. The tensile strength of the castings depends on the cooling rate. The former and the latter alloys solidified at the cooling rate 1.5°C/s have average tensile strength 38 and 30kg/mm² respectively. The density also depends on G/R and hydrogen absorption. Directional solidification and decrease in hydrogen absorption result in improving the quality of castings. The alumina-base mold ensures increases in cooling rate and G/R, modified dendritic structure and decrease in micro-shrinkage. Less residual water in the alumina-base mold results in reducing hydrogen absorption of molten metals and improving soundness of the casting.

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The "hydrostatic tensile stress-fracture strain-temperature diagram" was determined by using Bridgeman-type specimens. The higher the hydrostatic tensile stress and the lower the testing temperature, the lower the fracture strain is. These relationships depend on the heat treating conditions. The fracture mode changes depending on the hydrostatic tensile stress and on the heat treating conditions on the basis of fractography.

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A mixture of titanium dioxide and graphite vacuum pressed into a briquette and sintered was reduced in a plasma arc furnace at 2600° to 2900°C. Argon and argon-hydrogen mixtures (H₂ 5 to 20%) were used as plasma arc generating gases. The optimum mixing ratio C/TiO₂ is about 2.10. The mixture 4g in weight is fused within 1 to 4min. Reduction proceeds rapidly to produce 80% Ti in this period and then does slowly. When argon is used as an arc gas, the maximum Ti content does not exceed 87%. When the argon-hydrogen mixture is used, deoxidation proceeds. The Ti content approaches to 94%, if Ar-20%H₂ gas is used. The decarburization effect is not so expected.

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Microstructures during superplastic deformations of the equiaxial fine-grained Al-Zn eutectoid alloys were studied by scanning electron microscopy and the plastic-carbon replication technique. Grain-boundary sliding (GBS) is a predominant deformation mode in the initial stage of strain (ε_??_50%). The GBS decreases as the increase in strain and the elongation of the Zn-rich phase along the tensile direction predominates after large strains (ε_??_100%). Grain-growth of the Zn-rich phase is also observed, while that of the Al-rich phase is hardly seen. The Al-rich phase becomes a round shape (spheroid) and is surrounded by the Zn-rich phases. Therefore, the initial equiaxial structure of the alloy has broken after large strains, but the superplastic deformation continues. No evidence of crystallographic slip in the grains is observed. Fractographs of the alloy strained superplastically to fracture show a transgranular cleavage-like appearance. Large ductility of the Zn-rich phase caused by preferential diffusion of Zn is a significant deformation mode for this alloy.

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The influences of Fe and Fe+Mn contents were studied by a double torsion bending test. The fracture toughness of as cast and aged alloys is unsusceptible to Fe concentration less than 0.57wt%. When the Fe content is increased up to 1wt%, the fracture toughness lowers by about 20%. Although increase in Fe+Mn content from 0.32 to 1.67wt% has little effect on the fracture toughness, the alloy containing Fe 1wt% and Mn 0.71wt% has improved fracture toughness.

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The electrical resistivity measurement and transmission electron microscopy were performed on the binary alloys containing Mg 5 to 15at%. The electrical resistivity of the quenched alloys is well expressed as ρ=2.37+5.3C(100-C)•10^-2nΩm. The change of electrical resistivity during isothermal aging at temperatures up to 453K can be explained by a complex growth process of GP zones and dislocation loops. The resistivity gradually lowers during aging at temperatures above 300K where well developed dislocation loops are observed by TEM. This is attributed to solute dilution in the matrix. The resistivity apparently rises during aging at temperatures below 300K relating to the growth of GP zones. A reversion phenomenon is observed for those GP zones. A metastable phase diagram for GP zones in Al-Mg binary system is proposed.

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