Microsegregation and homogenization of magnesium in cast and rolled Al-5.5%Mg alloys were measured by means of EPMA and the influence of chromium on them was clarified. Chromium addition results in grain refinement in Al-5.5%Mg alloy and lowering minimum Mg concentration at the center of primary dendrite arm and increasing amount of non-equilibrium compounds crystallized. In Al-5.5%Mg alloy, homogenization rate of magnesium at 450°C is about 2 times faster than that at 430°C. However, homogenization rate at 450°C in the Cr-added alloy is slower than those at 430°C in both alloys with and without chromium. This phenomenon is due to the stagnation of magnesium diffusion which temporarily occurs with precipitation of Al₁₈Mg₃Cr₂ compounds in large quantities in the earlier stage of homogenization at 450°C. Cold rolling makes the homogenization faster, but in the case of chromium addition the homogenization is still slower than that in non-addition, owing to promotion of precipitation of the compounds by rolling.

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The effect of heat treatment on improving the resistance to stress-corrosion cracking (SCC) of 7475 alloy was investigated in relation to localized corrosion behavior, strained electrode property and precipitation microstructure. The resistance to SCC of 7475 alloy can be enhanced by shorter-time treatments of over-aging and reversion from the T6 condition, with little loss of strength. The constant extension rate technique (CERT) used for a SCC test of this alloy is available for a rapid method to determine ranking of the heat-treated materials respect to SCC resistance. Preferential grain boundary attack occurs in the T6 material, and its groove acts as sharp notch for initiation of intergranular SCC in the specimen stressed in ST direction. However occurrence of transgranular SCC is observed during CERT test of T6 specimen in L direction. Changes in the resistance to SCC by the heat treatments have been explained in terms of homogeneity of slip deformation and concentration of anodic dissolution at the grain boundaries.

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Microstructures of aluminum containing lithium up to 9.75% solidified at various cooling rates from 10^-1 to 3× 10⁵°C/s were examined. The microstructures of these alloys are classified into three types in accordance with the cooling rate and lithium content; i) aluminum solid solution. ii) aluminum solid solution+precipitated Al₃Li(δ')iii) eutectic Al₃Li(δ). The precipitation of the metastable δ' during cooling is not suppressed. The lithium content that metastable δ' particles precipitate is independent on the cooling rate. The grain size of aluminum alloys corresponds to lithium content and cooling rate.

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Ribbon specimens of Al-4 to 33mass%Cu alloys were prepared by single roller and twin roller techniques. The solid solubility of Cu in Al is extended up to about 20mass%. The eutectic alloy solidified at the cooling rates of about 10⁵-10⁶K/s consequently has lamellar, degenerate, banded and fine periodic structure. The diffraction pattern of the fine periodic structure is identical to that of GP(2) zone in Al-Cu system, but the distribution of the Cu-rich layers is quite different from that of the conventional GP(2) zone. The rapidly solidified Al-4mass%Cu solid solution decomposes in the identical sequence to the bulk material quenched from the solid state. The former requires, however, longer pracipitation time for GP zones than the latter. A fine periodic structure precipitates in the alloys of higher Cu concentration in the early stage of decomposition. The decomposition behavior of rapidly quenched ribbons depends greatly on the heating rate to aging temperature.

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The relationship between the toughness and the inclusion originated in the impurity of Al-Zn-Mg-Cu alloys was investigated in various tests. It was observed that the filtration reduced the coarse inclusion of the iron impurity. But it didn't influence much on the toughness. The extruded material 7475 showed the highest toughness value than the others when their inclusion diminished much more in volume. Particularly this phenomenon is caused by the rise of the fracture propagation energy. As for the fracture toughness, the effect of filtration wasn't confirmed. About the extruded materials, the fracture toughness has a tendency to increase it's value in accordance with the decrease of the volume fraction of the inclusion.

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In order to obtain the effect of taper heating in extrusion, the temperature distribution with the lapse of time was obtained in terms of billet, die and container, by applying the difference equation method to two typical examples, and calculating the heat generated in billet and heat transfer in billet, die and container during extrusion. Taper heating will not increase to a larger extent the temperature difference of products at the final stage of extrusion process, even though the billet temperature is decreased more than by uniform heating. However, taper heating is effective to decrease the product temperature and increase extrusion speed at the same time.

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