Variation of hardness with position in the grain was measured during aging and reversion of Al-2 mass%Cu alloy. Age-hardening was suppressed in the surface layer relative to the interior of the specimen aged at 273K after quenching from 823K. Rate of reversion was faster in the surface layer than in the interior when the age-hardened specimen was annealed below 403K where few secondary defects should decay. When the specimen aged after quenching from high temperature was annealed at 403K, the surface layer and the interior softened nearly at the same rate. Those softenings appeared also in the regions near grain boundary.

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The repeated micrography on transverse sections in Al-5 mass%Mg alloys unidirectionally solidified was carried out at intervals of about ten micronmeters until the first twin boundary disappeared in order to make clear the generation process of feathery crystals. Microstructures near the chilled end show that a curved grain boundary progressively straightens with growing of crystals, that is, the grain boundary transforms successively into a twin boundary. It is suggested that the transformation starts at the point where two neighboring crystals hold a (111) plane in common on the boundary. Either of crystals associated with the formation of twin boundary may be resulted from anneal-twinning with regard to solidifying conditions for generation of feathery crystals.

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Feathery crystals formed in Al-5 mass%Mg alloys unidirectionally solidified were microscopically observed at intervals of about ten micronmeters for examining multiplication of twin boundaries. Two types of site for multiplication of feathery crystals are found. Type I is that a new twin boundary originates at a site separating from preexisting twin boundaries. And type II is that a new twin crystal originates at a site on the subgrain boundary generated in either individual of a preexisting twin crystal. These types of twin multiplication have particular features of the variations of length and spacing of twin boundaries.

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Fracture behavior of polycrystalline aluminum specimen coated with liquid Ga was investigated by means of tensile test and observations of structure. The fracture stress (σ_f) and fracture strain (ε_f) of specimen coated with liquid Ga increase with increasing strain rate (ε). The Ga penetration into the specimen is recognized before the flow stress reaches to the fracture stress. The fracture stress (σ_f) of specimen coated with liquid Ga is illustrated in the following equation;
σ_f=log(Bε^A)-kt^1/2
where A, B and k are constants, ε is an initial strain rate, t is the holding time after coating with liquid Ga.

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Temperature dependence of tensile strength, ductility, toughness, work-hardenability, the parameter of serrated deformation and fracture morphology were investigated in the temperature range from 7 to 293K for under-aged and peakaged specimens of Al-2.32Li-1.20Cu-0.67Mg-0.12Zr alloy (by weight%). Uniform elongation, reduction of area, work done for fracture are improved significantly as temperature decreases, and the maximum value of each property is achieved at about 20K. The remarkable improvement in these properties is attributed to the remarkable increase in the work-hardenability which is due to increasing difficulties of the cross slip of dislocations as temperature decreases. Therefore, the addition of some elements which decrease the stacking fault energy may cause more improvement in ductility and toughness at very low temperatures. The serrated deformation occurs remarkably below about 20K. The load drop is due to thermally assisted discontinuous glide of dislocations. Disturbance of the uniform deformation which is due to the discontinuous glide of dislocations may be the main cause of the gradual degradation of the mechanical properties below about 20K.

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The phase diagrams of Al-Si system under pressure of 0 and 2.1GPa were obtained experimentally and theoretically. The solubility of silicon in aluminum at 2.1GPa is larger than that at 0GPa. The maximum-solubility of Si at 2.1GPa is 4.9at.% and this value is about three times large as one at 0GPa. The solidus and liquidus lines shift with pressure toward the higher temperatures and higher concentration ranges. The calculated results agree with the experimental data.

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