The segregation mechanism in nuggets of aluminium alloy spot welds was investigated. The nugget was grown under electrical currents during the period of weld cycles, and the formation of micro-structures in the nugget was highly dependent on the numbe of decay cycles during cooling process. The magnitude of the macro-segregation increased with increasing weld cycles and decreased with increasing decay cycles. The solution treatment of the weld decreased the segregation to a slight degree that was equal to the degree of the recovery of the micro-segregation formed at the solidification. These results indicated that this segregation was a type of the "macro-inverse-segregation" of the eutectic solute element owing to the rapid melting by the joule heat of a large electrical current and the rapid cooling under the high pressure through the loaded electrode.

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A commercial pure Ti foil 50μm in thickness of insert metal was diffusion-welded to mild steel at temperatures above 760°C for 30 min under welding pressure 0.17kg/mm². The joint has tensile strength higher than that of the 6063 base alloy. 6063 alloy was then diffusion welded to the overlayed steel with a Ti foil at temperatures above 590°C for 30 min under welding pressure 0.04 kg/mm². The joint welded just below the solidus of 6063 alloy has nearly the same tensile strength as the 6063 base alloy. Intermetallic compound interlayers of TiC and Al₃Ti are formed at S20C-Ti and Ti-6063 alloy joint interfaces, respectively. As these interlayers are thickened, the welded joint is strengthened.

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Al matrix composites containing discontinuous SiC fibers, SiC whiskers and Al₂O₃ particles were fabricated by a prepack-press and hot extrusion method. Tensile tests were performed at temperatures from 25° to 600°C. Both the SiC fibers and SiC whiskers are fractured to fine fragments by hot extrusion. Al₂O₃ particles/7075 alloy composites aged at 160°C has ultimate tensile strength 63 kg/mm² the highest in this experiment. Pure Al composites containing 30 vol% of Al₂O₃ particles have elongation up to 5% and ultimate tensile strength about 40 kg/mm².

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The present analysis was based on the incremental strain theory in which an extended Kirchhoff-Love's hypothesis proposed by Nagai was used. The distribution of stresses and strains and deflection of the plates are numerically obtained. Taking no account of the shear deformation in analysis causes underestimation of the deflection of the plates. Theoretical distribution of strains well coincides quantitatively with the experimental ones. If taking no account of shear deformation, only a qualitative coincidence is achieved. The calculated shear angle well coincides with the experimental ones.

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Strain distributions in the deformed layer of Al alloys strained by abrasion with emery papers were studied by X-ray diffraction. The strain in the tensile and tear tested specimens was also studied. The equivalent plastic strain is the strongest on the specimen surface and weakens with the depth from the specimen surface. The specimen surfaces abraded with emery papers of #120, #700 and #1000 have equivalent plastic strains 4.5, 6.4 and 1.8% respectively bearing an indistinct relation to the roughness of emery papers. The deformation layer thins down with the roughness of the papers. When machined by a shaper, the equivalent plastic strain amounts to 58%. When two regions differently deformed coexist, the equivalent plastic strain is greatly determined by a smaller strain. Measured and calculated strains in the necked region in the tensile tested bars have a good correlation up to the reduction of area about 40%. Tear test specimens have large values of equivalent plastic strain over a wide range from the tip of the crack.

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390 alloy die castings having differences in transverse strength at different positions were studied by measuring molten metal flowing behaviors in a die cavities. A part in a die casting having low transverse strength is that in which solid-liquid mixture of high volume fraction of solid including scattered structures has been filled at slow injection velocity. Primary silicon easily segregates in this part. To reduce the interval from pouring in a sleeve to injection, to increase the metal-filling ratio in the sleeve, and to fill the die cavity homogeneously and quickly result in minimizing segregation of primary silicon and recovery of transverse strength. 390 alloy is die cast without difficulities such as fusioned penetration.

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Al-3.5%Mg-0.2%Si-0.4%Mn alloy castings were solution treated at 580°C, quenched in water at 25°C, preaged and artificially aged at various conditions. These castings have ultimate strength, impact strength and elongation identical to those of AC7A castings and have yield strength identical to that of T6 treated AC4C castings. They have poor quench sensitivity, and their mechanical properties are independent of preaging. The maximum hardness of the castings is achieved by aging at a temperature higher than that for AC4C castings. These phenomena are attributed to the large binding energy of vacancy with Mg atoms.

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Rotation bending fatigue tests were performed. The higher the stress level, or the shorter the fatigue life at the same stress level, the larger is the number of main fracture origin. At the stress level close to the fatigue strength at 10⁷ cycles, fracture originates mostly at a point in the specimen endured above certain number of cycles. The relation between the fatigue life and the number of main fracture origin is approximately estimable on the P-N_f diagram. The transition site lies at a position on the fracture surface nearer to the specimen surface, as the stress level becomes higher or the fatigue life shortens at the same stress level. At the stress level close to the fatigue strength at 10⁷ cycles, the transition site lies at nearly a constant depth in the specimen endured above certain number of cycles. The relation between the fatigue life and the depth to the transition site is also approximately estimable on the P-N_f diagram.

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