Effects of four factors on five mechanical properties of aluminum tubes were statistically investigated using the design of experiments (L₂₇ containing dummy level). The four factors were direction of uniaxial tension A_i (longitudinal one A_z, and circumferential one under internal pressure A_θ), length of reduced section (at three levels) of cylindrical specimen k_i, inner diameter as recived D_i, and ratio of mean radius of specimen to thickness S_i. The mechanical properties were proof stress σ_S, tensile strength σ_B, F and n values (approximated on the stress-strain curve by the expression σ=Fεⁿ), and stress ratio σ_{_??_}/σ_B (σ_B being reduced from the F and n values). K_i is only a factor having no effect on the mechanical properties mentioned above. σ_B is independent of the position of wire strain gauge, and is the most reliable when assessing various factorial effects. The stress ratio σ_B/σ_B is significantly affected (significant at 5%) only by interaction of A_i × S_i. The aluminum tube has the statistical average proof stress and tensile strength 5 to 7% higher in circumferential direction than in longitudinal one.

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Al-10%Mg alloys into which Ti 0.05 to 0.15% had been added were unidirectionally solidified. The amount of nonequilibrium eutectic phase and the minimum solute concentration in the dendrite arm in the solidified alloys having equiaxed grains were measured by means of microscopic field plotting and EPMA respectively. The amount of nonequilibrium eutectic phase decreases and the minimum concentration of Mg rises with increase in average cooling rate during solidification. These facts are similar to those of columnar structure in unidirectional solidification and opposite to those of equiaxed structure in non-directional solidification. The minimum Mg concentration of dendrite arm at the start of solidification rises when cooling is accelerated.

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A procedure to determine a minimum riser volume required for producing AC2B alloy castings of automobile intake manifold free from shrinkage porosities was investigated. The solidification state diagram for the final stage of primary solidification (solid fraction 0.5) and the specific gravity distribution diagram of castings were used. The area surrounded by a closed loop isochronic line where the solidification front is discontinuous in the solidification state diagram is identical with the porous shrinkage area in defective castings unacceptable in pressure tightness. The minimum riser volume required for effective metal feeding can be determined by the form of a solidification front which opens toward the riser and its movement direction. The casting plan derived from this procedure ensures economically producing sound castings free from shrinkage porosities.

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The intergranular corrosion susceptibility of Al-Mn alloys containing Mn up to 1.22% depends on Mn content and heat treatments. Al-0.5%Fe-0.15%Si alloys containing Mn0.3% or more are susceptible to intergranular corrosion. Heating at brazing temperature near 600°C results in recrystallization and dissolution of Al₆Mn or Al₆(Mn, Fe) in the Al-Mn alloys. Al₆Mn or Al₆(Mn, Fe) compounds precipitate preferentially at grain boundaries during cooling or aging after heating at brazing temperature. Cathodic polarization of the Al-Mn alloys decreases with increase of Al₆Mn or Al₆(Mn, Fe) precipitation. The Al-Mn alloys in which Al₆Mn or Al₆(Mn, Fe) precipitates at random and ones in which Mn dissolves in the matrix are unsusceptible to intergranular corrosion. The intergranular corrosion susceptibility of Al-Mn alloys is, however, intensified by precipitation of Al₆Mn or Al₆(Mn, Fe) at grain boundaries.

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Precipitate structures of an (α+η)-type Al-5.90%Zn-1.03%Mg alloy subjected to different heat-treatments were examined by means of transmission electron microscopy. The heat-treatment conditions for formation of η´, X and η phases were descrived. The η phase is uniformly formed through X phase as well as through η´ phase. The η´, X and η phases are always formed through heterogeneous nucleation. The precipitation reaction isas follows
Solid solution. G. P. zones →η´→η Solute-vacancy→xη
where G. P. zones containing some amounts of vacancies (a sort of solute-vacancy clusters) are taken into account besides G. P. zones in a usual sense.

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