The cathodic charge method was used in which cathodic current 5mA/cm² was applied in 2N-H₂SO₄ solution at room temperature. Hydrogen content increases with charging time and saturates at about 10min. Hydrogen is appreciably evolved during aging at room temperature but not so completely to recover the original level. No hydride is formed. Aluminum lattices are expanded and lattice strain is relaxed by penetration of hydrogen anisot-ropically in (111) plane. Although the ratios of half width of diffraction lines change corresponding to hydrogen content, those of (111) plane are almost at the same level irrespective of hydrogen content if a certain quantity of hydrogen penetrates. Relaxation of lattice strain by penetration of hydrogen is attributed to hydrogen occuping a position near aluminum atoms rather than near magnesium atoms. Hydrogen atoms in fcc lattices are more stable in a tetragonal site and probably may occupy an octahedral site.

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Al-4.3%Zn-1.5%Mg-0.6%Mn, Al-4.3%Zn-1.5%Mg-0.6%Mn-0.6%Si, and Al-4.3%Zn-1.5%-0.3%Mn-0.3%Si alloys were DC cast and homogenized in various conditions. Precipitation and dissolution of the alloying elements during the homogenizing treatment were examined by electric resistometry, X-ray diffraction, optical microscopy and electron microscopy. Extrudability of the homogenized DC castings were estimated by measuring the maximum extrusion pressure at a constant extrusion condition. Such properties of the extrusions in T5 temper were examined as tensile strength, toughness, susceptibility to stress corrosion and resistance to exfoliation corrosion. The extrudability of the alloy free from Si is impossible to improve by any homogenizing condition. Extrusion pressure is lowered in the alloys containing Si, since Mg precipitates in the form of Mg₂Si phase during cooling after homogenization. Precipitation of transition elements is accelerated by addition of Si. Fine precipitates of α-AlMnSi phase are uniformly distributed over dendrite cell in the Si-containing alloys. Si addition remarkably improves stress corrosion resistance of the extrusions, although strength, toughness and resistance to exfoliation corrosion decrease more or less.

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Age-hardening behavior in final aging of TMT, in which plastic deformation is applied after pre-aging but prior to final aging, has been studied. The hardening behavior in this type of TMT is in general correlation with that in two-step aging. The strength of TMT materials increases with rising pre-aging temperature. The amount of age-hardening is degreased by plastic deformation prior to final aging due to heterogeneous precipitation on dislocations. Pre-aging prior to plastic deformation is more effective in increasing the maximum hardness in final aging than in two-step aging. This is attributed to retardation of heterogeneous precipitation on dislocations. In commercial 6061 alloy, the strength can be increased by TMT as high as 10% in contrast to the high purity alloy of the same Mg₂Si content. Such differences in two-step aging and TMT behaviors between high purity and commercial alloys are attributed to metallographic heterogeneity existing in the latter.

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This work concerns correlation between crystal growth direction and cutting properties for unidirectionally solidified AC7A castings having cast anisotropy and isotropy. When work pieces having columnar crystals are two dimensionally cut, fluctuations caused by casting anisotropy are found in cutting resistance, shear angle, shear stress on shear surface, compression stress and friction angle. But, work pieces having isotropy are free from such a tendency. In the three dimmensional cutting tests on work pieces having columnar crystals, such a fluctuation in cutting resistance as two cycles per one revolution is found in the directions parallel and perpendicular to the crystal growth direction. The fluctuation range is more significant for an extended feed. A periodic fluctuation is also observed in surface roughness. Considerable surface roughness is found in a position parallel to columnar crystals. These facts may be attributed to the mechanical properties of the anisotropic casting.

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The impedance of films on magnesium electrodes anodized in NaF solutions of various concentrations was examined by an A. C. bridge. The corrosion potential attains noble with time in 0.5N NaF otherwise in 0.1N NaF corresponding to the thickness of the formed film. The film mainly composed of MgF₂ is identified by electron diffraction. The peak of the current density in the polarization curves in 0.5N NaF is extremely low probably by reason that the grain film covers the network film so the dissolution of the concave surface of the network film is controlled. The grain film is found by scanning electron microscopy to the most degree on the surface immersed in 0.5N NaF. The magnesium electrode will be covered with the film at a potential approximately -1.80V in 0.5N NaF.

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