Thermomechanical treatment (TMT) which consists of preaging, cold-rolling and final aging was applied to sheet specimens of 6061 alloy, and mechanical properties of the TMT materials treated under various conditions were examined and compared with those of the T6 materials. The maximum hardness of the TMT materials in final aging is higher by 10% at the best than the two-step aged materials. It also increases more rapidly with rising the preaging temperature than in two-step aging. When final-aged to the maximum hardness at 170°C, both 0.2% proof stress and tensile strength can be increased by the amount as high as 6kg/mm² by applying TMT. Both elongation and reduction of area in tensile tests are decreased by TMT. The energy value for impact fracture is also decreased appreciably by TMT. When such ductility as 10% elongation and 20% reduction of area is required, this type of TMT would have some practical significance in improving the mechanical properties of 6061 alloy.

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Aging processes of Al-6%Zn-2% Mg alloy weld metals obtained under the heat input of 10, 000, 5, 400 and 3, 600J/cm were examined by means of hardness measurements. X-ray small angle scattering methods and transmission electron microscopy. Aging characteristics of the weld metals strongly depended on weld heat input; the initial aging rate was least in the medium heat input. The age hardenability decreased as weld heat input increased. These results were discussed in terms of effects of cooling rate during and after solidification on aging characteristics of the alloy rapidly solidified. Introduction of dislocations during solidification retarded the initial aging rate of the weld metal. Precipitation of equilibrium phases during cooling after solidification and solute segregations decreased the age hardenability of it.

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The tensile and stress corrosion tests were made on the Al-8%Mg alloy aged at 200°C for various periods after aging at 150°C for 24hr followed cold rolling by 0.30 and 50%. The stress corrosion behavior was tested in the 3.5% NaCl solution by loading of 80% of 0.2% proof stress of the alloy with the anodic current of 5mA/cm². The two-step aging is not effective, but the thermomechanical treatment is effective in strengthening of the alloy. The effect of thermomechanical treatment is due to a synergetic effect of refining the structure of precipitates and presence of dislocations. The stress corrosion susceptibility is improved especially in the overaging state. This is also due to refinement of the precipitates in the matrix. It seems that presence of stabilized dislocation structure slows down propagation of cracks by affecting the mechanism of embrittling of the grain boundary area.

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The impedance of oxide films on magnesium electrodes anodized in NaOH solutions of various concentration was examined by use of an A.C. bridge. Impedance measurements showed that the formation of porous films in the active state proceeded with dissolution of magnesium. The current density in the passive state depended on the potential, but independed on it in near the oxygen evolution range. Magnesium was anodically oxidized under potentiostatic conditions. The slope of the logarithmical current-time transient for a series of potentials in the passive state range was -1/2, which suggested that the film was insulated oxide. The X-ray diffraction and scanning electron microscopy showed the Mg(OH)₂ film grown potentiostatically for up to 1000min at 2.0V.

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A low density composite of hollow volcano glass microspheres and aluminum (SBAC) was prepared by filling a mold with the microspheres (SB) and forcing the molten aluminum alloy into the mold. Composite effects for the mechanical properties and fracture mechanism of the composite were examined through uniaxial compressive tests. An yielding phenomenon of the composite is attributed to fracture of the hollow microspheres. The fractured microspheres can not transmit the stress. The compressive strength is given as a mean stress at which the narrowest parts of network structure of the matrix metal are ruptured by the stress concentration caused by fracture of the microspheres. Both the apparent mean elastic modulus (E^SB_a) and compressive strcngth (σ^SB_c) of the microspheres are directly proportional to the ratio of the mean radius to the mean wall thickness of the microspheres. The apparent mean elastic modulus (E^SBAC_a)and yielding strength (σ^SBAC_c) of the composite are;
E^SBAC_a=E^SB_aV^SB_a+E^M_a(1-V^SB_a)
and
σ^SBAC_c=σ^SB_cV^SB_a+σ^M_c(1-V^SB_a)
where V^SB_a is the volume fraction of unfractured microspheres in the composite, E^M_a the apparent elastic modulus of the matrix metal, and σ^M_c the stress of the matrix metal at the yielding strain of the composite.

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