Influences of precipitating condition of gibbsite from sodium aluminate solution on particle size, specific gravity, specific surface area and formation ratio of boehmite after calcination of gibbsite were studied. Gibbsite obtained from a solution of Na₂O/Al₂O₃ molar ratio 1.4 has the maximum specific gravity and minimum specific surface area and indicated maximum particle size of 6.33 μm. In this case, the formation ratio of boehmite was 33%. Gibbsite particles are coarsened with rising the stirring temperature and lowering the keeping temperature. The reaction rate of gibbsite decomposition to boehmite, χ-Al₂O₃ and γ-Al₂O₃ was investigated by D. S. C. technique. The decomposition at an early stage from a part of gibbsite to boehmite at 220°C is controlled by chemical reaction, and that at a later stage is controlled by nucleation of boehmite. The remaining gibbsite changes into χ-Al₂O₃ at 300°C being controlled by chemical reaction. The change from boehmite to γ-Al₂O₃ at 500°C is controlled by nucleating reaction.

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TEM studies were made on an Al-13.2%Ag alloy to examine the precipitation of intermediate γ' phase affected by secondary defects or G. P. zones. Specimens 0.3 mm in thickness were solution-treated at 560°C, quenched, and subsequently aged at 150 or 200°C. The secondary-defect structure mainly consists of dislocation loops differing from helical dislocations. The γ'-precipitates form on these dislocation loops at an early stage of aging. The γ'-precipitates are also found to form by the aid of G. P. zones after disappearance of the dislocation loops. The latter type of precipitation, as well as the former, is observed both at 150 and 200°C, but is never observed under the condition of low concentration of quenched-in excess vacancies even when the size of G. P. zones in-creases.

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Aging behavior and structure of Al-1.6wt%Li-5.7wt%Mg (Al-6at%Li-6at%Mg) alloys containing a small amount of Ag, Cu, or Zn were studied by means of hardness measurement and transmission electron microscopy, etc. These additional elements improve the age-hardenability of the ternary alloy. This effect is remarkable in the alloys containing 0.1at%Ag or 0.6at%Zn. The fact is considered to be partly due to the finer distribution of δ' phase and partly due to the enhanced precipitation of a phase analogous to T (Al₂LiMg). Energy dispersive X-ray spectroscopic (EDXS) analysis on precipitates reveals that neither Mg nor additional elements are enriched in δ' phase but that they are enriched in the phase analogous to T.

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Forming conditions such as a proper convergence angle were investigated to overcome the defects often encountered in tubing BA11 aluminum alloy 20 mm in outside diameter and 0.8 mm in thickness. Forming states of the skelp under the test conditions were evaluated. The effective forming condition is to control the proper convergence angle by widening the edges of the skelp already formed into a circle compulsively with seam guide rolls. The reasons are sufficient controlling of the faying edges and little forming at the squeeze rolls. The deflection being brought about on the edges by girth-reducing of the skelp at squeeze rolls, that is, hollow sinking also is a relative factor. The effect of deflection is moderated by decrease in drawing resistance, smooth deformation in drawing and transition into compressive strain.

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Aluminum single crystals having various orientations were scratched with a diamond cone stylus to clarify the deformation mechanism of finished surface by machining. The method is considered as a simplified model for the deformation which occurs in chipless micro-machining, lapping and courses of friction and abrasion. Both the scratching force and scratched track width periodically fluctuate in accordance with the fluctuation of scratching direction even if the crystal plane is identical. The angle of slip lines observed around the scratched tracks is in good agreement with that calculated from the active slip system. The deforming process in the end of scratched track is explained also by the active slip system.

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