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Researches on aging during one hundred years of Duralumin were projected by Prof. Masaji GOTO and cooperators in Metallugical division of the Aeronautical Research Institute, Tokyo Imperial University.Test pieces were prepared in 1927 and has been preserved by Prof. Shiro ISida and subse-quently by Prof. Hiroshi ASADA.Preparation of the test pieces was as follows:Aluminium wire bar made in Aluminium Co. of England, magnesium ingot, electrolytic copper and Cu-Mn mother alloy were melted in graphite crucible. Standard composition: Grop I-Cu4%, Mg2Si0.75%, Mn0.5%, Al the balance. Group II-Cu4%, Mg2Si0.75%, Si1%, Al the balance. Maximum temperature for melting was 750°C. Ingot was 30×100×120mm of size and was hot-rolled at 450°C to 6mm of thickness and annealed at 350°C for 30 minuts and cold-rolled to 5mm of thickness. Tensile test pieces were quenched in water from 520°C after keeping in salt bath for two hours.The test pieces had been preserved in a storage room of basement for some periods until 1934 without any protection, since when they have been preserved in a steel-locker in ordinary room.It seems that, after 28 years, tensile strength has become more or less lower and elongation more or less higher.

In order to improve quality of the die-cast, it is important to control heat (temperature) together with the design of dies, character of die-casting machine, etc., and we studied the effects of shot number and water cooling on variation of distribution of die-temperature.A method of qualitative improvement for uniform temperature of cavity might be found and an equation for efficiency of water cooling might be proposed by the measurement of die temperature.

The mechanical properties of die-castings, the effects of casting conditions upon these, and the relation between the microstructure and the strength of the products have been studied. The results are summarized as follows.1. The mechanical properties of the die-cast tensile specimens were sensitively affected by the casting temperature, but not by the die-temperature.2. The injection pressure affects upon the mechanical properties. A sufficiently high pressure is needed for improving the strength.3. The proof stress at 0.2 percent offset of the silumin die-cast tensile specimens lies almost within the range between 12 and 14kg/mm2, and was nearly constant regardress of the tensile strength when its strength was above 17kg/mm2.4. The average elongation in 50mm of the above-mentioned specimens was 2.8% for the nominal tensile strength (24.5kg/mm2 of ASTM), which was lower than the nominal value.5. The relation between the microstructure and the mechanical properties of the die-cast automobile parts were examined, but the difference of strength which depended on the micro-structures could not exactly be decided.6. The roughness of surface of the die-casting and the die cavity was tested. It is considered from these tests that the roughness of surface of the davity is propertional to numbers of shot.

The work-hardening of Al-Mg alloys (2-7 pct. Mg) at low temperature is not so dependent on temperature as pure aluminium, but is the material is deformed with creep at -196°C.The recovery of stress, hardness, and electrical resistance of cold-worked Al-Mg alloys, and its recrystallization process have been investigated. The electrical resistance is recovered with the activation energy of 0.34eV between 0°C and 100°C. The stress is recovered rapidly between 100°C and 200°C, and the activation energy is 1.10-1.25eV with the increase of Mg content.The recrystallization process seems to depend on Mg content and deformation temperature.

Measurements of decreases in electric resistance of polycrystalline commercial aluminium and superpure aluminium annealed at various temperatures after deformation at liquid-nitrogen temperature reveal that some form of recovery occurs. The apparent activation energies for these recovery processes are 0.55ev for -80--50°C in commercial and superpure aluminium, 0.75ev for -50-0°C in commercial aluminium and for -50--25°C in superpure aluminium, and 0.4ev for -25-0°C in superpure aluminium. The activation energies are discussed in comparison with the recovery processes of copper.Measurements of X-ray patterns of polycrystalline commercial aluminium annealed at recrystallization temperature after prior deformation at liquid-nitrogen temperature reveal that there are much more subgrains and finer recrystallized grains than that annealed at recrystallization temperature after prior deformation at room temperature.

A new apparatus for measuring stress distribution and dynamic friction coefficient in cold rolling of aluminium plates was made by the authors. It consists of a small tungsten pin which is set along the radius direction of the under roll, and a wire strain gauge which changes with deformation of the small pin. The wire strain gauge is sufficiently sensitive even to a small load, as the bobbin of gauge is made of cloth-bakelite.With the apparatus a series of experiments was carried out to clarify rolling stress distribution, stick-slip and dynamic friction coefficient in cold rolling of aluminium plates.The results are as follows: Many slips exist in cold rolling of aluminium plates; generally, curves between rolling stress and angle of contact part are of bell-type, and the maximum rolling stress increases proportionally to an increase of rolling reduction ratio; and dynamic friction coefficients are calculated at the neutral point, and the coefficient increases with an increase of rolling reduction ratio, too.

The recovery phenomena of electrical resistance and tensile stress of aluminium-magnesium alloys (2, 4 and 6 percent wt. magnesium) annealed at various temperature after deformation at liquid-nitrogen temperature were studied.The following result was obtaind: (1) The increase in electrical resistance appeared by annealing at a range of temperature between -75°C and +20°C for 4 and 6 percent magnesium, but the decrease in electrical resistance was obserbed for 2 percent magnesium. (2) The tensile stress increases by annealing at a range between -75°C and +60°C for 2 percent magnesium and between -75°C and +30°C for 6 percent magnesium.These experimental ressults were interpreted by assuming that the interaction between solute magnesium atom and excess lattice vacancy was introduced during deformation at liquid-nitrogen temperature.