Reversion (Rückbildung) test on hardness and dissolving rate and change in microstructure due to ageing were studied. Reversion test was carried out by heating the aged specimen at 200°C for 1min. (in silicone oil bath).
The results obtained were as follows.
(1) Before reaching the maximum point on dissolving rate-ageing curve (that is at the 1st stage) by heating the specimen at 200°C for 1min., both dissolving rate and hardness which had been increased due to ageing dropped to the initial values as quenched, respectively. The above period was considered to be a reversible one, when cluster and G. P. zone were formed. In the period after passing through the above maximum point, it was assumed that intermediate phase was precipitated.
(2) The equilibrium phase was preferentially precipitated in the grain boundary, and then, it was precipitated within the grains in the period after passing through the maximum point on hardness-ageing curve. At the 3rd stage of ageing, it was supposed that an equilibrium phase was precipitated.

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The effects of Si, Cu, Fe, Mn, and Cr on the ageing characteristics of Al-4%Zn-1%Mg alloy were studied by measuring changes in hardness, dissolving rate, etc.
The results obtained were as follows.
(1) On the effect of age-hardening: Si retarded the hardening of the initial ageing and lowered the maximum hardness. The same effect was produced for Mn, when the ageing was carried out at 120°C. On the contrary, Cu accelerated hardening, but Fe and Cr had no remarkable effects.
(2) Cu, Fe, Mn and Cr reduced the time for attaining maximum dissolving rate. Accordingly, it was considered that intermediate phase was promoted to be precipitated by these elements.
(3) Fe, Mn, and Cr refined grain size: in particular, the effect of Cr was most remarkable.

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Being continued from the previous report, the tapping machinability of wrought aluminum alloys, i.e., 17S-F, 24S-F, and 56S-F, were discussed in regard to the relation between the theoretical analysis and experimental value of tapping torque, chips formation and its effects, built-up edge, etc.
The results were summarized as follows.
Orthogonal cutting tests, which were regarded as cutting mechanism approximate to tapping, were conducted in turning to obtain the specific cutting resistance of the material. Then, the theoretical tapping torque was calculated. As the results, the theoretical value of 24S-F was almost equal to the experimental value, but in 17S-F and 56S-F, there was a great difference between the both values. The above results may be mainly due to the factthat the torque was greatly affected by chips removal in tapping. In other words, 24S-F formed finely divided chips which were easy to be removed. However, the chips of 17S-F and 56S-F were filled and to select the tapflute and in many cases they formed the shape of flute. In consequence, it would be necessary compressed in the having proper twisted flute, shape of flute, clearance angle, etc. according to the materials.

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In drilling sheets of aluminum and its alloys, burrs were formed around the exits of holes by the action of drill. These burrs were not in the same state, according to the worked material, drilling conditions, drill dimension, etc.; and the mechanism of their formation was not also the same.
Five sorts of R-materials, i.e., 1070, 1100, 5005, 5050, and 5052, were used as specimens and the effects of drilling conditions and the drill dimensions, in particular, chisel edge and lip clearance, on the size of burrs are discussed in this paper. The size of burrs was indicated by the thickness of burrs on the surface (exit-side) and its measuring method was originated. The experiments were pursued on drilling under constant feeding speed and constant forced pressure by using the twist drill having the constant point angle, 118°, and various lip clearances. The results were summarized as follows.
Burrs increased with the increase of the feeding speed but were little affected by the cutting speed. In drilling under constant feeding speed, aluminum sheets showed minimum size of burrs at the lip clearance of about 13°, but the size was much varied according to the lip clearance. However, for aluminum alloys, the size was not so changed according to the lip clcarance. In drilling under constant forced pressure, in both cases of aluminum and its alloys, the size was varied according to the lip clearance and the change of its figures was more complex.

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When Zn and Mg were contained together in die-casting aluminum alloys by the content equivalent to ADC 12, the effects of the both metals on the mechanical properties and corrosion resistance at room temperature and the effects on the change of mechanical properties after tempering (T5 treatment) were investigated.
The following results were obtained.
(1) The effects on the mechanical properties at room temperature were the same in die-cast specimens and mold cast specimens. Zn and Mg contents had little effects on tensile strength, but yield strength (0.2%), elongation, hardness, and impact value were affected by Mg content more remarkably as compared with Zn. Yield strength (0.2%) and hardness were higher for higher Mg content (0.30%), while elongation and impact were higher for lower Mg content (0.08%). On the other hand, yield strength (0.2%) was almost constant for the increase of Zn content, but hardness slightly increased with the increase of Zn. Furthermore, elongation and impact value had also the same tendency as above.
(2) The suitable tempering (T5 treatment) conditions of the specimens (having chemical components used in these experiments) would be at 150°C and for 8hr in the air atmosphere. The effects on mechanical properties were more sensitive after T5 treatment was performed. Especially, yield strength (0.2%) and hardness of higher Mg content specimens were substantially increased. The effects of T5 treatment on tensile strength were not observed for any contents of Mg. Elongation and impact value had the same tendencies in almost uniform decreasing with the increase of tempering time for any contents of Mg. However, they were always higher for lower Mg content (0.08%) than higher one (0.30%).
(3) In salt water (3% NaCl) immersion test, the specimens, which had been cast by permanent molds, showed weight loss directly proportional to immersion time. Mg content had almost no effects, but Zn content had slight effects on corrosion resistance. On the other hand, in die-cast specimens, which had undergone salt spray (5±1wt.%) test at 35°C, yield strength (0.2%) even after 2 months period test was not different from that value at room temperature. However, the effects of spraying time appeared on tensile strength, elongation, and impact value. The above effects were more remarkable in Zn content as compared with Mg in all specimens.
(4) In specimens of higher Mg content (0.30%), the presence of S compound (Al₂CuMg) was microscopically observed. It was supposed that the above compound had the very effects on mechanical properties and other properties after ageing and T5 treatment.

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Diantipyrylmethane has been found as a selective reagent for forming a yellow complex with titanium in hydrochloric acid. Slow developing of color appeared, but fully developed color solution was stable for a long period. The color developing depended on temperature, addition amount of the reagent, and concentration of hydrochloric acid. The present method would be applied to the determination of titanium in various aluminum alloys with almost no effects of co-existent elements. The recommended procedure was as follows.
The aluminum alloy was dissolved in dil. hydrochloric acid and insoluble matter was filtered off. Then, the solution was diluted to a known volume. An aliquot of the solution was transferred to a volumetric flask, into which ascorbic acid was added and allowed to settle. Then, diantipyrylmethane solution was added to it and it was allowed to stand for 1hr. Optical density of the solution was measured at 390mμ by comparing it with a control solution prepared in the same way, but containing no diantipyrylmethane, and titanium was determined by the calibration curve.

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