The precipitation hardening and its effects on recrystallization were investigated on Al-0.3wt.%Zr alloys containing various amounts of Fe and Si. The results were summarized as follows.
(1) The rate of precipitation hardening of Al-0.3wt.%Zr alloys, solution heat-treated at a temperature as high as 640°C, was very low. The time required to reach the maximum hardness was more than 6000hr. at 250°C, about 1000hr. at 350°C, and about 400hr. at 450°C.
(2) In general, the height of peak hardness increased with the drop of ageing temperature. However, at 450°C, the alloys were scarcely hardened in precipitation.
(3) The precipitation hardening of these alloys was much accelerated by the addition of small amounts of Fe and Si. As the results, the time required to reach the peak hardness was shorter and the height of peak was also larger.
(4) In hight temperature aging, the so-called grain boundary reaction was shown in high grade alloys, but not in alloys having high contents of Fe and Si.
(5) A rod-shaped insoluble compound appeared on the grain boundary in low grade alloys. It was confirmed by scanning analysis with X-ray micro-analyzer that the compound had higher contents of Fe, Si, and Zr; but its accurate composition and crystal structure were not determined.
(6) The effects of the precipitate on the prevention of recrystallization and boundary migration were expected to be most remarkable at some optimum size of the precipitate. Smaller particles seemed to be unstable and larger ones seemed to have little effects.

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Resistance to compressive deformation of 6063 alloy billets was determined by experiments with a cam plastometer. The effects of heat treatment and macro-structure on the resistance to deformation were examined for strain rates of 1.6-31/sec. at between room temperature and 500°C. The following conclusions were drawn.
(1) The relationship between resistance to deformation and reduction ratio in all the specimens was expressed by exponential function curves.
(2) Deformation resistance in cold working was saturated by high strain rate. However, in specimens, which had been solution heat-treated and fully aged, the resistance also tended to be saturated by some strain rates.
(3) The resistance to deformation tended to decrease with the rise of working temperature. For example, the stress for the compression of specimens at 500°C was 4-6kg/mm², which was expressed by strain rates of 1.6-31/sec. and almost independent of the effects of heat treatment.
(4) The relation between strain rate sensitivity (N) and relative temperature coefficient (T_h) was expressed by straight or broken lines, which was evaluated to be the effects of heat treatment.
(5) Resistance to deformation of billets consisting of feathery crystals was gradually approximate to that consisting of granular crystals with the rise of working temperature. However, the former billets showed nonuniform flow, which suggests unsolved problems related to shearing deformation of materials.

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The corrosion characteristics of commercially pure aluminum immersed in ion-exchanged pure water containing a few ppm of various reagents were investigated under stagnant water conditions. Most of the tests were conducted at 35°C, but some of them were at 20° and 50°C for comparison. Increase of weight and loss of metal were measured as rates of corrosion and the relation between time and corrosion rates was determined.
Change in the composition of testing water had remarkable effects on corrosion. The dependence of these effects was greater on anion rather than cation in the water. The pH of water also had some effects, but they were dependent upon the kinds of anion even at the same value of pH. The effects of anion were divided into two groups. Anions of the 1st group produced general corrosion of aluminum similar to that in pure water. On the contrary, anions of the 2nd group more retarded the general corrosion with the increase in concentration.
The authors deduced a theory to explain these effects of anions. Although, pittings were hardly observed in these experiments and a hypothesis was presented to explain the effects of ions on the formation of pittings.

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The mechanical properties of Al-Zn-Mg alloys depend upon conditions of heat treatment and the resistance to stress corrosion cracking is varied according to grain structure of the material resulting from the metal flow pattern induced by production.
The experiments were conducted on the effects of heat treatment on the resistance to stress corrosion cracking.
The stress corrosion cracking of Al-4.2%Zn-1.4%Mg alloy was conducted by the test method of cantilever loading system in aqueous solution of 5.3%NaCl-0.3%H₂O₂.
The results obtained were summarized as follows.
(1) The mechanical properties were almost equal in three sampling directions (longitudinal, long transverse, and short transverse). However, the resistance to stress corrosion cracking depended on the sampling direction and the resistance in short transverse direction was lower than those in other two directions.
(2) When the alloy was overaged at high temperature, the resistance to stress corrosion cracking increased in short transverse directions, but its mechanical strengths decreased.
(3) The resistance to stress corrosion cracking in short transverse direction depended upon conditions of heat treatment. Its values after T4 heat treatment were lower than those after T6 and T7 treatments. The values after T7 heat treatment was higher than those after T6 treatment.
(4) The values of threshold stress in short transverse direction were about 13-14kg/mm² after T6 and T7 treatments, but the values after T4 treatment were lower than the former two.

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