Abnormal grain growth was observed in 5056 alloy.
Metallographic examinations were made for the following two series of alloys.
Series A: Al-Mg binary system, hot and cold rolled.
Series B: Al-5%Mg alloys containing small amounts of Mn and/or Cr, hot and cold rolled.
The results obtained were as follows.
(1) The abnormal grain growth in 5056 alloy was closely related with Cr and/or Mn contents. The phenomenon took place at under 0.3%Cr contents and/or 0.4% of Mn contents.
(2) The secondary recrystallization temperature was higher and the ultimate maximum grain size was smaller with the increase in Mn and/or Cr contents.
(3) The abnormal coarse grains in the outer layer of the plate were discoidal; while, the grains in the middle layer remained fine.

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With the object of clarifying the heat resisting mechanism of Al-Zr alloys, the recrystallization process of Al-0.31%Zr alloy was studied by means of the measurements of micro-Vickers hardness, tensile strength, and electric resistivity, and X-ray and electron microscopic observations.
Two typical heat treatments were selected before final cold working; one was quenching after heating at 630°C for 5hrs. (solution heat treatment) and the other was slow cooling after heating at 400°C for 5hrs. (precipitation heat treatment).
The results obtained were as follows.
(1) The recrystallization temperature of the alloy was much improved by the addition of 0.31% of Zr to Al. However, the recrystallization behavior highly depended upon the condition of heat treatment before cold working.
(2) In spite of the precipitation heat treatment at 400°C for 5hrs., most of the soluted Zr atoms were not precipitated in the form of Al₃Zr, but it seemed that their form in the solution state was changed to such as cluster of the atoms or nucleus of Al₃Zr.
(3) The material, which had suffered solution heat treatment, was excellent in thermal stability at lower temperatures below about 300°C, and the material suffered precipitation heat treatment was excellent at higher temperatures.
(4) Solution heat treated material was completely recrystallized with no fine precipitates of Al₃Zr; while, precipitation heat treated material seemed to be extremely resistant to complete recrystallization, owing to subboundary precipitation of Al₃Zr.
Consequently, it may be believed that the heat resisting mechanism of the alloy is attributed to the soluted Zr itself at lower temperatures below about 300°C, and to the precipitates of Al₃Zr at higher temperatures.
(5) The following consideration may be given that the recrystallization process of the alloy is more attributed to the coalescence and growth of subgrains, and the dissipation of subboundaries rather than nucleation and growth mechanism.

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The effects of the addition of Cr, Ti or Be on the mechanical properties at high temperatures(150°C, 250°C) and the casting-structural evaluation test of Al-5%Si-0.5%Mg-(0.72%)Zn alloys were investigated and the following results were obtained.
The tensile strength of these alloys at test temperature 150°C were similar values, but at test temperature 250°C, the alloys containing Be always were superior to alloys without Be addition. These values of alloys containing Be were comparable to those of heat resisting Al alloys now used.
Generally, in casting-structural evaluation test the mechanical properties of the alloys containing Be were superior to those alloys not containing Be. When alloys were cast in green sand mold with chill-plates, the bending test value of ZH alloy containing 0.3%Be was 660kg but the value of ZH alloy not containing Be was 620kg. The effects of Be addition was favourable. When alloys were cast in green sand mold with chill-plates, the notch tensile strength of ZH alloy containing 0.3%Be was 5052kg/mm² and the strength of ZI alloy without Be addition was 41kg/mm², and so the effect of Be addition was remarkable.
It was reasonable that Al-5% Si-0.5 % Mg-2% Zn alloy was used as the basic alloy. About aging conditions after solution heat treatment at 550°C for 10hr, with respect to tensile strength and proof stress aging at 150°C for 20 hr is favourable, and with respect to elongation aging at 100°C for 50 hr is good.

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Tensile tests were performed on Al-0.5 at.%Cu and Al-1 at.%Cu solid solution alloys. The effects of temperature and strain rate on the serrated flow were investigated. The relation of ε∝ε₀^2.1 was obtained at temperatures below 22°C, in which ε is the strain rate and ε₀ is the strain at the start of serrated flow. At these temperatures, the value of activation energy for vacancy migration obtained was O.5 eV. The form of the serrated flow was different at between the temperatures of above and below 22°C. When the flow stress was plotted as a function of temperature, the peaks on the curves appeared at about 50 and 75°C for Al-0.5 at.%Cu and Al-1 at.%Cu alloys, respectively. The temperature at which change in the form of the serrated flow occurred corresponded with that at which the flow stress began to increase with the rise in temperature.

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Barrier layer thickness of aluminum, which had been subjected to corrosion tests in water containing a few ppm of various reagents, was determined by the polarization method proposed by M. S. Hunter and P. Fowle.
The thickness of barrier layer formed in the air decreased with increasing time of immersion in pure water up to 100hrs. The same behavior was also observed on aluminum tested in water containing any one of NaNO₃, NaCl, NaOH, and HCl. While, in water containing any one of NaF, Na₂SO₄, Na₂SiO₃, H₂SO₄, and H₃PO₄, the thickness of the layer formed in the air once decreased at the initial stage of immersion, and then, began to increase.
These results were compared with the corrosion rate of aluminum tested in the solutions mentioned above.
It was concluded that there was inverse correlation between the corrosion rate of aluminum and the barrier layer thickness after the tests in the various testing solutions for 100hrs. Further studies shall be made in future to reveal the reason of specific effects of anion in testing solutions on the barrier layer thickness of aluminum which was immersed in the solutions.

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