The diffusivities of gold and copper in pure aluminum were determined by residual-activity method with radioactive tracers (Au¹⁹⁸ and Cu⁶⁴) in the range of temperature between 290650°C and 375619°C, respectively. Almost all the penetration curves of both gold and copper in aluminum were found to consist of three regions, which represented near-surface effect, volume diffusion, and short-circuit diffusion, respectively. All the three regions were distinctly observed at low temperatures, but the near-surface effect disappeared at high temperatures.
The dependence of diffusion coefficients of gold and copper on temperature were given by the following equations:
D_Au/Al=(2.2^+1.0_-07)exp(-32, 000±1, 000/RT)cm²/sec. and
D_Cu/Al=1.3exp(-33, 000/RT)cm²/sec.
The pre-exponential factor and activation energy for diffusion of gold in aluminum were very similar to those for diffusion of aluminum, copper, silver, and zinc in aluminum, and it was suggested that the volume diffusion of gold in aluminum occurred by single vacancy mechanism.
The diffusivities of gold in aluminum were found rather greater than those of aluminum and copper in aluminum. Such a difference of diffusivities between the both would be due to the variation in activation entropy.
Although gold has extremely low solid solubility in aluminum, the characteristics of the diffusion of gold in aluminum was substantially different from those of other elements in particular, transition elements which are slightly soluble in aluminum where the short-circuit diffusion takes precedence of the volume diffusion. The present result provided one of the best examples that the behavior of impurity diffusion was not thoroughly explained only by low solubility.
The diffusivities of copper in aluminum derived from the results of the present work were in good agreement with the results in the past. Therefore, the procedures of the present work in experiments and analyses were proved to be satisfactory.

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The abnormal grain growth of 5056 alloy was reported in the previous papers.
This paper describes the same phenomena of the alloys containing under 5% of magnesium.
The following results were obtained:
(1) The abnormal grain growth occurred in the alloys containing above 1% of magnesium.
(2) The relation between the average grain diameter and dispersed particles of the secondary phase corresponded well with M. Hillert's theory of abnormal grain growth.

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The effects of heat treatments on the behaviour of manganese, iron, silicon and copper in an Al-Mn alloy ingot containing 1.15wt%Mn, 0.57wt%Fe, 0.29wt%Si and 0.13wt%Cu were studied with an X-ray microanalyzer, an electron microscope, etc.
Most of iron as cast in the ingot formed eutectics with manganese on the subgrain boundaries. Iron in the eutectics was not subjected to heat treatment; whereas, iron as cast in the matrix was precipitated by heat treatment at about 400°C.
Manganese as cast in the matrix was precipitated by heat treatment at about 400°C in the same way as iron and was diffused into the eutectics at near 630°C.
Silicon as cast was contained in both of the matrix and eutectics, and the silicon in the matrix was diffused into the eutectics containing Mn and Fe by heat treatment at about 630°C.
Copper as cast was uniformly distributed and was not changed by the subsequent heat treatment.

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Gallium and iron in aluminum metal were extracted with methyl isobutyl ketone from the solution of the specimen in 6N hydrochloric acid. Then, the both elements were determined by flame photometric method.
The extract was directly atomized into oxy-hydrogen flame (under the pressure of oxygen, 1.0kg/cm² and of hydrogen, 0.1kg/cm²) and flame intensities were measured at 417.2mμ for gallium and at 372.0mμ for iron. The accuracy and precision of the results were examined with ALCOA standard samples and were proved satisfactory.
This procedure was rapider and simpler than other analytical methods such as fluorometric analysis and absorptiometrie method; and the lower limit of analysis was 0.0002% for both of gallium and iron.

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Ageing process of an Al-4%Cu-0.5%Mn alloy was examined by means of hardness measurements, X-ray diffraction, electron microscopy, and electrical resistivity measurements. Significant effects were found to be given in the final ageing process when the pre-ageing treatment was carried out at 100120°C. The effects were produced in two different types, according to the ranges of temperature for the final ageing, i. e., the ranges of lower than 160°C and higher than 170°C. The results obtained were as follows:
(1) The alloy was not age-hardened at room temperature for several weeks. Its electrical resistivity was increased to some extent at the early stage of ageing, but the value was little changed after it reached a limited value. Pre-ageing at room temperature had no effects on the subsequent artifical ageing process.
(2) When the ageing treatment was made immediately after quenching, ambiguous two-stage hardening process took place at 150°C, but single-stage hardening process at 160°C. Whereas, the pre-ageing at 120°C for 100min, showed clear two-stage hardening process for any of 150 and 160°C treated specimens. The first stage hardening process due to G. P. zones was accelerated, but the second stage one mainly due to the precipitation of Θ"was retarded. The values of maximum hardness between the specimens with and without pre-ageing were nearly the same, but they were likely to be lowered to some extent for the pre-aged specimens.
(3) Single-stage hardening process took place in the case of ageing at 170180°C for any of the specimens either pre-aged or not. However, the hardening rate and the maximum hardness were much higher for the pre-aged specimens, which would be owing to the acceleration of precipitation of Θ".
(4) On ageing the pre-aged specimens at 170180°C, the process of decreasing electrical resistivity due to the precipitation of Θ' was retarded.
Electron microscopy showed that the fine structure of the pre-aged specimens was still maintained after they were over-aged.
(5) The effects of pre-ageing perfectly disappeared at temperatures higher than 200°C.

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