Isothermal aging curves of various aluminum alloys have been often plotted against logarithm of aging time. However, the discussion on the shape and slope of these curves is usually done without taking serious considerations on the time scale. In this paper, some significant differences between the logarithmic and the linear plotting were discussed. The results obtained were as follows:
(1) Even in the situation where the aging occurs monotonously with an increasing rate, which itself decreases as the aging proceeds, the aging curve can take a complicated form when the logarithmic time scale is adopted; it can have an incubation period, abrupt acceleration, a two stage change, etc, depending on the increasing rate.
(2) It has been found that if most of the aging curves, reported previously, are replotted in the linear time scale, the shapes of these curves become very simple, and the complicated features seen in the logarithmic expression disappear.
(3) It is proposed, therefore, that the various previous considerations on the shape of the aging curve in the logarithmic expression should be reexamined.

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The specific electrical conductivity of the molten salts of sodium fluoride-calcium fluoride-barium fluoride-aluminum fluoride was measured.
(1) The specific electrical conductivity of the NaF-AlF₃ binary molten salts was 5.17 to 2.33ohm^-1cm^-1 up to the concentration of 50wt% of AlF₃ at 1000°C and agreed fairly well with the values reported in other works.
(2) When the concentrations of CaF₂ and BaF₂ were 5 to 20wt% and 30 to 50wt%, respectively, the electrical conductivity of the quaternary system was 4.13 to 0.73ohm^-1cm^-1 at 950°C.
(3) If the concentration of both CaF₂ and BaF₂ was constant, the electrical conductivity decreased almost linearly with an increase of AlF₃. An increase of CaF₂ and BaF₂ also decreased the conductivity.
(4) In the quaternary system, such compounds as Na₃AlF₆, NaAlF₄, Na₅Al₃F₁₄, NaCaAlF₆, NaBaAlF₆, CaAlF₅ and BaAlF₅ were formed and sevearl complex ions such as AlF₆^3- and AlF₄^- etc. were considered to exist. The structures of the molten salt were not clearly known. The validity of the additivity law in the electrical conductivity by each component was questioned.
(5) The specific electrical conductivities of Hurter's and Sumitomo's bath at 750 to 950°C were 0.96 to 1.25ohm^-1cm^-1 and 0.87 to 1.10ohm^-1cm^-1.
(6) It appears that some other compositions of the quaternary system can be used as an electrolyte of aluminum refining, besides Hurter's and Sumitomo's bath.

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Structures of splat-cooled Al-Fe alloys were studied by transmission electron microscopy and the Mössbauer spectrocopy. Three types of structures were observed; globular, lamellar and eutectic phase free structures. The globular structure was prevalent in thick areas (>1μ), while the lamellar structures occupied thin areas between two globular structures. The area free from the eutectic phase occurred near the edge of the foil, where the thickness was less than the cell size. The mechanisms of the formation of these structures was discussed from the microstructural observation. Fe segregated in cell walls of the globular structure as fine particles. From the Mössbauer spectra, it appeared that the phase was solid solution iron.

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Aging behavior of Al-Fe alloys was examined by transmission electron microscopy and Mössbauer spectroscopy to understand the good mechanical strength maintained at elevated temperatures. Following results were obtained:
(1) A fine iron rich eutectic phase at cell walls was found stable up to 400°C, above which needle shaped FeAl₃ nucleated at walls.
(2) Iron concentration in the matrix remained high up to 400°C. However, it decreased upon growth of FeAl₃ needles.
(3) An intermediate phase appeared in the matrix even below 250°C. It transformed at higher temperatures and finally decomposed above at 350°C.
(4) Boundary precipitation of metastable FeAl₃ occurred at 400°C, while the Oswald growth of FeAl₃ in the matrix was prominent above at 450°C.
These results suggest the unusually slow diffusion of iron atoms in the alloy and can explain that the dispersion strengthening effect is maintained up to 350°C

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Effect of ingot homogenizing on aging characteristic, stress corrosion cracking and exfoliation corrosion of Al-6%Zn-1.8%Mg and Al-6%Zn-1.8%Mg-1.5%Cu alloys containing less than 0.7%Cr was studied. The results obtained are as follows:
(1) Homogenizing of ingots above 400°C resulted in remarkable increase of the resistance to stress corrosion cracking and in decrease in the age hardening at high temperatures of the alloys with Cr, mainly because Cr-rich insoluble compounds of 0.03-0.2μ in size were formed during homogenizing. Low temperature age hardening and exfoliation corrosion were not particularly influenced by homogenizing.
(2) Slow heating to 450°C and prolonged homogenizing of ingots facilitated the precipitation of the Cr-rich compounds. Heating above 500°C promoted resolution and coagulation of the Cr-rich compounds.
(3) It was concluded that homogenizing of ingots at 400°C to 500°C was necessary to obtain sufficient resistance to stress corrosion cracking and exfoliation corrosion and considerable age hardenability in the ternary or the quaternary alloy with 0.2%Cr without introducing giant Cr-rich compounds in practical casting.

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