Effects of ions, Cu²⁺, Fe²⁺, Cl^-, SiO₃^2-, SO₄^2-, HCO₃^- and NO^-3, on pitting corrosion of aluminum were studied by using artificially synthesized neutral water. The results obtained are as follows:
(1) Both cations, Cu²⁺ and Fe²⁺, increased the number of pits. However, the pit depth decreased as the Cu²⁺ content increased.
(2) Cl^- ions showed an interaction with SO₄^2- and increased the number of pits. However, the amount of Cl^- had no effect on the pit shape.
(3) When it was below 60ppm, SiO₃^2- markedly increased the number of pits. The ratio of the pit depth to the pit diameter decreased with an increase of the SiO₃^2- content.
(4) SO₄^2- showed a remarkable inhibiting effect on pitting corrosion. Few pits were formed when the content of SO₄^2- was more than 60ppm. SO₄^2- less than 60ppm, produced shallow and wide pits.
(5) 10 to 30ppm of HCO₃^- or NO₃^- inhibited pitting corrosion unless more than 30ppm of Cl^- were present in the solution. However, the addition of more than 30ppm showed no inhibiting effect. The pit shape was not influenced by HCO₃^- and NO₃^-.

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Shapes and habit planes of primary silicon in sand and metal molded Al-15 to 40%Si alloys were studied with a metallurgical and a gonio-microscope by using polished alloys or extracted silicon crystals. The results obtained are as follows:
(1) The crystal shapes strongly depended on the Si content, cooling rate and refining treatment.
(2) The silicon particles in high silicon alloys were coarse and irregular while those in low silicon alloys with less than 15%Si were of fine polyhedral form.
(3) The irregular particles were composed of thin hexagonal flakes, the flat surfaces of which seemed to be {111} or {100}.
(4) The silicon particles in rapidly cooled alloys were smaller than those in slowly cooled ones. Their shapes suggested that they consisted of polyhedral Si crystals.
(5) With addition of phosphorus, most small Si crystallised independently. They were bounded by {111} faces and had forms of polyhedrons growing along the <110> direction or of hexagonal pyramids.
(6) It was suggested that the silicon particles, of octahedral or other shapes, in refined alloys were single crystals.

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Electrolytic extraction methods of Al-Fe intermetallic compounds from aluminum of commercial purity and low alloy ingots were studied. The most adequate solution was produced in the following manner: 10gr of E. D. T. A. 2Na, Disodium-ethylenediamine-tetraacetate dihydrate, was added to a solution of 100ml of 0.2N HCl and 250ml of 0.2N potassium biphthalate. The solution was diluted by the deionized water to volume the 2, 000ml of the elctrolytic solution. By using this solution, no less than 71% of the intermetallic compounds, in terms of Fe content, could be recovered from the A1100 ingot.

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The relationship between the cast structure of commercially pure aluminum ingots and the intermetallic compounds were studied by using an E. P. M. A., a scanning electron microscope, an X-ray diffractometer and a Mössbauer effect spectrometer. The intermetallic compounds were extracted out of several regions of A1100 ingots made by semi-continuous casting with the method reported previously. The size of the intermetallic compounds was found within the range of 0.8μ and 50μ. The intermetallic compounds in the inner region of the "Fir tree" structure were mainly Al₆Fe, while outside this region the intermetallic compounds were mostly Al₃Fe. However, besides these two major compounds, the unknown compound, which presumably corresponded to the Al-Si-Fe phase, was also found.

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An attempt to define the relationship among temperature gradient G in liquid ahead of the interface, freezing rate R and initial solute concentration C₀, governing the cellular/dendritic transition, was made from observations of the solid/liquid interface in the unidirectionally solidified Al-Fe and Al-Zn alloys.
By increasing C₀ and R or decreasing G, the solid/liquid interface morphology changes successively from broken hexagonal cell to dendritic cell and dendrite. In both alloys, the C₀ vs. G/R relationship for the transition from broken hexagonal cell to dendritic cell is curved, while the C₀ vs. G/R^1/2 is linear. In the Al-Fe alloys, the transition occurs at smaller C₀ R^1/2/G than in the Al-Zn alloys. The side branches of dendrite in the Al-Fe alloys are rod-type and tend to grow parallel to heat flow direction. The high enrichment of Fe solute ahead of the interface, which leads to the formation of the FeAl₃ compound at boundaries, suppresses the linear growth of the side branches. In the Al-Zn alloys, only slight enrichment of Zn solute and no side branches are observed; the branches are plate-like and the dendrite is described as cellular dendrite. The size of hexagonal cell in both alloys is proportional to the inverse of the cooling rate.

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