Factors which give unstationary actions to molten aluminum were introduced to alternating electromagnetic stirring. The factors included currents in which two or more frequencies were superimposed, periodical intermittent currents and narrow electrodes to produce current density distribution within the melt. The first two factors have a little effect on grain refining, but the last one has a significant effect. This difference in grain refining effect is attributed to the different modes of molten metal action. In the former case, the elastic melt action reesults in minute displacement of the melt. An oscilating flow generated in the latter case results in the displacement much greater than the former

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Origination and growth of pores in Al-Si alloys having different morphologies of macroscopic solid-liquid interface were investigated. Pores originate and grow in Al-Si alloys in a similar way as in pure aluminum. Pores originate in the melt in which hydrogen has supersaturated and reached at the critical concentration for pore formation and grow with the aid of diffusion of hydrogen from surrounding melt. The growth and shape of pores formed are affected by morphologies of macroscopic solidifying interface and by solidification rates. Primary silicon crystals in Al-16%Si alloy act as nuclei for pore formation. The distribution of hydrogen in solidified alloys corresponds to that of silicon.

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Aluminum and Al alloys containing Zn up to 0.75%, Cu up to 0.6% and Mn up to 0.3% were tested in sodium chloride solutions. Cu in aluminum has dominant effects on electrochemical properties. The pitting potential effectively lowers and unusual anodic polarization characteristics are found in aluminum containing a small amount of Zn. Zn in the alloys containing Cu has little effect. The corrosion weight loss of aluminum in immersing corrosion test increases with Zn content, while that in salt spray test increases with Cu content and remains unchanged with Zn content. The pitting corrosion resistance of aluminum can be evaluated in the alternating immersion corrosion test in which immersing in the solution follows by drying in flowing hot air. Pitting corrosion is suppressed by appropriate additions of Zn and Mn, but promoted by Cu in this test. The corrosion resistance has relations to such electrochemical properties as polarization characteristics but not to pitting potentials.

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Dry cutting tests of 5056 alloy were carried out using test bars whose properties had been controlled in such a way that DC billets homogenized at different temperatures, extruded under different working ratios and cold drawn. The cutting tool wear of 5056 alloy is explained in terms of ultimate tensile strength and Charpy impact value. The tool wear is moderated for the test bars having lower ultimate tensile strength and Charpy impact value. The tool wear is also moderated when the alloy cotains the Al-Mg non-equilibrium second phase which melts at cutting temperature and lowers friction resistence and tool wear.

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Property of oxide film of aluminum hydrated in deionzied water was studied by measuring anodic polarization curves in ammonium tartrate solution. The anodic polarization curves show the initial stage of hydration. The hydrated films consists of the duplex oxide layers of fine and cylindrical crystals.

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A method for evaluation resistance to stress-corosion cracking (SCC) in short transverse direction in high-strength aluminum alloys was examined and was tried to appply to 7N01 alloy. A valid fracture toughness balue can be obtained from the stress-intensity (K₁) determination for the DCB specimen. SCC growth rate da/dt as a function of K₁ in NaCl aqueous solution was determined for the specimens aging treated in different manners. Rankings of da/dt corresponding to region II are consistent with those of SCC resistance developed with a smooth spacimen aged at 120°C for 24h have resistance higher two orders of magnetude than the T4-specimen aged at R.T. for 2months. Over aging treatment T7 (at 180°C for 3h) impproves not so effectively resistance to SCC propagation.

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