In situ measurement of solidification process was attempted by detecting acoustic emission (AE) signals through a wave guide in the final freezing zone of casting which solidified at various freezing conditions and had different types of casting defects such as cavities and hot-tearing. AE signals with remarkable peak voltage which are never detected in the early stage of solidification are detected not only at the end of solidification in all the castings but also in the later stage of solidification in the alloy castings having numerous cavities or remarkable hot-tearing. AE signals accompanied with fracture of solidifying castings at the solid-liquid co-existing state is detectable. These facts mean that formation of cavities or hot-tearing in the solidification process is detectable by a non-destructive, AE signal measurement.

View full abstract

A new process for producing porous aluminum by the foaming technique was developed. In the process, molten aluminum into which Ca has been added before the stage of viscosity rise is stirred to disperse oxide films into the melt. Adding Ca results in considerable shortening of the time for viscosity rise because of promoting oxidation of the melt. Another advantage of Ca addition includes that the foaming agent is mixed easily and quickly in the melt by the vortex method. This also allows to diminish a required amount of expensive foaming agents such as TiH₂ and ZrH₂ and to utilize economical foaming agents such as volcano ash (Shirasu). Only about 0.4%Ca is required both for viscosity rise of the melt and mixing of foaming agents. The optimum viscosity of the melt for foaming is about 8.6cP.

View full abstract

The casting defects are reduced by increasing the molten metal velocity near the defects. When the linear runner, where flowout volume through the lower runner gate was greater than the volume through the upper one, was used, the molten metal unequally filled up the cavity and the molten metal velocity suddenly decreased at a final filling portion. Therefore, the casting defects frequently occurred at the final filling portion. On the other hand, when the stair shaped runner was used, the molten metal equally filled up the cavity without a turbulent flow, and the molten metal velocity did not decrease at the final filling portion. Therefore, the molten metal filled up the cavity with inconsiderable casting defects in a short time.

View full abstract

Crystallinity of barrier oxide films formed, by anodic oxidation, on aluminum in an aqueous solution of 1 g/l ammonium dihydrogen phosphate at 85°C was found to be strongly dependent, among other factors, on the immersion time of aluminum specimens in the anodizing bath prior to anodic oxidation. When electropolished aluminum specimens were anodized immediately after they had been introduced in the anodizing bath, normal amorphous film formation was observed. However, when the immersion time was about 30 sec or longer, the resulting films consisted of both amorphous and crystalline γ'-alumina. Extensive examinations of the surface of aluminum specimens after immersion in the anodizing bath have shown the presence of trace amounts of hydrous oxide along the grain boundaries or cell boundaries of the aluminum surface. Good correlations were found between the manner of formation and distribution of hydrous oxide and the growth of γ'-alumina.within the barrier oxide. The development, within the barrier oxide, of γ'-alumina can be explained reasonably if it is assumed that the trace amounts of hydrous oxide present along the grain boundaries or cell boundaries are incorporated within the growing barrier oxide and subsequently dehydrate to fine crystallites of γ'-alumina which act as nuclei for. amorphous to γ'-alumina transformation.

View full abstract

In this paper, fatigue test was performed by using Schenck's plane-bending machine on the parent metal and buttwelded joints of extruded 7003-T5 alloy, and the relation between the crack initiation and the P-N diagrams were studied. At high stress levels, the P-N line shows a linear relation on the log-normal probability representation. However, when the stress level is close to the fatigue strength at 10⁷ cycles, the P-N curve is composed of two straight lines. In the case of the former and the short life region of the later, the initiation of main fatigue crack develops at intermetallic compounds, blow hole, dent of the toe of bead and cross slip zone on the surface. In the long life region of the later, the main fatigue crack initiates at the defects, such as intermetallic compounds or blow holes locating inner surfaces.

View full abstract

Electrochemical polarization measurements have been carried out to establish electrochemical evaluation of corrosion resistance of aluminum alloys for can stocks in lower Cl- ion beverages. While no pitting corrosion was obtained in deaerated beverage, corrosion rate increased and pitting corrosion occurred in aerated one. Anodic polarization characteristics depended greatly on temperature and potential scanning rate. When greater difference between E_pit, (pitting potential) and E_rep (repassivation potential) was obtained, E_rep, not E_pit could be the characteristic potential of pitting corrosion. Corrosion resistance was well understood in terms of polarization characteristics and, especially, pitting possibility could be estimated in the relation between E_corr and E_rep.

View full abstract

Interdiffusion has been investigated in α-solid solutions of Al-Cr, Al-Hf and Al-Mn systems. The interdiffusion coefficients were presented by,
D(Cr)=2.9×10^-1exp(-257kJ/RT),
D(Hf)=1.2×10^-2exp(-242kJ/RT),
D(Mn)=3.7×10^-3exp(-203kJ/RT).
Activation energy in metals was discussed in terms of the size effect. Activation energies of diffusion in aluminum increase with the parameter of (Nr³_i/k_i).

View full abstract

Wear resistance of Al-Si alloy is increased with increasing the silicon content at low sliding speed, and severe scuffing wear occurs easily in the hypo-eutectic Al-Si alloy at high sliding speed or high load. However, desirable oxide wear by protective oxide film formed during slide is more remarkable in the hypo-eutectic Al-Si alloy than that of eutectic or hyper-eutectic alloy. An addition of Mg or Cu to Al-Si alloy is effective to improve the wear resistance but Cu is more effective than Mg. Wear resistance of AC4B is superior to AC4C, and that of AC4B is nearly same as AC8C or ADC 12. T₆ treatment gives rather unpreferable effect for wear resistance of these alloys. Lubrication gives a notable effect to protect the sliding-wear of aluminum and its alloys.

View full abstract