Anodic polarization behavior and time dependences of anodic current of 99.99% aluminum in 0.5N NaCl solution (pH=4, 6, 8.5, 10 and 12) were examined potentiostatially. Surface conditions of the specimens tested were also observed by scanning electron microscope, and the pitting mechanism of pure aluminum was discussed. Pitting corrosion of pure aluminum in 0.5N NaCl of pH=8.5 was seemed to be caused by Cl- entered through cracks at the interface between film and hexagonal substance, which was formed at less noble than the potential inducing pits. This hexagonal substance was only observed at pH8.5, but not at pH4, 6 and 10 in 0.5N NaCl solution. In 0.5N NaCl solution of pH=12, pitting corrosion was effected by chemical dissolution, thus pitting potential became rather noble. The limiting current observed on the anodic polarization curves in the solution of pH=8.5, 10 and 12 seemed to be controlled by diffusion of OH^-. Initial potentials inducing pitting corrosion for pure aluminum in 0.5N NaCl were about -0.743V (pH=4), -0.757V (pH=6), -0.760V (pH=8.5) and -0.710V (pH=10).

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This paper describes a research on adhesion mechanism of plastic plating using PP resin as the base material. It is considered that since PP resin is a high crystalline polymer, its crystalline morphology is different depending on cooling methods. The influence of cooling methods on the adhesion strength, was determined at first. However, it appears that the adhesion strength was also influenced by other factors, then, it was also examined how the adhesion strength was affected by the kinds of pre-etching solvents, the wettability of etched resin, the NaHSO₃, treatment or the time of ageing. The results of the experiments were summarized as follows: 1) The amount of carbonyl radical generated as a result of etching was proportional to the etching temperature and time. 2) Crystalline fraction of PP resin when molded became large with cooling time. 3) Crystalline fraction by etching increased with the etching time. 4) The test pieces prepared by cooling in the air were larger in their adhesion strength than those of rapid cooling. 5) Organic solvents used in pre-etching caused some effects on the adhesion strength. 6) Adhesion strength and wettability held good, but the influence of which wettability exerts on adhesion strength was smaller than that of surface shape. 7) Cr⁶⁺, adsorbed on PP resin, as a result of etching with chromic acid, has an effect on adhesion. 8) Increase of adhesion strength, after ageing, might be attributed to the chemical change in interface.

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In these experiments, the authors discussed the relation between the nitriding temperature of salt bath and the fatigue strength due to alternating bending tests of sorbites, SCM-1 and SK-5, which had been subjected to nitriding. The results obtained were as follows. The maximum fatigue limit was obtained at about 600°C of nitriding temperature for SCM-1 and about 575°C for SK-5. The relations between fatigue strength and any of surface hardeness, depth of hardening, compound layer, residual stress, etc. due to nitriding at various temperatures were examined. As the results, the fatigue strength was likely to increase with the increase in surface hardness, and the susceptibility to brittle repture increased with increase in thickness of hardening depth, which led to the decrease in fatigue limit.

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The authors studied the dip-coating of aluminum with cold-drying acrylic resin paints containing organic solvents as diluents and the thicknesses of film coated on aluminum in stationary and transient states were observed. The experiments were conducted on 6 kinds of paints and 4 kinds of organic solvents to determine the relations between the partial pressure of solvent and any of residual coefficient and setting time under the following conditions. Withdrawing speed: V_W=0.3-30cm/sec. Density of paint: ρ=0.900-0.913g/cm³ Viscosity of paint: μ=0.190-0.386 poise Surface tension of paint: σ=27.0-30.5dyn/cm Partial pressure of solvent: P=3.3-46.7mmHg The values of residual coefficients were in a range of 0.73-0.95 and the setting time was 150-1, 000sec. The following results were obtained by the above experiments. (1) The theoretical formulas in stationary and transient states were applicable to organic solvent paints as well as water soluble paints. However, there was a great difference between the obtained value of film thickness and the theoretical value in the transient state as in water soluble paints when the withdrawing speed was too low. Therefore, the theoretical formulas should be corrected. (2) The partial pressure of solvent was approximately in inverse proportion to the setting time. (3) The relation between the setting time (t) and residual coefficient (K) was expressed by a linear function and K was larger when t was shorter; K≅1 when t=0. (4) According to the above results, it was possible to estimate the value of residual coefficient (K) from the determination of partial pressure of solvent.

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In order to obtain the anodic films of high abrasion resistance, Al-alloys of high tensile strength were anodized in the baths containing metallic salts, and then heat-treated in the air. Hard anodic oxide films were formed in the baths containing cobalt acetate, and this might be attributed to the inhibitor effect of cobalt acetate. The oxide films anodized in the baths containing zinc acetate, on the other hand, were soft, but the hardness of these films increased remarkably by heat-treatment in the air. Spinel oxides could not be observed by X-ray diffraction method with the anodized films thus obtained.

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