Studies on aluminum enamelling carried out heretofore have so far revealed that the most important factor is the pretreatment of the aluminum plate. As reported in the first paper, the anodic film coated by means of anodic oxidation in dilute sodium perborate solution had satisfactry properties, both in adhensiveness and luster.
In the present studies, further investigations have been carried out as follows:
α-alumina coating has been made by submitting the aluminum plates to anode treatment in the aqueous solution of borate (sodium perborate, lithium borate, Na-borate, K-borate, etc.) or silicate (water glass) of B₂O₃, SiO₂ (glass net-work formers), Na₂O, Li₂O, K₂O, etc. or Li Na, K, etc. (glass modifiers). Mixed aqueous solutions of these borates or silicates have also been used. When the aluminum enamel flit is applied on these surfaces, it was expected that a semi-glass net-work former would be produced between the α-alumina and the flit, and that an improvement in adhension would be obtained.
The results may be summarised as follows:
(1) Impact test
Lithum borate, sodium borate, water glass, and potassium borate were the most effective in mono-component aqueous solutions. Amongst binary mixtures, the system lithium borate-water glass was the most effective. Furthermore, ternary mixture also gave satisfactory results.
(2) Bending test
Sodium borate, lithum borate, potassium borate, and water glass were the most satisfactory compounds in aluminum enamelling in mono-compound aqueous solutions. Among binary mixtures the above mentioned system was the most effective.
Among ternary mixtures, aqueous solutions containing sodium borate-water glass as the main constituent gave especially good results.
(3) Thermal shock tests
Similarly to the cases (1) and (2), treatments with mixtures were superior to those with mono-component solutions.
Aqueous solutions containing potassium ions were satisfactory in all cases.
Thus samples submitted to anodic treatment in mixed solutions showed superior results in every respect to those treated in mono-component solution.

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With remarkable development of zinc diecast in recent years, plating on such diecast is becoming popular. However, not all the plating on zinc diecast has been perfect; there have been a number of plating works that have easily been corroded or peeled off. Defects of this nature are difficult to remedy under the present technical level. Howerver, the plating on diecast is in increasing demand in the market. Under the situation, the following experiments were conducted with an object of preventing corrosion of the plated surface.
The experiments consisted of giving a clear lacquer coationg over the plated surface and checking on the adhesiveness and the liability to corrosion under different circumstances. In these experiments, a variety of clear lacquer were tried to see which variety was the most effective.
As a result, vinyl lacquer was found to be the most practically efficient. The durability of the plating thus coated was nearly double that of the plating without anti-corrosion lacquer coating.

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For the purpose of investigating the mechanism of electro-depositing in the anodized coating, various anodized coatings have been observed by the electron-microscope. The results of the observations are as follows:
i) The cell structure of the anodized coating is clear and the pore diameter is increased with voltage rise, and the latter is decreased with treating time increase.
ii) Further, it seems that the pore diameter is affected by the concentration of the bath. In the case of about 10% or less solutions of phosphoric acid the diameter is the largest, whereas in the case of more than 30% it is almost unaffected by the concentration.
iii) The number of the pores in the case of phosphoric acid is (6-47)×10⁹/cm² and the diameters of the pores are 0.03-0.19μ. In case of oxalic acid, the number of the pore are near the highest range and the diameters the lowest range.
iv) A number of fine asperities appear all over the surface treated by the phosphoric acid bath. The eroded traces are left on each surface treated by oxalic or sulphuric acid which are quite different from the former.
v) The observations of the oxide film replica and the carbon replica show that even under same treating conditions these appearances are markedly defferent, but appreciable analogies exist between them.

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Among the elements composing enamelling frit for aluminum, Li₂O plays an important role next to SiO₂ and B₂O₂. As compared with Na₂O or K₂O, Li₂O has stronger reaction as flux, and forms the frit of smaller expansion coefficient and greater resistance against thermal shock. U₄ frit of borosilicate, as reported previously, with fusing temperature of 520-540°C, easily furnishes good enamelling in wetting, gloss, and a adhesion, which, however, is poor againt corrosion.
SLIO frit, obtained as a result of improvement of this frit, has excellent properties in wetting, gloss, and adhesion. The followings are the results of investigation concerning the effects of Li₂O on frit when Li₂O content varies from 1%, 3%, 5%, to 10%.
1. In the impact test, the enamel containing Li₂O has desirable qualities as compared with the iron enamel. The more Li₂O the better.
2. In the bending test, the enamel containing 3% and 5% Li₂O is not much different from the iron enamel, but the one containing 10% Li₂O shows the best result. Even when the sample is bent by 180° more than 5 times, the enamel does not come off at all.
3. Li₂O has no effect on hardness. In the boiling water and sanitation test, the one containing 10% Li₂O shows about the same result as the iron enamel. In the thermal shock test, the one containing Li₂O does not come off, but the ones containing 3% and 5% have the tandency to come off.
4. In the corrosion test, the more Li₂O it contains the more resistant is it against inorganic acid and 5% and 10% NaOH solution, but not against boiling water. Against 10% Na₂CO₃ solution, it has the same tendency as against boiling water.

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