As base metals 3 kinds of aluminium plates of different composition (99.9% Al, commercial aluminium, and 52S) are used in the experiments. Specimens are made by plating the anodized and plate mentioned above. The examination of the adhesive property of these specimens shows that the low grade aluminium has the best adhesive property. The cause of the difference in the adhesive properties is investigated, and the following results are obtained: i) The electron-microscopic observation of the oxide film shows that the inherent pores are slightly larger for the higher purity aluminium than the lower one. When the phosphoric acid bath is used, no relation exists between the adhesive property and pore size. The cell structure of the oxide film is more uniform and continuous in the high purity aluminium, while the low grade aluminium has many defects in the oxide film. ii) The anodized surface of low grade aluminium macro or micro-scopically rough. iii) The nucleation during initial plating is selective as a rule, and the higher the purity of aluminium is, the higher is the selectivity. iv) In the case of nickel bath, the lower the grade is, the higher is the electric potential, and the easier is the plating operation. This agrees with the well known fact that the nobler the metal is, the easier is the plating operation. The potential rises due to the anodizing, and the highest possible potential becomes almost as high as that obtained by using iron plates.
As a means of clarifying the mechanism of brightening, the upper and lower limits of the range of brilliance were investigated. As a result, it was qualitatively proved that the upper limit coincided with the potential of hydrogen gas generation and the lower limit with that of brightener crystallization. From the above, an observation on the mechanism of brightening was done summarizing all the results in the Reports 1-4.
Behaviors of various plating solution of Co-Ni alloy series used in our country are investigated and properties of the electrodeposited alloys are examined. The result obtained is as follows: (1) Formate is an effective baffer indispensable to the plating solution of low pH value. As a buffer for cathode film boric acid is also effective. (2) Hardness of the deposit of Co-Ni alloy bright plating is between 500 and 600 Vickers, and is not affected by the adition of organic brightener and magnesium sulphate. (3) Electron-diffraction examination reveals that the deposit of Co-Ni alloy plating has no clear orientation, but consists of fine grains.
Experiments on electroplating of Cu-Sn alloys under various conditions were carried out in the plating solution composing mainly of copper cyanide and sodium stanate, of which five kinds were used varying the ratio of Cu/Sn from 7/10 to 16/1. The results of X-ray diffraction examination are as follows: 1. Sn content in the electrodeposited Cu-Sn alloys varies from 10 to 78%. Phases in the alloys are classified into four groups, namely, (a) α only, (b) α+η, (c) η only, and (d) θ+ξ. 2. In the electrodeposited alloys, the phase of (η+ζ), which exists in the equilibrium phase diagram of Cu-Sn alloy, can not be seen, and the region of this phase is displaced by η and (θ+ξ) phases. 3. β, δ, and ε phases, which exist in the phase diagram at high temperature, also can not be seen in the deposited alloy. 4. In the electroplated alloy of speculum plating, only (α+η) or η phase is crystallized and the number of diffraction patterns in this case is significantly small as compared with that in the other cases. 5. The composition of the deposited alloy is decided mostly depending upon the composition of plating solution, but not mach upon other plating conditions such as current density, stirring, etc.
The carburized and quenched bolt often fractures when used after cadmium plating. The cause of such fractures is investigated and the following result is obtained. The hardness of the carburized layer of the bolt increases by about 100-150Hv due to the cadmium plating, while the elongation of the bolt decreases slightly. This phenomena should be caused due to the so-called hydrogen embrittlement, which can be eliminated by heating at about 150°C. On the other hand, the poor metallurgical properties of the base metal, and the improper conditions of the heat treatment and of the mechanical working result in the notch effect and the dispersion in the tensile strength readings.