The pitting corrosion resistance of an Al-Mg alloy produced by continuous rotation evolutional control (CREO) was investigated by means of polarization curves in solutions containing 0.1mol/L Na2SO4 and 300ppm Cl−, and by surface analysis. The pitting potential of Al-Mg alloy was evidently shifted to the noble direction by CREO, and the time required for initiating pitting corrosion of the Al-Mg alloy while kept at a constant potential of −0.1V was longer with CREO than without, indicating improvement in the pitting corrosion resistance by application of CREO. Al-Mg alloy contained such precipitates as Al-Fe intermetallic compounds and trace quantities of Si, around which pitting corrosion occurred. CREO pulverized these precipitates. The time-dependence of corrosion potential and the polarization resistance determined by the AC impedance technique suggest that the resistance of Al oxide films was increased with CREO. Therefore, it was concluded that the improvement of pitting corrosion resistance of Al-Mg alloy with CREO was caused by both decreasing the size of the precipitates which acted as cathodes during corrosion and increasing the film resistance of Al oxide.
The aim of this study is to examine the effect of silicon in DLC-Si films on friction properties, and to clarify the mechanism of low friction under dry sliding conditions. The friction coefficient of DLC-Si films was measured using a ball-on-disk type tester at a load of 10N and a sliding velocity of 0.2m/s with no lubricant in an ambient air atmosphere. Compared to DLC films without Si, DLC-Si films exhibited an extremely low friction coefficient (about 0.05) ranging from 4 to 17at. % in silicon. On the wear surface of DLC-Si coated disks, the formation of Si-OH was eventually detected using derivatization-XPS. In order to explain the relation between Si-OH formation and low friction behavior, model samples with Si-OH, Si-H and their mixture on the silicon wafer were prepared, and the friction coefficient of the samples was measured with a ball-on-plate type tester. Compared to Si-H, Si-OH had a lower friction coefficient. Furthermore, Si-OH surface analyzed by ATR-IR showed spectra with broad band at around 3400cm−1, indicating the existence of adsorbed water on the Si-OH surface. From the results obtained, it was suggested that DLC-Si films exhibited a low friction property caused by the formation of Si-OH and adsorbed water in it under the dry sliding condition.
In a magnetic field, an electrochemical reaction generates a macroscopic solution flow called MHD flow by the Lorentz force, which enhances mass transfer in the diffusion layer (MHD effect). In electroplating, the MHD effect comes from two-dimensional (2D) nucleation in an electrical double layer accompanied by the unstable growth of non-equilibrium fluctuations (called asymmetrical fluctuations). Electroplating under a magnetic field provides the other magnetic field effect called the micro-MHD effect, which emerges with micro-MHD flow and symmetrical non-equilibrium fluctuations in a diffusion layer, and suppresses three-dimensional (3D) nucleation. That is to say, the MHD effect acts as a positive catalyst, whereas the micro-MHD effect is employed as a negative catalyst, or inhibitor. Furthermore, owing to the strong penetration of the magnetic field into the materials, micro-MHD flows are effectively induced even in the inside of a complicated minute structure. Therefore, by controlling the magnetic field, we can expect high quality plating in the through-hole plating. In this paper, along with its application to through-hole plating, copper magneto-electroplating is examined from various aspects.
Tin displacement plating has been used for improvement of soldering adhesion. Conventional displacement plating methods need a masking process for pattern plating. In the present study, we developed a non masking displacement plating method by using an alginate gel particles. A 10×10−3 cm3 sodium alginate solution was dropped into an aqueous solution containing 5 wt% tin sulfate and 0.83 mol dm−3 thiourea by using a microsyringe. The spherical gel particles were prepared by crosslinking between alginate and Sn2+. The average diameter of the gel particles was about 2 mm. A copper sheet was used as a substrate. An alginate gel particle containing electrolytes was attached to the copper surface and left for 30 min at 25°C. A circular tin film formed on the copper substrate with high uniformity and a sharp edge line. The diameter and thickness of the tin film was about 450 μm and 0.4 μm respectively.