Recently, a newly developed lead-free bronze casting alloy was designated as CAC411 under Japanese Industrial Standards. CAC411 has a unique metallographic feature: tiny sulfide（Cu2S and ZnS）particles are dispersed in the bronze matrix, unlike conventional copper alloys. Earlier research results demonstrated that the sulfides have different electrochemical properties from those of the bronze matrix. At or under −1.20 V vs. Ag/AgCl, Cu2S suffered reduction and dissolution in neutral NaCl aqueous solution under cathodic polarization. The Cu2S dissolution reaction is regarded as affecting the alloy surface morphology in cathodic treatments such as electroplating. This study was conducted to elucidate effects of the sulfide on Cu-, Ni-, and Cr-electroplatings on CAC411. Results show that Cu-plating and Ni-plating affected the sulfide dissolution only slightly. Their plating surfaces were smooth and bright. However, the Cr-plated alloy surface was fogged. The fogged surface resulted from Cr cluster deposition on the sulfides. Presumably, the sulfide dissolved under the cathodic conditions was oxidized to HSO4- by Cr6+. The HSO4- behaved as catalyst for Cr deposition. Cu-plating or Ni-plating before the Cr-plating was found to be effective for obtaining a smooth and bright Cr-plating surface on CAC411.
To form glossy plating of Al on a Cu substrate, electroplating of Al was conducted in an ionic liquid mixture of 1-ethyl-3-methylimidazolium chloride and aluminum chloride (EMIC-AlCl3) containing 1,10-phenanthroline (Phen). The electroplated surface smoothness obtained using an Al-plate counter electrode was improved by stirring of the electrolyte. The reflectivity at the center of the specimen surface formed by a stirring rate of 400 rpm was the highest at 74.7% with stirring rates from 0 to 400 rpm and the reflectivity of the specimen was higher at the edge than at the center. The results suggest that the glossy surface of the substrate was enhanced by uniformity of the electrolyte in contact with the substrate. When the counter electrode was replaced with the Al mesh, the electroplated surface was glossy throughout the surface without stirring. Diffusion of the electrolyte through the Al mesh might have produced an effect similar to stirring of the electrolyte.
To improve the wear resistance of deposited films, Ni multilayer films containing copper （Cu） or phosphorus （P） were prepared electrochemically by application of pulses of a constant current from a NiSO4 aqueous solution in the presence of copper sulfate （CuSO4） or phosphoric acid （H3PO3）. Films prepared on the copper （Cu） substrates have structures （Ni/Cu or Ni/Ni-P） that include a Ni layer of controlled thickness and a thin Cu or Ni-P layer, where the two layers （Ni and thin Cu layers or Ni and thin Ni-P layers） are laminated alternately. The wear resistance of the prepared Ni/Cu and Ni/Ni-P multilayer films was higher than those of conventional Ni-P bulk films or an Ni/Cu multilayer film composed of Ni and Cu layers having equal thickness. It is noteworthy that the Ni/Ni-P multilayer film wear resistance improved with decreasing thickness of the Ni layer, even for Ni layer distance less than 10 nm. The Ni/Ni-P multilayer exhibited the best wear resistance performance at the minimum Ni layer distance used in this study: 3 nm. A new wear resistive multilayer was developed.
Traditionally, manufacturers perform etching with chromic acid to adhere a plating film to acrylonitrilebutadienestyren（eABS）resin, which is widely used as a material in automobiles and consumer electronics. However, recent environmental regulations have raised the importance of establishing a novel chromium-free pre-treatment method. We have been investigating improvement of the adhesion of plating films using an alternative method for chromic acid etching, specifically by modifying the ABS resin surface using UV irradiation from a low-pressure mercury lamp. However, that process requires that ABS resin be irradiated for more than one minute, which impedes productivity. To overcome this difficulty, we conducted experiments using a high-powered UV lamp, which markedly reduced the UV-irradiation processing time and produced adhesion strength comparable to that obtained using a conventional method with the low-pressure mercury lamp. A similar reforming effect is obtainable even with increased irradiation distance, making it applicable to three-dimensional molded articles.