To elucidate the electropolishing behavior of Au-Ag-Cu alloys in solutions containing thiourea, which forms stable complexes with gold, we investigated the effects of electrolytes, concentrations, and stirring conditions on electropolished surfaces. The concentrations of electrolytes and thiourea were fixed at 0.5 mol dm－3. Electropolishing was done using various electrolytes. Electropolishing at 0.6 V (vs. Ag/AgCl) using sulfuric acid as an electrolyte induced a high gloss surface with surface roughness of Ra=53 nm and Rz=391 nm. The dissolution of gold alloys was promoted by the increase in the concentrations of sulfuric acid and thiourea. Glossy surfaces were obtained using sulfuric acid and thiourea with respective concentrations of ≧0.2 mol dm－3 and ≧0.5 mol dm－3. During the rotating electrode process, the electrode potential at which the electropolished surface was sulfurated became more positive by increasing the rotation rate of the rotating disk electrode. Under a no-stirring condition, the surface was sulfurated at 1.0 V, although stirring the surface exhibited high gloss at 1.0 V. Moreover, electropolishing at 1.0 V under stirring conditions produced a polished surface with surface roughness (Ra=47 nm, Rz=369 nm) and glossiness (Gs (60°)=730) comparable to those of a buff-polished surface, and did so in a shorter time than electropolishing at 0.6 V under the no-stirring condition.
Aeronautic structural components made of high strength aluminum alloys are often shot peened in order to improve the fatigue property and then anodized to prevent corrosion. However, anodic coating on high strength aluminum alloy surface possibly spoils fatigue life. In the present study, the fatigue life of high strength aluminum alloy, 7050-T7451 under the combined influence of shot peening and anodizing was investigated. Two levels of shot peening intensity, 0.08mmA (SP 8A) and 0.15mmA (SP 15A) were respectively applied to the specimen surface, and then, they were coated with a chromic acid anodizing (CAA), the thickness of which was between 1 and 3 μm. Uni-axial cyclic loading of R ratio equal to 0.1 was applied to the flat coupon specimen, and fatigue lives were evaluated. The peeing effect on the fatigue lives from both as-machined condition and anodized one was investigated. Despite the fatigue trigger morphologies were different in two levels of shot peened specimens with CAA coating, the fatigue properties of them resulted in almost the same. The fatigue crack in SP 8A + CAA were initiated from the bottom of anodized pit. In SP 15A + CAA coupons, either of anodized pits larger than 0.1mm or just a surface cracks was found. The activated fatigue triggers morphology and the fatigue lives improvements by the different shot peeing levels were discussed with the stress intensity factors taking account of the residual stress induced by shot peening.