We investigated film thickness effects of sulfuric acid anodized aluminum when galvanically coupled with carbon fiber reinforced plastic（CFRP）. The CFRP was electrically coupled to aluminum alloys 1050, 5052, 6061, and 7075 in 3.5 wt.% NaCl solution at 35 ℃. Galvanic current passing from the CFRP to the 1050 and to the 6061 decreased as the anodic oxide film thickened. For galvanic current between 5052 and CFRP, the elapsed time until the galvanic corrosion current density value increased tended to increase as the anodic oxide film thickened. Galvanic current passed from the CFRP to the 7075 irrespective of the anodic oxide film thickness.
Observations of surface and cross sections of 1050, 5052, and 6061 revealed large cracks in the discolored part, with corrosion progressing in the lower part of the film. It is probable that the residue after pretreatment became a defective part of the anodized film, which became the starting point for progress of the galvanic corrosion with CFRP. It is probable that the 7075 had cracks during the anodizing treatment. The test solution came into contact with the substrate in the cracks which reached the substrate. Then galvanic corrosion progressed.
After gold recovery using silicon powder from an ammonium thiosulfate leaching solution containing copper（II）sulfate（oxidizing agent for gold dissolution）, copper was also recovered. After a certain period of time, redissolution of copper occurred. Then gold was redissolved. The depletion of silicon in the solution during the recovery process leads to redissolution.