Abstract
Outboard motors use aluminum die-cast components extensively to cut down their weight. They are also cooled directly by the raw water including saline water. Corrosion protection is the critical issue for outboard motors because of these characteristics. Currently, the coating is the primary measures taken to assure the corrosion resistance and to give originality to the appearance. However, the complicated cooling passages cannot be coated appropriately with the spray-paint process. Such disadvantages can be compensated by the electrodeposition coating technique. In the case of electrodeposition coating, the coating film is generated electrically in the coating material bath by means of deposition. The process is widely applied to the automobile bodies made of steel plate, because it provides higher transfer efficiency and lower VOC (VOLATILE ORGANIC COMPOUNDS) emission. However, the traditional electrodeposition coating material presented various issues when it comes to the application to the aluminum components. These issues are attributable to the behavior of the coating film in the course of deposition process. The new electrodeposition coating material has been developed to deal with these issues, and has been applied to the outboard motor components. The new coating material gives higher anticorrosion property to the components, and also allows the reduction of VOC emission and the elimination of hexavalent chromium. This report describes the efforts made to work out the engineering issues for applying the new electrodeposition coating material to the actual production process.
Keywords: Coating, Electrodeposition coating, Cooling water passage, Corrosion resistance