Abstract: The invention relates to a washing solution for a tin plating film after electroless tin plating and before water washing. The invention also relates to a method for forming a tin plating film, the method includes a step of washing step using the washing solution. The washing solution according to the present invention is an acidic aqueous solution containing an acid, a complexing agent, a stabilizer and a chloride ion. The washing solution has a chloride ion concentration of 2 wt % or more, and a tin concentration of 0.5 wt % or less. The washing solution according to the present invention has good washing property for a tin plating film surface, and allows a tin plating film to easily maintain its properties. In addition the washing solution causes little influence on a tin plating film surface even when continuously used and is excellent in temporal stability.

Abstract: Invention provides a zinc immersion coating solution used in the double-zincate method for applying first and second zinc immersion coating treatments to aluminum or aluminum alloy. Zinc immersion coating solution used for first zinc immersion coating treatment at least contains a zinc compound, alkali hydroxide, iron salt, chelating agent for complexation of iron ions, and zinc immersion coating inhibitor that is at least one out of the group consisting of a polymer of a secondary amine, polymer of a tertiary amine, and polymer of a quaternary amine, or copolymer containing the same, and zinc immersion coating solution used for second zinc immersion coating treatment at least contains a zinc compound, alkali hydroxide, iron salt, chelating agent for complexation of iron ions, and zinc immersion coating inhibitor that is at least one out of the group consisting of a primary and secondary amines, and a tertiary amine.