Abstract: The present invention aims to provide an etchant that can provide good deposition of a metal plating such as a nickel plating, despite its acidity, and a method of surface treatment of aluminum or an aluminum alloy using the etchant. Included is an etchant containing a zinc compound and a fluorine compound and having a pH of 4.5 to 6.5.

Abstract: The present invention aims to provide a metal displacement solution that can provide good adhesion to a plating film (metal film), and a method for surface treatment of aluminum or an aluminum alloy using the metal displacement solution. Included is a metal displacement solution which contains a zinc compound, a nickel compound, a germanium compound, and a fluorine compound.

Abstract: The electroless gold plating bath includes a gold sulfate, a thiosulfate, ascorbic acid compounds, and hydrazine compounds, the hydrazine compounds being at least one selected from the group consisting of adipic dihydrazide, propionic hydrazide, hydrazine sulfate, hydrazine monohydrochloride, hydrazine dihydrochloride, hydrazine carbonate, hydrazine monohydrate, sebacic dihydrazide, dodecanediohydrazide, isophthalic dihydrazide, hydrazide, 3-hydro-2-naphtboic hydrazide benzophenone hydrazone, phenylhydrazine, benzylhydrazine monohydrochloride, methylhydrazine sulfate, and isopropylhydrazine hydrochloride.