A method for coating metallic surfaces with an aqueous composition, which contains an aqueous solution of a zinc salt, by flooding, spraying and/or immersion, wherein, for spraying or immersion, the initial temperature of the substrate lies in the range from 5 to 400° C., in that, for flooding, the initial temperature of the substrate lies in the range from 100 to 400° C. and in that an anticorrosive nanocrystalline zinc oxide layer is formed on the metallic surface. Corresponding aqueous composition, the nanocrystalline zinc oxide layer and the use of the coated substrates are also disclosed.