Borate-free, aqueous composition for cleaning and treating metallic substrates

The present invention relates to a borate-free, aqueous cleaning and treating composition comprising at least one metasilicate (A); at least one orthophosphate (B); at least one phosphate (C) selected from the group consisting of diphosphates and triphosphates; at least one surfactant (D) selected from the group consisting of anionic surfactants and non-ionic surfactants; and wherein the aqueous cleaning and treating composition has a pH value at 20 DEG C in the range from 11.0 to 12.8; and possesses a molar ratio of Si atoms to P atoms being from 0.75:1 to 1:0.75, based on the sum of the Si-containing metasilicates (A) and the sum of the P-containing orthophosphates (B), diphosphates (C) and triphosphates (C). The invention further relates to solid mixtures. The invention also relates to a method for cleaning and treating metallic substrates making use of the compositions and the use of the compositions to clean metallic substrates and treat metallic substrates by forming a Si-containing layer on the surface