Aqueous Pickling Compositions and Their Use

Disclosed herein is an aqueous composition having a pH value at 55° C. in the range from 5 to 9, containing at least two different amino organophosphonic acid derivatives of formula (I)where residues R independently of each other are CH2-PO(OR″)2, residues R′ independently of each other are alkylene residues with 2 to 4 carbon atoms, residues R″ independently of each other are H, Na, K, Li or NH4; and n is an integer from 0 to 4; and where the at least two different amino organophosphonic acid derivatives differ in the value of n. Further disclosed herein is a concentrate to produce such compositions, a pickling method for pickling metallic substrates making use of the compositions, a coating method for coating metallic substrates including the pickling method and a method of using the compositions for pickling metallic substrates.