Method for corrosion-protective serial surface treatment of metallic components

A method for serial wet chemical surface treatment of metallic components, comprising:

• a) contacting metallic components having surfaces of aluminum and surfaces of zinc with a wet chemical pretreatment comprising an alkaline bath solution which is stored in a system tank, said alkaline bath solution having a pH greater than 10 and free alkalinity of at least 0.5 points but less than 50 points, and
• b) after step a) performing a wet-on-wet conversion treatment of at least the surfaces of aluminum of the metallic components,
• wherein content of dissolved zinc in the alkaline bath solution of the system tank is held below a maximum value of dissolved zinc “Znmax” according to Formula I:
• Znmax=0.0004×(pH−9)×[FA]+0.6×[Y] (I)
• where:
• pH:
• pH value;
• Znmax:
• maximum value of the concentration of dissolved zinc, in mmol/L;
• [FA]:
• free alkalinity in mmol/L;
• [Y]:
• concentration in mmol/L of complexing agents Y in the form of water-soluble condensed phosphates calculated as P2O6, and/or in the form of water-soluble organic compounds which contain at least one functional group selected from —COOX1/n, —OPO3X2/n, and/or —PO3X2/n, where X represents a hydrogen atom, an alkali metal and/or an alkaline earth metal atom having a respective valence n;
• and
• further comprising a step of preventing exceedance of the maximum value Znmax in the wet chemical pretreatment by adding a water-soluble source of sulfide ions, to at least one portion of the alkaline bath solution of the system tank, and optionally separating a solid portion comprising zinc formed in said at least one portion of the alkaline bath solution, from the alkaline bath solution.