METHOD FOR CORROSION-PROTECTIVE SERIAL SURFACE TREATMENT OF METALLIC COMPONENTS

摘要

The present invention relates to a method for serial surface treatment of metallic components comprising aluminum surfaces, wherein an alkaline pretreatment is followed by a conversion treatment. According to the invention, the intention during the alkaline pretreatment is that a maximum value for the concentration of dissolved zinc is not exceeded, in order to ensure a sufficient quality of the corrosion-protective coating on the aluminum surface of the components following the surface treatment. In a preferred embodiment, the content of dissolved zinc is effectively held below the respective bath-typical maximum value of dissolved zinc by the addition of compounds constituting a source of sulfide ions. The functionality of the surface treatment can be additionally increased by likewise controlling the content of dissolved aluminum in the alkaline pretreatment such that, by adding compounds constituting a source for silicate anions, a threshold value for dissolved aluminum is not exceeded.

主权项

1. A method for serial wet chemical surface treatment of metallic components, in which method metallic components having surfaces of aluminum as well as components having surfaces of zinc are subjected to wet chemical pretreatment by bringing them into contact with an alkaline bath solution which is stored in a system tank, and a wet-on-wet conversion treatment of at least the surfaces of aluminum of the metallic components subsequently takes place, the pH of the alkaline bath solution in the wet chemical pretreatment being greater than 10, and the free alkalinity being at least 0.5 points but less than 50 points, wherein the following maximum value for the concentration of dissolved zinc in the alkaline bath solution of the system tank is not exceeded:
Znmax=0.0004×(pH−9)×[FA]+0.6×[Y] 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 either a hydrogen atom or an alkali and/or alkaline earth metal atom having the respective valence n.