Two-stage conversion treatment

Abstract

The invention relates to a chromium-free, corrosion prevention treatment for steel, zinc or zinc alloys, aluminum, magnesium or alloys thereof in which the metal surfaces are contacted in a first step with a first aqueous solution having a pH of 1.5 to 5 which contains Ti and / or Zr and / or Si ions and at least such a quantity of fluoride that the atomic ratio of Ti to F and / or Zr to F and / or Si to F is in the range from 1:1 to 1:6 and then, optionally after rinsing with water, and thereafter in a second step are contacted with a second aqueous solution having a pH of 1.5 to 5 which contains Ti and / or Zr and / or Si ions and at least such a quantity of fluoride that the atomic ratio of Ti to F and / or Zr to F and / or Si to F is in the range from 1:1 to 1:6, and which additionally contains such a quantity of soluble anions of oxo acids of Mo (VI) and / or W (VI) that the total concentration of molybdenum and / or tungsten is in the range from 5 to 1500 mg / l.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation under 35 USC Sections 365(c) and 120 of International Application No. PCT / EP2004 / 012323, filed 30 Oct. 2004 and published 7 Jul. 2005 as WO 2005 / 061761, which claims priority from German Application No. 103 58 310.6, filed 11 Dec. 2003, each of which is incorporated herein by reference in its entirety. FIELD OF THE INVENTION [0002] This invention relates generally to the anti-corrosion treatment of metal surfaces, for example of vehicle bodies or domestic appliances. In this treatment, a corrosion-inhibiting layer is produced on iron-containing surfaces, such as steel surfaces for example, and / or on selected nonferrous surfaces, such as for example zinc or zinc alloys (for example galvanized or alloy-galvanized steel), aluminum, magnesium or alloys thereof. This corrosion-inhibiting layer improves protection against corrosion and the adhesion of a subsequently applied layer based on organic polymers, s...

AI Technical Summary

Benefits of technology

[0025] The problem addressed by the present invention was to make the process chain involved in car manufacture, for example, more economical and ecological. The process according to the invention has the following, and other, objects: Avoiding the formation of waste containing heavy metals, more particularly toxic heavy metals, such as chromium or nickel; shortening the process chain, i.e. steps, in relation to conventional phosphating; shortening the physical length of the production line and reducing the number of necessary rinsing steps, thereby saving water. Desirably the foregoing objects are achieved and the conversion layer produced matches a conventional phosphating layer in its quality in regard to corrosion protection and paint adhesion.

Problems solved by technology

In particular, the activating baths are exhausted relatively quickly compared with phosphating baths, so that they have to be renewed at short intervals of a few days to a few weeks.

Accordingly, the monitoring and management of the activating baths represent a significant part of the cost of managing and monitoring a phosphating line.

These at least three necessary baths and the rinsing baths additionally present between them lead to a high space requirement and capital investment and thus increase the cost of manufacturing vehicle bodies and domestic appliances.

In addition, waste containing heavy metals is formed during the phosphating step and has to be expensively disposed of.

So far, however, none of these alternative processes has been able to displace phosphating as a pretreatment before painting in car manufacture.