Alkaline Passivation Composition for Zinc Surfaces
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Solution Overview
Problem
Existing methods for passivating zinc surfaces in the automotive industry fail to provide adequate corrosion resistance and paint adhesion, especially when compared to steel surfaces, leading to issues with corrosive infiltration and paint delamination.
Innovation Solution
An aqueous alkaline composition containing at least 50 ppm iron(III) ions, 100 ppm phosphate ions, and 100 ppm of specific complexing agents, with a free alkalinity of 1 to 6 points and a pH of 10.5 or higher, is used for alkaline passivation, which can be combined with nonionic surfactants for enhanced cleaning and passivation in a single step, followed by an acid passivation step for improved corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If acid chromium-free passivating solutions are used, then chromium content is reduced, but zinc surfaces fall behind steel surfaces in corrosion protection
Solution Approach 1:
The patent changes the chemical parameters of the passivation solution by introducing iron(III) ions, phosphate ions, and specific complexing agents at controlled concentrations, with pH adjusted to 10.5-13.5. This parameter optimization creates a passivation layer that achieves both corrosion protection and paint adhesion on zinc surfaces, resolving the contradiction between reducing chromium content and maintaining reliable paint adhesion.
2Object-affected harmful factors
If multi-step phosphating method is used, then corrosion protection and paint adhesion are improved, but material turnover rates increase and process complexity increases
Solution Approach 1:
The patent merges multiple passivation functions into a single treatment step by combining iron(III) ion deposition, phosphate layer formation, and cleaning actions in one aqueous composition application. This unified approach achieves the corrosion protection and paint adhesion benefits of multi-step phosphating while eliminating the complexity and high material turnover rates associated with multiple separate process steps.
3Object-affected harmful factors
If alkaline passivation is added to acid passivation, then corrosion resistance and paint adhesion are improved, but process steps increase
Solution Approach 1:
The patent performs preliminary cleaning and surface preparation actions within the alkaline passivation step itself, using nonionic surfactants and the chemical composition to remove contaminants before the acid passivation step. This preliminary action eliminates the need for a separate cleaning step, maintaining high productivity while achieving superior corrosion resistance and paint adhesion through the combined alkaline-acid passivation sequence.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The described method achieves significant improvements in corrosion resistance and paint adhesion on zinc surfaces, suppressing corrosive infiltration and delamination, while allowing for a single-step cleaning and passivation process that is cost-effective and resource-conserving.
Implementation Method 1
The aqueous compositions (A) according to the present invention can additionally contain nonionic surfactants, so that such compositions are suitable for utilization in a method in which both cleaning and alkaline passivation of the metallic component occur in one step
Implementation Method 2
The aqueous compositions (A) according to the present invention can additionally contain nonionic surfactants, so that such compositions are suitable for utilization in a method in which both cleaning and alkaline passivation of the metallic component occur in one step
Implementation Method 3
a free alkalinity in the range from 1 to 6 points being established, and the pH being equal to at least 10.5
Data Source
AI summary
The present invention relates to an aqueous alkaline composition (A) for alkaline passivation of metallic components comprising at least in part surfaces of zinc or zinc alloys, containing iron(III) ions, phosphate ions, and one or more complexing agents, where a free alkalinity ranges from 1 to 6 points, and the pH is at least 11. The aqueous compositions (A) can additionally contain nonionic surfactants, so that such compositions are suitable for use in a method in which both cleaning and alkaline passivation of the metallic component occur in one step. The present invention further relates to a method for alkaline passivation of metallic components by contacting them with composition (A), and further a method for surface treatment in automobile body production, in which the alkaline passivation step using composition (A) is followed by an acid passivation step using a composition (B).