Electrolytic Trivalent Chromium Coating Process

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Solution Overview

Problem

Current non-chromium conversion coatings fail to meet corrosion resistance and paint bonding requirements, and hexavalent chromium coatings pose health and environmental risks, necessitating a safer alternative with similar protection levels.

Innovation Solution

An electrolytic process that passes current through a conversion coating electrolyte at a cathodic or anodic current density of up to 3.0 A/ft² for ≤60 minutes, promoting faster coating growth and producing trivalent chromium-containing coatings with superior corrosion resistance and improved thickness without adverse effects on paint adhesion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If trivalent chromium conversion coatings are used to replace hexavalent chromium coatings, then health and environmental safety is improved, but corrosion resistance deteriorates

Engineering Contradiction:

Improvehealth and environmental safetyVSAvoidcorrosion resistance

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent applies electrolytic current to the conversion coating process, changing the kinetic parameters of coating formation. This electrolytic assistance enables Cr(III) coatings to achieve thicknesses and corrosion resistance levels comparable to Cr(VI) coatings by controlling current density (0.1-3.0 A/ft²) and immersion time (1-60 minutes), thereby resolving the contradiction between safety and performance

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates composite conversion coatings containing Cr(III) ions, fluorosulfonate anions, and aluminum substrate components. This composite structure, formed through electrolytic processing, achieves superior corrosion resistance by combining the safety benefits of Cr(III) with enhanced coating morphology and adhesion, effectively replacing harmful Cr(VI) coatings

Inventive Principle:

Principle #40Composite materials

2Reliability

If traditional diffusion-controlled coating growth is used, then process simplicity is maintained, but coating thickness and corrosion resistance are limited

Engineering Contradiction:

Improvecorrosion resistanceVSAvoidprocess complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces the passive diffusion-controlled mechanism with an active electrolytic process. By applying electrical current through a power supply system with anode and cathode configurations, the coating formation kinetics are dramatically enhanced, producing thicker, more adherent coatings with superior corrosion resistance while maintaining relatively simple process implementation

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If hexavalent chromium coatings are used to achieve excellent corrosion resistance, then protection performance is improved, but health and environmental hazards increase

Engineering Contradiction:

Improvecorrosion resistanceVSAvoidhealth and environmental hazards

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent converts the traditionally harmful Cr(VI) chemistry into beneficial Cr(III) chemistry by applying electrolytic current. The electrical energy drives the formation of protective Cr(III) conversion coatings that would otherwise form poorly, transforming a safe but underperforming system into one that achieves Cr(VI)-level protection without the toxicity, thereby converting the 'harm' of Cr(III) limitations into a benefit through electrolytic enhancement

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 process significantly enhances corrosion resistance and coating thickness, achieving performance comparable to hexavalent chromium coatings while eliminating health and environmental risks, with improved paint adhesion and detection of localized corrosion.

Implementation Method 1

The process involves the passage of current through a conversion coating electrolyte in which the work surface is either the cathode or anode

Methodology Applied

Scientific EffectElectrolysis: Electrolysis

Implementation Method 2

The cathodic or anodic current density is equal to or less than 3.0 A/FT2, and the immersion time is equal to or less than 60 minutes. The electrodeposited coatings afford superior corrosion resistance

Methodology Applied

Scientific EffectElectrodeposition: Electrodeposition

Data Source

PatentUS11155928B2Electrolytic process for deposition of chemical conversion coatings

Publication Date: 2021.10.26 THE UNITED STATES OF AMERICA AS REPRESENTED BY THE SECRETARY OF THE NAVY

AI summary

This invention is directed to a process of coating metal in a trivalent chromium conversion-electrolyte coating wherein the metal anode or cathode is subjected to a current density ranging up to about 3.0 amperes per square foot for a period ranging up to 60 minutes.