Pre-Oxidized Fastener Joint Insulation Against Galvanic Corrosion
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Solution Overview
Problem
Galvanic corrosion in fastener joints involving dissimilar materials is a significant issue due to differences in physical and chemical properties, leading to accelerated corrosion of anodic materials in aqueous environments.
Innovation Solution
A fastener with an adherent, electrically insulating oxide layer grown in place on its surface through a pre-oxidation process, which reduces galvanic current density and prevents delamination during joining processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metallic coating is applied to the fastener, then corrosion resistance is improved, but galvanic corrosion risk increases due to complex galvanic circuits
Solution Approach 1:
An electrically insulating oxide layer is grown on the fastener surface as an intermediary between the metallic coating and the corrosive environment. This oxide layer acts as a mediator that provides both corrosion protection and electrical insulation, breaking the galvanic circuit while maintaining the protective function of the coating system.
Solution Approach 2:
The electrical conductivity parameter of the fastener surface is changed by growing an insulating oxide layer. This parameter change transforms the surface from electrically conductive (which creates galvanic circuits) to electrically insulating (which breaks galvanic circuits), while maintaining corrosion resistance through the protective oxide barrier.
2Object-affected harmful factors
If a polymeric coating is applied to the fastener, then galvanic corrosion is reduced, but wear resistance decreases and melting temperature is low
Solution Approach 1:
A composite coating system is created by combining an electrically insulating oxide layer with a metallic coating. The oxide layer provides electrical insulation and high-temperature stability, while the metallic coating provides wear resistance and structural integrity. This composite structure eliminates the weaknesses of individual coating materials.
Solution Approach 2:
The thermal stability parameter is improved by using an inorganic oxide layer that can withstand high temperatures, unlike polymeric coatings. Simultaneously, the wear resistance is maintained through the hard metallic coating, achieving both high-temperature stability and wear resistance that neither polymeric nor bare metallic coatings can provide alone.
3Object-affected harmful factors
If the oxide layer is made thicker to increase electrical insulation, then galvanic corrosion protection is improved, but adhesion decreases due to delamination risk
Solution Approach 1:
The thickness parameter of the oxide layer is optimized to a specific range that balances electrical insulation performance with adhesion strength. By controlling the oxide layer thickness within this optimal range, sufficient electrical insulation is achieved to break galvanic circuits while maintaining strong metallurgical bonding to prevent delamination during joining operations.
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 oxide layer significantly reduces galvanic corrosion by increasing interfacial resistance to cathodic reactions, providing up to 99% reduction in galvanic current density, and maintaining adherence and wear resistance during high-temperature and high-wear applications.
Implementation Method 1
The oxide layer is of sufficient thickness to provide the desired level of electrical insulation along the interface between the fastener and the joined materials
Implementation Method 2
an adherent, electrically insulating oxide layer grown in place on the surface of the fastener in a pre-oxidation process
Data Source
AI summary
A fastener for use in joining dissimilar materials manufactured by the process of producing the fastener with an external surface that forms an electrically insulating oxide layer when subjected to oxidation and, after manufacture and prior to use, subjecting the fastener to a pre-oxidation process to grow the desired oxide layer in situ on the external surface of the fastener. The present invention also provides a dissimilar material joint in which the pre-oxidized fastener is used to mechanically join dissimilar materials with the oxide layer electrically insulating the fastener from at least one of the dissimilar materials. The fastener may be a rivet used in friction self-piercing riveting (F-SPR). The fastener may be fabricated from an alloy capable of forming Al2O3 or Cr2O3 by thermal oxidation. The fastener may be pre-coated with Al or Cr that functions as a seed layer to form Al2O3 or Cr2O3.