Rapid-Cure Thermoset Coatings for Dissimilar Metal Joints
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Solution Overview
Problem
Galvanic corrosion occurs when dissimilar metals with different electro-potentials are in contact in the presence of an electrolyte, leading to structural integrity issues and aesthetic problems, particularly in the automotive and aerospace industries, where lightweight materials like aluminum and magnesium are used but require steel fasteners due to mechanical property concerns and cost factors.
Innovation Solution
A metal article with at least one surface partially or entirely covered by a rapid-cure thermoset coating, such as a cross-linked epoxy coating, which cures in minutes when exposed to induction heating, combined with a lubricant coating to prevent electron transfer and maintain mechanical properties under varying environmental conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If lightweight materials like aluminum and magnesium are used in body and drive train components, then vehicle weight is reduced and fuel efficiency is improved, but galvanic corrosion occurs when these materials contact steel fasteners in the presence of electrolytes
Solution Approach 1:
A polymeric coating is applied as an intermediary barrier layer between the lightweight metal component (aluminum or magnesium) and the steel fastener. This coating prevents direct contact between dissimilar metals, thereby eliminating the galvanic corrosion pathway while allowing the lightweight material to maintain its structural and weight advantages.
Solution Approach 2:
The solution employs a composite structure consisting of the lightweight metal substrate combined with a polymeric protective coating. This composite approach allows the system to benefit from the low weight of aluminum/magnesium while the polymeric layer provides corrosion resistance, effectively combining the advantages of different material types.
2Strength
If steel fasteners are used with lightweight materials, then mechanical strength and cost-effectiveness are maintained, but galvanic corrosion accelerates the degradation of the less noble material
Solution Approach 1:
The polymeric coating serves as a mediating barrier that allows steel fasteners to maintain their mechanical strength and cost-effectiveness while preventing the harmful galvanic corrosion interaction with lightweight materials. The coating enables the continued use of steel fasteners without compromising the integrity of the aluminum or magnesium components.
3Reliability
If polymeric coatings are applied to prevent galvanic corrosion, then corrosion protection is achieved, but the coating may interfere with the engagement of the bolt with a female member or increase friction
Solution Approach 1:
The polymeric coating is applied selectively to specific surfaces of the lightweight component where galvanic corrosion would occur (such as the contact surface with the fastener), while leaving other surfaces uncoated or minimally coated. This localized application maintains corrosion protection at critical interfaces while preserving the mechanical engagement properties and reducing friction where the coating is not needed.
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 thermoset coating effectively inhibits galvanic corrosion in dissimilar metal systems, maintaining structural integrity and mechanical properties over extended periods, including high temperatures and corrosive environments, as demonstrated by reduced pitting and tension loss in simulated tests.
Implementation Method 1
which cures in minutes when exposed to induction heating
Implementation Method 2
capable of preventing galvanic corrosion from occurring when the article is in contact with a dissimilar metal or other material in the presence of an electrolyte
Data Source
AI summary
A method to prevent corrosion of a susceptible article of a two-article system, in which first and second articles of the two-article system have surfaces facing one another and in which the two articles have different anodic indices includes applying a coating material to the surface of the first article and curing the coating material on the surface of the first article. The method further includes contacting and securing the surface of the first article with the surface of the second article. The two articles exhibit substantially no corrosion following exposure to a corrosive environment under standard GMW17026 for a 15 year simulated test.