Mechanical Fastener Isolation for Corrosion-Free Magnesium Joining
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Solution Overview
Problem
The challenge in the automotive industry is to join mixed material stacks, particularly with a magnesium upper layer, while avoiding corrosion between the fastener and the magnesium, which limits the use of magnesium in vehicle assembly due to direct metal-to-metal contact and galvanic potential differences.
Innovation Solution
Incorporating an isolation barrier, such as a layer of aluminum or tape, between the fastener and the magnesium top layer to prevent direct contact and corrosion, allowing the use of metal mechanical fasteners like rivets, screws, or bolts without compromising weight or cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If metal mechanical fasteners are used to join magnesium top sheet to other materials, then joining strength and structural integrity are improved, but galvanic corrosion occurs between the fastener and magnesium due to direct metal-to-metal contact
Solution Approach 1:
The patent introduces a non-metallic intermediate layer (such as polymer, composite, or adhesive material) positioned between the metal mechanical fastener and the magnesium top sheet. This intermediary material acts as a galvanic isolation barrier, preventing direct electrical contact between dissimilar metals while still allowing the fastener to mechanically join the magnesium sheet to other materials. The intermediate layer maintains structural integrity of the joint while eliminating the galvanic corrosion pathway.
2Weight of moving object
If magnesium is used as top sheet material for weight reduction, then vehicle weight decreases and fuel economy improves, but corrosion concerns limit the application of metal fasteners in magnesium joining
Solution Approach 1:
The patent employs composite material structures where a non-metallic intermediate layer (polymer, composite material, or adhesive) is integrated between the metal fastener and magnesium top sheet. This composite approach allows the system to benefit from both metal fastener strength and magnesium weight savings while the composite intermediate layer provides corrosion protection. The solution enables magnesium's weight advantages to be realized without compromising manufacturing feasibility through reliable joining.
3Reliability
If direct metal-to-metal contact is avoided between fastener and magnesium, then corrosion is prevented, but additional isolation materials increase device complexity
Solution Approach 1:
The patent integrates the corrosion protection function into existing joining components or processes. The non-metallic intermediate layer is combined with the fastening system in a unified structure, where the isolation material may be pre-applied to the fastener, integrated into the joint design, or combined with adhesive bonding processes. This merging approach prevents corrosion while minimizing additional complexity by consolidating multiple functions into integrated components rather than separate add-on elements.
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
This solution effectively prevents corrosion, enabling broader application of magnesium in vehicle assembly by isolating the fastener from the magnesium layer, thus enhancing joining capabilities and reducing production costs and weight.
Implementation Method 1
corrosion between the fastener and the magnesium upper layer is avoided by insulating the fastener from the magnesium upper layer
Data Source
AI summary
A system is provided for attaching a layer of a metal to other layers in a material stack-up using a metal mechanical fastener that does not allow for direct contact between the fastener and the metal layer, thereby neutralizing any galvanic reaction between the metal sheet and the fastener and avoiding corrosion. The metal layer may be any of several metals, including magnesium. The fastener is a rivet, a screw or a bolt. The disclosed inventive concept uses an insulating layer to insulate the magnesium layer. In one embodiment, a layer of a thin metal is formed over the insulating layer. Where the fastener is a rivet and the metal is magnesium, the insulating layer and thin metal provide a barrier between the magnesium layer and the rivet prongs following rivet insertion, thus isolating the rivet. The system enables a greater application of fastener joining, particularly with magnesium and mixed material joining.