Galling is a common wear mechanism that occurs when two metal surfaces slide against each other under pressure, leading to the transfer of material from one surface to another. It can cause surface damage, increased friction, and even the seizure of moving parts. Aluminum and stainless steel, while valued for their corrosion resistance, strength, and appearance, are particularly prone to galling under certain conditions.
This article explains the galling phenomenon, why it affects aluminum and stainless steel, its consequences in industrial and mechanical applications, and the methods to prevent or reduce it.
1. What Is Galling?
Galling is a form of adhesive wear that happens when the protective oxide layers on metal surfaces break down under load and sliding contact. Without this protective barrier, the exposed metal atoms from each surface bond together, creating high friction. As movement continues, chunks of metal can transfer from one surface to another, creating rough, damaged surfaces and increasing the risk of mechanical failure.
2. Why Aluminum and Stainless Steel Are Prone to Galling
Both aluminum and stainless steel have natural oxide layers that protect them from corrosion. However, these oxide films are relatively soft and can be damaged under pressure or during sliding contact.
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Aluminum: Soft and ductile, aluminum tends to deform under load, causing the oxide layer to wear away quickly and exposing fresh, reactive metal.
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Stainless Steel: Although harder than aluminum, stainless steel is tough and has a strong tendency for cold welding under high contact pressure, making it susceptible to galling without lubrication.
3. Factors Contributing to Galling
3.1 Contact Pressure
Higher contact forces accelerate oxide layer breakdown, increasing the risk of adhesion.
3.2 Sliding Speed
Faster sliding can generate heat, softening the metals and increasing adhesion.
3.3 Surface Finish
Rougher surfaces with higher asperities are more likely to experience galling due to increased localized contact points.
3.4 Temperature
Elevated temperatures reduce hardness and promote material transfer.
3.5 Lack of Lubrication
Without a lubricant film, direct metal-to-metal contact becomes more likely.
4. Galling in Aluminum Components
Aluminum’s low hardness makes it vulnerable to galling in threaded connections, sliding bearings, and clamping mechanisms. In manufacturing, aluminum parts can gall when machined without adequate lubrication.
Common Examples:
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Bolted joints in aerospace and automotive assemblies
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Sliding rails in industrial equipment
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Aluminum fasteners used in marine environments
5. Galling in Stainless Steel Components
Stainless steel, especially austenitic grades like 304 and 316, is notorious for galling in threaded fasteners and high-load sliding parts. This is because its oxide layer is thin and, once broken, the underlying metal quickly cold welds to the mating surface.
Common Examples:
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Nuts and bolts in chemical plants
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Conveyor system components
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Pump shafts and couplings
6. Consequences of Galling
Galling can lead to:
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Increased friction and heat generation
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Permanent damage to surfaces, requiring part replacement
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Seizure of moving components, leading to equipment downtime
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Reduced load-bearing capacity of mechanical joints
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Costly maintenance and repair cycles
7. How to Prevent Galling in Aluminum and Stainless Steel
7.1 Proper Lubrication
Using anti-seize compounds, dry film lubricants, or grease can reduce direct metal-to-metal contact.
7.2 Surface Hardening
Processes such as anodizing aluminum or nitriding stainless steel improve surface hardness and galling resistance.
7.3 Coatings and Plating
Applying coatings like PTFE, hard chrome, or nickel can create a low-friction barrier.
7.4 Material Selection
Choosing alloys with lower galling tendencies, such as duplex stainless steels or hard-anodized aluminum, can help.
7.5 Design Adjustments
Using finer threads, larger clearances, or incorporating rolling elements in sliding systems can reduce contact pressure.
7.6 Controlled Assembly Practices
Tightening bolts at proper torque levels and avoiding excessive load can prevent galling in fasteners.
8. Industrial Applications Where Galling Prevention Is Critical
Aerospace Industry:
In aircraft structures, both aluminum and stainless steel components must resist galling to ensure safe and reliable performance.
Marine Engineering:
Marine environments accelerate galling due to salt and moisture exposure, requiring proper coatings and lubrication for aluminum and stainless steel parts.
Food Processing Equipment:
Stainless steel machinery must be galling-resistant to maintain hygiene and avoid contamination from wear particles.
Automotive Manufacturing:
Engine and suspension components with aluminum and stainless steel parts rely on anti-galling measures for longevity.
9. Testing for Galling Resistance
Standards such as ASTM G98 provide test methods to evaluate galling tendencies. These tests measure the load at which galling initiates, allowing engineers to compare materials and coatings before selecting components for service.
10. Cost and Maintenance Considerations
While galling prevention measures may increase upfront costs (for coatings, better materials, or lubrication systems), they significantly reduce long-term maintenance expenses by:
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Extending component life
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Minimizing downtime
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Lowering replacement part costs
11. Future Developments in Galling Prevention
Advances in materials science are producing new alloys and coatings with improved galling resistance. Solid lubricant-infused metals and nanostructured surface treatments are promising solutions for high-performance aluminum and stainless steel components.
12. Conclusion
Galling is a serious issue in aluminum and stainless steel applications, but it can be managed through proper design, material selection, and surface treatment. For industries where reliability is critical—such as aerospace, marine, and food processing—addressing galling is essential to ensure long-term performance and cost efficiency.
As a trusted supplier, sasaaluminum offers high-quality aluminum and stainless steel materials with excellent surface finishes and optional coatings to help prevent galling, ensuring durability in even the most demanding environments.
Post time: Aug-14-2025