Steel vs. Aluminum Flat Washers: Performance Comparison Guide

The steel versus aluminum flat washer decision is one of the most common and consequential material choices engineers make, affecting weight, strength, corrosion behavior, cost, and long-term assembly performance. Both materials are widely available, well-understood, and capable of serving many of the same applications, but each has clear advantages that make it the superior choice in specific operating conditions. After manufacturing both materials for over a century, we understand exactly where each wins and where a wrong selection creates problems that could have been prevented with proper material specification.

The choice is rarely obvious on surface examination, since both steel and aluminum flat washers appear as commodity fastening components available from any industrial distributor. The performance gap widens dramatically in demanding applications involving high loads, corrosive environments, elevated temperatures, or tight weight budgets where the wrong material fails prematurely or adds unnecessary cost.

Material Properties Head-to-Head

Four fundamental material properties drive most steel versus aluminum selection decisions:

• Tensile Strength: Mild steel flat washers offer 60,000 to 80,000 PSI tensile strength while standard 6061-T6 aluminum flat washers provide 45,000 PSI; steel is stronger by default, but high-strength 7075 aluminum closes the gap at 83,000 PSI for demanding structural applications requiring both strength and weight optimization
• Weight: Aluminum flat washers weigh approximately one-third of steel washers at identical dimensions, delivering dramatic weight savings critical for aerospace, portable equipment, and weight-sensitive automotive assemblies where every gram affects fuel consumption or payload capacity
• Corrosion Resistance: Aluminum flat washers naturally resist atmospheric corrosion through oxide layer formation, while carbon steel washers rust rapidly without protective coating; stainless steel eliminates the corrosion disadvantage but at significantly higher material cost
• Electrical Conductivity: Aluminum flat washers conduct electricity at 61% IACS, far better than steel’s 10 to 15% IACS, making aluminum preferable in grounding and electrical bonding applications where conductivity affects system performance and safety

No single material wins across all four dimensions simultaneously, which is why application context rather than generic material superiority determines the right choice.

When Aluminum Flat Washers Win

Aluminum flat washers are the clear choice in any application where weight is a primary design constraint or acceptance criterion. In aerospace assemblies, the 3x weight advantage over steel translates directly to improved fuel economy, increased payload capacity, or extended range, and these savings compound across thousands of identical fastener locations throughout an airframe.

Corrosion resistance in marine and atmospheric environments is aluminum’s second decisive advantage, where the native oxide layer prevents the rust that makes uncoated steel unacceptable for long-term outdoor service without maintenance. Aluminum flat washers in coastal architectural hardware, marine deck equipment, outdoor electrical enclosures, and exposed structural assemblies remain serviceable for decades without painting, coating touch-up, or corrosion inspection that steel requires.

Thermal conductivity applications where heat dissipation matters favor aluminum’s 118 BTU per hour per foot per degree Fahrenheit, approximately five times higher than steel’s 26 BTU per hour per foot per degree Fahrenheit. Electronics mounting hardware, LED fixture assemblies, and thermal management systems all benefit from aluminum’s superior heat transfer capability that steel cannot match.

When Steel Flat Washers Win

Steel flat washers maintain clear advantages in high-load structural applications where aluminum’s lower yield strength would require significantly larger washer geometry to distribute equivalent bearing loads without exceeding substrate material strength. Heavy machinery, structural steel connections, and high-torque fastener assemblies in industrial equipment benefit from steel’s higher bearing strength that allows smaller washer envelopes.

High-temperature applications where aluminum loses strength and creeps under load require steel washers for any operating temperature above 350°F. Aluminum loses meaningful tensile and yield strength above this threshold, while steel maintains useful strength to 700°F and even higher with appropriate alloy selection. Engine compartments, exhaust system hardware, industrial heating equipment, and high-temperature process assemblies require steel washers to maintain joint integrity through thousands of thermal cycles.

Cost optimization in high-volume, non-critical applications where weight, corrosion, and conductivity are all non-issues justifies standard steel flat washers as the economical default. Basic equipment assembly, non-structural hardware mounting, and general-purpose fastening applications where none of the special properties of aluminum add measurable value should specify steel to minimize procurement cost.

Performance Comparison by Application

Five common applications illustrate where material selection follows logically from operating requirements:

1. Aerospace Structural Fastening: Aluminum flat washers are standard throughout airframe assembly where weight savings are paramount and corrosion resistance in atmospheric exposure is required; titanium replaces both materials in the highest-load or highest-temperature zones where neither aluminum nor steel meets combined requirements
2. Marine Hardware: Aluminum flat washers serve most above-waterline marine applications well for deck hardware and superstructure assemblies; below-waterline hardware requires stainless steel due to galvanic corrosion concerns between aluminum and copper-based antifouling coatings used on hull surfaces
3. Industrial Equipment: Steel flat washers are standard for heavy machinery where loads are high, weight is irrelevant, and indoor environments prevent atmospheric rust; stainless steel handles wash-down environments in food processing and pharmaceutical facilities where corrosion resistance is required
4. Electronics and Electrical Assemblies: Aluminum flat washers are preferred for grounding, bonding, and heat dissipation in electronic enclosures and power distribution equipment; steel is used only in non-electrical structural applications within electrical assemblies where conductivity is not required
5. Automotive Assembly: Steel flat washers dominate chassis and drivetrain applications for load capacity and cost optimization; aluminum is increasing in body panel, door, and hood fastening as manufacturers pursue aggressive weight reduction targets to meet fuel economy standards

These five categories cover the most common environments where the steel versus aluminum decision is made repeatedly. Material selection follows logically from the property comparison covered earlier, and our custom precision parts capabilities support both materials in any geometry.

Cost and Procurement Considerations

Aluminum raw material costs more per pound than carbon steel but weighs one-third as much, making cost per part comparison more nuanced than a simple price per pound analysis would suggest. For washers of equal geometry, aluminum parts typically cost 30 to 50 percent more than equivalent carbon steel parts due to material price differential. However, the weight savings may justify the premium in applications where weight has direct economic implications such as fuel consumption in transportation equipment or shipping cost in high-volume distribution.

Lead times and material availability are equivalent for both steel and aluminum flat washers in standard thicknesses, which we maintain in inventory for rapid delivery from stock. Custom thicknesses in both materials require material procurement that adds one to two weeks to standard production lead times, but both materials carry equivalent lead times for new tooling creation and production scheduling.

Our no-tooling-charge approach applies equally to both materials, eliminating one of the traditional cost barriers to custom geometry washers regardless of material selection. Neither aluminum nor steel incurs tooling charges for custom geometries at Brewster Washers, meaning the material cost difference is the only price driver beyond geometry complexity and order quantity.

Hybrid Approaches and Design Optimization

Some applications benefit from hybrid designs that use both steel and aluminum washers in the same assembly for different functions. Aluminum washers can provide electrical isolation or thermal conduction while steel backup washers behind them distribute higher structural loads across soft substrates.

Coating and plating can extend the useful range of steel flat washers into moderately corrosive environments where uncoated steel would fail but aluminum would add unnecessary cost. Zinc plating, cadmium plating, and passivated finishes protect steel from atmospheric corrosion for limited service lives in outdoor applications. These coatings add cost and require touch-up maintenance but can be more economical than switching to aluminum for borderline corrosion environments.

Material selection optimization across an entire assembly rather than on a per-fastener basis often reveals opportunities to standardize on one material for procurement simplicity while using the other material only where its unique properties are genuinely required. Reducing the material count in your bill of materials simplifies inventory management, reduces supplier qualification burden, and streamlines receiving inspection even if it means accepting a slightly higher per-unit cost on some individual washers.

Material Selection Decision Framework

Start by identifying whether your application has hard requirements that eliminate one material immediately: temperatures above 350°F require steel, weight budgets below steel’s capability require aluminum, and high electrical conductivity requirements favor aluminum. These bright-line rules resolve most selection decisions quickly without detailed analysis of secondary factors.

For applications where both materials could theoretically work, evaluate corrosion environment, load magnitude, and cost sensitivity in that priority order. Corrosive outdoor or marine environments favor aluminum unless loads are high enough to require steel’s strength. High-load indoor environments favor steel unless weight budgets require aluminum. Low-load indoor environments favor steel on cost unless weight or conductivity requirements tip the balance toward aluminum.

When the application falls genuinely near the boundary between steel-preferred and aluminum-preferred service conditions, request quotes for both materials and evaluate total cost including any secondary operations like coating that steel would require. The per-unit price difference between the two materials is often smaller than engineers assume, particularly when coating costs for steel are factored against aluminum’s corrosion immunity.

Get Custom Aluminum or Steel Flat Washers

At Brewster, we have manufactured aluminum flat washers and steel flat washers in custom geometries for over 100 years, serving aerospace, marine, industrial, automotive, and electronics customers with demanding material and quality requirements. Both aluminum and steel flat washers are available in all standard and custom thicknesses with complete material certifications, dimensional inspection reports, and Certificates of Conformance as part of our standard documentation package. Contact us today for help finding the right washers for your needs.