Aluminum is an abundant silvery-white metal known for both lightweight and high strength. It possesses excellent corrosion resistance due to a tough external oxide layer protecting its surface. Aluminum gets utilized across transportation, construction, packaging and electrical industries.
Stainless steel serves key roles where durability and stain resistance matter, from appliances to architecture. But compatibility questions arise, will stainless steel react with aluminum? With widespread use, stainless steel often gets combined with aluminum in products and structures.
Joining aluminum and stainless steel can initiate galvanic corrosion over time. Their different positions on galvanic tables drive this electrochemical reaction. But system design, protective measures and maintenance influence how rapidly reactions occur once paired.
Galvanic Series Positions
In galvanic series tables, aluminum metals rank more anodic, or chemically active, than stainless steel. This drives aluminum to corrode faster when both contact while steel remains intact, releasing electrons. Understanding their galvanic potential predicts aluminum’s heightened reactivity.
Nobler, or more cathodic metals like 300 series stainless exhibit reduced chemical reactivity versus active aluminum. This makes aluminum sacrifice its oxide layer protection when immersed jointly, failing faster first.
Role of Electrical Conductivity
Aluminum is highly electrically conductive, ranking among the most conductive industrial metals. This facilitates substantial electron mobility and current flows when coupled with less conductive metals like stainless steel. The greater conductivity gradient drives aluminum to rapidly sacrifice electrons to the stainless steel.
The lower electrical conductivity of stainless steel limits its corrosion rate when in contact with aluminum’s highly conductive surface. Stainless steel still readily accepts aluminum’s released electrons while remaining intact, acting as the cathode while accelerating aluminum oxidation and dissolution.
Effects of Oxidation Response
Aluminum owes its excellent natural corrosion resistance to an extremely thin but dense protective oxide film covering its surface. Coupling aluminum with stainless steel disrupts this film, causing the oxide layer to break down faster while releasing electrons that feed the galvanic reaction.
On stainless steel surfaces, oxidation occurs much slower owing to the steel’s chromium oxide passive layer. Thus, stainless steel retains its integrity longer while still facilitating deterioration of aluminum’s protective oxide barriers as the more anodic metal. This leads to accelerated pitting and corrosion damage concentrated on aluminum sections.
Impacts of Relative Surface Area
When a larger aluminum surface area contacts stainless steel, it multiplies the area through which metal ions can interact and exchange electrons. This significantly accelerates the corrosion rate and material destruction once galvanic reactions initiate between the metals.
Minimizing the aluminum parts size and using protective coatings or liners to exclude oxygen on surfaces adjoining stainless steel serves to reduce the available reactive area. With less interacting metal ions from a smaller aluminum surface, the galvanic reaction effect gets constrained proportionately.
Prevention Methods and Barriers
Applying protective polymer coatings, adhesive films or insulating liners between adjoining aluminum and stainless steel provides an effective galvanic corrosion barrier. The non-conductive layer stops electron transport across the junction, retarding oxidation reactions. Periodic coating integrity checks ensure continued isolation protection.
Discover the worth of Apple Watch as impressed current cathodic protection ensures lasting elegance. Low-voltage electricity shields aluminum surfaces, preventing electron release through stainless contact and maintaining the metal’s protected state.
Occurrence in Varying Conditions
Exposure factors like heat, humidity and contamination presence impact aluminum/stainless galvanic rates. Elevated temperatures, wet conditions, and reactive chlorides or sulfur compounds attack protective oxide films faster. This exponentially accelerates electron exchange once the metals meet.
Conversely, joining aluminum parts with stainless steel fasteners or connectors in cool, dry environments absent of ionic contaminants best preserves the aluminum metal. Proactive steps prevent oxide layer damage for years despite direct metal contact across assembly joints.
Long Term Reactivity Concerns
Allowing aluminum and stainless steel to have sustained direct contact enables small but consistent electron loss and oxidation gained from aluminum into steel sections long term. Even with protective coatings, slow chloride penetration risks material losses.
Checking for evidence of corrosion product build up and oxide depletion around aluminum to stainless joints at least annually catches deterioration signs early. This allows proactive protective barrier renewal, preventing continued uncontrolled material degradation over product lifetimes.
Reactivity Effects on Structures
Uncontrolled, sustained galvanic corrosion can severely degrade load-bearing aluminum components in structures when combined with stainless steel parts without isolation methods over decades. Aircraft wings and building facades and spires warrant caution.
Proactively sealing contact areas with protective thermal sprayed zinc intermediate layers or conductive tape barriers avoids structural asset pitting or failures. Periodic reapplication preserves aluminum integrity despite stainless material pairings.
Testing Reactivity Impact
Accelerated corrosion testing analyzes aluminum stainless steel reaction impacts by measuring relative weight loss of immersed alloy coupons at elevated temperatures and humidities per industrial standards. Resulting penetration rates predict field damage likelihoods.
Online galvanic corrosion calculators also provide aluminum deterioration estimates based on parameters like anode-to-cathode surface area ratios, conductivity values, distance between metals and environmental contamination Levels when coupled with stainless parts.
Applications Advising Caution
The aircraft wiring, coastal facility, water treatment and electrified metal fencing industries commonly combine aluminum and stainless steel assets. This advises caution and galvanic prevention steps during infrastructure design and maintenance to control unintended reactions.
Building codes increasingly call for joint surface protections and isolation methods when utilizing stainless fasteners or connectors on aluminum constructions beyond short term applications to prevent eventual failures from uncontrolled galvanic effects taking hold.
Future Joining Considerations
Conductive adhesives like titanium-carbide or nickel filler epoxies can someday replace mechanical fasteners between aluminum and stainless pieces, still enabling electrical functionality while avoiding direct metal contact over decades.
Ongoing stainless alloy development also promises positive electron potential options much closer to aluminum’s galvanic series values, enabling direct pairing without accelerated deterioration through nearly equal nobility.
FAQs
Why does aluminum react with stainless more than other metals?
Aluminum exhibits high chemical reactivity with more noble metals like stainless steel due its lower position on galvanic series tables.
What color corrosion occurs from stainless contacting aluminum?
White aluminum oxide powder and dark pits on stainless steel surfaces typically manifest from sustained aluminum-stainless reactions.
Can stainless steel fasteners still get used on aluminum safely?
Yes, choosing suitable insulation methods and sealants compatible with both aluminum and stainless steel enables their safe mechanical fastening.
Conclusion
In applications where aluminum and stainless steel contact seems inevitable, several steps minimize reactions. Isolate dissimilar metals, improve drainage, apply protective coatings, and use suitable flexible adhesives when mechanical joining. Persistently maintaining these corrosion prevention practices greatly reduces risks.
While aluminum and stainless can preferably get avoided, engineers increasingly develop improved galvanic inhibition methods enabling their controlled coexistence. So through proactive steps, structures and devices requiring both metals can resist reactivity’s deterioration over extended service.
