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Does Aluminum Never Rust? The Misunderstood Truth About Durability and Corrosion.

Why Does Rust-Proof Aluminum Get Damaged Silently?

When it comes to metal corrosion, many people first think of rust—iron products gradually turn red, become brittle in water and air, and eventually "rot away completely". But aluminum obviously doesn't rust, so why does it develop spots, holes, or even structural failure after long-term use?

01 | First, Distinguish Two Terms: Rusting ≠ Corrosion

In daily language, rusting and corrosion are often used interchangeably, but in the fields of materials science and engineering, they are completely different concepts—this is the key to understanding aluminum corrosion.
Comparison DimensionRustingCorrosion
Applicable MaterialsIron or iron-based alloys (e.g., carbon steel)All metals (aluminum, copper, magnesium, etc.) and non-metallic materials
Reaction ProductsHydrated iron oxide (Fe₂O₃・nH₂O), i.e., the red rust we seeMetal oxides, salts, etc. (e.g., aluminum's corrosion product is aluminum oxide)
Protective EffectPorous and easy to peel off; cannot protect the underlying metal, but accelerates corrosion insteadVaries by material; aluminum's oxide film is dense and protective
Engineering RisksWithout protection, directly reduces the strength of steel structuresDiverse risk types; need to be judged based on material characteristics and environment
💡 Quick Note
Rusting: Specific to iron/iron-based alloys; the product is porous, easy-to-peel hydrated iron oxide that accelerates metal damage.
Corrosion: A degradation reaction that can occur in all metals/non-metallic materials; aluminum's corrosion product is dense aluminum oxide.
Key Conclusion: Aluminum does not rust, but it can corrode.

02 | Aluminum's Natural Protection Mechanism

The core reason why aluminum exhibits excellent corrosion resistance in most environments is that it can "wear" an invisible protective coat—an aluminum oxide film—for itself.
When a fresh aluminum surface is exposed to air, it reacts with oxygen in a fraction of a second to form a layer of aluminum oxide (Al₂O₃).

  • Ultra-thin and dense: Only 2–5 nanometers thick, yet effectively blocks oxygen and moisture.

  • Strong adhesion: Tightly bonds with the aluminum substrate and does not peel off like rust.

  • Self-healing: A new oxide film regenerates quickly after being scratched.

📌 This is why an aluminum spoon or an aluminum alloy window can remain intact for a long time in daily environments—this "invisible armor" is aluminum's natural protection system.

03 | Four Typical Corrosion Modes of Aluminum

1️⃣ Pitting Corrosion

  • Trigger Condition: Chloride ions (seawater, salt spray, deicing salt)

  • Characteristics: Tiny local corrosion pits form and deepen inward continuously

  • Risk: The surface appears intact, but the internal load-bearing capacity is severely weakened

2️⃣ Galvanic Corrosion (Electrochemical Corrosion)

  • Trigger Condition: Direct contact between aluminum and steel, copper, or stainless steel in a humid environment

  • Principle: Aluminum acts as the anode and corrodes preferentially

  • High-Risk Areas: Bolts, brackets, grounding connections

3️⃣ Crevice Corrosion

  • High-Risk Scenarios: Lap joints, under gaskets, bolted compression zones

  • Mechanism: Local oxygen deficiency → chemical environment imbalance → film failure

  • Hazard: Spreads along crevices and weakens connection strength

4️⃣ Intergranular Corrosion

  • High-Risk Materials: 7xxx series high-strength aluminum alloys

  • Cause: Selective corrosion caused by precipitates at grain boundaries

  • Risk: Normal appearance, but internal structure has been disrupted

💡 Quick Note
👉 Three types of environmental factors that accelerate aluminum corrosion:
Chlorides: The primary threat, directly damaging the stability of the aluminum oxide film.
Extreme pH: Strong acids/alkalis dissolve the oxide film, causing uniform corrosion.
Temperature and mechanical damage: High temperatures accelerate reactions; repeated scratches damage the film's self-healing ability.
Corrosion TypeTrigger ConditionTypical Hazards
Pitting CorrosionChloride environment (seawater, salt spray, deicing salt)No obvious surface signs; deep holes form internally, easily leading to structural failure
Galvanic CorrosionContact with dissimilar metals such as steel/copper/stainless steel in a humid environmentAluminum corrodes preferentially as the anode; high incidence at fastener locations
Crevice CorrosionClosed crevices such as lap joints, under gaskets, and bolted areasOxygen deficiency forms an acidic environment, spreading along crevices to weaken connection strength
Intergranular CorrosionHigh-strength aluminum alloys such as 7xxx series, improper heat treatment/serviceInternal damage occurs; the shape remains intact but brittle fracture is likely

04 | Three Key Means of Aluminum Corrosion Protection

① Choose the Right Alloy

  • 1xxx series: Pure aluminum, excellent corrosion resistance, low strength

  • 5xxx series: Aluminum-magnesium alloy, seawater corrosion resistant

  • 6xxx series: Excellent comprehensive performance, commonly used in construction and automobiles

  • 7xxx series: Highest strength, requires additional protection

② Surface Treatment

  • Anodizing: Thickens and stabilizes the oxide film

  • Coating system: Powder or liquid coating + conversion film

③ Structural Design Optimization

  • Avoid direct contact with dissimilar metals such as steel and copper

  • Increase drainage and ventilation to prevent moisture retention

  • Reduce complex lap joints and corrosion dead zones

Common Questions

Will aluminum rust in seawater?
No, it will not rust, but corrosion dominated by pitting will occur. It is recommended to use ship-class alloys (e.g., 5xxx series) with protective measures.
Why does the aluminum surface turn white or powdery?
It is mostly aluminum oxide or aluminum hydroxide, which are corrosion products. Unlike rust, this indicates an unfavorable environment.
Does anodized aluminum prevent rust?
It does not prevent rust, but significantly improves corrosion resistance. Systematic protection is still required in extreme environments.
How to prevent galvanic corrosion of aluminum?
Electrically isolate dissimilar metals, use appropriate fasteners, and apply a complete coating to cut off the electrochemical path.


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