アルミニウムは錆びるのか？

You left a metal tool outside—it turned brown and flaky. But your aluminum ladder? Still shiny. So, does aluminum rust?

Aluminum doesn’t rust like iron. Instead, it forms a protective oxide layer that resists corrosion and prevents structural damage.

This is one of the reasons aluminum is a top choice in architecture, transportation, and outdoor products.

What is rust and does aluminum form it?

Not all corrosion is the same. Rust is specific to certain metals—mainly iron.

Rust is a reddish-brown flaky oxide (Fe-o?·nh-o) that forms when iron reacts with oxygen and water. Aluminum does not rust because it contains no iron.

Rust vs. Oxidation

• Rust is a form of iron oxide that occurs with water and air.
• Aluminum oxide (Al-o?) forms instantly when aluminum is exposed to air.

Unlike rust, which flakes and weakens the metal, aluminum oxide sticks tightly and protects the surface.

なぜ重要なのか

Rust eats away at steel. It makes bridges crumble and pipes burst. But aluminum’s oxide layer acts like a shield. It prevents deep corrosion and keeps the metal strong.

特徴	Rust (Iron Oxide)	Aluminum Oxide
カラー	Red/Brown	White/Silver
構造	Flaky, weak	Hard, tight bonding
Impact on Metal	Damages over time	Protects from corrosion
Reformation Ability	いいえ	Constantly self-healing

How does aluminum oxidize compared to iron?

At first glance, oxidation sounds bad. But for aluminum, it’s actually a good thing.

Aluminum oxidizes quickly, forming a thin, stable layer of aluminum oxide that prevents further corrosion—unlike iron, which keeps rusting deeper.

Iron Oxidation

Iron continues to corrode once it starts rusting. Water and oxygen enter the flaky rust, reaching deeper layers. Over time, iron breaks apart.

Aluminum Oxidation

When aluminum touches air, a layer of aluminum oxide forms instantly—just a few nanometers thick. This passive layer seals the surface and prevents moisture or chemicals from reaching the bare metal.

It’s self-healing. If you scratch it, it reforms in seconds.

メタル	Oxide Formation	Corrosion Effect	保護層
鉄	Slow, ongoing	Weakens metal	いいえ
アルミニウム	Instant, stable	Prevents deeper damage	はい

表面外観

• Iron rust is visible and rough.
• Aluminum oxidation often appears as a dull gray film, not always noticeable.

Why does aluminum resist rust?

Aluminum’s corrosion resistance is one of its most valuable features—especially in tough environments.

Aluminum resists rust because its oxide layer forms quickly and acts as a barrier against further corrosion, unlike rust which damages iron.

Passive Protection

The oxide layer is chemically bonded to the surface. It doesn’t flake or break away. Even in water or humid air, the layer remains intact.

Resistance to Chemicals

Aluminum resists:

• Freshwater
• Seawater (with limitations)
• Mild acids
• Organic solvents

In construction, aerospace, and marine environments, this resistance lowers maintenance costs and increases lifespan.

Anodizing for More Protection

Manufacturers often アノダイズ aluminum to thicken the oxide layer. This improves:

• 耐摩耗性
• Scratch protection
• Color absorption

特徴	結果
Oxide Layer Formation	Instant upon air exposure
Durability of Oxide	Strong and self-healing
陽極酸化処理	Enhances surface hardness
Environmental Tolerance	高い

How to protect aluminum from corrosion?

Even though aluminum resists rust, it still needs care—especially in harsh conditions.

To protect aluminum from corrosion, apply surface treatments like anodizing, powder coating, or painting, and avoid contact with incompatible metals.

表面処理

1. 陽極酸化処理: Enhances natural oxide layer; makes aluminum harder and more resistant to chemicals.
2. パウダーコーティング: Adds colored, protective resin layer.
3. 絵画: Barrier against salt, moisture, and UV rays.

Avoid Galvanic Corrosion

When aluminum touches another metal (like copper or steel) in the presence of moisture, galvanic corrosion can occur. This causes the aluminum to corrode faster.

To prevent this:

• Use insulating washers
• 保護コーティングを施す
• Avoid water traps between metals

Clean Regularly

Dirt, salt, and industrial pollutants can slowly break down unprotected aluminum. Rinse with fresh water and use non-acidic cleaners.

方法	保護レベル	一般的な使用
陽極酸化処理	高い	Architecture, electronics
パウダーコーティング	高い	Windows, furniture
絵画	ミディアム	Vehicles, fences
Regular Cleaning	ベーシック	Marine and outdoor equipment

結論

Aluminum doesn’t rust like iron. It protects itself with a strong, self-healing oxide layer. With or without coatings, aluminum offers long-term durability—even in challenging conditions.