Does Aluminum Rust

Properties of Aluminum

aluminum is a strong, lightweight, corrosion-resistant, and electrically conductive metal that is utilized in a wide range of applications. Here are some properties of aluminum:

1. High strength: While aluminum has a lower density, it still possesses high strength. The strength of aluminum can be further improved through processes like alloying and heat treatment.
2. Lightweight: Aluminum has a lower density than commonly used metals like iron and steel, only one-third of their density. This characteristic provides aluminum with advantages in both weight and strength.
3. Corrosion resistance: Aluminum exhibits excellent corrosion resistance due to its oxide layer, which protects it from corrosion and oxidation in various environments.
4. Good Conductivity: Aluminum is an excellent conductive material commonly used in power transmission and electronic devices.
5. Recyclability: Aluminum also can be recycled. Recycling aluminum uses significantly less energy and has lower environmental effects compared to producing new aluminum.

Can Aluminum Rust? 

Aluminum doesn’t rust, but it can corrode. It’s essential to recognize that aluminum is a highly reactive metal, particularly in its pure form. In fact, pure aluminum would dissolve if it came into contact with water. However, this reactivity actually helps protect aluminum from environmental damage. When exposed to oxygen in the water, air, or soil, aluminum reacts to create a thin coating of aluminum oxide, which chemically bonds to its surface. This protective layer helps prevent further corrosion.

Aluminum oxide forms a greyish-white powdery layer on aluminum, similar to how rust develops on metals such as steel. However, unlike rust, which flakes off and exposes raw metal to corrosion, aluminum oxide seals the aluminum’s surface. This protective layer prevents further reactions with corrosive elements.

Rust vs Corrosion

The terms “rust” and “corrosion” are usually used interchangeably, but they refer to different processes that affect certain metals. Rust occurs explicitly in iron and its alloys, while aluminum does not rust because the sheets used for production typically contain no traces of iron. Here’s a closer glance at the differences between rust and corrosion:

• Rust: Rust is a type of corrosion that occurs only on iron and steel. It develops over time, primarily due to moisture in the air. As the outer layers of metal peel away, new layers beneath are revealed.
• Corrosion: Prolonged exposure to oxygen can change the appearance of certain metals, such as aluminum, brass, and copper. Unlike some other materials, these metals do not flake; instead, they may change color due to environmental conditions. The corrosion process usually halts when aluminum atoms fully bond with oxygen atoms.

Does Aluminum Corrode?

Yes. While aluminum offers advantages over many metals, it is not corrosion-resistant. The protective aluminum oxide layer is highly resistant and can self-renew after damage, but certain factors may destabilize it.

The most ordinary type of aluminum corrosion is galvanic corrosion, which happens when aluminum comes into contact with other metals. This type of corrosion occurs when two different metals are arranged to create an electrical circuit. In this process, one metal becomes strengthened while the other is weakened. As aluminum is a mightily reactive metal, it usually ends up being the one that weakens.

Extreme pH levels can lead to aluminum corrosion because they often break down the protective coating more quickly than it can repair itself. Aluminum generally performs best in a pH range of 4.5 to 8.5, which can potentially create issues in areas with clay soil.

Aluminum Oxidation vs. Aluminum Corrosion

Aluminum Oxidation

Aluminum undergoes a corrosion process similar to that of stainless steel. Aluminum atoms have a strong affinity for oxygen, so the atoms on the surface rapidly react with oxygen in the air to create aluminum oxide. Just like the chromium oxide layer on stainless steel, this aluminum oxide layer eventually reaches a depth that prevents further oxidation from occurring.

The oxidation process of aluminum is easy to observe. When aluminum is freshly cut, it has a bright, shiny, silver-like appearance. However, it quickly dulls to a gray color due to surface oxidation. This process is self-healing: if you scratch a piece of aluminum, the freshly exposed metal reacts with oxygen atoms, causing it to revert back to its dull gray appearance.

Unfortunately, this is not the entire story regarding aluminum corrosion.

Aluminum Corrosion

Aluminum can be vulnerable to corrosion under certain conditions, particularly when exposed to chlorides, sulfides, and galvanic corrosion. Chlorides are commonly found in saltwater and in the air near maritime areas. Sulfides may also result from saltwater exposure, but they can also originate from other sources, including emissions from equipment that burns coal, oil, or, to a lesser extent, natural gas.

Chlorides and sulfides have the ability to penetrate the oxide layer on the surface of aluminum. This typically occurs at specific locations rather than uniformly across the entire surface, leading to pitting. If left untreated, pitting can weaken the metal and potentially cause failures in areas under high stress.

Galvanic corrosion often occurs in saltwater environments. When two different metals are submerged in saltwater, they create a weak electrical circuit, similar to a battery. This circuit causes electrons to flow between the metals, which leads to the deterioration of the more galvanically active metal of the two.

Aluminum has a higher galvanic potential compared to most other metals. This means that the aluminum will corrode if saltwater creates a circuit between aluminum and mild or stainless steel. This process can occur surprisingly quickly, so it’s essential for owners of aluminum boats to be aware of it.

It’s important to understand that the corrosion rate of aluminum can be influenced by its specific composition. In general, alloys with higher copper content tend to corrode more quickly. Among the aluminum series, the 3xxx, 5xxx, and 6xxx alloys typically exhibit slower corrosion rates compared to the 2xxx series. Copper-free 7xxx series alloys are known for their good corrosion resistance, whereas those with significant copper content are more prone to corrosion.