Aluminum is one of the most corrosion-resistant metals in everyday use, but plenty of things can break it down. Bacteria, fungi, liquid metals, strong acids, strong bases, and even the tomato sauce simmering in your kitchen all “eat” aluminum under the right conditions. The key to aluminum’s durability is a microscopically thin oxide layer that forms instantly when the metal contacts air. Anything that disrupts or dissolves that protective skin exposes the raw metal underneath, and that’s where the real damage begins.
Why Aluminum Resists Attack (Until It Doesn’t)
When aluminum meets oxygen, it forms a hard, transparent coating of aluminum oxide in milliseconds. This layer is remarkably stable in environments between roughly pH 4 and pH 9, which covers most everyday conditions. Outside that range, the shield dissolves. Strong acids (below pH 4) and strong bases (above pH 9) strip the oxide away, leaving bare aluminum exposed to rapid chemical attack.
Understanding this oxide layer is essential because nearly everything that “eats” aluminum does so by finding a way around it: dissolving it chemically, cracking it mechanically, or sneaking beneath it at the atomic level.
Mercury and Gallium: Metals That Destroy Aluminum
Two liquid metals are especially devastating to aluminum. Mercury and gallium don’t just corrode the surface. They infiltrate the metal’s internal crystal structure and tear it apart from within, a process called liquid metal embrittlement.
Mercury breaks through aluminum’s oxide layer at concentrations as low as 300 parts per million. Once metallic mercury contacts bare aluminum, it forms an amalgam, a mixture of the two metals. Aluminum atoms then migrate through the liquid mercury to the surface, where they oxidize and flake off. This creates wide, undermining cavities as the aluminum is consumed from below. The process doesn’t require any added salt or acid to get started; mercury alone is enough.
Gallium works by a different but equally destructive path. It seeps into the boundaries between aluminum’s crystal grains, replacing the strong aluminum-to-aluminum bonds with much weaker aluminum-to-gallium bonds. This change transforms the metal from flexible and tough to brittle and crackable. Research on aerospace-grade aluminum (7075-T6) confirmed that gallium infiltration shifts the fracture mode from ductile to brittle, meaning the metal snaps instead of bending. The infiltration follows diffusion, so higher temperatures speed it up, and the depth of damage increases steadily over time at any given temperature. This is why a small drop of gallium on an aluminum beam can, over hours, cause the entire piece to crumble.
Strong Bases and Acids
Sodium hydroxide (lye) is one of the fastest and most aggressive aluminum destroyers. When a strong alkaline solution contacts aluminum, it dissolves the protective oxide layer almost instantly and reacts vigorously with the metal underneath. The reaction is exothermic, meaning it generates significant heat, and it produces hydrogen gas. This is why drain cleaners containing lye can damage aluminum plumbing, and why industrial processes have explored the reaction as a method for generating hydrogen fuel.
Strong acids like hydrochloric and sulfuric acid also dissolve aluminum, though the reaction is generally slower than with strong bases. Even milder acids can cause problems given enough time, which brings us to your kitchen.
Acidic Foods in the Kitchen
Cooking acidic foods in aluminum pots and pans slowly dissolves the metal into your food. The amounts are small but measurable. Tomato sauce cooked in aluminum picks up about 2.7 to 4.9 milligrams of aluminum per 100 grams of sauce, with sugar reducing the leaching slightly. Red cabbage cooked with lemon juice (pH 2.6) absorbed 5.1 milligrams per 100 grams. Storing acidic leftovers in aluminum containers in the fridge doesn’t dramatically increase those numbers over 48 hours, but the initial cooking does most of the damage.
These levels are well below amounts considered acutely harmful, but they illustrate that everyday acids like citrus juice, vinegar, and tomatoes genuinely eat into aluminum cookware over time. This is why most cooking advice steers you toward stainless steel or glass for long-simmered tomato sauces.
Fungi That Corrode Aluminum
Several species of fungi attack aluminum by producing organic acids as metabolic byproducts. The most studied is Aspergillus niger, a common black mold found in soil and damp environments. Research on aerospace aluminum alloy 2024 showed that A. niger accelerates corrosion primarily through the oxalic acid it secretes. The acid creates pitting on the aluminum surface that closely matches the damage pattern seen when aluminum is exposed to oxalic acid alone, confirming the fungus’s acid output as the main culprit.
In aviation, a fungus historically known as the “fuel bug,” Hormoconis resinae, was once the dominant contaminant in jet fuel tanks, where it grew at the fuel-water interface and corroded the aluminum tank walls. Changes in fuel composition over the years have shifted the microbial community. Modern jet fuel tanks are now more commonly colonized by bacteria from the genus Bacillus, along with the fungi Aureobasidium and Penicillium. Despite this shift in species, the microbial community retains the ability to corrode aluminum alloy fuel tanks, as confirmed by electrochemical testing.
Bacteria on Aluminum Surfaces
Bacteria colonize aluminum in virtually every environment, from industrial water systems to the deep ocean. A study that submerged aluminum alloys at nearly 5,800 meters deep in the Pacific Ocean’s Yap Trench found distinct bacterial communities forming biofilms on the metal. On pure and standard aluminum alloys, sulfur-oxidizing bacteria (Sulfurimonas) dominated, making up about 27% of the biofilm community, alongside a group called PS1 Clade at roughly 15%. When the aluminum alloy contained copper, the community shifted to include Stenotrophomonas, Cobetia, and Vibrio.
These bacteria don’t “eat” aluminum the way you’d eat a sandwich. Instead, they create microenvironments on the metal surface where pH, oxygen levels, and chemical byproducts differ sharply from the surrounding water. These localized conditions can break down the protective oxide layer in spots, leading to pitting corrosion. The process, called microbiologically influenced corrosion, is a major concern for underwater infrastructure, pipelines, and marine vessels.
Industrial Bioremediation
The ability of microorganisms to interact with metals has practical applications in cleaning up contaminated land. In soil remediation, consortia of filamentous fungi have reduced heavy metal concentrations by 42 to 62% over 144-day treatment periods. Early efforts using single bacterial strains like Pseudomonas putida and Bacillus subtilis showed promise in lab settings but gave inconsistent results in real-world soil due to varying conditions. More recent approaches use mixed microbial communities, sometimes combined with soil conditioners or hydrogel carriers that help the organisms survive long enough to do their work. While much of this research targets metals like arsenic and chromium, the same biological principles apply to aluminum-contaminated industrial sites.
What Damages Aluminum Fastest
If you’re thinking about this practically, here’s a rough hierarchy of what attacks aluminum most aggressively:
- Liquid metals (gallium, mercury): Structural destruction within hours. Gallium visibly crumbles thick aluminum pieces overnight.
- Strong bases (sodium hydroxide): Rapid dissolution with visible fizzing and heat, often within minutes.
- Strong acids (hydrochloric, sulfuric): Moderate to fast dissolution depending on concentration.
- Mild acids (citrus, vinegar, tomato): Slow surface leaching over the course of cooking or storage.
- Fungi and bacteria: Gradual pitting corrosion over weeks to months, significant mainly in industrial and marine settings.
The common thread is that anything capable of breaching aluminum’s oxide layer, whether through chemistry, biology, or atomic infiltration, can then consume the reactive metal underneath. Aluminum’s reputation as a durable, corrosion-resistant material holds true in neutral, dry, sterile conditions. In the messy reality of kitchens, oceans, fuel tanks, and industrial sites, the list of things that eat it is longer than most people expect.