Can I use oven cleaner or a strong degreaser on aluminium?

Why the usual answer works

Strong alkalis remove baked-on grease by saponification: they react with fats to produce soaps, which then dissolve and rinse away. Polymerised oven soil barely responds to detergent, so the caustic route is genuinely the effective one and that is why oven cleaners are formulated that way.

Usually recommended: Sodium carbonate.

Why it must not be used here

Aluminium is amphoteric — attacked by strong bases as well as by strong acids. The alkali dissolves the protective oxide film and then the metal beneath, leaving a dull grey or blackened surface that is not a deposit and cannot be cleaned off. There is a second consequence that is a safety matter rather than a cosmetic one: a US state hazardous substance fact sheet records that sodium hydroxide reacts with metals including aluminium to form flammable and explosive hydrogen gas, which is not what anybody expects from cleaning an oven tray in a confined space.

This damage cannot be undone by cleaning. There is nothing left on the surface to remove.

More about aluminium and grease.

What to do instead

Take the contact-time route instead of the chemical-strength route. Soaking in hot water with an ordinary detergent softens polymerised soil given long enough, and repeating a mild treatment is the trade's stated sequence for burnt-on deposits precisely because the aggressive alternatives damage surfaces. Where the item is unquestionably steel rather than aluminium the caustic route is available, so the first thing worth establishing is which metal you have — aluminium trays and steel trays look similar and behave completely differently. If a caustic product has already been used, ventilate and do not enclose the item while it is reacting.

• Soaking — Extending contact time so chemistry can do work that would otherwise need force. Often the difference between scrubbing and wiping.
• Detergent — A surfactant-based cleaner. The general-purpose answer for greasy and particulate soil, and the correct first choice far more often than any specialist product.
• Rinsing and drying — The step people skip, and the one that decides whether cleaning protected the surface or damaged it. Residue left behind is exposure that continues after you stop.

The chemistry behind both halves

• pH in cleaning — Why the acid or alkali choice decides both what a cleaner removes and what it damages. The two are the same property seen from opposite sides.
• Contact time — The variable people ignore and the one that most often decides the outcome — in both directions. Longer works better, and longer is also how damage happens.
• Material compatibility — The reason a useful answer is about the surface rather than about the product. The same agent is the right answer and the wrong answer depending on what it lands on.