It's generally not recommended to heat aluminum in a microwave as it can cause safety hazards and damage to the microwave itself. Microwaving aluminum can lead to electrical arcing, which can damage the microwave, cause sparks, and even lead to a fire.
The microwaves work by emitting electromagnetic waves that excite water molecules in the food, generating heat. Metals, including aluminum, reflect these microwaves, which can result in uneven heating, sparking, and potentially damaging the microwave.
If you need to warm up aluminum, it's better to use a different method. For instance, you can place the aluminum item on a stovetop on low heat or use an oven to warm it. Just remember to exercise caution and ensure that the item is suitable for the chosen heating method.
When using a microwave, stick to microwave-safe containers and avoid putting any metal, including aluminum foil or containers, inside the microwave to ensure safe and efficient operation.