How to Tell the Difference Between Stainless Steel and Aluminum

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Magnet Test:

Hit with a magnet. If it sticks, it is not aluminum, but rather 400 grade stainless steel, or just normal steel.
The only elements that stick to a magnet are nickel, cobalt, and of course, iron.
As an aside, tungsten carbide doesn’t stick to a magnet. In fact, tungsten carbide is actually a powder. What is commonly called “carbide” is actually cemented carbide, which is cobalt impregnated with tungsten carbide (WC). The cobalt is what causes carbide tools to attract a magnet. (I have written about scrap carbide before)

If you grind the steel with a grinding wheel, and it throws off a glow of sparks, then it is steel. otherwise it isn’t steel. So if it is non-magnetic and it gives off sparks, then it is most likely 3xx series stainless steel.
Rust Test:
Aluminum doesn’t rust. Stainless steel CAN rust, and contrary  to popular belief WILL rust eventually, especially in extreme conditions.
Density test:
Grab a similarly sized chunk of regular steel. Aluminum is about 3 times lighter than stainless steel. If your sample doesn’t seem light compared to the regular steel, then it is probably also steel.

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