Aluminum, the result of a complex production process, stands out among other metals for its various unique properties, making it a preferred choice for manufacturers across various industries. It has an exceptional strength-to-weight ratio, excellent corrosion resistance, high conductivity, is malleable, and 100% recyclable. Aluminum is found in a wide variety of applications, from consumer goods to mission-critical aerospace and defense uses. But how is it made? Today, we will do a deep dive into the complex process that produces pure aluminum and its many alloys.
Aluminum’s main ingredient is aluminum oxide (Al2O3), commonly known as alumina, which is extracted from bauxite ore. Bauxite is one of the most abundant elements in the Earth’s crust and contains 30-60% aluminum oxide.
How Is Aluminum Made?
Aluminum production begins with extracting alumina from the bauxite, which is no simple process. Following is an overview of the key production steps:
- First, the bauxite is crushed into powder, mixed with water and heated with sodium hydroxide (NaOH), which dissolves the aluminum and allows impurities to be filtered out. This results in sodium aluminate.
- The sodium aluminate is seeded with alumina crystals, which attract other crystals, forming groups.
- These crystals are then washed to remove impurities and heated to over 2000° F to completely remove the water. The result is a fine white alumina powder (Al2O3), a firmly bonded combination of aluminum and oxygen.
- This powder is then smelted into aluminum using the Hall-Héroult process, where the powder is dissolved in molten salt and aluminum fluoride inside steel boxes lined with carbon.
- Electric current is then added to this solution, which reduces the alumina molecules into aluminum and oxygen. The oxygen combines with the carbon on the electric anode probe and forms carbon dioxide, which rises to the surface.
- The molten aluminum is then siphoned off and more alumina is added as the process continues until the desired quantity of aluminum is achieved.
It takes about 2 pounds of alumina to make a pound of aluminum. The aluminum created during this process is over 99% pure. It can then be further purified or “alloyed”. Alloying adds small but tightly controlled amounts of other elements, increasing the aluminum’s strength or enhancing other desired properties, such as heat treatability or lower melting points. Typical alloying elements include copper, zinc, and magnesium, among others.
The aluminum is then cast into ingots of various sizes. It can also be cast into sheet ingots for further rolling and processing into coiled strip. The aluminum, in these multiple forms, is then ready for manufacturing processes such as stamping, forming, and others to produce a seemingly limitless range of products and components for common and specialty uses.