Aluminum Basics: A Guide to Types and Machining Characteristics
When you think of aluminum products in your daily life, items like soda cans, aluminum foil, and small coins might come to mind. Aluminum is used in a wide range of applications because it is lightweight, corrosion-resistant, and non-toxic even when in contact with food. In the United States, while we often see it in everyday consumer goods, it’s important to note that most “aluminum” we encounter is actually an aluminum alloy—mixed with other metals to enhance its properties. Pure aluminum (99%+) is relatively rare in industrial use, though it is sometimes used in specialized electrical or chemical applications.
In this article, we’ll introduce the characteristics of this versatile, lightweight metal.
What is Aluminum?
Aluminum is refined from bauxite, a reddish-brown ore composed mainly of aluminum oxide. The aluminum is extracted and then processed through electrolysis. It is then formed into various shapes through rolling, extrusion, or casting. While aluminum is the most abundant metal in the Earth’s crust, it was only discovered as a distinct metal in the 1800s—much later than copper or iron. In the U.S. and internationally, the Aluminum Association (AA) standards are the most common way to categorize the many alloys that have been developed since then.
Aluminum is lightweight and very soft in its pure form, which can be a drawback for structural applications. To overcome this, elements like copper, manganese, silicon, and magnesium are added to create aluminum alloys that are strong yet remain lightweight.
Characteristics of Aluminum
– Lightweight (Low Density): The specific gravity of aluminum is 2.7, which is about one-third that of steel (7.8) or copper (8.9). This makes it essential for the U.S. aerospace and automotive industries, where reducing weight improves fuel efficiency and performance. – Corrosion Resistance: Like stainless steel, aluminum forms a natural oxide layer that prevents rust. In many American coastal or industrial environments, aluminum is preferred for its ability to withstand harsh conditions. – High Conductivity: While copper is a better conductor, aluminum is much lighter. For the same weight, aluminum can carry twice the current of copper, which is why it’s the standard for power transmission lines across the U.S. grid. – Thermal Conductivity: Its thermal conductivity is about three times higher than steel. It heats up and cools down quickly, making it ideal for CPU heat sinks, automotive radiators, and high-performance cookware. – Non-Magnetic: Aluminum is non-magnetic, making it vital for MRI rooms and sensitive electronic housings. – Excellent Machinability: Aluminum is easy to shape through rolling, extrusion, and CNC machining. However, American machinists must be careful with “gummy” alloys (like the 1xxx or 3xxx series) that can clog cutting tools. Using high-speed steel (HSS) or carbide tools with sharp rake angles is a common practice in U.S. shops to prevent this. – Low-Temperature Strength: Unlike many steels that become brittle in the cold, aluminum actually gets stronger at cryogenic temperatures. This is why it’s used for liquid natural gas (LNG) tanks and space exploration equipment (NASA frequently utilizes 2xxx and 7xxx series alloys).
Types and Characteristics of Aluminum Alloys (US/ASTM Standards)
In the U.S., aluminum alloys are classified by a 4-digit system established by the Aluminum Association. Below is a guide to the most common grades used in North American manufacturing: