Aluminum & Steel - Comparing their Properties
Let's compare one of the most common structural steels, A36 carbon steel, to one of the most popular structural aluminum alloys, 6061-T6 aluminum.
As an example, consider a 20-foot-long angle with 2-inch legs and a 1/4-inch thickness. The A36 steel angle weighs 3.19 pounds per foot, while the 6061-T6 aluminum angle weighs just 1.11 pounds per foot. That means the aluminum angle weighs only about 35% as much as the steel version, making it significantly easier to transport, handle, and install.
Here's how the two materials compare mechanically:
| Property | A36 Carbon Steel | 6061-T6 Aluminum |
|---|---|---|
| Yield Strength | 36 ksi | 40 ksi |
| Tensile Strength | 58–80 ksi | 45 ksi |
| Modulus of Elasticity (Stiffness) | 29,000 ksi | 10,000 ksi |
At first glance, many people are surprised to see that 6061-T6 aluminum actually has a slightly higher yield strength than A36 steel. Yield strength is the amount of stress a material can withstand before it begins to permanently deform. In other words, aluminum can resist bending permanently just as well—and in this case, even slightly better—than A36 steel.
However, A36 steel has a clear advantage in ultimate tensile strength, meaning it can withstand greater loads before it fractures. Depending on the specific material, A36 steel has a tensile strength ranging from 58 to 80 ksi, compared to approximately 45 ksi for 6061-T6 aluminum.
The biggest difference between these materials is stiffness. Steel has a modulus of elasticity of approximately 29,000 ksi, while aluminum is only about 10,000 ksi. This means steel is nearly three times stiffer than aluminum. Under the same load, an aluminum angle of identical size will flex roughly three times as much as a steel angle. That's why aluminum structural members are often designed with larger cross sections to achieve the same rigidity as steel.
So, which material is better?
If your priority is reducing weight, 6061-T6 aluminum is an excellent choice. It offers an outstanding strength-to-weight ratio, excellent corrosion resistance, and is widely used in trailers, marine applications, transportation equipment, architectural projects, and other applications where every pound matters.
If your priority is maximum stiffness, load capacity, and economy, A36 structural steel remains the material of choice. Its higher tensile strength, greater rigidity, ease of fabrication, and lower cost make it ideal for buildings, machinery, equipment frames, and countless structural applications.
The takeaway is that lighter doesn't necessarily mean weaker, and stronger doesn't always mean better. Understanding the differences in yield strength, tensile strength, stiffness, and weight allows you to choose the material that best fits the demands of your project.