The Truth About Hardness: 7075 Aluminum vs. Steel

In the world of engineering materials, the 7075 aluminum alloy is renowned as a "warrior" for its outstanding strength. This raises an interesting question: Is 7075 aluminum actually harder than steel? To answer this, we need to directly compare their mechanical properties based on international standards.

Essentially, the answer is "both yes and no." 7075 aluminum is harder than some mild steels but cannot match the hardness of high-grade alloy or tool steels.

A Direct Comparison Based on Data

For an objective view, let's compare the key properties of 7075-T6 Aluminum (its most common temper) with several common types of steel, according to ASTM B209 and other steel standards.

Analysis from the data table:

• Hardness: 7075-T6 Aluminum (150 HB) is significantly harder than A36 carbon steel (120 HB), but it is softer than 304 Stainless Steel (170 HB) and far inferior to SKD11 tool steel (215 HB in its annealed state).
• Tensile Strength: Similarly, 7075 aluminum (572 MPa) is stronger than A36 and 304 stainless steel, but still weaker than tool steel.
• The Absolute Advantage: With a density only one-third of steel's, the strength-to-weight ratio of 7075 aluminum is exceptional, which is its greatest asset.

So Why the "7075 is Harder Than Steel" Misconception?

This confusion often arises from an apples-to-oranges comparison. When a person holds a sheet of 7075 aluminum and a sheet of common carbon steel, they will notice the aluminum is much lighter yet very difficult to bend or deform, creating a sense of "sturdy hardness." This notion is correct when comparing it to low-cost, mild structural steels.

Conclusion: Choosing the Right Material for the Application

The final answer is: No, 7075 aluminum is not harder than all types of steel. It is only harder than some low-carbon steels.

• Choose 7075 Aluminum when your application requires:
  • Extremely light weight as a top priority (aerospace, sporting goods).
  • A high strength-to-weight ratio.
  • Precise and fast CNC machining capability.
• Choose Steel when your application requires:
  • Absolute hardness and wear resistance (tool steel).
  • High structural strength at a large scale for a low cost (carbon steel).
  • Better corrosion and heat resistance (stainless steel). A comparison between stainless steel types also reveals a wide variety of choices.