How does the toughness of 7075 aluminum compare to steel?

Torn between aluminum and steel for a high-performance part? Don’t ignore toughness—it could make or break your design.

7075 aluminum has lower fracture toughness than steel. Steel is 2–6 times tougher, making it better for impact, fatigue, or cold environments.

While 7075 aluminum is famous for strength-to-weight ratio, it doesn’t match steel in energy absorption before breaking. Let’s break down what toughness really means and when each material is best.

What is the toughness definition?

Confused by strength, hardness, and toughness? You’re not alone. They’re not the same.

Toughness means how much energy a material can absorb before breaking. It depends on both strength and ductility.

What toughness really measures

Toughness is the ability of a material to withstand shock and resist fracture. Technically, it’s the area under the stress-strain curve. The more energy it can absorb before breaking, the tougher it is.

The most common metric used in engineering is:

• Fracture toughness (K_IC), measured in MPa·√m
• Used to evaluate resistance to crack growth

Key toughness components

• Strength: How much load it can carry
• Ductility: How much it can stretch or deform before breaking
• Notch Sensitivity: How it reacts to flaws or cracks

Materials with high toughness resist sudden fractures. Those with low toughness may crack under stress or impact.

How do toughness values compare?

Thinking all strong materials are also tough? Not quite.

7075 aluminum has fracture toughness of ~29 MPa·√m, while common steels range from 50 to 175 MPa·√m. Steel is usually 2–6 times tougher.

Table: Fracture Toughness Values

7075 aluminum is strong and light. But it’s relatively brittle compared to steel. If your part is likely to see impacts, drops, or heavy vibrations, this matters.

Aluminum cracks earlier under stress concentration or impact. Steel’s ability to absorb shocks without breaking is why it’s still used in bridges, tools, and armor.

In which applications does steel outperform?

Wondering when steel is the better choice? It’s all about stress, shock, and fatigue.

Steel outperforms aluminum in impact-heavy, fatigue-prone, and low-temperature applications due to its higher toughness.

Key advantages of steel

• Shock Resistance: Steel absorbs more energy without cracking
• Fatigue Life: Lasts longer under repeated stress cycles
• Cold Weather Use: Aluminum may become brittle; steel stays tough
• Weldability: Steel is easier to weld and retains strength post-weld

Typical uses where steel wins

Aluminum parts often fail first when exposed to shock, cracks, or defects. Steel resists these better, making it safer for structural use or heavy-duty tools.

When is 7075 aluminum preferable?

Think steel is always better? Not really. Aluminum has its place.

7075 aluminum is ideal when you need high strength with low weight, like in aerospace, racing, or lightweight frames.

Why aluminum wins in some cases

• High Specific Strength: Strong relative to its weight
• Weight Reduction: Critical in vehicles, bikes, and planes
• Machinability: Easier to cut, shape, and drill
• Corrosion Resistance: Good with proper coating or anodizing

When to choose 7075

7075 aluminum delivers enough strength for most loads and can be designed to avoid fracture points. It performs especially well where every gram counts.

It’s not for rough handling or welding—but perfect for smartly engineered, lightweight structures.

Conclusion

7075 aluminum is strong and light, but steel is much tougher. If impact and fatigue are key, steel wins. If weight and machinability matter most, 7075 shines. Pick based on your real-world needs.