Aluminum 2024 and Aluminum 7075 are two of the most commonly used aluminum alloys in aerospace, automotive, and structural applications. Both alloys are valued for their high strength-to-weight ratios, corrosion resistance, and machinability, but they differ significantly in their chemical composition, mechanical properties, and applications.
Chemical Composition
Aluminum 2024 is primarily an aluminum-copper alloy. It contains approximately 3.8-4.9% copper, 0.3-0.9% manganese, 1.2-1.8% magnesium, and small amounts of other elements such as iron and silicon. The high copper content gives 2024 aluminum its excellent strength but also makes it more susceptible to corrosion compared to other aluminum alloys.
Aluminum 7075, on the other hand, is an aluminum-zinc alloy with significant amounts of magnesium and copper. It typically contains 5.1-6.1% zinc, 2.1-2.9% magnesium, 1.2-2.0% copper, and trace amounts of chromium, iron, and silicon. The combination of zinc and magnesium contributes to its exceptional strength and hardness, making it one of the strongest commercially available aluminum alloys.
Mechanical Properties
Strength
One of the primary differences between 2024 and 7075 aluminum is their tensile strength. Aluminum 2024 has an ultimate tensile strength of approximately 470 MPa (68,000 psi) in the T3 temper and can reach up to 483 MPa (70,000 psi) in the T4 temper. It is commonly used in applications requiring a good balance between strength and weight.
Aluminum 7075, however, significantly surpasses 2024 in terms of strength. Its ultimate tensile strength ranges from 572 MPa (83,000 psi) in the T6 temper to 606 MPa (88,000 psi) in the T73 temper. This makes it an ideal material for highly stressed structural components, especially in aerospace and military applications.
Yield Strength
The yield strength of aluminum 2024 is approximately 324 MPa (47,000 psi) in the T3 temper, which is lower than that of 7075. Aluminum 7075 has a yield strength of around 503 MPa (73,000 psi) in the T6 temper, providing significantly higher resistance to deformation under load.
Hardness
The hardness of an aluminum alloy is an important factor in determining its wear resistance. Aluminum 2024 has a Brinell hardness of around 120 HB in the T3 condition, whereas 7075 in the T6 condition has a hardness of approximately 150 HB. This increased hardness in 7075 makes it more resistant to wear and abrasion.
Fatigue Strength
Fatigue resistance is crucial in aerospace and structural applications where cyclic loading occurs. Aluminum 2024 has a fatigue strength of about 138 MPa (20,000 psi) in the T3 temper, while 7075 has a fatigue strength of around 159 MPa (23,000 psi) in the T6 temper. This suggests that 7075 is slightly better suited for applications experiencing repeated stress cycles.
Machinability
Both 2024 and 7075 aluminum exhibit good machinability, but there are some differences. Aluminum 2024 is generally easier to machine due to its lower hardness and strength. It allows for smoother cutting and less tool wear. In contrast, aluminum 7075’s higher strength and hardness can lead to increased tool wear and require more aggressive cutting parameters.
Corrosion Resistance
Corrosion resistance is a critical factor in material selection, especially in marine and aerospace applications. Aluminum 2024, due to its high copper content, is more prone to corrosion, particularly in marine and humid environments. It often requires protective coatings, such as anodizing or cladding, to enhance its corrosion resistance.
Aluminum 7075 also contains copper but in lower amounts than 2024. However, due to its high zinc content, it is still susceptible to stress corrosion cracking. While 7075 provides better general corrosion resistance than 2024, it still requires protective coatings in harsh environments.
Weldability
Neither 2024 nor 7075 aluminum are particularly well-suited for welding. Aluminum 2024 is considered difficult to weld because it is prone to hot cracking, and post-weld heat treatment is often required to restore strength. Similarly, aluminum 7075 is generally not recommended for welding due to its susceptibility to cracking and loss of mechanical properties in the heat-affected zone.
Applications
Aluminum 2024 is widely used in aerospace applications where strength and fatigue resistance are essential. It is commonly found in aircraft structures, fuselage components, and wing skins. It is also used in automotive and military applications where lightweight and high-strength materials are required.
Aluminum 7075, with its superior strength, is used in aerospace and high-performance applications. It is a preferred material for aircraft frames, structural components, and high-performance bicycles. It is also used in sporting goods, such as rock climbing equipment and firearm components, where strength and weight are critical factors.
Cost Considerations
The cost of aluminum 2024 and 7075 varies depending on availability, processing methods, and required treatments. Generally, aluminum 7075 is more expensive than 2024 due to its superior strength and performance characteristics. The increased cost is justified in applications where the highest strength is needed.
Conclusion
Aluminum 2024 and 7075 each offer unique advantages and are suited for different applications based on their mechanical properties, corrosion resistance, and machinability. Aluminum 2024 is an excellent choice for applications requiring good strength, fatigue resistance, and machinability, while aluminum 7075 is ideal for high-stress applications demanding maximum strength and hardness. The selection between the two alloys ultimately depends on the specific requirements of the application, including environmental conditions, cost considerations, and performance needs.