When engineers compare materials for high-stress applications, 7075 aluminum alloy often emerges as a standout contender, offering a strength-to-weight ratio that approaches that of many steels while maintaining the lightweight advantages of aluminum. With a density of just 2.81 g/cm³ and a tensile strength exceeding 570 MPa in the T6 temper, 7075 achieves specific strengths (strength-to-density ratios) that rival or surpass those of common structural steels like A36 or 1018. This unique combination makes it indispensable in industries where every gram counts, from aerospace frames to high-performance automotive components. The alloy’s ability to deliver near-steel strength at approximately 64% less weight per unit volume is a game-changer for design engineers seeking to optimize performance without compromising structural integrity.
1. 7075 Basic Information
7075 is a precipitation-hardened aluminum alloy belonging to the 7xxx series, primarily alloyed with zinc as the major element. Developed in the 1940s for aircraft applications, it has since become a benchmark for high-strength aluminum alloys. Its low density (2.81 g/cm³) compared to steel (7.85 g/cm³) provides a weight reduction of approximately 64% for equivalent volumes, while its ultimate tensile strength in the T6 temper (570 MPa) approaches that of mild steel (400-550 MPa). The alloy exhibits excellent fatigue resistance, with a fatigue strength of 160 MPa at 5×10⁸ cycles, and good corrosion resistance when properly protected. However, it is less weldable than other aluminum alloys and requires careful heat treatment to achieve optimal properties. The T6 temper involves solution heat treatment at 470-490°C, followed by quenching in water or polymer, and artificial aging at 120-130°C for 24 hours. This process precipitates fine MgZn₂ particles that impede dislocation movement, resulting in the alloy’s characteristic high strength. The T651 temper adds a stress-relieving stretch of 1-3% after solution treatment to minimize residual stresses and improve dimensional stability during machining.
2. Chemical Composition
The precise chemical composition of 7075 aluminum alloy is critical to its mechanical performance. The following table provides the standard composition ranges per ASTM B209 and EN 573-3 specifications:
| Element | Content (%) | Role in Alloy |
|---|---|---|
| Aluminum (Al) | Balance (87.1-91.4%) | Base metal, provides lightweight matrix |
| Zinc (Zn) | 5.1-6.1 | Primary strengthening element via precipitation hardening |
| Magnesium (Mg) | 2.1-2.9 | Enhances strength through MgZn₂ precipitates |
| Copper (Cu) | 1.2-2.0 | Improves strength and stress corrosion resistance |
| Chromium (Cr) | 0.18-0.28 | Controls grain structure, reduces quench sensitivity |
| Silicon (Si) | ≤0.40 | Impurity, kept low to avoid brittleness |
| Iron (Fe) | ≤0.50 | Impurity, reduces ductility if excessive |
| Manganese (Mn) | ≤0.30 | Minor grain refiner |
| Titanium (Ti) | ≤0.20 | Grain refiner during casting |
| Others (each) | ≤0.05 | Trace impurities |
| Others (total) | ≤0.15 | Sum of all trace elements |
The zinc-to-magnesium ratio of approximately 2.5:1 optimizes the formation of MgZn₂ precipitates during aging, which are responsible for the alloy’s high strength. Copper additions further enhance strength by forming Al₂CuMg phases, while chromium prevents recrystallization during hot working. The tight control of impurities like silicon and iron is essential; silicon above 0.40% can form brittle AlFeSi phases that reduce fracture toughness, while iron above 0.50% promotes coarse intermetallic compounds that degrade fatigue performance. The alloy’s composition is designed to achieve a balance between strength, ductility, and corrosion resistance, with the copper content being particularly critical for stress corrosion cracking (SCC) resistance. In the T6 temper, the alloy exhibits a SCC threshold stress of approximately 200 MPa in the short transverse direction, which can be improved to 300 MPa by using the T73 overaging temper.
3. Mechanical & Physical Properties
7075 aluminum alloy exhibits a range of mechanical properties that vary with temper condition. The most common tempers are T6 (solution heat-treated and artificially aged) and T651 (stress-relieved by stretching). Below are detailed properties for the T6 temper:
| Property | Value (T6 Temper) | Unit | Standard |
|---|---|---|---|
| Ultimate Tensile Strength | 570 | MPa | ASTM B209 |
| Yield Strength (0.2% offset) | 505 | MPa | ASTM B209 |
| Elongation at Break | 11 | % | ASTM B209 |
| Hardness (Brinell) | 150 | HB | ASTM E10 |
| Hardness (Rockwell B) | 87 | HRB | ASTM E18 |
| Fatigue Strength (5×10⁸ cycles) | 160 | MPa | ASTM E466 |
| Modulus of Elasticity | 71.7 | GPa | ASTM E111 |
| Shear Strength | 330 | MPa | ASTM B769 |
| Poisson’s Ratio | 0.33 | – | ASTM E132 |
Physical properties further distinguish 7075 from other materials:
| Property | Value | Unit |
|---|---|---|
| Density | 2.81 | g/cm³ |
| Melting Point Range | 477-635 | °C |
| Thermal Conductivity (25°C) | 130 | W/m·K |
| Electrical Conductivity | 33 | %IACS |
| Specific Heat Capacity | 0.86 | J/g·°C |
| Thermal Expansion Coefficient (20-100°C) | 23.6 | µm/m·°C |
| Electrical Resistivity | 5.15×10⁻⁸ | Ω·m |
Compared to steel, 7075 offers a specific strength (strength/density) of approximately 203 kN·m/kg, versus 70-100 kN·m/kg for structural steels, making it ideal for weight-critical applications. However, its elongation of 11% is lower than many steels (typically 20-30%), indicating reduced ductility. The alloy’s fracture toughness, measured as KIC, is approximately 25-30 MPa√m in the T6 temper, which is lower than 6061-T6 (40 MPa√m) but sufficient for most structural applications. For improved toughness, the T73 temper reduces strength to 505 MPa tensile and 435 MPa yield but increases elongation to 13% and KIC to 35 MPa√m. The fatigue endurance limit at 10⁷ cycles is 160 MPa for smooth specimens, but this drops to approximately 80 MPa for notched specimens (Kt=3), emphasizing the importance of surface finish and stress concentration avoidance in design.
4. CNC Machining Characteristics
7075 aluminum alloy is highly machinable, but its high strength and hardness require optimized parameters to achieve precision and surface finish. The alloy’s thermal conductivity (130 W/m·K) aids in heat dissipation, reducing tool wear and thermal distortion. Below are recommended CNC machining parameters for common operations:
| Operation | Cutting Speed (m/min) | Feed Rate (mm/rev) | Depth of Cut (mm) | Tool Material | Coolant |
|---|---|---|---|---|---|
| Rough Milling | 200-350 | 0.10-0.25 | 2.0-5.0 | Carbide (K10-K20) | Water-soluble emulsion |
| Finish Milling | 350-500 | 0.05-0.15 | 0.2-1.0 | PCD or coated carbide | Mist or dry |
| Drilling (Ø5-10 mm) | 80-150 | 0.05-0.12 | – | HSS-Co or carbide | Flood coolant |
| Turning (Rough) | 250-400 | 0.15-0.30 | 1.0-3.0 | Carbide (C2-C3) | Water-soluble |
| Turning (Finish) | 400-600 | 0.05-0.10 | 0.1-0.5 | PCD or CBN | Mist or dry |
| Threading | 50-100 | 0.02-0.05 | – | Carbide thread mill | Flood coolant |
Key machining considerations for 7075 include:
- Chip Control: The alloy produces short, segmented chips that are easy to evacuate, reducing chip packing and tool damage. Chip thickness should be maintained at 0.05-0.15 mm for optimal evacuation.
- Surface Finish: Achievable surface roughness (Ra) down to 0.4 µm with PCD tools and optimized parameters. For mirror finishes, diamond turning can achieve Ra 0.1 µm.
- Tool Wear: Carbide tools typically last 30-60 minutes at recommended speeds; PCD tools can exceed 200 minutes. Flank wear should be monitored and tools replaced when VB reaches 0.3 mm.
- Heat Management: Use of coolant is recommended for deep cuts to prevent work hardening; dry cutting is feasible for light finishing. The alloy’s thermal conductivity helps dissipate heat, but cutting temperatures can reach 300-400°C at the tool-chip interface.
- Dimensional Stability: Stress-relieved tempers (T651) minimize distortion during machining, holding tolerances of ±0.01 mm. For high-precision parts, stress relief after roughing (e.g., 2 hours at 150°C) can further reduce distortion.
- Cutting Forces: Specific cutting force for 7075-T6 is approximately 800-1000 N/mm², which is 20-30% higher than 6061-T6, requiring rigid machine setups and vibration damping.
For micro-machining operations (features < 0.5 mm), recommended parameters include cutting speeds of 100-200 m/min with 0.01-0.03 mm/rev feed and 0.05-0.2 mm depth of cut using micro-grain carbide tools (0.5-2 µm grain size). The alloy's hardness (150 HB) can cause burr formation on edges; deburring with ceramic brushes or electrochemical methods is recommended for critical surfaces.
5. Applications
7075 aluminum alloy is widely used across industries where high strength and low weight are critical. Key applications include:
- Aerospace: Aircraft wing spars, fuselage frames, landing gear components, and helicopter rotor hubs. For example, the Boeing 747 uses 7075-T6 for wing skins and stringers, while the F-16 fighter jet employs 7075-T73 for bulkheads and longerons. The alloy’s fatigue strength of 160 MPa at 5×10⁸ cycles makes it suitable for components subjected to cyclic loading.
- Automotive: High-performance suspension arms, brake calipers, and chassis components in racing cars (e.g., Formula 1 wishbones). The alloy’s specific strength allows for weight reduction of 30-40% compared to steel equivalents, improving acceleration and fuel efficiency.
- Defense: Military vehicle armor plates, missile components, and firearm receivers (e.g., M16 rifle upper receivers). The alloy’s hardness (150 HB) provides good ballistic resistance, with 12.7 mm thick plates stopping 7.62 mm rounds at 100 meters.
- Sports Equipment: Bicycle frames (e.g., high-end mountain bikes), golf club shafts, and baseball bats. The alloy’s high strength allows for thinner wall sections, reducing weight while maintaining stiffness.
- CNC Machining Parts: Precision enclosures for electronics, mold bases, and jigs/fixtures requiring high stiffness. The alloy’s dimensional stability (0.01 mm tolerance) makes it ideal for high-precision tooling.
- Marine: Lightweight structural components in racing yachts, though protective coatings are needed for saltwater exposure. The alloy’s corrosion resistance in T6 temper is rated as “fair” in marine environments, requiring anodizing or epoxy coatings for long-term service.
6. Why Choose Dongguan Stirling Metal Products Co., Ltd.
Dongguan Stirling Metal Products Co., Ltd. combines over 15 years of expertise in CNC machining with a deep understanding of 7075 aluminum alloy. Our capabilities include:
- Material Sourcing: We supply 7075 in all tempers (T6, T651, T7351) with full mill test certificates (MTC) and traceability to ASTM B209/EN 573 standards. Our inventory includes plate, bar, and custom extrusions with thicknesses from 0.5 mm to 200 mm.
- Precision Machining: 5-axis CNC centers with positioning accuracy of ±0.002 mm, achieving tolerances down to ±0.005 mm on critical features. Our machines include DMG Mori and Mazak models with spindle speeds up to 20,000 RPM and rapid traverse rates of 60 m/min.
- Surface Finishing: In-house anodizing (Type II and III), hard coat anodizing (up to 50 µm thickness), and chemical conversion coating for corrosion protection. We also offer chromate conversion (MIL-DTL-5541) and powder coating with RAL color matching.
- Quality Control: CMM inspection with 0.5 µm resolution, plus hardness testing (Brinell/Rockwell) and tensile testing per ASTM E8. Our ISO 9001:2015 certified facility includes a dedicated metrology lab with Zeiss CMM and Keyence vision systems.
- Lead Times: Prototypes in 3-5 days, production runs of 100-10,000 parts in 7-15 days, with rush options available. We offer 24/7 production for urgent orders with 50% expedite fee.
- Cost Efficiency: Competitive pricing at $15-25/kg for machined parts (depending on complexity), with volume discounts for orders over 500 units. Our automated quoting system provides instant pricing for standard geometries.
Contact us at +86-769-2288-1234 or email sales@stirlingmetal.com for a free quote on your next 7075 project. Our engineering team is available for design for manufacturability (DFM) reviews to optimize your part for cost and performance.
