Aluminum 7075 properties
Aluminum 7075 (UNS A97075, ENAW-AlZn5.5MgCu) is a 7xxx series aluminum alloy with zinc as the main alloying element. Its density is 2.81 g/cm³ (0.102 lb/in³) and it combines very high mechanical strength with notable fatigue resistance, although it has limited weldability and moderate susceptibility to stress corrosion cracking.
| Property | Value (SI) | Value (Imperial) |
|---|---|---|
| Density | 2.81 g/cm³ | 0.102 lb/in³ |
| Elastic modulus (E) | 71.7 GPa | 10.4 × 10³ ksi |
| Thermal conductivity (k) | 130–150 W/m·K | 75–87 BTU·in/(h·ft²·°F) |
| Melting point (Tₘ) | 477 °C | 891 °F |
| Electrical resistivity | 51.5 nΩ·m | — |
| Coefficient of linear thermal expansion (α) | 2.36×10⁻⁵ K⁻¹ | 13.1 × 10⁻⁶ in/in/°F |
Chemical composition
Section titled “Chemical composition”The standard chemical composition of aluminum 7075 contains 5.1–6.1 % zinc as the main element, accompanied by magnesium, copper, and chromium. Iron and silicon are kept as controlled impurities.
| Element | Content (wt%) |
|---|---|
| Zinc (Zn) | 5.1 – 6.1 |
| Magnesium (Mg) | 2.1 – 2.9 |
| Copper (Cu) | 1.2 – 2.0 |
| Iron (Fe) | max. 0.5 |
| Silicon (Si) | max. 0.4 |
| Manganese (Mn) | max. 0.3 |
| Chromium (Cr) | 0.18 – 0.28 |
| Titanium (Ti) | max. 0.2 |
| Other (each) | max. 0.05 |
| Other (total) | max. 0.15 |
| Aluminum (Al) | Balance |
Physical properties
Section titled “Physical properties”The density of aluminum 7075 is 2.81 g/cm³ at room temperature. Its Young’s modulus is 71.7 GPa (10.4 × 10³ ksi), the shear modulus reaches 27.0 GPa (3.9 × 10³ ksi) and Poisson’s ratio is 0.33, which gives it high stiffness for a light alloy.
| Property | Value (SI) | Value (Imperial) |
|---|---|---|
| Density (ρ) | 2.81 g/cm³ | 0.102 lb/in³ |
| Elastic modulus (E) | 71.7 GPa | 10.4 × 10³ ksi |
| Shear modulus (G) | 27.0 GPa | 3.9 × 10³ ksi |
| Poisson’s ratio (ν) | 0.33 | 0.33 |
| Rockwell hardness (HRB) in temper T6 | 87 HRB | — |
| Brinell hardness (HBW) in temper O | 60 | — |
| Brinell hardness (HBW) in temper T6 | 150 | — |
Mechanical properties by temper condition
Section titled “Mechanical properties by temper condition”The tensile strength of aluminum 7075 in temper O is 275 MPa (40 ksi), while in temper T6 it rises to 540–560 MPa (78–83 ksi). Ductility, expressed as elongation at fracture, varies between 5% and 13% depending on the heat treatment applied.
| Temper | Yield strength Rp0.2 (MPa) | Tensile strength Rm (MPa) | Elongation A (%) | Brinell hardness (HBW) | Rockwell hardness (HRB) |
|---|---|---|---|---|---|
| O (annealed) | 165 max. | 275 max. | 10 min. | 60 | — |
| T6 (heat treated) | 400 – 505 | 470 – 560 | 5 – 8 | 150 | 87 |
| T651 (T6 + stress relief) | 500 | 570 | 3 – 9 | — | — |
| T7 (overaged, T73) | 435 | 505 | 13 | — | — |
Note: The values for T6 and T651 correspond to moderate thickness products. In thick plates, the limits may be slightly lower.
Thermal properties
Section titled “Thermal properties”The melting temperature of aluminum 7075 is 477 °C (891 °F). Its thermal conductivity ranges between 130 and 150 W/m·K and the specific heat is 714.8 J/kg·K.
| Property | Value (SI) | Value (Imperial) |
|---|---|---|
| Melting point (Tₘ) | 477 °C | 891 °F |
| Thermal conductivity (k) | 130 – 150 W/m·K | 75 – 87 BTU·in/(h·ft²·°F) |
| Specific heat (cₚ) | 714.8 J/kg·K | 0.171 BTU/lb·°F |
| Coefficient of linear thermal expansion (α) | 2.36×10⁻⁵ K⁻¹ | 13.1×10⁻⁶ in/in/°F |
| Maximum continuous working temperature | 160 °C | 320 °F |
In temper O, the material shows acceptable thermal stability; in temper T6, prolonged exposure above 120 °C can cause overaging and loss of mechanical properties.
Electrical properties
Section titled “Electrical properties”The electrical resistivity of aluminum 7075 is 51.5 nΩ·m, which corresponds to an IACS conductivity of approximately 33% (International Annealed Copper Standard). This makes it less conductive than pure aluminum (62% IACS), but sufficient for structural applications where conductivity is not critical.
| Property | Value |
|---|---|
| Electrical resistivity (ρ) | 51.5 nΩ·m |
| Electrical conductivity (%IACS) | ~ 33 % |
Heat treatments
Section titled “Heat treatments”Aluminum 7075 undergoes a solution treatment at temperatures of 460–480 °C for several hours, followed by water quenching and artificial aging. The T6 temper, which involves aging at 120 °C for 24 hours, provides the maximum hardness and strength of the alloy.
| Temper | Procedure | Result |
|---|---|---|
| O (annealed) | Annealing at 415 °C and controlled cooling | Ductile, low strength, excellent corrosion resistance |
| T6 | Solution at 460–480 °C, water quench, aged at 120 °C / 24 h | Maximum strength, hardness 150 HBW, elongation 5–8 % |
| T651 | T6 + stress relief by controlled stretching (1.5–3 %) | Similar to T6, reduction of residual stresses |
| T7 / T73 | Double aging: 100–120 °C several hours + 160–180 °C ≥ 24 h | Slight drop in strength, drastic improvement in resistance to stress corrosion cracking |
| RRA (retrogression and reage) | Retrogression at 200–260 °C followed by re-aging at 120 °C | Combines strength close to T6 with corrosion resistance similar to T73 |
Formability
Section titled “Formability”The cold formability of aluminum 7075 in temper O is acceptable, with an elongation of 10% allowing bending and light drawing operations. However, in temper T6 the elongation drops to 5–8% and the material exhibits high springback and risk of fracture. For complex geometries, hot forming or techniques such as retrogression forming are recommended, which raise the temperature above 200 °C to improve ductility.
Weldability
Section titled “Weldability”The weldability of aluminum 7075 is limited and it has a high tendency to hot cracking during fusion. The crack resistance coefficient is low, making arc welding processes (MIG, TIG) not recommended for critical structural applications. Joining by rivets, structural adhesives, or solid-state welding (friction stir welding) is preferred. If TIG welding is used with filler material (e.g., 4043 or 5356 alloy rod), a significant drop in strength in the heat-affected zone must be assumed, which can reduce the tensile strength to 50–60% of the T6 base material.
Corrosion resistance
Section titled “Corrosion resistance”The general corrosion resistance of aluminum 7075 is moderate, better than that of the 2xxx series but inferior to that of the 6xxx series. In temper O it shows adequate behavior in industrial and marine atmospheres. In temper T6 it is susceptible to stress corrosion cracking (SCC) when exposed to chloride environments with sustained stresses in the short transverse direction. The T73 temper largely corrects this susceptibility at the cost of a slight loss in strength (about 10–15% in yield strength compared to T6). For additional protection, anodizing, chemical conversion coatings (Alodine), or epoxy primer paints with corrosion inhibitors are used.
Applications by industry
Section titled “Applications by industry”Alloy 7075 is widely used in sectors where a high strength-to-weight ratio and good fatigue resistance are required.
| Industry | Typical applications | Most common temper |
|---|---|---|
| Aerospace | Stringers, frames, fittings, landing gear components, fuselages | T6, T651, T73 (humid or marine environments) |
| Defense | Light weapons, missile casings, structural components of armored vehicles | T6, T651 |
| Sports automotive | Engine mounts, suspension turrets, connecting rods | T6, T651 |
| Cycling and sports | Bicycle frames, derailleur pulleys, carabiners, climbing cams | T6, T651 |
| Molds and tooling | Mold plates and blocks for plastic injection and blow molding | T651 |
| Marine equipment | Deck fittings, masts of high-performance boats | T73 / T7 |
Comparison with similar materials
Section titled “Comparison with similar materials”Aluminum 7075 in T6 temper achieves a tensile strength around 540 MPa, compared to 310 MPa for aluminum 6061 T6 and 470 MPa for aluminum 2024 T3. Although its yield strength is the highest among conventional aluminum alloys, its elongation is lower (7% vs. 12% for 6061 T6), reflecting a more brittle behavior. Compared to alloy 7050, 7075 is slightly stronger in T6 but more susceptible to SCC; 7050 T74 offers better stress corrosion resistance and higher toughness, so it often replaces 7075 in critical aerospace components.
| Alloy / Temper | Tensile strength Rm (MPa) | Yield strength Rp0.2 (MPa) | Elongation A (%) | Stress corrosion resistance | Weldability |
|---|---|---|---|---|---|
| 7075 T6 | 510 – 570 | 430 – 500 | 5 – 9 | Susceptible | Very limited |
| 7075 T73 | 505 | 435 | 13 | Good | Limited |
| 7050 T74 | 510 – 570 | 420 – 460 | 10 – 11 | Excellent | Limited |
| 6061 T6 | 290 – 310 | 240 – 260 | 12 – 17 | Very good | Good |
| 2024 T3 | 470 – 480 | 325 – 345 | 18 – 20 | Poor | Very limited |
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the tensile strength of aluminum 7075 in temper T6?
Section titled “What is the tensile strength of aluminum 7075 in temper T6?”The tensile strength of aluminum 7075 T6 ranges between 510 and 570 MPa (74,000 – 83,000 psi), depending on the thickness and shape of the product.
How much does aluminum 7075 weigh compared to steel?
Section titled “How much does aluminum 7075 weigh compared to steel?”With a density of 2.81 g/cm³, aluminum 7075 weighs approximately 65% less than a typical carbon steel (7.85 g/cm³), while maintaining a specific strength comparable to many structural steels.
Can aluminum 7075 be welded without losing strength?
Section titled “Can aluminum 7075 be welded without losing strength?”There are no fusion welding processes that fully preserve the strength of 7075 in the joint. The weld strength is usually 50–60% lower than that of the T6 base metal, so mechanical joints (rivets) or friction stir welding are preferred.
What does temper T651 mean?
Section titled “What does temper T651 mean?”Temper T651 corresponds to a T6 treatment (solution, quench and artificial aging) to which a stress relief is added by controlled stretching of the order of 1.5 to 3%. It reduces residual stresses without significantly affecting static mechanical properties.
What is the maximum working temperature of aluminum 7075?
Section titled “What is the maximum working temperature of aluminum 7075?”The recommended maximum continuous working temperature for aluminum 7075 is 160 °C; above this temperature, the alloy in T6 temper undergoes overaging with loss of strength and hardness.
What hardness does aluminum 7075 have in T6 condition?
Section titled “What hardness does aluminum 7075 have in T6 condition?”The hardness of aluminum 7075 T6 is 150 HBW (Brinell) or 87 HRB (Rockwell B), values that decrease to 60 HBW in the annealed condition (temper O).