Aluminum 7075-T6 is a aluminum alloy used in aerospace applications. Melting point: 477 °C. Tensile strength: 572 MPa.
Aluminum 7075-T6 is one of the strongest aluminum alloys you can buy, with strength approaching that of many steels while weighing only about a third as much. That trade has made it a workhorse of rockets and aircraft since the 1940s.
Quick facts
- What it is: A high-strength aluminum alloy. The “7075” marks it as a 7000-series alloy whose main added ingredient is zinc (along with magnesium and copper).
- Main ingredients: Roughly 5.6-6.1% zinc, 2.1-2.5% magnesium, and 1.2-1.6% copper, with the rest aluminum plus trace amounts of other elements.
- Strength: Ultimate tensile strength (the pull it can take before breaking) of about 510-570 MPa, or 74,000-83,000 psi.
- Density: 2.81 grams per cubic centimeter, about one-third the weight of steel.
- Stiffness: Young’s modulus of about 71.7 GPa (a measure of how much it resists flexing).
- Hardness: About 150 HB / 87 HRB.
- First made: Developed by Sumitomo Metal in Japan in 1935, reverse-engineered by Alcoa in 1943, and standardized for aerospace use in 1945.
What it is and how it works
An alloy is a metal blended with other elements to improve it, and 7075 owes its strength to a process called precipitation hardening (also called age hardening). The “T6” part of the name is the recipe used to reach peak strength.
That recipe has three steps. First the metal is solution heat-treated, meaning it is heated to around 450 C so the alloying elements dissolve and spread evenly through it. Then it is quenched, or cooled very quickly. Finally it is artificially aged, held at about 120 C for roughly 24 hours. During aging, tiny zinc-magnesium particles called precipitates form throughout the metal, including along the boundaries between its crystal grains.
Those particles are nanoscale, far too small to see, but they do something important: they block the movement of dislocations, the tiny defects that let a soft metal slip and bend. Picture a crowd trying to shuffle across a field; scatter thousands of posts across it and movement grinds to a halt. That blocking action is what makes 7075-T6 so much stronger and harder than the same alloy in its soft, freshly quenched state.
The same zinc-rich structure has a downside. It makes 7075 hard to weld, because welding heat destroys the carefully built temper and leaves the joint crack-prone, and it makes the alloy prone to stress-corrosion cracking, where stress and a corrosive environment combine to split the metal over time. For that reason, parts are usually machined from solid blocks or plate and joined with rivets and bolts rather than welds. Corrosion is held off with anodizing or with “Alclad,” a thin pure-aluminum coating bonded to the surface.
Why it matters
In a rocket or an aircraft, every kilogram of structure is a kilogram that cannot be payload, so engineers chase the most strength for the least mass. With near-steel strength at roughly a third the density, 7075-T6 offers an outstanding strength-to-weight ratio, along with good resistance to fatigue (cracking from repeated stress) and easy machining. That combination made it a foundational material for high-stress, weight-sensitive parts.
It also resists corrosion better than the 2000-series copper-based aerospace alloys. Because of its sensitivity to stress-corrosion cracking, though, engineers often choose over-aged tempers such as T73 or T7351 when long-term durability matters more than absolute peak strength, accepting a little less strength in exchange for much better resistance. A close relative, the copper-based alloy 2024, is generally less strong but tougher against crack growth, so the two are often used in complementary roles on the same vehicle.
Where it is used
On the Saturn V moon rocket, the first stage’s forward skirt and thrust-structure skin were built from corrugated 7075-T6 panels stiffened with rings, frames, and stringers, and the second stage used 7075 in its skirt and interstage structures. The Space Shuttle used the alloy in solid rocket booster nozzle and external-tank-related components.
Its aviation history runs even deeper. The Mitsubishi A6M Zero was the first mass-production aircraft to use the original 7075 alloy in its airframe, the very application that prompted Alcoa to reverse-engineer it. Today 7075 remains widespread in aircraft wing and fuselage structure, helicopter rotor components, missile and satellite frames, and the structural fittings and brackets found across modern launch vehicles.
Al 87.1-91.4%, Zn 5.1-6.1%, Mg 2.1-2.9%, Cu 1.2-2.0%, Cr 0.18-0.28%
| DENSITY | 3 kg/m³ |
| TENSILE STRENGTH | 572 MPa |
| YIELD STRENGTH | 503 MPa |
| STRENGTH-TO-WEIGHT | 203558.7 kN·m/kg |
| MELTING POINT | 477 °C |
| MAX SERVICE TEMPERATURE | 150 °C |
| THERMAL CONDUCTIVITY | 130 W/m·K |
| THERMAL EXPANSION | 23.6 µm/m·K |
| CATEGORY | Aluminum Alloy |
| DESIGNATIONS | UNS A97075, AMS 4045, AMS 4078 |
| MANUFACTURER | Alcoa / Arconic |
| DENSITY | 3 kg/m³ |
| TENSILE STRENGTH | 572 MPa |
| YIELD STRENGTH | 503 MPa |
| MELTING POINT | 477 °C |
| MAX SERVICE TEMP | 150 °C |
| THERMAL CONDUCTIVITY | 130 W/m·K |
| THERMAL EXPANSION | 23.6 µm/m·K |
| CORROSION RESISTANCE | Fair |
| WELDABILITY | Poor |
| MACHINABILITY | Good |
| COST RATING | Low |
