Overview of Aluminum 7075 Alloy
Aluminum 7075 is a heat-treatable alloy built on zinc, magnesium and copper, and it is one of the highest-strength aluminum grades available in commercial sheet, plate and extruded bar. After appropriate solution treatment and artificial ageing it reaches tensile strengths that overlap the lower range of alloy steels while retaining roughly one third of steel density. That combination is why 7075 is associated with airframe structures, highly loaded fittings and demanding mechanical components. The trade-off is a lower general corrosion resistance than the 6000 series and poor weldability, so the alloy is normally used in mechanically fastened or adhesively bonded assemblies rather than welded ones.
Density is approximately 2.81 g/cm3, elastic modulus about 71.7 GPa, and the alloy responds well to machining, giving bright finishes and stable dimensions when parts are stress-relieved before final cutting.
Chemical Composition
Nominal registered ranges for the alloy, in weight percent, are listed below. Composition control is the main reason the grade reaches its characteristic strength after ageing.
| Element | Content (wt%) | Role |
|---|---|---|
| Zinc (Zn) | 5.1 - 6.1 | Principal strengthening element with magnesium |
| Magnesium (Mg) | 2.1 - 2.9 | Forms the strengthening precipitates |
| Copper (Cu) | 1.2 - 2.0 | Raises strength, also lowers general corrosion resistance |
| Chromium (Cr) | 0.18 - 0.28 | Controls grain structure and stress-corrosion behaviour |
| Iron (Fe) | 0.50 max | Impurity; low levels protect toughness |
| Silicon (Si) | 0.40 max | Impurity |
| Manganese (Mn) | 0.30 max | Impurity, controlled for toughness |
| Titanium (Ti) | 0.20 max | Grain refiner |
| Others (each / total) | 0.05 / 0.15 max | Residual elements |
| Aluminum (Al) | Remainder | Matrix |
Mechanical Properties by Temper
The following typical longitudinal values illustrate how temper selection changes the property balance. Sheet and plate deliveries are commonly certified to ASTM B209/B209M, while extruded bar and profiles follow ASTM B221 and European equivalents such as EN 755-2; minimum values vary with product form and thickness.
| Temper | Yield strength Rp0.2 (MPa) | Tensile strength Rm (MPa) | Elongation (%) | Typical hardness (HBW) |
|---|---|---|---|---|
| O (annealed) | about 100 | about 230 | 17 | about 60 |
| T6 | about 500 | about 570 | 11 | about 150 |
| T651 (plate) | 470 min | 540 min | 9 min | about 150 |
| T73 / T7351 | about 435 | about 505 | 13 | about 135 |
T6 and T651 give the highest strength and are used where stiffness and load capacity dominate the design. T73 and T7351 are over-aged tempers that sacrifice roughly ten percent of strength in exchange for markedly better resistance to stress-corrosion cracking, which makes them the preferred choice for parts that carry sustained tensile stress in a corrosive environment.
Physical and Thermal Properties
| Property | Typical value |
|---|---|
| Density | 2.81 g/cm3 |
| Elastic modulus | 71.7 GPa |
| Melting range | about 477 - 635 degrees C |
| Thermal conductivity (25 degrees C) | about 130 W/(m.K) |
| Coefficient of thermal expansion | about 23.6 micrometre/(m.K), 20 - 100 degrees C |
| Electrical conductivity | about 33 percent IACS |
Machining, Forming and Joining
Machining. Rated fair to good. Sharp positive-rake tooling, high spindle speed and ample chip evacuation produce excellent surface finish; rough machining followed by a stress-relief pause and a light finishing cut minimises distortion of thin sections.
Forming. Formability in T6 is limited, so tight bends are normally produced in the annealed condition and aged afterwards, or by hot forming.
Welding. Generally not recommended. Fusion welding loses a large part of the parent-metal strength in the heat-affected zone and raises cracking risk; riveting, bolting and adhesive bonding are the usual joining methods.
Corrosion protection. Anodizing, chemical conversion coating and primer systems improve durability, and bare surfaces should not be left in contact with dissimilar metals in wet service.
Surface finish. The alloy polishes and takes protective coatings well, which is why it is used for moulds and precision tooling that demand both hardness and a fine finish.
Typical Applications
Aircraft wing skins, stringers, frames, fuselage components and landing-gear parts
Aerospace and defence fittings and brackets carrying high concentrated loads
High-performance bicycle frames, components and sports equipment
Moulds and tooling that require high hardness combined with polishability
Precision machine parts, gears, shafts and prototype hardware
Marine hardware only when protected against corrosion and isolated from other metals
FAQ
Q: What makes 7075 stronger than most other aluminum alloys?
Its zinc, magnesium and copper content forms a dense distribution of fine precipitates during artificial ageing, which blocks dislocation movement and produces very high yield strength in T6 and T651 tempers.
Q: When should T73 or T7351 be chosen instead of T6?
When a part carries sustained tensile stress in a corrosive environment or where stress-corrosion cracking would be a safety concern. The over-aged temper gives noticeably better cracking resistance at a modest strength penalty.
Q: Can 7075 be welded?
Fusion welding is not recommended because the heat-affected zone loses strength and becomes crack sensitive. Mechanical fastening, bonding or a change to a weldable alloy such as 6061 should be considered instead.
Q: How does 7075 compare with 6061?
7075 offers considerably higher strength, while 6061 provides better corrosion resistance, weldability, formability and lower cost. General fabrication usually favours 6061, and weight-critical high-stress parts usually favour 7075.
Q: Does 7075 resist salt water?
It is the least corrosion-resistant of the common high-strength alloys. With suitable coating, anodizing and isolation from dissimilar metals it can be used in marine environments, but unprotected exposure is not advised.
Q: What product forms are available?
Sheet, plate, extruded bar, rod and profiles are standard, with plate commonly supplied in T651 and extruded products in T6 or T6511 depending on the mill and the ordered dimension.
