All About 7075 Aluminum Alloy
Learn more about 7075 aluminum alloy and how it's used in manufacturing.
7075 aluminum employs a high zinc content and achieves some significant improvements in performance over other contemporary grades. It has very good mechanical properties such as: tensile strength, ductility, toughness, and fatigue resistance. 7075 aluminum is quite susceptible to embrittlement because of microsegregation (relatively poor homogeneity), but greatly improves the corrosion resistance of the 2000 series alloys. It is widely employed in highly stressed structural applications, particularly in the structural parts of aircraft.
7075 aluminum was first developed by Sumitomo Metal in Japan in 1935 and was heavily employed in military aircraft production. It was reverse engineered by Alcoa in the US in 1943 and was a significant component in the rapid improvement in military aircraft design among the Allies.
This article will discuss the composition of 7075 aluminum alloy, its characteristics, material properties, and applications.
What is Aluminum Alloy?
Aluminum alloys are metals that consist primarily of aluminum and are combined with small percentages of other elements, such as: silicon, copper, magnesium, tin, and manganese. The combination results in the alterations of the properties of aluminum. This alteration is generally produced by a combination of lattice strain from “misfit” atoms and modified crystalline structures by precipitation processes or by directly influencing grain growth.
Alloy Composition of 7075 Aluminum
The alloy composition of 7075-grade aluminum alloy is: 87.1–91.4 % aluminum, 5.1–6.1 % zinc, 1.2–2.0 % copper, 0.0–0.3 % manganese, 0.0–0.4 % silicon, 0.0–0.5 % iron, 2.1–2.9 % magnesium, 0.18–2.0 % chromium, 0.0–0.2 % titanium, and 0.05–0.15 % of other elements. These small amounts of modifying elements each have particular desirable influences, either alone or in concert with others.
Characteristics of 7075 Aluminum
The characteristics of 7075 aluminum are: high strength, average corrosion resistance, and poor weldability. 7075 aluminum was the first aluminum alloy to benefit from the combination of high zinc content and relatively high chromium content. Zinc has dual effects in that it assists with precipitation hardening but at elevated levels in this alloy and delivers higher yield stress and ultimate tensile strength. It is speculated that research models indicate that zinc enhances strength by inhibiting partial dislocation. The relatively high chromium content reduces crystal growth, enhancing ductility and toughness.
7075 alloy, also known as aircraft aluminum or aviation aluminum, is widely used for structural parts and skin elements. Structural parts tend to be T651 temper, whereas skin sheets are generally T6 temper. Fatigue resilience is similar to 2000-series alloys, making 7075 aluminum ideal for most aircraft and the structural components of rockets.
| Property | 7075-O | 7075-T6-T62 | 7075-T73 |
|---|---|---|---|
Property Density | 7075-O 2.7–2.85 g/cm3 | 7075-T6-T62 2.7–2.85 g/cm3 | 7075-T73 2.7–2.85 g/cm3 |
Property Tensile strength | 7075-O 228 MPa | 7075-T6-T62 572 MPa | 7075-T73 505 MPa |
Property Yield strength | 7075-O 103 MPa | 7075-T6-T62 503 MPa | 7075-T73 435 MPa |
Property Modulus of elasticity | 7075-O 71.7 GPa | 7075-T6-T62 71.7 GPa | 7075-T73 72.4 GPa |
Property Brinell hardness - 500g weight, 10 mm ball | 7075-O 60 | 7075-T6-T62 150 | 7075-T73 128 |
Property Elongation at break (12.7 mm test piece) | 7075-O 16% | 7075-T6-T62 19% | 7075-T73 5% |
Property Shear modulus | 7075-O 26.9 GPa | 7075-T6-T62 26.9 GPa | 7075-T73 27 GPa |
Property Shear strength | 7075-O 152 GPa | 7075-T6-T62 331 MPa | 7075-T73 296 GPa |
Property Fatigue strength | 7075-O N/A MPa | 7075-T6-T62 159 MPa | 7075-T73 117 MPa |
Property Thermal expansion coefficient | 7075-O 23.6 µm/m°C | 7075-T6-T62 23.6 µm/m°C | 7075-T73 23.2 µm/m°C |
Property Solidus | 7075-O 477 °C | 7075-T6-T62 477 °C | 7075-T73 477 °C |
Property Liquidus | 7075-O 635 °C | 7075-T6-T62 635 °C | 7075-T73 635 °C |
Property Annealing temperature | 7075-O 413 °C | 7075-T6-T62 413 °C | 7075-T73 413 °C |
Property Solution temperature | 7075-O 466–482 °C | 7075-T6-T62 466–482 °C | 7075-T73 256 °C |
Property Thermal conductivity | 7075-O 173 W/mK | 7075-T6-T62 130 W/mK | 7075-T73 151 W/mK |
Property Specific heat capacity | 7075-O 0.96 KJ/Kg°C | 7075-T6-T62 0.96 KJ/Kg°C | 7075-T73 0.96 KJ/Kg°C |
Where 7075 Aluminum Alloy Is Used
7075 aluminum is widely employed in the aerospace sector as it offers among the highest strength-to-weight ratios available. It is used both in structural members and in aircraft skins, although this use is diminishing in favor of some 6000-series alloys. Other common uses for 7075 aluminum are in the manufacture of rock climbing gear and bicycle components, and as a key material in the US military M16 rifle. It is one of the backing materials used in ceramic composite armor of military vehicles because of its high strength-to-weight ratio and good corrosion resistance.
What To Consider When Choosing an Aluminum Grade
The factors to consider in choosing an aluminum grade are:
- Strength: Can the design accommodate the volume of material required to deliver the required strength?
- Fatigue Resistance: While many aluminum grades are resilient for aluminum, there are better, non-aluminum options, if fatigue exposure is extreme.
- Processing: Not all processes are suitable for all alloys. So, for example, the need for minimum weight may drive the use of forging for a component.
- Construction: If a structure requires welding to form the assembly of parts, some alloys are suited to this while others are ruled out.
- Corrosion: Several aluminum alloys offer poor corrosion resistance. They can be ruled out of wet and, particularly, marine applications—whereas others are well suited to long-term (mildly) corrosive environments.
- Damage Resilience: Life-critical structures that are at risk of major failure must be designed to withstand partial failure without cascading into total collapse. Some grades offer considerably higher elongation at a break along with high strength; when the unthinkable happens, they are more likely to survive damage, which can save lives.
- Cosmetics: Some grades are better suited than others for aesthetically pleasing surfaces and parts.
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