Young’s modulus, also called the modulus of elasticity, measures a material’s resistance to elastic deformation under tensile or compressive loading.
The Young’s modulus of aluminum is approximately 69 GPa, or 10,000 ksi, at room temperature.
Most common aluminum alloys have values between approximately 68.9 and 73.1 GPa. Alloy composition causes small differences, while heat treatment has a much greater effect on strength than stiffness.
This article explains the Young’s modulus of aluminum, common alloy values, influencing factors, testing methods, and comparisons with other engineering metals.
Definition and Formula of Young’s Modulus
Young’s modulus describes the relationship between normal stress and normal strain within the linear elastic region.
The basic formula is:
E = σ / ε
Where:
- E is Young’s modulus
- σ is tensile or compressive stress
- ε is axial strain
Stress is calculated by dividing the applied force by the original cross-sectional area:
σ = F / A
Strain is the change in length divided by the original length:
ε = ΔL / L₀
A material with a higher Young’s modulus experiences less elastic deformation under the same stress.
A material with a lower Young’s modulus stretches or compresses more under the same load.
Young’s modulus applies only to the elastic region. Once the applied stress exceeds the yield strength, permanent deformation begins.
Example
Consider a 6061-T6 aluminum bar subjected to a tensile stress of 100 MPa.
Using a Young’s modulus of 68.9 GPa:
ε = σ / E
- ε = 100 MPa / 68,900 MPa
- ε = 0.00145
The elastic strain is approximately 0.145%.
If the original bar length is 500 mm:
ΔL = ε × L₀
- ΔL = 0.00145 × 500
- ΔL ≈ 0.73 mm
The bar will return to its original length after unloading, provided the stress remains below its elastic limit.
Young’s Modulus of Aluminum
Commercially pure aluminum has a Young’s modulus of approximately 68–69 GPa at room temperature.
This value can also be expressed as:
- 68,000–69,000 MPa
- 9.9–10.0 × 10⁶ psi
- 9,900–10,000 ksi
Compared with many structural metals, aluminum has a relatively low elastic modulus.
This means an aluminum component will deform more than a steel component with the same dimensions and applied load.
However, aluminum has a density of approximately 2.70 g/cm³. Its low weight allows larger or more efficient cross-sections to be used without excessive mass.
The tensile and compressive moduli of aluminum are close, although some material data sheets list the compressive modulus slightly higher than the tensile value.
Young’s Modulus of Common Aluminum Alloys
The Young’s modulus of most commercial aluminum alloys falls within a narrow range.
| Aluminum Alloy | Temper | Young’s Modulus | Typical Use |
|---|---|---|---|
| Commercially Pure Aluminum | — | 68–69 GPa | Electrical products, chemical equipment and formed parts |
| 6061 | T6 | 68.9 GPa | Structural parts, machined components and general fabrication |
| 6063 | T6 | 68.9 GPa | Architectural and industrial extruded profiles |
| 6082 | T6 | 70.0 GPa | Structural sections and machined components |
| 5083 | H116 | 70.3 GPa | Marine structures, tanks and welded assemblies |
| 7075 | T6 | 71.7 GPa | High-strength aerospace and mechanical components |
| 2024 | T3 | 73.1 GPa | Aircraft structures and fatigue-resistant components |
The differences between common aluminum alloys are relatively small.
For example, 7075-T6 has much higher yield and tensile strength than 6061-T6. However, its Young’s modulus is only about 4% higher.
This means replacing 6061 with 7075 may greatly increase strength, but it will not produce an equally large reduction in elastic deflection.
Young’s Modulus Comparison with Other Metals
Aluminum is less stiff than steel, titanium, and copper, but stiffer than common magnesium alloys.
| Material | Representative Young’s Modulus | Density |
|---|---|---|
| Magnesium Alloy | 44–45 GPa | Approximately 1.8 g/cm³ |
| Aluminum Alloy | 69–73 GPa | Approximately 2.70 g/cm³ |
| Titanium Grade 5 | 113.8 GPa | Approximately 4.43 g/cm³ |
| Copper C10100 | Approximately 117 GPa | Approximately 8.94 g/cm³ |
| Carbon Steel | Approximately 205 GPa | Approximately 7.85 g/cm³ |
Carbon steel has a Young’s modulus close to three times that of aluminum.
Under the same stress, an aluminum part will therefore experience approximately three times the elastic strain of a similar steel part.
However, steel is also almost three times as dense. Aluminum remains useful where low weight, corrosion resistance, formability, and structural efficiency are important.
Titanium is stiffer than aluminum but has a higher density and cost.
Magnesium is lighter than aluminum but has a lower Young’s modulus.
Young’s Modulus vs Yield Strength
Young’s modulus and yield strength describe different material properties.
Young’s modulus measures stiffness. It indicates how much a material deforms elastically under an applied stress.
Yield strength measures resistance to permanent deformation. It indicates when the material begins to retain deformation after unloading.
Heat treatment can greatly increase the yield strength of aluminum without causing a similar increase in Young’s modulus.
For example, 6061-O and 6061-T6 have very different strengths, but both have a Young’s modulus of approximately 68.9 GPa.
A higher-strength aluminum alloy is therefore not necessarily much stiffer.
Factors Affecting Young’s Modulus of Aluminum
Several factors can influence the measured or effective Young’s modulus of aluminum.
Temperature
Young’s modulus generally decreases as temperature rises.
Higher temperatures increase atomic vibration and reduce the resistance of the metallic bonds to elastic deformation.
At cryogenic temperatures, the elastic modulus normally increases.
For elevated-temperature calculations, room-temperature values should not be used without correction.
Therefore, aero-engine components (such as compressor blades) should be made of 7xxx series aluminum alloys, which have a better modulus retention rate (approximately 85%) at 150°C than 6xxx series (approximately 75%).
Alloy Composition
Copper, magnesium, silicon, zinc, lithium, and other alloying elements can change the elastic modulus.
The effect is usually modest in conventional aluminum alloys.
Most common wrought grades remain within the approximate range of 69–73 GPa.
Temper and Heat Treatment
Annealing, solution heat treatment, and artificial aging strongly affect strength and hardness.
Their effect on Young’s modulus is much smaller.
This is why different tempers of the same alloy often use the same nominal modulus value.
Manufacturing Direction
Rolling, extrusion, forging, and other forming processes can create crystallographic texture.
This may produce small differences between longitudinal and transverse measurements.
For general calculations, wrought aluminum is often treated as isotropic. Direction-specific data may be required for precision analysis.
Porosity and Defects
Voids, casting porosity, cracks, and weak interfaces can reduce the effective stiffness of a component.
The intrinsic modulus of the aluminum matrix may remain unchanged, but the measured stiffness of the part can be lower.
This effect is more important in porous materials, castings, foams, and metal-matrix composites.
Applications and Engineering Significance
Young’s modulus is important whenever the elastic deformation of an aluminum component must be estimated.
Common applications include:
- Structural aluminum frames
- Extruded profiles and beams
- Aerospace and automotive components
- CNC-machined housings and brackets
- Tubes, plates, and support structures
- Precision instruments and fixtures
- Building façades and curtain-wall systems
Young’s modulus is used to calculate axial elongation, beam deflection, elastic buckling, vibration behavior, and structural stiffness.
It should be considered together with part geometry, wall thickness, load direction, support conditions, and yield strength.
In many aluminum structures, changing the cross-sectional geometry has a greater effect on stiffness than changing between conventional aluminum alloys.
Measurement Methods
Young’s modulus can be measured using static or dynamic methods.
Tensile Test
A tensile specimen is loaded while an extensometer measures axial strain.
Young’s modulus is calculated from the slope of the linear section of the stress–strain curve.
This is the most common method for metals.
Accurate strain measurement is important because the elastic strain range is small.
Compression Test
A specimen is compressed while the applied stress and axial strain are recorded.
The compression modulus is calculated from the initial linear stress–strain relationship.
For aluminum alloys, the compression modulus may be slightly higher than the tensile modulus.
Resonance Testing
A specimen is excited at its natural resonant frequencies.
The dynamic Young’s modulus is calculated from specimen geometry, mass, and resonant frequency.
Dynamic modulus values may differ slightly from static tensile values.
Ultrasonic Testing
The velocity of longitudinal and shear waves through the material can be used to calculate elastic constants.
Ultrasonic testing is non-destructive and useful for material characterization and quality control.
ASTM E111 provides a standard method for determining Young’s modulus, tangent modulus, and chord modulus of structural materials.
Young’s Modulus and Shear Modulus
Young’s modulus describes resistance to axial tensile or compressive deformation.
Shear modulus describes resistance to angular or shear deformation.
For an isotropic material, the relationship is:
E = 2G(1 + ν)
Where:
- E is Young’s modulus
- G is shear modulus
- ν is Poisson’s ratio
For aluminum, typical values are:
- Young’s modulus: approximately 69 GPa
- Shear modulus: approximately 26 GPa
- Poisson’s ratio: approximately 0.33
These values are related, but they are not interchangeable.
Summary
The Young’s modulus of aluminum is approximately 69 GPa, or 10,000 ksi, at room temperature.
Most common aluminum alloys have values between approximately 68.9 and 73.1 GPa.
6061-T6 and 6063-T6 are approximately 68.9 GPa.
6082-T6 is approximately 70 GPa.
7075-T6 is approximately 71.7 GPa.
2024-T3 is approximately 73.1 GPa.
Aluminum is less stiff than steel, titanium, and copper, but its low density provides useful stiffness-to-weight performance.
Alloying and heat treatment can greatly change aluminum strength. Their effect on Young’s modulus is comparatively small.
FAQs
What is the Young’s modulus of aluminum?
The Young’s modulus of aluminum is approximately 69 GPa, or 10,000 ksi, at room temperature.
What is the Young’s modulus of 6061 aluminum?
6061-T6 aluminum has a typical Young’s modulus of 68.9 GPa, or 10,000 ksi.
What is the Young’s modulus of 6063 aluminum?
6063-T6 aluminum has a typical Young’s modulus of 68.9 GPa, or 10,000 ksi.
What is the Young’s modulus of 7075 aluminum?
7075-T6 aluminum has a typical Young’s modulus of 71.7 GPa, or 10,400 ksi.
What is the Young’s modulus of 2024 aluminum?
2024-T3 aluminum has a typical Young’s modulus of 73.1 GPa, or 10,600 ksi.
Does heat treatment increase the Young’s modulus of aluminum?
Heat treatment has only a small effect on Young’s modulus. It has a much greater effect on yield strength, tensile strength, and hardness.
Is aluminum more elastic than steel?
Aluminum has a lower Young’s modulus than steel, so it experiences more elastic deformation under the same stress. This does not mean it can always withstand more deformation before yielding.
