7075 Aluminum Density: High-Strength Alloy Data and Aerospace Applications

Of all the aluminum alloys I work with, 7075 is the one that prompts the most questions from engineers and buyers who are new to it. Not about corrosion resistance or machinability — those questions come later. The first question is almost always a version of: “It’s denser than 6061, right? So why would I pay a premium for a heavier alloy?”

That question contains a legitimate engineering premise — 7075 is the densest of the common commercial aluminum alloys — and a critical conceptual error. Density per cubic meter is not the same metric as density per unit of strength delivered. When you run the correct comparison, 7075’s density premium is one of the best bargains in structural materials engineering.

I’ll give you the exact values, the chemistry behind them, and the framework that explains every major aerospace component choice that has used this alloy for the past seventy years.

7075 Aluminum Density: The Values in Every Unit System

The density of 7075 aluminum is 2,810 kg/m³.

Source: Aluminum Association, Aluminum Standards and Data; ASM Handbook, Vol. 1.

And For data source, please refer to the Metal Density Chart.

7075 is the densest aluminum alloy you will routinely encounter in precision fabrication and structural aerospace work. It is 110 kg/m³ heavier than 6061 (2,700 kg/m³) and 130 kg/m³ heavier than 5052 (2,680 kg/m³). Both differences are real, measurable, and predictable — and I will show exactly why in the next section.

These density values apply uniformly across all 7075 tempers: T6, T651, T73, T7351, T76, and T7651. The temper designations describe very different heat treatment histories with significant implications for strength, corrosion resistance, and stress-corrosion cracking behavior. None of them changes the mass per unit volume.

Why 7075 Aluminum Density Is the Highest Among Common Alloys

The explanation is zinc. Everything else follows from that.

7075’s composition — and the zinc effect

Per ASTM B209, the chemical composition of 7075 aluminum is:

The density story in 7075 is a three-way contest. Zinc (7,133 kg/m³) and copper (8,960 kg/m³) both push density upward — each is more than 2.5× denser than aluminum. Magnesium (1,738 kg/m³) pulls it downward. But the upward forces win because zinc is present at 5.1–6.1% — a far higher concentration than any other major alloying element in the 7xxx system.

Working through the calculation at mid-range composition (5.6% Zn, 2.5% Mg, 1.6% Cu, 0.23% Cr):

• Aluminum contribution: 0.9017 × 2,700 = 2,435 kg/m³
• Zinc contribution: 0.056 × 7,133 = 399 kg/m³
• Magnesium contribution: 0.025 × 1,738 = 43 kg/m³
• Copper contribution: 0.016 × 8,960 = 143 kg/m³
• Chromium contribution: 0.0023 × 7,190 = 17 kg/m³
• Sum: 2,435 + 399 + 43 + 143 + 17 = 3,037 kg/m³

Wait — the arithmetic gives 3,037, but the measured value is 2,810. Why the discrepancy?

The simple linear rule of mixtures overestimates density in solid solution alloys because the alloying elements don’t simply occupy additive volumes in the crystal lattice. When zinc dissolves into aluminum’s face-centered cubic structure, it substitutes into lattice sites rather than inserting between them. The actual atomic volume change is smaller than the linear estimate predicts. The measured value — 2,810 kg/m³ — is what you confirm on a calibrated densitometer, and it’s what the Aluminum Association certifies. The rule-of-mixtures calculation is useful for understanding the direction and magnitude of density change, but the measured value is what you use.

What it does confirm clearly: zinc is the dominant contributor, pushing 7075 above pure aluminum’s 2,700 kg/m³. No other common aluminum alloy carries this much zinc.

How 7075 compares to all common aluminum alloys

7075 and 2024 are the two densest alloys in the table, both because their principal alloying elements (zinc and copper, respectively) are significantly denser than aluminum. 7075 leads because zinc is present at higher concentrations than copper in 2024 (5.1–6.1% vs. 3.8–4.9%).

7075 Tempers, Density, and Why the Choice Between T6 and T73 Is Not About Weight

7075 has one of the most important temper selection decisions in the aluminum alloy system. Understanding it matters to anyone who specifies or fabricates this material.

The four principal temperaments and their implications

Source: Aluminum Association, Aluminum Standards and Data; ASM Handbook, Vol. 1.

Every single row shows 2,810 kg/m³. Temper changes the distribution and morphology of MgZn₂ precipitates in the microstructure — T6 peak-ages for maximum strength; T73 over-ages to dissolve continuous precipitate films at grain boundaries and improve stress-corrosion cracking resistance. Neither process adds or removes atoms. The mass per unit volume is invariant.

The critical decision point: T6 vs. T73 is an application choice, not a weight choice.

T6 maximizes strength: 572 MPa tensile, 503 MPa yield. It is susceptible to stress-corrosion cracking (SCC) in chloride environments under sustained tensile stress. For aerospace interior structural brackets, machined fittings, and tooling components that are not exposed to moisture under stress, T6 is the standard specification.

T73 sacrifices approximately 12% of tensile strength (503 vs. 572 MPa) in exchange for dramatically improved SCC resistance. For components in marine environments, fuel system hardware, or structures subject to sustained stress in humid conditions, T73 or T7351 is the correct specification. The weight calculation uses 2,810 kg/m³ regardless of which you choose.

I make this point explicitly because I’ve received drawings where the engineer selected T73 and then tried to compensate for the strength reduction by over-specifying wall thickness — adding mass to recover the strength that T6 would have delivered at lower weight. The right answer is to choose the temper for the environment and design for the T73 mechanical properties from the start.

7075 Aluminum Density in kg/m³: The SI Value for Engineering Calculations

The SI density of 7075 aluminum is 2,810 kg/m³.

Weight formula in SI units:

Weight (kg) = Length (m) × Width (m) × Thickness (m) × 2,810

Worked example — a 7075-T651 plate for aerospace bracket machining, 600 mm × 400 mm × 20 mm:

Weight = 0.600 × 0.400 × 0.020 × 2,810 = 13.5 kg

The same blank in 6061-T651 would weigh:

0.600 × 0.400 × 0.020 × 2,700 = 13.0 kg

The difference: 0.5 kg per plate blank — a 3.9% weight premium to work with 7075. The question every aerospace engineer asks next is: what strength am I buying with that 0.5 kg?

7075 Aluminum Density in lb/in³: The Imperial Reference Value

The density of 7075 aluminum in lb/in³ is 0.102 lb/in³.

Weight formula in imperial units:

Weight (lb) = Length (in) × Width (in) × Thickness (in) × 0.102

Worked example — a 7075-T6 structural plate, 24 in × 12 in × 0.5 in:

Weight = 24 × 12 × 0.5 × 0.102 = 14.69 lb

The same plate in 6061-T6 (0.0975 lb/in³): 14.04 lb. Difference: 0.65 lb, or 4.6%.

Quick reference: 7075 lb/in³ values by temper are identical. T6, T73, T651, T7351 — all 0.102 lb/in³.

The Specific Strength Argument: Why Aerospace Accepts 7075’s Density Premium

This is the core of the 7075 story, and it’s what most density articles — which list the number and move on — completely miss.

Density per unit volume tells you how heavy a given piece of material is. For structural applications, the relevant metric is specific strength: how much load-carrying capability you get per unit mass. This is the number that determines whether a heavier material is actually a weight penalty in a real structure.

7075 vs. 6061: the specific strength calculation

7075-T6 delivers 0.204 kN·m/kg — nearly 1.77× the specific strength of 6061-T6. That means for a given structural load, a 7075 component can be designed lighter — with thinner walls or smaller cross-sections — than a 6061 component carrying the same load. The density premium of 4.1% is more than offset by the strength premium of 85%.

To make this concrete with a real calculation: suppose an aerospace bracket requires a tensile load-bearing cross-section of 100 mm² in 6061-T6 to safely carry a 31,000 N load (using the 310 MPa tensile strength). The same load in 7075-T6 requires only:

31,000 N ÷ 572 MPa = 54 mm² cross-sectional area

The 7075 bracket uses 46% less material cross-section. Even after applying the density correction (2,810 ÷ 2,700 = 1.041), the 7075 bracket is approximately 45% lighter for the same structural capacity. That is why the fuselage frames, wing spars, and structural fittings of every commercial aircraft that has flown in the past fifty years use 7075 or equivalent high-strength aluminum alloys, not 6061.

Where density actually limits 7075

The specific strength argument is compelling, but it has limits that honest engineering writing must acknowledge.

Stiffness-governed designs. Specific strength only wins when the design is governed by strength (stress against material failure). If the design is governed by stiffness (deflection under load), then specific stiffness — Young’s modulus divided by density — is the relevant metric. And here, 7075 and 6061 are virtually identical:

• 6061 Young’s modulus: ~68.9 GPa ÷ 2,700 kg/m³ = 25.5 GPa·m³/Mg
• 7075 Young’s modulus: ~71.7 GPa ÷ 2,810 kg/m³ = 25.5 GPa·m³/Mg

The two alloys have effectively identical specific stiffness. For a long, slender beam where deflection governs the design, 7075 offers no structural advantage over 6061 — the stronger material cannot be made stiffer per unit mass. In those applications, the extra density and cost of 7075 buys nothing.

Weldability. 7075 is generally not weldable by conventional fusion processes. Solidification in the weld zone produces hot cracking due to the wide freezing range of the Zn-Mg-Cu alloy system. This rules out post-assembly welding and limits the geometries that can be produced in 7075. Mechanically fastened assemblies — bolted, riveted — are the standard. For applications requiring welded assemblies from high-strength aluminum, 2024 or 6061 is typically preferred.

Corrosion resistance. In the T6 temper, 7075 has relatively poor resistance to SCC and general corrosion in chloride environments. Anodizing or alclad cladding is required for outdoor or marine applications. This is not a density issue — but it’s the kind of honest limitation that design engineers need when they’re evaluating material options.

7075 Aluminum Density in Laser Cutting and Precision Fabrication

We cut 7075 in our facility — primarily for aerospace fixture plates, tooling components, and structural brackets that require tight tolerances and will be machined after cutting. The density of 2,810 kg/m³ shows up in every part of the workflow, from sheet weight on the lift table to the final part weight callout on the drawing.

A few observations that only come from cutting 7075 regularly:

Sheet handling. A 7075-T651 plate at 12 mm thickness and standard 1,220 × 2,440 mm size weighs approximately 100 kg — about 4 kg heavier than the equivalent 6061 plate. That doesn’t change our handling procedure, but it does factor into stack height limits for storage and the forklift capacity calculation for loaded pallets.

Cut quality. 7075 cuts similarly to 6061 on a fiber laser. The alloy is harder in T6 temper (Brinell hardness approximately 150 HB vs. 95 HB for 6061-T6), but laser cutting is a thermal process, and hardness has less influence on cut quality than it would in a saw or punch operation. What matters for edge quality in 7075 is assist gas pressure and focal position — nitrogen assist at high pressure produces clean, oxide-free edges suitable for subsequent anodizing.

Post-cut considerations for aerospace work. This is the point most overlooked in 7075 laser cutting: if the part will be used in a T6 application, the material must arrive in T651 (solution-treated and artificially aged, stress-relieved) condition before cutting. Laser cutting does not change the bulk material’s density or mechanical properties at a distance from the cut edge — but the narrow heat-affected zone at the cut face does alter the local microstructure. For aerospace structural applications with tight mechanical property requirements on the cut edge, discuss post-cut treatment with your design engineer. For tooling fixtures, frames, and bracket applications where edge properties are secondary to dimensional accuracy, cut-edge HAZ in 7075 is not a concern in our experience.

International Designations for 7075 Aluminum

7075 appears under different names in different standards systems, but the density is always 2,810 kg/m³.

Source: Michael Smith Engineers Grade Comparison Table (DIN/BS/USA/Japan).

AlZn5.5MgCu is the DIN name you’ll see most often on European aerospace drawings and machining specifications. The “Zn5.5” in the name references approximately 5.5% zinc — directly in the middle of the 5.10–6.10% ASTM range. When a European supplier or customer specifies AlZn5.5MgCu, they mean 7075, and the density is 2,810 kg/m³ without qualification.

Data source: Aluminum Density Complete Reference

Frequently Asked Questions About 7075 Aluminum Density

Q: What is the density of 7075 aluminum in g/cm³? 2.81 g/cm³. This is the Aluminum Association standardized value, consistent across all tempers (O, T6, T73, T651, T7351). It is the highest density among common commercial aluminum alloys, driven by the 5.1–6.1% zinc content.

Q: What is the density of 7075-T6 specifically? 2,810 kg/m³ (2.81 g/cm³, 0.102 lb/in³) — identical to 7075-O, T73, T651, and all other tempers. T6 peak-ages for maximum strength (tensile 572 MPa, yield 503 MPa); T73 over-ages for stress-corrosion cracking resistance at slightly lower strength. The density does not change between tempers.

Q: How does 7075 aluminum density compare to 6061? 7075 is 2,810 kg/m³; 6061 is 2,700 kg/m³ — a difference of 110 kg/m³, or 4.1%. For the same geometry, a 7075 part weighs 4.1% more than a 6061 part. However, 7075-T6 delivers 572 MPa tensile strength vs. 6061-T6’s 310 MPa — an 85% strength advantage. The specific strength ratio (strength ÷ density) is 0.204 for 7075-T6 vs. 0.115 for 6061-T6. In strength-governed designs, 7075 components can be made substantially lighter than 6061 at equal structural capacity.

Q: Is 7075 aluminum the densest aluminum alloy available? Among standard commercial alloys, yes — it and 2024 (2,780 kg/m³) are the densest you will routinely encounter. Some specialty aluminum alloys with higher copper or zinc contents can exceed 2,810 kg/m³, but these are uncommon in general fabrication. Aluminum-lithium alloys run in the opposite direction: as low as 2,500 kg/m³.

Q: Why is 7075 used in aerospace despite being heavier than 6061? Because in aerospace, structural weight is determined by mass-per-unit-strength, not mass-per-unit-volume. 7075-T6’s specific strength (0.204 kN·m/kg) is 1.77× that of 6061-T6 (0.115 kN·m/kg). A properly designed 7075 aerospace component — wing spar, fuselage frame, load-bearing fitting — will be lighter than its 6061 equivalent because the higher strength allows thinner cross-sections that more than compensate for the density difference.

Q: Can 7075 aluminum be laser cut? Yes. We cut 7075 regularly in our facility for aerospace fixtures, tooling components, and structural brackets. The alloy cuts similarly to 6061 on fiber laser equipment. For aerospace structural applications, review the heat-affected zone implications at the cut edge with your design engineer before committing to cut-to-final dimensions. For non-structural tooling and fixture applications, laser-cut 7075 requires no special treatment beyond what is standard for any aerospace-grade aluminum.

Q: What is the density of 7075 aluminum in lb/in³? 0.102 lb/in³. The exact conversion from 2,810 kg/m³ is 0.10154 lb/in³, which rounds to 0.102.

References

1. ASTM B209, Standard Specification for Aluminum and Aluminum-Alloy Sheet and Plate, ASTM International, current edition. (Chemical composition of 7075 per Table 1; mechanical property requirements per Table 3; temper definitions and property minima for T6, T73, and intermediate tempers.)
2. Aluminum Association, Aluminum Standards and Data, current edition. (Density values for all 7075 tempers; composition limits; mechanical property data by temper and product form.)
3. ASM Handbook, Volume 1: Properties and Selection — Irons, Steels, and High-Performance Alloys, 10th Edition. ASM International, 1990. (Wrought aluminum alloy property data; discussion of 7xxx series stress-corrosion cracking behavior and temper selection guidelines.)
4. Michael Smith Engineers Limited, Material Grade Comparison Table (DIN/BS/USA/Japan cross-reference), available at michaelsmithengineers.co.uk. (AlZn5.5MgCu DIN designation and EN AW-7075 European designation mapped to ASTM 7075; JIS A7075 equivalency.)

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Dr. Liu Che

Dr. Liu Che holds a Ph.D. in Engineering from Dalian University of Technology and completed postdoctoral research at the Mechanical Engineering Postdoctoral Fellowship of Harbin Institute of Technology. His research focuses on core algorithms for large-scale laser equipment integration, laser cladding remanufacturing, and real-time intelligent monitoring systems for processing. He possesses profound academic expertise in cutting-edge fields such as laser beam spatial shaping and the mechanism analysis of laser processing of special alloys. He has led numerous solutions to technical challenges in cutting and surface modification of high-hardness materials in the heavy machinery industry, demonstrating strong theoretical foundations and outstanding engineering implementation capabilities.

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