7075-T651 Aluminum Plate properties at a glance
Values labeled typical are orientation- and section-dependent references, not design allowables. Use the current governing specification and the supplied mill certificate for acceptance.
| Property | Reference value | How to use it |
|---|---|---|
| Density | 0.1015 lb/in³ (2.81 g/cm³) | Nominal reference density |
| Ultimate tensile strength | 83 ksi typical | Representative T651 plate value; thickness and direction matter |
| Yield strength | 73 ksi typical | Representative value; use the governing design allowable |
| Elongation | 11% typical | Direction, thickness, and specimen geometry affect results |
| Hardness | 150 HB typical | Reference value rather than a universal acceptance limit |
History of 7075
The alloy family behind 7075 emerged in the mid-1930s from Japanese work on zinc-magnesium-copper aluminum for aircraft. Similar high-strength material entered American wartime production as 75S, and the modern 7075 designation followed the standardized wrought-alloy naming system. Its exceptional specific strength made it a defining airframe material and later a staple for high-load machined hardware.
T651 grew from the need to machine thick, quenched plate with less distortion. The plate is solution heat treated, stretched to relieve residual stress, and artificially aged near the high-strength T6 condition. That processing provides a predictable machining blank, but it does not erase the metallurgical tradeoff: peak-aged 7xxx material needs careful attention to stress-corrosion cracking, especially in unfavorable grain directions and environments.
- 1930s
A high-strength 7xxx alloy emerges
Zinc-magnesium-copper aluminum development establishes the alloy family that becomes 7075.
- 1940s
Aircraft use expands
The material enters large-scale airframe production under earlier company designations.
- Today
T651 remains the strength-first plate choice
Designers use it for highly loaded, mechanically fastened, and deeply machined components.
Choose T651 for strength, not universality
7075-T651 is appropriate when static strength and stiffness-to-weight justify the cost and fabrication limits. It is common in airframe fittings, high-load brackets, precision tooling, robotics, and performance hardware. It is a poor default when the part must be fusion welded, bent aggressively, or exposed to a severe corrosive environment without protection.
Compare it with T7351 before releasing the drawing. T651 is the strength-first choice; T7351 is overaged to improve stress-corrosion resistance at a cost in tensile and yield strength. The correct answer depends on load direction, sustained stress, environment, section thickness, and the design authority—not a generic “aerospace grade” label.
Machining and corrosion control
7075-T651 machines cleanly with sharp carbide tooling and good chip evacuation. Because the starting strength is high, workholding and thin-section strategy matter. Stretch stress relief helps, but heavy one-sided removal can still release enough residual stress to move a part. Balanced roughing and a delayed finish pass improve stability.
The alloy is not normally selected for conventional structural welding. Protect bare surfaces as the service environment requires, avoid galvanic couples that keep the aluminum anodic, and pay attention to end-grain exposure. Stress-corrosion risk cannot be judged from alloy name alone; grain direction, sustained tensile stress, and environment all contribute.
Certification and ordering checks
Specify 7075-T651 plate with the exact ASTM or AMS callout from the drawing, required thickness, dimensions, and any ultrasonic, fracture-toughness, origin, or lot-traceability requirement. Aerospace specifications can impose tests beyond ordinary commercial plate, so “meets chemistry” is not enough.
Read the cert for alloy, temper, product form, specification and revision, heat or lot, test direction, and measured results. Keep T651 and T7351 physically and digitally separated: the two can look identical, while their design purpose and strength values are not interchangeable.
Specifications and purchase callouts
The controlling drawing decides which specification applies. A similar alloy name or typical-property table does not demonstrate compliance.
- ASTM B209
- SAE AMS 4045
- AMS-QQ-A-250/12 (legacy federal callout)
Frequently asked questions
What is 7075-T651 aluminum used for?
It is used for high-load machined parts such as airframe fittings, structural brackets, tooling, robotics components, and performance hardware where high strength-to-weight matters. It is normally joined mechanically rather than by structural fusion welding.
What is the difference between 7075-T651 and T7351?
T651 is peak-aged for higher strength after stretch stress relief. T7351 is overaged after stress relief to improve stress-corrosion resistance, with lower tensile and yield strength. The drawing and service environment should decide between them.
Can 7075-T651 be welded?
It is generally unsuitable for conventional structural MIG or TIG welding because of hot-cracking susceptibility and degraded heat-affected-zone performance. Designers usually use fasteners, interference fits, or other mechanical joining methods.
Does T651 eliminate machining movement?
No. Stretching reduces residual stress but cannot eliminate every source of distortion. Thick-to-thin transitions, one-sided pocketing, aggressive clamping, and unfavorable grain orientation can still move the workpiece, so use balanced roughing and finish stock.
Primary references
Technical standards change. These sources support the history and reference discussion; obtain the current specification revision for design or acceptance work.
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