Why 7075-T7351 Is Used for Thick Aluminum Plate and CNC Machining

Why 7075-T7351 Is Used for Thick Aluminum Plate and CNC Machining

7075 aluminum is widely used for highly stressed machined components because it combines low density with very high strength. For thick plate and parts requiring substantial CNC material removal, however, alloy designation alone is not enough. The temper can strongly influence strength, stress-corrosion resistance and dimensional stability during machining.

7075-T7351 is particularly relevant to thick aluminum plate because it combines the overaged T73 property direction with stress relief by controlled stretching. This makes it useful when a buyer needs high-strength 7075 plate but also wants better stress-corrosion resistance and reduced residual-stress-related movement during heavy machining.

Why Thick 7075 Plate Can Move During CNC Machining

Thick rolled aluminum plate contains residual stresses created during rolling, solution heat treatment, quenching and subsequent processing. These stresses may remain balanced while the plate is intact.

When CNC machining removes a large amount of material from one side, pocket or internal cavity, that balance changes. Residual stresses redistribute, and the component may bow, twist or move away from the original machining datum.

This is especially important for aerospace structures, tooling parts, fixtures, frames and other components machined from thick plate. A blank can meet its incoming dimensional tolerance but still move after deep pockets or asymmetric material removal.

The machining strategy, part geometry and workholding remain important, but choosing a stress-relieved plate condition can reduce one major source of dimensional instability.

What Does T7351 Mean?

The temper designation provides information about how the alloy was processed after solution heat treatment. For 7075 plate, the difference between T6, T651, T73 and T7351 is therefore much more than a suffix on the material name.

Temper	Main Processing Direction	Buyer Relevance
T6	Solution heat treated and artificially aged	High peak-strength direction
T651	T6 property direction with stress relief by stretching	Commonly relevant to thick plate and CNC machining where dimensional stability matters
T73	Solution heat treated and overaged/stabilized	Lower peak strength than T6 but improved stress-corrosion resistance
T7351	T73 property direction with stress relief by stretching	Useful for thick plate requiring SCC resistance and improved machining stability

T7351 can therefore be understood as a temper designed around two important requirements: the T73 overaged property condition and additional stress relief from stretching.

7075-T651 vs T7351: The Real Engineering Trade-Off

For thick plate procurement, the more useful comparison is often not simply T6 vs T73. It is T651 vs T7351 because both conditions are highly relevant to machined plate.

Selection Factor	7075-T651	7075-T7351
Strength Direction	Higher peak-strength direction	Lower than T651 because of overaging
Stress-Corrosion Resistance	Lower than T73/T7351 conditions	Improved relative to peak-strength T6/T651 conditions
Stress Relief	Stress relieved by stretching	Stress relieved by stretching
Machining Direction	Highly relevant to precision-machined plate	Highly relevant where machining stability and SCC resistance are both important
Selection Driver	Maximum practical strength from stress-relieved plate	Balance of high strength, SCC resistance and machining stability

The correct choice is therefore a trade-off. T651 may be preferred when maximum strength is central to the design, while T7351 may be more appropriate when stress-corrosion resistance becomes a greater concern and the part is also heavily machined.

For peak-strength plate applications, buyers can review 7075-T651 aluminum plate when comparing product-form requirements.

Why Stress-Corrosion Cracking Matters in 7075

7075 achieves very high strength through its zinc-magnesium-copper alloy system and precipitation-hardening response. Peak-strength conditions provide excellent mechanical performance, but highly stressed components can become more sensitive to stress-corrosion cracking under certain environments.

Stress-corrosion cracking requires both a susceptible material condition and tensile stress in a suitable environment. Residual manufacturing stress, assembly stress and operating load can therefore matter alongside moisture, chlorides and other environmental factors.

The T73 family sacrifices part of the peak strength through overaging in order to improve resistance to this type of failure. This is why T7351 may be specified for highly loaded thick-plate components operating where SCC resistance is more important than achieving the maximum possible T6 strength.

Why Stress Relief by Stretching Matters for CNC Parts

Stress relieving by stretching is particularly valuable for thick rolled plate. After solution heat treatment and quenching, residual stresses can remain through the thickness. Controlled stretching plastically relieves part of this residual-stress system before final aging and supply.

This does not mean that a T7351 plate can never distort. Part geometry, stock-removal pattern, clamping, heat generated during machining and machining sequence still affect the final result.

However, for a component requiring large pockets, thin walls or extensive removal from both faces, starting from a stress-relieved plate condition can provide a more stable basis than using material without comparable residual-stress control.

For precision CNC work, buyers should also consider:

When T7351 Is Especially Relevant

T7351 is most relevant when several requirements occur at the same time rather than when only one property is important.

Application Situation	Why T7351 May Be Considered
Thick plate with deep CNC pockets	Stress-relieved condition can support dimensional stability during large stock removal
Highly stressed components exposed to moisture or corrosive environments	T73 property direction improves SCC resistance compared with peak-strength T6 conditions
Precision aerospace or mechanical structures	Combines high strength with stress relief and improved SCC behavior
Parts requiring extensive two-sided machining	Residual-stress control becomes more relevant as material removal increases

When T651 May Still Be the Better Choice

T7351 is not automatically the preferred temper for every 7075 plate application. T651 remains highly relevant when the design prioritizes maximum strength and the service environment does not require the improved SCC resistance associated with T73-type conditions.

For many precision-machined parts, T651 already provides both high strength and stress relief by stretching. Changing from T651 to T7351 solely because the latter appears more specialized can reduce available strength without creating a useful design benefit.

The engineering team should therefore compare the actual mechanical-property requirements, environmental exposure and applicable material specification before approving a temper change.

What to Check on the MTC

A certificate marked only “7075” does not provide enough information for a temper-critical machining order. The MTC should be reviewed against the purchase order and product specification.

• Alloy designation: 7075

• Ordered temper: T651, T73, T7351 or other required condition

• Applicable product standard

• Lot or batch identification

• Chemical composition

• Tensile and yield properties where required

• Elongation

• Plate dimensions

• Additional inspection results where required by the project

Temper identity should not be inferred from chemistry alone. T651 and T7351 use the same base alloy chemistry but have different processing histories and resulting property requirements.

Example RFQ for a Heavily Machined 7075 Plate

Providing the finished drawing is especially useful when the part will be heavily machined. It allows plate size, machining allowance and dimensional requirements to be reviewed before quotation rather than after material is purchased.

FAQ

What is the difference between 7075-T6 and T73?

7075-T6 is aged toward higher peak strength, while T73 is overaged to improve resistance to stress-corrosion cracking. T73 normally sacrifices some strength to obtain this improvement.

What is the difference between T73 and T7351?

T7351 follows the T73 property direction but includes stress relief by stretching. This makes T7351 especially relevant to plate used for substantial CNC machining where residual-stress control is important.

Is 7075-T7351 stronger than T651?

Generally no. T651 follows the higher-strength T6 aging direction, while T7351 sacrifices some peak strength to improve stress-corrosion resistance. Exact properties must be checked for the required plate thickness and standard.

Does T7351 prevent CNC machining distortion?

No temper can guarantee zero distortion. T7351 includes stress relief by stretching, which can reduce residual-stress-related movement, but machining sequence, component geometry, clamping and stock removal also affect dimensional stability.

Which 7075 temper is better for thick machined plate?

T651 is commonly considered when higher strength is the priority, while T7351 may be preferred when improved stress-corrosion resistance is also required. Both are stress-relieved conditions relevant to plate machining. Final selection should follow the drawing and service requirements.

Conclusion

7075-T7351 is not simply another version of 7075 aluminum. Its value for thick plate comes from combining the T73 overaged property direction with stress relief by stretching.

This makes the temper particularly relevant to heavily machined components where residual stress, dimensional stability and stress-corrosion resistance must be considered together. T651 remains important when maximum strength is the dominant requirement, so the two tempers should be compared against the real design rather than ranked universally.

For bulk plate procurement, specify the exact temper, plate dimensions, total quantity, product standard, finished machining requirements and inspection documents before quotation.