Alloy 2117 Rivets Are Heat Treated

If you've spent any time around aircraft structures, you've probably noticed that certain rivets get installed without any heating involved. On top of that, no torch, no heat tent, no waiting around for the metal to cool. Even so, you pull them out of the bag, set them with a rivet gun, and move on. And yet these rivets still meet the structural demands of an airframe.

That's not an accident. It's by design — and it comes down to how the rivet material is processed before it ever reaches your hand.

Alloy 2117 is one of the most widely used rivet alloys in aerospace and general aviation, and the reason it works the way it does — soft enough to set cold, strong enough to hold tight — is because it arrives at your workbench already heat treated. The process that gives it these properties happens at the mill, not in the hangar.

Let's walk through what that actually means, why it matters, and what you need to know to work with it correctly.

What Is Alloy 2117?

Alloy 2117 is an aluminum-copper alloy, part of the 2000 series aluminum family. The designation breaks down like this: 2117 is the specific alloy composition, and the "T4" you'll see on most rivet packages tells you about its temper condition — meaning the state of its heat treatment and how it's been processed to achieve certain mechanical properties.

The alloy itself contains copper as its primary alloying element, along with small amounts of magnesium and manganese. That combination, once properly processed, gives 2117 a useful balance: decent strength, good corrosion resistance (especially when compared to some other aluminum alloys), and critically, the ability to be deformed without cracking during installation.

This isn't a general-purpose hardware store rivet. 2117 is specified throughout aircraft manufacturing and repair because it handles the conditions airframes face — vibration, stress cycles, temperature swings — without giving up.

Why Heat Treatment Matters for This Alloy

Here's the thing: raw aluminum is soft. Copper makes it stronger, but not just by sitting there. The copper atoms in 2117 need to be arranged in a specific way at the microscopic level to give the material its desired properties — workable when you need it to be, strong once it's in place.

Heat treatment is the process that creates that arrangement. Without it, 2117 would either be too soft to use structurally, or so hard you couldn't set it without cracking the rivet head clean off.

For aircraft rivets, this matters in a specific way. When you're bucking a rivet in a wing skin or a fuselage frame, you need the material to flow plastically — to deform and fill the hole, creating a tight, load-bearing joint. Practically speaking, if the rivet were too hard, it would crack. Too soft, and it wouldn't hold. The T4 temper of 2117 puts it right in the workable range while still meeting the strength requirements of the repair or assembly.

Another reason this is important: in the field, you don't have access to heat treatment equipment. Which means a rivet that arrives in T4 condition stays in T4 condition at room temperature. You can set it whenever you're ready, as long as you've stored it properly. That's a huge practical advantage over alloys that need to be heated immediately before installation.

How the Heat Treatment Process Works

The heat treatment of 2117 into T4 temper follows a specific sequence. Understanding this isn't just trivia — it helps you see why certain field practices matter.

Solution Heat Treatment

The first step is solution heat treatment. The extruded or drawn rivet wire is heated to a temperature around 935°F (about 500°C). Here's the thing — at this temperature, the copper and other alloying elements dissolve into a uniform solid solution within the aluminum. Think of it like dissolving sugar in hot water — everything becomes one homogeneous phase.

The metal is held at this temperature long enough to ensure the microstructure is fully transformed, then it's quenched — rapidly cooled, usually by water immersion. On top of that, quenching "freezes" the dissolved atoms in place, creating a supersaturated solid solution. At this stage, the material is relatively soft and ductile.

Natural Aging

After quenching, the rivets are in the "T4" condition — solution heat treated and naturally aged. The aging part happens at room temperature over time. The supersaturated copper atoms slowly begin to precipitate out as fine particles within the aluminum matrix.

…what gives the alloy its characteristic increase in strength and hardness over time. As the supersaturated copper atoms diffuse, they form finely dispersed θ′ (Al₂Cu) precipitates that impede dislocation motion. This precipitation‑hardening mechanism is gradual at ambient temperature; after a few hours the rivet exhibits noticeable strength gains, and after several days it approaches the peak hardness associated with the T6 condition. Still, because the aging rate at room temperature is relatively slow, a rivet left in the T4 state retains sufficient ductility for bucking operations while still providing a baseline of load‑bearing capacity.

In practice, aircraft maintenance crews exploit this behavior by storing 2117 rivets in a cool, dry environment immediately after quenching. The low‑temperature aging continues uninterrupted, allowing the rivets to “self‑strengthen” while they sit on the shelf. When a repair is scheduled, the rivet can be removed from storage and bucked without any additional heating, confident that its strength has progressed toward the desired level but has not yet become so high that it risks cracking during deformation. If a higher strength is required for a critical joint, the rivet can be given a brief artificial aging treatment (e.g., 2–4 hours at 300 °F/150 °C) to accelerate precipitation and reach the T6 temper just before installation.

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The balance achieved by the T4 temper—adequate ductility for forming, coupled with a predictable, time‑dependent strengthening curve—makes 2117 uniquely suited for field‑riveted aircraft structures. It eliminates the need for on‑site heat‑treatment equipment, reduces logistical complexity, and ensures that each rivet performs reliably throughout the service life of the airframe.

Conclusion
The effectiveness of 2117 aluminum alloy rivets hinges on a carefully controlled heat‑treatment sequence that produces a supersaturated solid solution followed by natural aging. This process yields the T4 temper, which offers the ideal combination of workability for rivet bucking and a built‑in strengthening mechanism that continues at room temperature. By understanding and leveraging the precipitation‑hardening behavior, maintenance teams can store, handle, and install these rivets with confidence, knowing they will develop the necessary strength without sacrificing ductility—a critical advantage for the safety and efficiency of aircraft assembly and repair.

Beyond the fundamental metallurgy and storage protocols, successful field implementation relies on rigorous identification and traceability. Every 2117 rivet is marked with a distinct “dimpling” or raised dot on the manufactured head—specifically, a single raised teat—to differentiate it instantly from higher-strength 2017 (D) or 2024 (DD) rivets, which require refrigeration and prompt heat treatment. Worth adding: this visual cue is a critical safety feature; installing a 2024 rivet in the “as-received” condition without subsequent solution heat treatment and quenching would leave the joint dangerously weak, while attempting to buck a fully aged 2017 rivet without re-solutionizing would likely result in head fracture. The 2117’s “AD” designation and its unique head mark eliminate this ambiguity, allowing inspectors to verify material compliance at a glance during both installation and subsequent non-destructive inspections.

Corrosion performance further cements the alloy’s role in primary structure. Standard practice dictates the application of zinc-chromate or epoxy-based primer to the rivet shank and the surrounding hole before driving, creating a barrier that mitigates galvanic coupling with the higher-copper skin alloys. And 2–3. While 2117 does not match the pure aluminum cladding protection found on alclad 2024 sheet, its copper content is low enough—typically 2.0%—to provide respectable resistance to exfoliation and stress-corrosion cracking in the T4 temper, especially when the driven rivet shank expands to fill the hole tightly, limiting crevice formation. In environments prone to severe corrosion, such as maritime patrol aircraft, maintenance manuals may specify the use of 2117-T4 rivets with cadmium plating or the substitution of 5056 (B) rivets for non-critical shear applications, though the latter sacrifices significant shear strength.

Finally, the logistics of the “self-strengthening” supply chain warrant attention. Because the aging curve is predictable but not instantaneous, engineering orders often specify a minimum shelf-age—typically 48 to 72 hours post-quench—before rivets are released for structural use. This ensures the material has progressed sufficiently along the hardening curve to meet minimum shear and bearing allowables (typically 30 ksi shear ultimate for 2117-T4) while retaining the ductility needed for the shop head formation. Day to day, quality assurance programs track quench dates via batch lot numbers, and rivets exceeding a maximum shelf life (often one year, though studies show stability well beyond) are sampled for hardness verification per ASTM B594 rather than discarded outright. This data-driven approach to inventory management transforms what could be a metallurgical liability—unstable properties—into a controlled, auditable asset.

Final Summary
The 2117 aluminum alloy rivet represents a rare convergence of metallurgical elegance and operational pragmatism. Its T4 temper leverages the inherent kinetics of aluminum-copper precipitation to deliver a fastener that is soft enough to drive reliably by hand or pneumatic gun today, yet structurally competent to carry design

…loads throughout the service life of the airframe. In the T4 condition the rivet exhibits a predictable combination of shear strength (≈30 ksi ultimate) and bearing capacity that satisfies the primary‑structure allowables for most fuselage and wing skins. Because the alloy’s precipitation hardening continues slowly after installation, the joint actually gains a modest amount of strength during the first few hundred flight hours—a phenomenon known as “in‑service aging.” This self‑reinforcing characteristic reduces the need for over‑design and permits thinner skin gauges without compromising safety margins.

Fatigue performance is another area where 2117‑T4 rivets shine. The relatively low copper content limits the formation of brittle intermetallic networks that can act as crack‑initiation sites, while the tight hole fill achieved during driving suppresses fretting corrosion at the rivet‑skin interface. In real terms, laboratory S‑N curves for 2117‑T4 fasteners in 2024‑T3 sheet show endurance limits comparable to those of higher‑strength 7075‑T6 rivets, yet with a markedly higher ductility that translates into better resistance to overload‑induced shear tear‑out. As a result, maintenance programs often rely on routine visual inspections supplemented by periodic eddy‑current or ultrasonic scans to detect any loss of hole fill or surface cracking, confident that the underlying metallurgy will remain stable over the aircraft’s design life.

From a logistical standpoint, the alloy’s shelf‑age sensitivity is turned into an advantage rather than a drawback. That's why by tracking quench dates and enforcing a minimum post‑quench exposure, manufacturers guarantee that each batch meets the mechanical baseline before it reaches the line. Worth adding: the subsequent, gradual aging in service means that rivets stored beyond the nominal one‑year limit can still be employed after a simple hardness check, reducing waste and simplifying inventory control. This closed‑loop approach—quench → controlled shelf‑age → installation → in‑service strengthening—exemplifies how a seemingly modest alloy can be harnessed to deliver both manufacturing flexibility and long‑term structural integrity.

To keep it short, the 2117‑T4 aluminum rivet marries the practical benefits of low‑temperature formability with the performance advantages of age‑hardenable aluminum‑copper alloys. Its ability to be driven easily, to develop strength after installation, and to resist corrosion and fatigue makes it a workhorse for primary aircraft structures. When paired with proper surface treatments and disciplined inventory practices, the 2117 rivet provides a reliable, cost‑effective fastening solution that meets the rigorous demands of modern aviation while retaining the simplicity that has kept it in service for decades.

Alloy 2117 Rivets Are Heat Treated