Aluminum 2117: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

Alloy 2117 is a member of the 2xxx-series aluminum-copper family and is classified among heat-treatable Al-Cu alloys. Its chemistry centers on copper as the principal strengthening addition, supplemented by controlled amounts of manganese, magnesium, and trace elements to tailor strength, workability, and recrystallization behavior.

2117 strengthens primarily by solution heat treatment followed by precipitation hardening (ageing), producing fine Al2Cu (θ) and related precipitates; it also shows some work-hardening capacity in non-fully aged tempers. The alloy offers a balance of moderate-to-high strength, acceptable corrosion resistance when properly finished or clad, and limited weldability relative to pure Al; formability is good in annealed and lightly strained tempers.

Typical industries using 2117 include aerospace (secondary structures and fittings), defense (structural components), automotive (components requiring higher strength than 5xxx/3xxx families), and specialty commercial applications such as rivets, fasteners, and formed extrusions where a combination of heat-treatable strength and reasonably good formability is needed. Engineers choose 2117 where stronger Al-Cu behavior is required but where extreme strength of premium 2xxx alloys (e.g., 2024) is unnecessary or where better formability or lower cost is desired compared with higher-performance heat-treatable grades.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	20–35%	Excellent	Excellent	Fully annealed condition for maximum ductility and forming.
H12 / H14	Medium	8–18%	Good	Fair	Strain-hardened to intermediate strength; used for drawn/formed parts.
T3	Medium-High	8–15%	Good	Limited	Solution heat-treated, cold worked and naturally aged; balances strength and formability.
T4 / T5	Medium-High	10–18%	Good	Limited	Solution treated then naturally aged (T4) or artificially aged (T5) for stable properties.
T6 / T651	High	6–12%	Fair	Limited	Solution treated and artificially aged to peak or near-peak strength; T651 includes stress relief by stretch.

Temper selection strongly controls the strength/ductility tradeoff in 2117; annealed material is preferred for severe forming while T6/T651 is used where higher static strength and stiffness are required. Weldability and post-weld property retention generally worsen as tempers move toward higher artificial aging states, and designers should plan forming and joining in the annealed or lightly worked conditions followed by required heat treatments.

Chemical Composition

Element	% Range	Notes
Si	0.20 max	Controlled low silicon to limit brittle intermetallics and maintain machinability.
Fe	0.50 max	Impurity element; higher Fe lowers ductility and can form intermetallic phases.
Mn	0.30–0.9	Improves strength, grain structure control and imparts some resistance to recrystallization.
Mg	0.10–0.6	Small additions enhance precipitation response and contribute to strength.
Cu	3.0–4.0	Primary strengthening element forming Al2Cu precipitates during ageing.
Zn	0.25 max	Minor; retained low to avoid undesired interactions with Cu that can reduce corrosion resistance.
Cr	0.05–0.25	Trace addition for grain structure control; reduces grain boundary precipitate coarsening.
Ti	0.05–0.15	Grain refiner to improve cast/microstructure continuity in wrought products.
Others (each)	0.05 max	Residual elements; aluminium remainder to 100%

The copper content is the dominant factor in tensile and yield strength through precipitation hardening; manganese and chromium control grain structure and limit recrystallization, improving strength at elevated temperatures and during deformation. Minor Mg and trace additions tune the aging kinetics and can modestly increase precipitation-hardening response; low Si and Fe preserve ductility and avoid coarse brittle intermetallics that hurt toughness and formability.

Mechanical Properties

Tensile behavior of 2117 is typical of Al-Cu alloys: relatively high ultimate and yield strengths after appropriate solution and artificial ageing, with elongation values that decline as strength increases. Annealed material exhibits good uniform elongation and predictable work-hardening; peak-aged tempers show higher yield-to-tensile ratios and reduced total elongation, which must be considered for forming or crashworthiness design.

Hardness correlates strongly with temper; hardness increases significantly from O through T6/T651 as fine precipitates form in the matrix. Fatigue performance is moderate to good for Al-Cu alloys when surface finish and residual stress are controlled; fatigue crack initiation is sensitive to surface defects, corrosion pits, and coarse intermetallics, so finishing and corrosion protection strategies materially affect fatigue life.

Thickness affects achievable properties because through-thickness cooling rates during quenching influence supersaturation and precipitate distribution; thick sections tend to under-age or show reduced peak strength relative to thin sheet unless tailored heat treatments are used. Designers should expect some variability in properties with section thickness and specify tempering/aging consistent with component geometry.

Property	O/Annealed	Key Temper (T6/T651)	Notes
Tensile Strength	180–260 MPa	350–450 MPa	Wide range depending on aging, section thickness, and exact chemistry.
Yield Strength	70–150 MPa	300–380 MPa	Yield increases markedly with T6; T651 stress-relieved variants show improved dimensional stability.
Elongation	20–35%	6–12%	Ductility falls with increasing artificial ageing and strength level.
Hardness (HB)	40–70 HB	100–150 HB	Brinell hardness rises with precipitate formation; converted to HRC/Vickers as needed.

Physical Properties

Property	Value	Notes
Density	~2.78 g/cm³	Slightly higher than pure Al due to Cu additions; useful for mass calculations.
Melting Range	~500–640 °C	Alloying broadens the melting interval; solidus/liquidus depend on composition.
Thermal Conductivity	~120–150 W/m·K	Lower than pure Al (≈235 W/m·K) because Cu and alloying reduce conductivity.
Electrical Conductivity	~25–40 % IACS	Reduced conductivity relative to 1xxx series due to copper content and precipitates.
Specific Heat	~0.9 J/g·K	Typical for aluminium alloys; useful for thermal mass calculations.
Thermal Expansion	~22–24 ×10⁻⁶ /K (20–100 °C)	Similar coefficient to other Al alloys; consider in joined dissimilar material designs.

2117’s thermal and electrical conductivities are intermediate for aluminum alloys and reflect the trade-off between mechanical performance and transport properties inherent to Al-Cu systems. The density increment from copper should be accounted for in weight-sensitive designs, and the thermal expansion coefficient requires attention when joining to dissimilar materials to avoid thermal stress concentrations.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.3–6.0 mm	Excellent through-thickness response	O, H14, T4, T6	Widely used for drawn or formed panels and small structural parts.
Plate	6–100 mm	Reduced hardenability in thick sections	O, T3, T6 (tailored)	Thick plate needs specialized solution/quench cycles to achieve uniform properties.
Extrusion	Wall thicknesses 1–20 mm	Directional properties; good for complex sections	O, T6 (age after extrusion)	Extrusion requires controlled quench and artificial ageing to reach intended T-tempers.
Tube	OD 6–200 mm	Similar to extrusions; wall thickness affects strength	O, T6	Used for structural tubing and fitted assemblies.
Bar/Rod	Diameters 3–100 mm	Machinability and stability vary with diameter	O, T6	Bar stock for turned components and fasteners; temper selection affects machinability.

Processing routes differ significantly: thin-sheet production permits rapid quenching and uniform ageing, yielding higher peak strengths, while thick plate and large extrusions require tailored thermal cycles to avoid soft spots. For formed or drawn parts, supply in O or lightly worked tempers is advantageous, followed by ageing to required hardness; for welded assemblies, pre- and post-heat treatments or redesign to avoid welded joints are common design strategies.

Equivalent Grades

Standard	Grade	Region	Notes
AA	2117	USA	Primary designation under ASTM/AA systems for wrought 2117.
EN AW	—	Europe	No direct one-to-one ENAW equivalent; design governed by AA number and similar 2xxx listings.
JIS	A2117 (informal)	Japan	Some suppliers use A2117 designation but users must verify composition against AA spec.
GB/T	2A17 or similar	China	Local standards often use numeric codes close to AA designations; confirm chemistry and tempers.

Direct cross-references for 2117 are limited because regional standards sometimes do not list 2117 explicitly; manufacturers and specifiers typically rely on AA/ASTM chemistry and mechanical property calls. When procuring from different regions, verify certification showing elemental ranges and temper to ensure interchangeability, particularly for critical aerospace or defense applications.

Corrosion Resistance

Atmospheric resistance of 2117 is moderate and typical of Al-Cu alloys: it performs acceptably in industrial atmospheres but is more susceptible to localized corrosion than many Al-Mg or Al-Mn alloys. Surface treatments—anodizing, conversion coatings, or cladding—significantly improve service life; bare 2117 exposed to aggressive environments may form pitting at intermetallic sites.

Marine behavior requires caution; chloride environments accelerate pitting and crevice corrosion in Al-Cu alloys compared with 5xxx series. Use of sacrificial anodes, coatings, or isolation from dissimilar metals is recommended for long-term marine exposure.

Stress corrosion cracking (SCC) susceptibility is higher in some heat-treated Al-Cu alloys under tensile stress and elevated temperatures; T6 tempers can be sensitive, so engineers should avoid combinations of tensile residual stresses, corrosive media, and elevated temperatures. Galvanic interactions are important: 2117 is anodic to stainless steels and cathodic to many magnesium alloys; proper insulating of joints, fasteners, and selection of compatible materials will reduce galvanic driven corrosion.

Compared to other alloy families, 2117 offers better mechanical properties than 1xxx/3xxx/5xxx at the cost of higher corrosion susceptibility; compared with 6xxx series, it can have comparable strength but different corrosion and anodizing responses due to the copper content.

Fabrication Properties

Weldability

Welding 2117 is challenging relative to Al-Mg or Al-Mn families because copper increases hot-cracking tendency and reduces ductility in the fusion zone. TIG and MIG can be used with specialized practices, such as low-heat input techniques and appropriate filler alloys (Al-Cu fillers such as 2319 or other compatible Al-Cu systems), but welded joints often exhibit reduced strength and local softening in the HAZ. Post-weld heat treatments may partially restore properties but are often impractical for assembled structures; as a result, designers frequently avoid critical welded joints or replace them with mechanical fastening or adhesive bonding.

Machinability

2117 offers reasonable machinability for a heat-treatable alloy and can be machined faster than many high-strength aerospace alloys; tool life and surface finish depend on temper and heat treatment. Carbide tooling with positive rake and good chip evacuation is recommended, with moderate cutting feedrates and speeds to avoid built-up edge; the alloy tends to produce relatively continuous chips that require control for safety and finish. Pre- and post-machining temper selection (e.g., machining in a softer O or H12 condition followed by ageing) can optimize both tool life and final component strength.

Formability

Forming characteristics are favorable in O and lightly worked H tempers, enabling deep drawing, bending, and stretch-forming for complex geometries. Minimum bend radii and springback are governed by temper and thickness; annealed sheet permits small radii and high reduction during draw while T6 materials require larger radii and more conservative forming limits. For parts that require both forming and high strength, a common practice is to form in the O or T4 condition and then perform final artificially ageing to obtain the desired mechanical properties.

Heat Treatment Behavior

As a heat-treatable Al-Cu alloy, 2117 responds to solution treatment, quenching, and artificial ageing. Typical solution treatments are performed near the solvus temperature (commonly in the 500–540 °C range depending on section size) followed by rapid quench to retain copper and magnesium in supersaturated solid solution. Subsequent artificial ageing (e.g., 150–200 °C for several hours depending on section thickness and targeted T-temper) precipitates fine Al2Cu and related phases to achieve T5/T6 properties.

T temper transitions are reversible within processing limits: T4 (solution treated, natural age) can be converted to T6 (artificially aged) with controlled ageing profiles; T651 involves stress relief by stretching followed by ageing. Over-ageing reduces strength but can improve toughness and reduce SCC susceptibility, so ageing schedules are a trade-off between peak strength and environmental resistance. For non-heat-treated workflows, cold working followed by partial anneal is used to create H tempers, with predictable increases in strength due to work hardening.

High-Temperature Performance

2117 begins to lose significant strength above approximately 150–200 °C as precipitates coarsen and over-ageing occurs; service limits for sustained loads typically sit below this range. Creep resistance is modest; for sustained high-temperature applications or thermal cycling, other alloys engineered for elevated temperature should be considered. Oxidation of aluminium is self-limiting and generally not a major issue, but combined thermal exposure and corrosive environments can accelerate corrosive degradation, particularly near welds or in stressed regions.

HAZ behavior under thermal exposure is critical: local softening and overaging near welds or heat-affected regions can create mechanical weak spots and reduce fatigue life. Designers should consider thermal management, controlled heat inputs during welding, and post-weld heat treatments where possible to mitigate strength losses.

Applications

Industry	Example Component	Why 2117 Is Used
Aerospace	Secondary structure and fittings	Good combination of heat-treatable strength, machinability, and dimensional stability.
Automotive	Structural brackets and formed components	Higher strength than common 1xxx/3xxx alloys with reasonable formability and cost.
Marine	Hardware and fasteners (coated)	When properly treated/coated, acceptable corrosion performance with good strength-to-weight.
Electronics	Small conductive housings and mechanical supports	Balance of mechanical properties and thermal conductivity for compact components.

2117 is often selected for mid-to-high-strength applications where standard 2xxx behavior is desired without the tightness of higher-performance alloys. Its use is typical where moderate corrosion protection measures (coatings, anodizing, cladding) are acceptable and where its heat-treatable nature is leveraged to achieve needed strength after forming or machining.

Selection Insights

Alloy 2117 is a practical choice when engineers need a heat-treatable aluminum that provides higher strength than commercially pure grades while retaining good machinability and formability in annealed conditions. Compared with commercially pure aluminum (1100), 2117 sacrifices electrical and thermal conductivity and some formability in exchange for a substantial increase in yield and tensile strength; use 2117 when structural strength is required but conductivity is secondary.

Compared with common work-hardened alloys such as 3003 or 5052, 2117 offers higher peak strength after ageing but generally lower corrosion resistance in chloride-rich environments; choose 2117 when strength is prioritized and corrosion protection (coating or anodizing) is feasible. Compared with common heat-treatable alloys like 6061 or 6063, 2117 may be preferred where specific Al-Cu properties (such as precipitation behavior or machinability in certain tempers) are advantageous, despite typically lower peak strength or different corrosion behavior than those Al-Mg-Si alloys.

When selecting 2117, consider cost and availability relative to other 2xxx series materials, the necessity for post-forming heat treatment, and the environmental exposure—if marine exposure or welding is central to the design, alternative alloys or protective strategies may be more suitable.

Closing Summary

Alloy 2117 remains a relevant engineering material by delivering a useful balance of heat-treatable strength, machinability, and formability for mid-weight structural and fabricated components; its selection is justified when designers require Al-Cu precipitation-strengthened performance with manageable processing and corrosion control strategies.