Aluminum 2118: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

Alloy 2118 belongs to the 2xxx series of aluminum-copper alloys characterized by copper as the principal alloying element. This family is heat-treatable and designed to deliver elevated strength through precipitation hardening, with copper and minor alloying additions tuned to form strengthening precipitates during aging.

The major alloying constituents in 2118 are copper, with additional magnesium, manganese, and trace elements such as iron, silicon, chromium, and titanium. The combination produces high specific strength and good fatigue resistance relative to non-heat-treatable and commercially pure aluminum grades.

Strengthening is achieved primarily by solution treating, quenching and artificial aging to develop fine Al2Cu-based precipitates; this gives higher peak strengths than work-hardened alloys but also makes properties more sensitive to thermal exposure. Key traits include high tensile and fatigue strength, moderate corrosion resistance that typically requires protective coatings for harsh environments, and limited weldability compared with 5xxx/6xxx alloys unless appropriate procedures and fillers are used.

Typical industries using 2118 include aerospace structural fittings and fasteners, high-performance automotive components, and specialty marine and defense applications where strength-to-weight and fatigue life are critical. Designers choose 2118 when higher strength and fatigue performance are needed over common alloys such as 1100, 3003, or 5052, yet when the superior peak strength of 7xxx alloys is not required or where toughness and fracture behavior of 2xxx alloys are preferred.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed, maximum ductility and formability
H14	Medium-Low	Medium	Good	Fair	Strain-hardened to moderate strength for drawing applications
T4	Medium	Medium-High	Good	Fair	Solution heat-treated and naturally aged; good balance for further forming
T5	Medium-High	Medium	Fair-Good	Fair	Cooled from elevated temperature and artificially aged to develop strength
T6	High	Low-Medium	Limited	Poor-Fair	Solution-treated and artificially aged for peak strength; common engineering temper
T651	High	Low-Medium	Limited	Poor-Fair	Solution-treated, stress-relieved by stretching, then artificially aged for improved dimensional stability

Temper has a powerful influence on 2118’s balance of strength and formability, because the heat-treatment sequence controls precipitate size, distribution, and coherency. O and H variants are used when forming or drawing is the priority, while T6/T651 are selected when strength and fatigue performance are the primary design drivers.

Chemical Composition

Element	% Range	Notes
Si	0.2 max	Controlled low to limit brittle intermetallics and maintain toughness
Fe	0.5 max	Impurity that forms intermetallic particles affecting machinability and fatigue
Mn	0.3–0.9	Improves strength, grain structure and resistance to recrystallization
Mg	0.2–1.0	Contributes to precipitate strengthening with Cu and improves toughness
Cu	3.5–5.0	Principal strengthening element; controls precipitation hardening potency
Zn	0.25 max	Minor, kept low to avoid excessive age-hardening complexity
Cr	0.05–0.25	Microalloying to refine grain structure and stabilize properties during heating
Ti	0.02–0.12	Grain refiner, used to control as-cast grain size in ingots and extrusions
Others (each)	0.05 max	Trace elements and residuals; limits ensure predictable precipitation behavior

The copper content dominates the precipitation hardening response, producing Al2Cu and related phases on aging that raise strength and reduce ductility. Magnesium and manganese modify precipitate chemistry and matrix interactions; manganese suppresses grain growth and improves toughness while magnesium can enhance age-hardening when coupled to copper. Strict limits on iron, silicon and zinc are maintained to control ductility, fracture behavior and corrosion susceptibility.

Mechanical Properties

In tensile loading, 2118 exhibits high ultimate tensile strength and good yield retention in the T6/T651 tempers relative to many common aluminum alloys. Peak-aged conditions produce a microstructure of finely dispersed precipitates that restrict dislocation motion, giving high yield strength and good fatigue resistance. Elongation in peak tempers is reduced compared with annealed conditions, and designers must account for lower ductility during forming and crash or overload scenarios.

Fatigue performance of 2118 is generally favorable for a 2xxx-series alloy due to the combination of high static strength and precipitate-controlled crack initiation thresholds; however, fatigue life is sensitive to surface finish, notch geometry and local corrosion. Thickness effects are important: thinner gauge material can be aged more uniformly and often attains higher effective strength for a given temper, while thicker sections may require longer solution/aging cycles and can show lower toughness and slightly reduced strength.

Property	O/Annealed	Key Temper (T6/T651)	Notes
Tensile Strength	150–260 MPa	400–480 MPa	Wide range depending on exact composition, thickness and aging cycle
Yield Strength	60–150 MPa	320–380 MPa	Yield increases significantly with T6/T651 processing
Elongation	15–25%	7–14%	Ductility drops in peak-aged conditions; design for forming accordingly
Hardness (HB)	40–80 HB	120–160 HB	Brinell range; hardness correlates with tensile/yield performance

Physical Properties

Property	Value	Notes
Density	2.78 g/cm³	Typical for Al-Cu alloys; good specific strength versus steel
Melting Range	~500–640 °C	Alloying expands the solidus-liquidus interval relative to pure Al
Thermal Conductivity	120–150 W/m·K	Reduced compared with pure Al due to Cu additions but still high
Electrical Conductivity	25–40 % IACS	Lower than pure Al; conductivity degrades with alloying and cold work
Specific Heat	~0.88 J/g·K (880 J/kg·K)	Typical for aluminum alloys; used in thermal management calculations
Thermal Expansion	23–24 µm/m·K (20–100°C)	Moderate coefficient; dimensional change must be accounted in assemblies

2118 retains much of aluminum’s favorable thermal conductivity and low density, producing good strength-to-weight and heat dissipation capabilities for many components. The electrical conductivity is substantially reduced compared with commercially pure aluminum, so 2118 is not typically used where conductivity is primary.

The melting range and thermal expansion behavior mean that heat input during welding and thermal cycling during service will significantly affect microstructure and mechanical properties; these must be considered during joining, heat treatment and design for thermal loads.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.3–6 mm	Thin sheets respond well to T5/T6 aging; better uniformity in thin gauges	O, H14, T4, T5, T6	Used for formed panels and fitted structures
Plate	6–50+ mm	Thick sections require extended solution/aging cycles; can show lower toughness	O, T6, T651	Heavy structural parts and fittings
Extrusion	Wall thicknesses 1–20 mm	Extruded profiles allow directional strength; heat-treatment applied post-extrusion	O, T4, T6	Complex profiles for structural members
Tube	OD 6–200 mm	Performance depends on wall thickness and quench rate; fatigue-critical uses in T6	O, T4, T6	Used for lightweight structural tubing
Bar/Rod	Diameters up to 100 mm	Bars can be heat treated and aged to high strengths; machining stock	O, T6	Fasteners, pins, and machined components

Sheet and thin-gauge products are often preferred where formability and age-hardening uniformity are required, while plate and heavy extrusions need tailored thermal cycles because of slower quench rates. Extrusion and rolling routes also influence grain structure; extrusions permit complex cross-sections but require attention to quench and aging to reach target properties.

Manufacturers choose form-factors based on downstream processes: sheets for stamping and forming, extrusions for integrated profiles, and bar for machined components. Each product form also drives temper selection to achieve the necessary balance of formability and strength.

Equivalent Grades

Standard	Grade	Region	Notes
AA	2118	USA	Designation in ANSI/AA listings for this Al-Cu alloy
EN AW	None exact	Europe	No direct EN AW counterpart; most similar in behavior to EN AW-2014/2024 families
JIS	None exact	Japan	JIS has Al-Cu alloys (A2017/A2024) with similar properties but different limits
GB/T	None exact	China	Chinese standards have comparable Al-Cu alloys but not a one-to-one match with AA 2118

There is no single universal standardization translating 2118 directly to an EN, JIS or GB/T number; equivalents are best treated as “nearest-behavior” matches rather than direct replacements. Differences in allowed trace elements, heat-treatment response and temper designations mean that designers should consult specific datasheets and perform qualification testing when substituting across standards.

Corrosion Resistance

2118 offers moderate atmospheric corrosion resistance typical of heat-treatable Al-Cu alloys; protective coatings, anodizing or cladding are often employed for long-term exposure. In neutral to mildly corrosive atmospheres the alloy performs adequately, but localized corrosion can be aggravated by copper-rich intermetallics and by poor surface finishes.

In marine or highly chloride-containing environments, 2118 is less robust than magnesium-containing 5xxx alloys or corrosion-resistant 6xxx series; therefore, it typically requires cladding, sacrificial coatings or cathodic protection for structural marine service. Pitting and intergranular corrosion can occur where precipitate-free zones form at grain boundaries following improper heat treatment or prolonged thermal exposure.

Stress corrosion cracking susceptibility is higher in 2xxx-series alloys than in many non-heat-treatable grades, particularly under tensile stress and corrosive conditions. Galvanic interactions require attention: 2118 couples more anodically than steels but more cathodic than pure aluminum depending on surface treatment; isolation or compatible fasteners and coatings are often necessary. Compared with 6xxx series, 2118 trades corrosion resistance for higher strength and fatigue resistance, so selection balances environment versus mechanical requirements.

Fabrication Properties

Weldability

Welding 2118 is challenging relative to many other aluminum families because the Cu content promotes hot-cracking and HAZ softening. Gas tungsten arc (TIG) and gas metal arc (MIG) welding are possible with strict control of heat input, preheating/quenching practices, and selection of filler alloys such as Al-Cu-Mg fillers or lower-strength 4043/2319-type fillers to reduce cracking risk. Post-weld heat treatment can restore some strength but full restoration to T6 levels is difficult due to precipitate dissolution and coarsening in the HAZ.

Machinability

2118 machines well in the annealed and certain intermediate tempers, with good chip control and moderate tool wear due to the presence of copper and manganese particles. Carbide tooling with positive rake, rigid fixturing and flood cooling produce consistent surface finish and tight dimensional tolerance; speeds should be conservative for peak-age tempers to avoid rapid tool wear. Machinability index is generally superior to high-strength Al-Zn-Mg alloys but inferior to free-machining 2011 or commercial-purity 1100.

Formability

Forming is best performed in O, H14 or T4 tempers where ductility is sufficient for stamping, bending and drawing operations. Minimum bend radii depend on temper and thickness, but designers typically use 2–3× material thickness for tight bends in intermediate temper and larger radii for T6. Cold working increases strength by work hardening but can introduce residual stresses that interact with subsequent heat treatments; warm forming or pre-aging strategies may be used to optimize final properties.

Heat Treatment Behavior

As a heat-treatable alloy, 2118 responds to standard solution treatment, quench and aging cycles used for Al-Cu alloys. Typical solution treatment is performed near 495–505 °C to dissolve Cu-rich phases into the matrix, followed by rapid quenching to retain a supersaturated solid solution. Artificial aging is commonly carried out in the 160–190 °C range for several hours to generate fine precipitates and achieve T5/T6 conditions; aging time and temperature trade-off peak strength versus toughness and stress-corrosion cracking resistance.

Transitioning tempers is straightforward: solution-treated material can be naturally aged to T4 or artificially aged to T5/T6; T651 involves solution treatment, stretching to relieve residual stresses, and then artificial aging. Overaging at higher temperatures or prolonged aging times coarsens precipitates and reduces strength while improving ductility and corrosion resistance, so cycle control is critical for achieving the target engineering balance.

High-Temperature Performance

2118 shows notable strength loss with service temperature rise; sustained exposure above ~120–150 °C will reduce precipitate strengthening and progressively lower yield and tensile strength. Oxidation at elevated temperatures is limited in inert atmospheres but surface scale and changes in microstructure will occur if temperatures approach the solution-treat regime, which can irreversibly alter mechanical performance.

The heat-affected zone during welding experiences softening due to precipitate dissolution and coarsening, and recovery of properties through post-weld heat treatment is limited by quench-induced defects and residual stresses. For intermittent elevated-temperature use, designers should derate allowable stresses and consider alternative alloys optimized for high-temperature stability if operating temperatures frequently exceed 100 °C.

Applications

Industry	Example Component	Why 2118 Is Used
Aerospace	Fittings, brackets, and non-primary structural components	High specific strength and good fatigue resistance for weight-critical parts
Automotive	High-performance suspension members and structural brackets	Strength-to-weight and fatigue life balance for performance vehicles
Marine	Small structural elements and machined fittings	Good strength and machinability; requires coatings for corrosion protection
Defense	Missile and ordnance fittings	High strength and machinability for precision components
Electronics	Structural frames and thermal spreaders	Good thermal conductivity and stiffness per weight for assemblies

2118 is typically selected where a combination of high static and fatigue strength, acceptable machinability, and reasonable thermal conductivity are required. The alloy’s need for protective treatments in harsh environments is outweighed by its mechanical advantages in many aerospace and performance engineering contexts.

Selection Insights

Choose 2118 when elevated strength and fatigue resistance are primary design goals and when you can control corrosion protection and fabrication variables. It is particularly attractive for machined or formed components that benefit from heat-treatable strengthening and where higher-strength 7xxx alloys are either unnecessary or introduce unwanted brittleness or processing difficulty.

Compared with commercially pure aluminum (1100), 2118 sacrifices electrical conductivity and formability for markedly higher strength and fatigue life. Compared with common work-hardened alloys such as 3003 or 5052, 2118 offers substantially greater strength at the expense of weldability and inherent corrosion resistance, so 2118 is chosen when load-bearing performance outweighs ease of joining or forming. Compared with heat-treatable 6xxx alloys (e.g., 6061/6063), 2118 often provides better fatigue strength and higher peak strength for certain tempers, but it usually requires more careful corrosion protection and welding practices; select 2118 when its fatigue/strength profile fits the application and when the manufacturing chain can accommodate its heat-treatment and protection needs.

Closing Summary

Alloy 2118 remains a relevant engineering aluminum where the design requires a heat-treatable balance of high strength, good fatigue performance and acceptable machinability. Its use is optimized when engineers account for its temper-dependent ductility, corrosion protection needs, and fabrication sensitivities, allowing structures and components to achieve high performance at a favorable strength-to-weight ratio.