Aluminum 2018: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

Alloy 2018 is part of the 2xxx series of aluminum alloys, a class distinguished primarily by copper as the major alloying element. The 2xxx family is recognized for high strength produced by precipitation hardening, and 2018 typically contains elevated copper plus controlled amounts of manganese, iron, and magnesium to tailor strength and toughness.

2018 is a heat-treatable alloy that strengthens by solution heat treatment, quenching, and artificial aging to precipitate Al2Cu and associated phases; work hardening plays a secondary role in some tempers. The alloy delivers high static strength and good machinability but has relatively poor inherent corrosion resistance and limited weldability compared with many 5xxx and 6xxx alloys.

Typical industries using 2018 include aerospace fittings and structural elements, military hardware, tooling and fixtures, and certain high-strength automotive applications where strength-to-weight is paramount and corrosion can be managed by cladding or coatings. Engineers select 2018 when its combination of high strength, good fracture toughness after aging, and machinability outweighs penalties in atmospheric or marine corrosion resistance and weldability.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed; best for forming and brazing
H14	Moderate	Low–Moderate	Fair	Poor	Strain-hardened; limited ductility
T3	Moderate-High	Moderate	Fair	Poor	Solution heat-treated, cold worked, naturally aged
T4	Moderate-High	Moderate	Fair	Poor	Solution heat-treated and naturally aged
T5	High	Low–Moderate	Limited	Poor	Cooled from elevated temperature and artificially aged
T6	High	Low–Moderate	Limited	Poor	Solution heat-treated and artificially aged for peak strength
T651	High	Low–Moderate	Limited	Poor	T6 with stress relief by stretching to reduce distortion

Temper has a major influence on 2018 properties because the copper-rich precipitates control strength and toughness. Annealed (O) material is used where forming is dominant, while T6/T651 are used when maximum strength and dimensional stability are required despite reduced ductility.

Processing route (cold work prior to aging, stretch straightening) also adjusts residual stresses and fatigue life; specifying the temper must match intended fabrication and service conditions to avoid over- or under-designing components.

Chemical Composition

Element	% Range	Notes
Si	0.15 max	Impurity; low silicon minimizes brittle intermetallics
Fe	0.5–1.2	Impurity; increases strength but can reduce ductility
Mn	0.4–1.0	Controls grain structure and improves fracture toughness
Mg	0.2–0.8	Contributes to age hardening synergy with Cu
Cu	3.5–5.0	Principal strengthening element (forms Al2Cu precipitates)
Zn	0.25 max	Minor; limited contribution to strength
Cr	0.1–0.3	Grain structure control; reduces recrystallization
Ti	0.05–0.20	Grain refiner for wrought products
Others / Al balance	Balance	Residuals and trace elements; aluminum constitutes the balance

The performance of 2018 is dominated by copper content which enables precipitation hardening and high aged strength. Minor additions such as manganese and chromium refine grain structure and stabilize mechanical properties during thermal excursions and working, while iron and silicon levels are controlled to limit deleterious intermetallics that would embrittle the alloy.

Mechanical Properties

In peak-aged tempers (T6/T651) 2018 exhibits high ultimate tensile strength and good yield strength relative to most wrought aluminum alloys, making it suitable for high-load structural components. Elongation in peak tempers is constrained but adequate for many machined or lightly formed components; fatigue strength is reasonable but sensitive to surface finish and corrosion state.

Annealed (O) 2018 shows much greater ductility and lower yield/tensile strengths, which is beneficial for forming and bending processes but requires subsequent heat treatment for structural applications. Thickness also influences yield and tensile properties; heavier sections can be difficult to solution-treat uniformly and may show reduced aging response or differential properties across section thickness.

Hardness in peak tempers rises significantly relative to O condition and correlates with tensile metrics; however, hardness and strength degrade in heat-affected zones during fusion welding and during overaging at elevated service temperatures. Fatigue crack initiation in aged 2018 often originates at machining marks or corrosion pits, so surface treatment and design for crack arrest are critical.

Property	O/Annealed	Key Temper (e.g., T6/T651)	Notes
Tensile Strength	~200–260 MPa	~430–520 MPa	T6 yields substantially higher UTS due to precipitate strengthening
Yield Strength	~70–150 MPa	~320–380 MPa	Yield increases with age; cold working raises yield further in some H tempers
Elongation	>20%	~6–12%	Ductility drops in peak-aged tempers; depends on section thickness
Hardness (Brinell)	~40–60 HB	~110–140 HB	Correlates with tensile; HAZ softening reduces local hardness after welding

Physical Properties

Property	Value	Notes
Density	~2.78–2.82 g/cm³	Slightly higher than pure Al due to Cu content
Melting Range	~500–635 °C	Solidus–liquidus range; alloys melt over a range, not at a single point
Thermal Conductivity	~120–150 W/m·K	Lower than pure Al; Cu reduces conductivity
Electrical Conductivity	~20–35% IACS	Copper lowers conductivity compared to 1xxx alloys
Specific Heat	~0.88–0.92 J/g·K	Similar to other Al alloys; varies slightly with temperature
Thermal Expansion	~23–24 µm/m·K (20–100°C)	Comparable with other Al alloys; important for thermal cycling design

2018’s thermal and electrical transport properties are reduced relative to commercially pure aluminum due to copper and other alloying elements. These reductions matter when 2018 is chosen for thermal management; other alloys or copper may be preferable when conductivity is critical.

The melting and solidification characteristics affect heat treatments and welding; the relatively broad melting range increases susceptibility to hot cracking during fusion welding and requires controlled heating/cooling cycles during solution treatment to avoid incipient melting.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.5–6 mm	Good in T6; O for forming	O, T3, T4, T6, T651	Widely used for machined parts and small structures
Plate	>6 mm up to 150+ mm	Section sensitivity in heat treatment	O, T6 (where possible)	Thick plates are difficult to age uniformly
Extrusion	Profile dependent	Good axial strength; age-hardenable	T6 after ageing	Limited by hot-workability and dissolution of Cu phases
Tube	Various diameters/wall thicknesses	Similar to extrusions when aged	O, T6	Used for structural tubing and fittings when strength needed
Bar/Rod	Diameters from few mm to 150 mm	Good machinability in aged condition	O, T3, T6	Common for turned components and fasteners

Form factor and processing route significantly influence achievable mechanical properties because heat treatment effectiveness varies with section size and cooling rate. Sheets and thin extrusions can be solution treated and aged more uniformly than thick plates, so selection of product form must consider both fabrication and final mechanical requirements.

Cold working prior to aging (T3) provides a trade-off between dimensional stability and final strength, while O condition facilitates complex forming operations; designers should coordinate supplier capabilities (e.g., solution treating thick sections) with intended service loads.

Equivalent Grades

Standard	Grade	Region	Notes
AA	2018	USA	Primary Aluminum Association designation
EN AW	2018 / 2018A	Europe	Often listed as EN AW-2018A; chemical and mechanical spec tolerances may differ
JIS	A2018	Japan	Local spec differences in impurity limits and tempers
GB/T	2A01	China	Chinese standard designation; limited interchange without checking specs

Equivalent designations exist but are not universally identical; micro-alloy limits, allowed impurities, and temper specifications can vary between standards. Engineers must consult the precise standard and mill certificates when substituting material sourced from different regions to ensure matching mechanical properties and heat-treatment response.

Corrosion Resistance

2018 has significantly lower general atmospheric and pitting corrosion resistance than most 5xxx and 6xxx series alloys due to its copper content, which promotes localized corrosion and intergranular attack in aggressive environments. In marine and chloride-containing atmospheres, unprotected 2018 is prone to pitting and crevice corrosion, and it typically requires cladding (alclad) or robust coatings for long-term service.

The alloy is also more susceptible to stress corrosion cracking (SCC) than lower-copper alloys, especially when in high-strength tempers and under tensile stress in corrosive environments. Galvanic interactions must be considered: 2018 is anodic relative to stainless steels and copper-nickel alloys, creating galvanic currents if left electrically coupled in a conductive environment.

For applications where corrosion exposure is unavoidable, design measures such as coatings, cathodic protection, isolation with nonconductive fasteners, and specifying cladded products are common. Comparatively, 6xxx-series alloys offer much better weldability and corrosion resistance albeit at somewhat lower peak strength, which often drives alloy trade-offs.

Fabrication Properties

Weldability

Fusion welding of 2018 is challenging; the copper-rich matrix reduces weldability and increases susceptibility to hot cracking and porosity. Typical practice avoids fusion welding for highly loaded structures and instead uses mechanical fastening, brazing with appropriate fluxes, or friction stir welding which greatly reduces HAZ softening and cracking. When welding is necessary, matched or compatible filler alloys such as Al-Cu fillers (e.g., 2319/4043 variants depending on service) and strict pre/post-heat controls are recommended, with an expectation of reduced local mechanical properties in the HAZ.

Machinability

2018 is often rated as good to excellent for machinability among high-strength aluminum alloys because aged 2xxx alloys machine cleanly and produce predictable chip formation. Carbide tooling with positive rake, rigid setups, flood cooling, and chip breakers help control built-up edge and maintain dimensional accuracy. Typical practice uses moderate to high cutting speeds, relatively light depth of cut for finish passes, and tools designed for interrupted cuts when encountering work-hardened areas.

Formability

Formability of 2018 is strongly temper-dependent; O temper provides the best bend radii and stretch formability while T6/T651 have limited ductility and require larger bend radii. For bending, a minimum inside bend radius of approximately 1–2× material thickness is a practical starting point in O condition, while peak-aged tempers may need >3× thickness and careful die design. Where complex forming is required followed by high-strength service, forming in O condition followed by solution treatment and aging (if feasible) can be used, but this requires control of distortion and potential softening during subsequent heat treatment.

Heat Treatment Behavior

Solution treatment of 2018 is performed to dissolve Cu-rich phases into the aluminum matrix, typically at temperatures in the general range of approximately 500–535 °C depending on section thickness and foil/plate limitations. Uniform heating and rapid quench are critical to retain the solute in supersaturated solid solution; slower quench rates in thick sections can allow coarse precipitates to form and reduce subsequent age hardening potential.

Artificial aging (T6) is performed at temperatures commonly between ~150–190 °C for several hours to nucleate and grow fine Al2Cu precipitates that raise yield and tensile strengths; aging cycles are selected to balance peak strength with acceptable toughness and to avoid overaging. Overaging or exposure to elevated temperatures in service will coarsen precipitates and lower both hardness and strength, shifting properties toward T4-like conditions.

Temper designations reflect processing history: T3 indicates solution treatment, cold work, and natural aging whereas T4 is solution treated and naturally aged. Transitioning between tempers (for example, re-solution treating a T6 part) will reset the aging clock but can induce distortion and metallurgical changes; therefore, post-heat-treatment straightening or stress-relief (T651) are commonly specified for precision components.

High-Temperature Performance

2018 experiences significant strength loss with increasing temperature because the fine precipitates that provide age hardening coarsen and dissolve between approximately 120–200 °C, depending on aging condition and exposure time. As a result, long-term service is typically limited to moderately elevated temperatures, and components expected to see sustained temperatures above ~150 °C should be evaluated for creep and reduction in yield strength.

Oxidation at elevated temperatures is similar to other aluminum alloys and generally forms a passive aluminum oxide layer, but combined thermal and corrosive environments (e.g., hot salt sprays) can accelerate degradation. HAZ regions after welding can be particularly vulnerable to strength loss and grain growth at elevated service temperatures, so design margins and post-weld treatments must account for localized weakening.

Applications

Industry	Example Component	Why 2018 Is Used
Aerospace	Fittings, brackets, fasteners	High strength-to-weight and good fracture toughness in aged tempers
Military / Defense	Structural hardware, mounts	High static strength and machinability for critical components
Automotive	High-strength machined brackets, tooling	Strength with good machinability where corrosion is controlled
Tooling / Fixtures	Jigs, dies, mandrels	Dimensional stability (T651) and hardness for wear resistance
Electronics	Certain structural frames	Stiffness and strength for small structural elements

2018 is chosen for components where peak aged strength, machinability, and stable mechanical properties under static loads are required and where corrosion exposure can be mitigated. Coating, cladding, or controlled environments are typically used to extend service life in corrosive settings.

Selection Insights

For an engineer choosing between 2018 and low-alloy or commercially pure aluminum, trade-offs are clear: compared with 1100, 2018 sacrifices electrical and thermal conductivity and formability in favor of substantially higher strength, which is useful for load-bearing machined parts.

Against common work-hardened alloys such as 3003 or 5052, 2018 offers significantly higher peak strength and better machinability but poorer corrosion performance and worse weldability; choose 2018 when strength and fatigue life matter more than corrosion robustness.

Compared with heat-treatable alloys like 6061 or 6063, 2018 often provides comparable or higher strength in certain tempers and better machinability for specific machining-heavy components; however, 6061 offers better weldability, corrosion resistance, and a more forgiving aging response, so 2018 is preferred only when the specific strength, toughness, or wear resistance profile of Al-Cu precipitates is required.

Closing Summary

Alloy 2018 remains relevant where high static strength, reliable aging response, and good machinability are decisive selection criteria and where corrosion and welding constraints can be managed by design, cladding, or coating. Its role continues in aerospace, defense, and specialized industrial applications where the Al–Cu precipitation hardening system delivers mechanical performance not easily achieved by other wrought aluminum alloys.