Aluminum A206: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

A206 is a 2xx-series aluminum alloy in which copper is the principal alloying element and precipitation hardening is the dominant strengthening mechanism. The composition and processing make A206 a heat-treatable alloy capable of substantially higher strength than wrought Al-Mg and commercially pure grades while retaining reasonable fracture toughness for structural applications. Key traits of A206 include high specific strength, moderate-to-poor general corrosion resistance relative to Al-Mg alloys, limited weldability in high-strength tempers, and moderate formability that improves when supplied in softer tempers. Typical industries using A206 include aerospace fittings and forgings, high-performance automotive components, tooling plates, and defense components where strength-to-weight is critical and post-weld or post-form heat treatment is feasible.

Engineers select A206 when a combination of elevated tensile/yield strength and acceptable fatigue resistance are required in components that can be processed by solution treatment and artificial aging. The alloy is chosen over 1xxx/3xxx family alloys when strength greatly outweighs the need for maximum corrosion resistance or electrical conductivity. A206 is preferred over some higher-strength Al-Zn-Mg (7xxx) alloys when a balance of toughness, fatigue performance, and stable aging behavior is needed, or when crack propagation properties are prioritized. Suppliers and specifications vary, so design-level selection typically assumes supplier-provided certified mechanical and chemical data.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed condition for forming and drawing
H14	Medium	Moderate	Fair	Poor–Moderate	Strain-hardened for increased strength, limited to thinner gauges
T5	Medium–High	Moderate	Fair	Poor	Cooled from forming and artificially aged; good for cast/extruded parts
T6	High	Low–Moderate	Limited	Poor	Solution heat-treated and artificially aged for peak strength
T651	High	Low–Moderate	Limited	Poor	Solution treated, stress relieved by stretching, then artificially aged
H112	Medium	Moderate	Fair	Poor–Moderate	Partially annealed; specified for inconsistent tempers from processing

Temper choice controls the balance between strength and ductility for A206. O and H-temper variants are used for forming operations because they provide higher elongation and better bendability, while T-tempers (T5, T6, T651) deliver peak strength but reduce formability and increase susceptibility to cracking during welding. Designers must coordinate temper with downstream fabrication steps: forming operations should precede solution heat treatment where feasible to avoid springback and cracking in hardened conditions.

Chemical Composition

Element	% Range	Notes
Si	≤ 0.5 (typical)	Deoxidizer; higher Si lowers melting range and improves castability
Fe	≤ 0.5	Impurity element; small amounts reduce ductility and may form intermetallics
Mn	≤ 0.6	Grain structure control and strength via dispersion
Mg	0.1–0.8	Secondary strengthening element; influences age hardening kinetics
Cu	~3.5–6.0	Primary strengthening solute; drives precipitation hardening (Al2Cu-type precipitates)
Zn	≤ 0.25	Minor; excessive Zn can reduce corrosion resistance
Cr	≤ 0.2	Controls grain growth during solution treatment
Ti	≤ 0.15	Grain refiner during solidification and casting
Others (each)	≤ 0.05–0.15	Trace elements and impurity allowances; balance Al

Copper is the principal strengthening element in A206 and controls peak hardness and strength through controlled solution treatment and aging. Minor additions such as Mg and Mn modify precipitation kinetics and grain structure, respectively, improving toughness and resistance to overaging, while silicon and iron are typically kept low to avoid coarse intermetallics that degrade fatigue and toughness.

Mechanical Properties

A206 exhibits a wide span of mechanical behavior depending on temper and product form, from ductile annealed conditions to high-strength precipitation-hardened states. In T6-type conditions the alloy attains substantially higher tensile and yield strengths driven by a fine dispersion of Al-Cu intermetallic precipitates; however, ductility and fracture toughness are reduced relative to annealed material. Fatigue performance is generally favorable for fatigue initiation-resistant designs because the alloy combines high strength with a toughness that is better than some high-strength Al-Zn-Mg alloys, but surface finish and corrosion condition strongly influence fatigue life.

Thickness and processing history have meaningful effects on mechanical data: thicker forgings and plates can show slightly lower peak strengths due to differential quench rates and coarser precipitate distributions. Residual stresses, degree of cold work before aging, and temper stability during welding or local heating also alter the local yield and ultimate properties significantly. Designers should use supplier test certificates and production-specific mechanical curves when performing stress analyses.

Property	O/Annealed	Key Temper (e.g., T6 / T651)	Notes
Tensile Strength	~110–170 MPa (typical)	~400–480 MPa (typical peak range)	Values dependent on thickness, temp, and heat treatment; supplier data required
Yield Strength	~40–110 MPa	~300–380 MPa	T6 often yields ~300–360 MPa for common product forms
Elongation	15–30%	6–12%	Ductility falls with age-hardening; elongation varies with gauge and temper
Hardness (HB)	~30–55	~100–140	Brinell hardness correlates to tensile; higher in T6/T651 states

Physical Properties

Property	Value	Notes
Density	~2.77–2.83 g/cm³	Slightly higher than pure aluminum due to Cu content
Melting Range	Solidus ~500–520 °C, Liquidus ~630–650 °C	Alloy melting interval; important for casting and heat treatment control
Thermal Conductivity	~110–150 W/m·K (approx)	Reduced relative to pure Al due to alloying; depends on temper and microstructure
Electrical Conductivity	~20–35 % IACS (approx)	Lower than pure Al; copper additions reduce conductivity
Specific Heat	~0.86–0.90 kJ/kg·K	Typical for Al alloys near room temperature
Thermal Expansion	~23–24 µm/m·K (20–100 °C)	Typical thermal expansion; considerations for bolted assemblies and joins

A206’s thermal and electrical properties are intermediate between high-purity aluminum and heavily alloyed high-strength aluminum families. The copper content lowers conductivity and thermal diffusivity compared with pure Al but still permits reasonable heat spreading for many structural components. The melting range and quench sensitivity materially influence heat treatment processing windows and the potential for hot cracking or uneven properties in thicker sections.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.5–6 mm	Can reach T6 strengths after heat treatment	O, H14, T4, T5, T6	Thickness affects quench rate and final strength
Plate	6–100+ mm	Reduced peak strength in very thick sections due to slower quench	O, T6, T651	Often used for forgings, tooling, structural plates
Extrusion	Sections up to several hundred mm	Good for complex profiles; aging state required for peak strength	T5, T6	Extrusion cooling rate affects precipitate distribution
Tube	1–20 mm wall	Similar behavior to sheet for thin-walled tubes	O, T6	Used in structural and hydraulic applications
Bar/Rod	Ø2–100 mm	Forged or drawn bars show good fatigue and strength after aging	O, T6	Machinable grades are often provided in rod form

Form selection strongly affects final mechanical performance because section thickness controls cooling rates during quenching and thus precipitate size and distribution. Sheets and thin extrusions can reach near-peak tempers after standard solution treatment and quench, whereas thick plates and forgings may require more aggressive quench media, intercritical regimes, or modified temper specifications (e.g., T651) to manage distortion and residual stresses.

Equivalent Grades

Standard	Grade	Region	Notes
AA	A206	USA	Aluminum Association designation commonly used in supplier literature
EN AW	No direct equivalent	Europe	No single direct EN AW counterpart; nearest functional family is EN AW-2xxx (e.g., AW-2024)
JIS	No direct equivalent	Japan	JIS often maps to 2xx-series alloys but a direct JIS code for A206 is uncommon
GB/T	No direct equivalent	China	Chinese standards may list functional 2xx-series alloys; exact matches require cross-referencing

A206 does not always have a one-to-one equivalent in every regional standard; many suppliers will list the alloy as AA A206 or provide chemical and mechanical equivalence to better-known alloys such as 2024 for design intent. Subtle differences in impurity limits, trace elements, and permitted processing routes produce variations in fatigue, fracture toughness, and SCC susceptibility between nominally similar 2xx alloys. Always reference the exact specification sheet or international cross-reference provided by material certification.

Corrosion Resistance

In general atmospheric environments A206 displays moderate corrosion resistance but is inferior to Al-Mg (5xxx) and commercially pure (1xxx) alloys. The presence of copper increases susceptibility to pitting and intergranular corrosion, especially when exposed to chloride-rich marine atmospheres or in crevice conditions. Protective surface treatments such as cladding with purer aluminum, anodizing, or appropriate conversion coatings are commonly used to mitigate localized corrosion risks.

A206 is more prone to stress corrosion cracking (SCC) than many Al-Mg alloys when in peak-aged tempers; the SCC risk rises under sustained tensile stress in corrosive media. Galvanic interactions are significant: when coupled to more noble metals such as stainless steels or copper alloys, A206 will act anodic and corrode preferentially unless electrically isolated or coated. Compared with 7xxx zinc-bearing high-strength alloys, A206 can offer slightly better corrosion stability in some heat-treatment conditions, but inferior to Al-Mg alloys for long-term marine exposure.

Fabrication Properties

Weldability

Welding of A206 in high-strength tempers is challenging because copper-rich precipitates and a wide solidification range increase hot-cracking risk and produce significant heat-affected zone (HAZ) softening. Fusion welding techniques (TIG/MIG) typically require pre- and post-weld thermal treatments or the use of ductile filler alloys; Al-Cu filler alloys (e.g., 2319 family) or silicon-bearing fillers (e.g., 4043) are commonly used, but fillers influence final strength and corrosion behavior. Designers often avoid welding in T6 condition or plan for localized solution treatment and re-aging to restore properties.

Machinability

A206 has moderate machinability; the alloy machines better than many high-strength Al-Zn-Mg grades but not as well as leaded free-machining aluminum alloys. Carbide tooling with positive rake geometry and high-feed, moderate-speed strategies yield good surface finish and tool life. Chip control can be problematic when machining heavy sections; climb milling and chip-breaking features are recommended to avoid built-up edge formation.

Formability

Cold formability is best in the O or H-tempered states where elongation and bendability are high. Tight bend radii and complex stamping operations are typically performed in annealed condition, with subsequent solution heat treatment and aging if full strength is required. In T6 or other aged conditions the alloy has limited stretch formability and is prone to cracking at high deformation levels, so designers should specify forming tempers and consider warm forming for complex geometries.

Heat Treatment Behavior

As a heat-treatable Al-Cu alloy, A206 is conditioned by a solution heat treatment to dissolve Cu-bearing phases followed by rapid quenching and artificial aging to precipitate strengthening phases. Typical solution temperatures fall around the alloy’s solid-solution window (commonly about 500–535 °C for 2xx alloys), followed by water quench to room temperature to retain supersaturation. Artificial aging temperatures are commonly in the 150–190 °C range for times from a few hours up to tens of hours depending on desired hardness and overaging tolerance.

T temper transitions are critical: T4 (natural or stabilized) produces a relatively soft, ductile state, whereas T6 achieves near-peak hardness with higher yield strength. Overaging (e.g., prolonged aging or exposure to elevated service temperatures) coarsens precipitates, lowering strength but improving fracture toughness and SCC resistance. Proper control of quench rate and aging parameters is essential to avoid variability in properties across sections and to minimize distortion from heat treatment.

For production parts, stress-relief practices such as stretching (T651) are applied after quenching to reduce residual stresses and provide more stable dimensions during aging. Thick sections require attention to quench severity; interrupted quenching or tailored aging may be used to balance distortion control and mechanical performance.

High-Temperature Performance

A206 loses strength progressively with increasing temperature because precipitate stability decreases and diffusion-driven coarsening accelerates. Practical continuous-service limits for load-bearing structural applications are commonly kept below about 120 °C, while short-term exposures up to ~150–200 °C induce measurable softening and reduced yield strength. Oxidation is modest in air at these temperatures but prolonged high-temperature exposure will change microstructure and reduce peak-ageability.

Heat-affected zones from welding or localized heating during fabrication can exhibit substantial softening and loss of strength relative to the base T6 material. Designers must account for local property drops around joints and either perform post-weld heat treatments where feasible or design to the reduced HAZ properties in load-bearing calculations.

Applications

Industry	Example Component	Why A206 Is Used
Aerospace	Small structural fittings, forgings	High strength-to-weight and fatigue performance after aging
Marine	Motor mounts, non-exposed structural components	Good strength with moderate corrosion protection when coated or clad
Automotive	Suspension components, performance brackets	High static strength and fatigue resistance for lightweighting
Electronics	Enclosures, thermal spreaders (limited)	Acceptable thermal conductivity and machinability for structural housings

A206 is typically selected where high static and fatigue strengths are required and where components can be heat treated to achieve the necessary mechanical envelope. Surface protection strategies are routinely integrated when corrosion exposure is likely. The alloy's balance of machinability, formability in soft tempers, and the ability to reach high strength levels makes it suitable for aerospace and high-performance automotive detail parts.

Selection Insights

A206 is best selected when designers need stronger, heat-treatable aluminum than commercially pure grades and when the part processing sequence allows solution heat treatment and artificial aging. Specify O/H tempers for forming and T-tempers for final service when dimension control and strength are required. Consider coatings, cladding, or anodizing when corrosion exposure is significant.

Compared with commercially pure aluminum (1100), A206 trades conductivity and formability for substantially higher strength and better fatigue resistance, making it a poor choice where electrical or thermal conduction is primary but a strong choice for structural load-bearing parts. Compared with common work-hardened alloys (3003/5052), A206 offers higher peak strength but lower general corrosion resistance and weldability; use A206 when strength is the driving requirement and protective measures mitigate corrosion risk.

Compared with typical heat-treatable alloys such as 6061 or 6063, A206 can achieve comparable or higher yield at similar density in some tempers but often has worse weldability and corrosion behavior. Choose A206 over 6xxx alloys when higher intrinsic strength and specific fatigue or fracture properties are required and when fabrication can accommodate tailored heat treatments.

Closing Summary

A206 remains relevant in modern engineering as a high-strength, heat-treatable Al-Cu alloy that bridges the gap between conventional 6xxx structural alloys and very high-strength 7xxx alloys by offering a favorable combination of strength, toughness, and fatigue performance. Its utility depends on careful control of heat treatment, temper selection, and surface protection to manage corrosion and weldability trade-offs. For designs that require elevated strength with reasonable cost and machinability, A206 continues to be a practical choice when supplier certification and process controls are integrated into the manufacturing plan.