Aluminum 6061: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

6061 is a member of the 6xxx series of aluminum alloys, a family characterized by magnesium and silicon as the primary alloying elements that form the Mg2Si precipitate. This series is classified as heat-treatable; its mechanical properties are improved primarily by solution heat treatment, quenching, and subsequent artificial aging rather than by work-hardening alone.

The principal alloying elements in 6061 are magnesium (approx. 0.8–1.2%) and silicon (approx. 0.4–0.8%), with minor additions of chromium, copper, iron and other residuals that tune strength, toughness and grain structure. Typical traits include a favorable strength-to-weight ratio in T6 temper, good corrosion resistance in many environments, reasonable formability in annealed or T4 conditions, and excellent weldability using standard aluminum processes.

Industries that commonly use 6061 include structural automotive components, marine fittings, general-purpose aerospace hardware, heat exchangers, and consumer recreational products. Engineers select 6061 when a balanced combination of strength, corrosion resistance and machinability is required, and when post-fabrication welding or anodizing is anticipated; it often competes with 6063 for extrusions and with 5xxx alloys for corrosion-critical marine work.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed condition for maximum ductility
T4	Moderate	High	Very Good	Very Good	Solution heat treated and naturally aged; good for forming before final aging
T5	Moderate-High	Moderate	Good	Very Good	Cooled from elevated temperature shaping and artificially aged
T6	High	Moderate	Fair	Good	Solution heat treated and artificially aged; common structural temper
T651	High	Moderate	Fair	Good	T6 with stress relief by mechanical stretching; used for plate/extrusions
H14	Moderate	Moderate	Fair	Very Good	Strain-hardened and partially annealed; used for formed components
H18	High	Low	Poor	Very Good	Full hard by strain; limited forming capability

The temper chosen for 6061 directly correlates with its microstructure and precipitate state, which determines yield and tensile strengths as well as ductility. Solution treating and aging (T6) produces fine Mg2Si precipitates that raise strength but reduce formability and increase susceptibility to HAZ softening after welding; annealed or T4 conditions restore formability at the expense of peak strength.

Chemical Composition

Element	% Range	Notes
Si	0.4–0.8	Silicon combines with Mg to form strengthening Mg2Si precipitates
Fe	≤0.7	Iron is an impurity that can form intermetallics and affect corrosion and machinability
Mn	≤0.15	Present in small amounts; can refine grain structure slightly
Mg	0.8–1.2	Primary strengthening element via Mg2Si; controls age-hardening response
Cu	0.15–0.4	Improves strength and machinability but can reduce corrosion resistance
Zn	≤0.25	Minor; excessive Zn is avoided to prevent hot cracking and property shifts
Cr	0.04–0.35	Helps control grain structure and limits recrystallization during processing
Ti	≤0.15	Grain refiner in castings and some mill products
Others	≤0.15 (each)	Residuals and trace elements; Al balance

The alloy’s performance is dictated by the balance between magnesium and silicon, which together form Mg2Si precipitates during aging and provide the principal source of strength. Minor additions such as chromium and trace elements refine grain structure and reduce susceptibility to localized corrosion and hot working defects, while copper trades off some corrosion resistance for elevated strength and machinability.

Mechanical Properties

Tensile behavior of 6061 varies strongly with temper. In T6 condition, a fine distribution of Mg2Si precipitates gives relatively high yield and tensile strengths with moderate ductility; elongation is typically reduced versus annealed states.

Fatigue strength of 6061 is reasonable for light structural loading but is strongly influenced by surface finish, heat treatment and presence of welds; fatigue cracks can initiate at notches and weld HAZ-softened zones. Thickness and product form also alter mechanical response: thinner gauges often allow higher measured yield and elongation due to through-thickness cooling and residual stress differences, while thick plate may exhibit lower measured ductility and require T651-type stress relief.

Property	O/Annealed	Key Temper (T6 / T651)	Notes
Tensile Strength	~70–150 MPa (10–22 ksi)	~260–320 MPa (38–46 ksi)	T6 values commonly cited ~290 MPa; ranges depend on form and testing standard
Yield Strength	~35–90 MPa (5–13 ksi)	~240–275 MPa (35–40 ksi)	T6 yield commonly ~240 MPa; O condition much lower for forming
Elongation	15–25%	8–12%	Elongation decreases with increasing temper strength
Hardness	~30–60 HB	~80–110 HB	Hardness correlates with age-hardening; T6 substantially harder than O

Physical Properties

Property	Value	Notes
Density	2.70 g/cm³ (0.0975 lb/in³)	Typical for wrought aluminum alloys; favors lightweight structures
Melting Range	~582–652 °C	Solidus-liquidus range varies with minor constituents; Al base ~660 °C
Thermal Conductivity	~150 W/m·K	Good thermal conductor relative to steels; useful for heat sinks and exchangers
Electrical Conductivity	~30–40 % IACS	Lower than pure Al due to alloying; acceptable for some electrical applications
Specific Heat	~0.90 kJ/kg·K	High specific heat relative to many metals; affects thermal mass
Thermal Expansion	~23–24 µm/m·K (20–100 °C)	Moderate coefficient; important for differential expansion with mating materials

6061’s relatively high thermal conductivity and low density make it attractive where heat dissipation and lightweight design are both required, such as heat sinks and vehicle components. The melting range and thermal expansion govern choices in welding, brazing and design where dissimilar materials are used; coefficients of expansion may require allowance in joint design to prevent distortion.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.2–6.0 mm (0.008–0.25 in)	Good uniformity	O, H14, T4, T6	Widely used for panels and formed parts
Plate	6–200 mm (0.25–8 in)	Lower through-thickness ductility in thick sections	T651, T6	Thick plate often supplied stress-relieved (T651)
Extrusion	Profiles up to several meters long	Strength varies with section and cooling	T5, T6	6061 extrudes well; common for structural profiles and frames
Tube	Diameters small to large; welded or seamless	Similar to sheet/plate in temper behavior	O, T4, T6	Used for chassis, rails and hydraulic components
Bar/Rod	Diameters up to several inches	Homogeneous microstructure in drawn bars	O, T6	Common for machined components and fittings

Processing differences dictate which form and temper are chosen: extrusions are frequently T5 or T6 because they are artificially aged after shaping, while plate is often supplied in T651 for dimensional stability. Sheet and tube are selected based on forming needs; annealed (O) or T4 conditions permit deeper drawing and bending, whereas T6 gives better as-fabricated strength but limits cold formability.

Equivalent Grades

Standard	Grade	Region	Notes
AA	6061	USA	Aluminum Association designation for wrought 6xxx series alloy
EN AW	6061	Europe	EN AW-6061 is the common European designation (wrought alloy)
JIS	A6061	Japan	JIS grade A6061 corresponds to similar chemistry and tempers
GB/T	6061	China	GB/T 6061 is the commonly used Chinese standard for this alloy

Standards across regions are harmonized by chemistry and temper definitions but differ in permitted impurity limits, mechanical test methods and temper suffix nomenclature. Buyers should verify the specification sheet for the applicable standard to ensure required minimum properties, heat-treatment history and permitted tolerances, since nominal “6061” can vary slightly between suppliers and national standards.

Corrosion Resistance

6061 exhibits good general atmospheric corrosion resistance owing to the protective aluminum oxide film and the relatively low content of copper compared with some 2xxx series alloys. In rural and industrial atmospheres it performs well, and anodizing further enhances surface corrosion protection and appearance.

In marine environments, 6061 provides acceptable performance for many structural and non-critical applications, but it is less durable than the 5xxx (Mg-based) series when continuously exposed to chloride-rich seawater. Localized pitting can occur in stagnant, highly saline conditions; design attention to drainage, coating, and anodizing is important for long-term performance.

Stress corrosion cracking (SCC) is not a prominent hazard in 6061 for many service conditions, but susceptibility increases in high-strength tempers and when exposed to elevated stresses in chloride environments. Galvanic interaction with more noble metals (e.g., stainless steel, copper) can accelerate localized corrosion, so electrical isolation or sacrificial anode strategies should be considered in mixed-metal assemblies.

Fabrication Properties

Weldability

6061 welds very well by common fusion methods such as TIG (GTAW) and MIG (GMAW); weldability is one of its key engineering advantages compared to higher-strength heat-treatable alloys. Typical filler alloys are 4043 (Al-Si) for improved fluidity and reduced cracking tendency, and 5356 (Al-Mg) when higher-strength welds and color match are desired; filler choice influences corrosion resistance and strength of the joint.

Post-weld heat-affected zones will typically soften relative to T6 parent metal due to dissolution or coarsening of precipitates, so for critical structural parts a post-weld heat treatment or use of T651/base in design is recommended. Hot-cracking risk is low relative to some Al-Cu alloys, but joint design, restraint and cleanliness are essential to avoid porosity and incomplete fusion.

Machinability

6061 is considered to have good machinability among aluminum alloys; it machines cleaner and faster than many high-strength alloys while providing a good surface finish. Carbide tooling is commonly used at moderately high cutting speeds, and lubricants/coolants reduce built-up edge and improve chip evacuation; chips are generally short and easily managed if parameters are controlled.

Feed and speed selection should account for temper and section thickness; higher strengths (T6) raise cutting forces and tool wear relative to annealed material. For precision components, control of burr formation and secondary deburring is often necessary.

Formability

Formability depends strongly on temper: annealed (O) and T4 states form well and tolerate tight bends and deep draws, while T6 has limited cold formability and is prone to cracking at high strain. Recommended minimum inside bend radii for 90° bends in annealed sheet typically approach R/t ≈ 1–2 for mild forming, whereas T6 requires larger radii or pre-heat/solution treatment and re-aging to achieve comparable shapes.

When moderate forming is required followed by final aging, a T4 forming-to-T6 aging sequence is commonly used to optimize both geometry and final strength. Designers should account for springback and anisotropy from rolling, choosing appropriate grain direction and tooling to minimize cracking.

Heat Treatment Behavior

Solution treatment for 6061 is typically performed in the range of approximately 520–560 °C to dissolve Mg2Si and other soluble constituents into a supersaturated solid solution, followed by rapid quenching to retain solute in supersaturation. Artificial aging is then performed at lower temperatures (commonly 160–190 °C) for several hours to precipitate fine, strengthening Mg2Si particles and produce the T6 condition; the time-temperature profile controls the balance of strength and toughness.

T4 is the naturally aged state after solution treatment and quenching, offering good formability for subsequent shaping before artificial aging to T6 or T5. Stabilized tempers such as T651 include a controlled stretching or stress-relief operation after quench to reduce residual stresses and distortion in thick plate and extrusions.

High-Temperature Performance

6061 experiences progressive strength loss as temperature increases; significant reductions in yield and tensile strength occur above approximately 100–150 °C, with recommended continuous-use limits generally below ~120 °C for load-bearing structural applications. At elevated temperatures the stability of Mg2Si precipitates is reduced, and creep may become relevant for sustained loads at high temperature or in aggressive environments.

Oxidation at service temperatures typical for 6061 is minimal compared to steels, but protective coatings or anodizing are still used to manage long-term surface degradation and appearance. The HAZ of welded components can exhibit altered high-temperature behavior because of precipitate coarsening, so thermal exposures should be controlled to preserve design margins.

Applications

Industry	Example Component	Why 6061 Is Used
Automotive	Structural brackets, chassis rails	Balanced strength, weldability and corrosion resistance
Marine	Boat fittings, railings	Good corrosion resistance and weldability in moderate marine use
Aerospace	Fittings, adaptors, interior structures	Favorable strength-to-weight and good machining characteristics
Electronics	Heat sinks, housings	High thermal conductivity and ease of machining
Recreational	Bicycle frames, camping equipment	Lightweight, weldable and cost-effective

6061 is favored in applications where a combination of machinability, weldability, moderate-to-high strength and corrosion resistance is required without the premium cost or specialized processing of higher-strength aluminum alloys. Its versatility across product forms and temper options supports a wide range of engineering designs.

Selection Insights

When selecting an aluminum for general structural and welded components, 6061 is a good first choice if you need a balance between strength, corrosion resistance and ease of fabrication. Its T6 temper provides respectable yield and tensile strength while retaining weldability with common filler metals, though designers must account for HAZ softening in welded assemblies.

Compared with commercially pure aluminum (1100), 6061 trades some electrical and thermal conductivity and formability for markedly higher strength and better machinability. Compared with work-hardened alloys such as 3003 or 5052, 6061 offers higher strength from heat treatment but typically less ductility and somewhat reduced chloride corrosion resistance.

• Choose 6061 over 6063 when higher strength and improved machinability are needed despite 6063’s slightly better extrusion surface finish and anodizing characteristics.
• Prefer 5xxx alloys for continuous, highly chloride-exposed marine service where corrosion resistance is the overriding requirement.
• Select annealed or T4 tempers when forming complexity is high, then age to T6 where post-forming strength is required.

Closing Summary

6061 remains one of the most widely used wrought aluminum alloys because it offers a pragmatic balance of strength, corrosion resistance, weldability and machinability across many product forms and tempers. Its adaptability to standard heat treatments, maturity of supply, and predictable performance make it a reliable choice for designers and manufacturers in diverse industries.