Aluminum A6061: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

6061 is a member of the 6xxx series of wrought aluminum alloys, characterized primarily by magnesium and silicon as the principal alloying elements. It is a heat-treatable alloy that attains strength through precipitation hardening (Mg2Si) after solution treatment, quenching, and artificial aging.

Typical traits include a favorable combination of moderate-to-high strength, good corrosion resistance in many environments, excellent weldability, and reasonable formability in softer tempers. This blend of properties makes 6061 attractive for structural components, transport and vehicle frames, general-purpose aerospace fittings, marine hardware, and instrumentation housings.

Engineers choose 6061 when a balance of strength, machinability, weldability, and corrosion performance is required without the premium cost or processing complexity of higher-strength 7xxx alloys. It is selected over softer 1xxx or 3xxx family alloys when structural load capacity is necessary, and over 2xxx family alloys when improved corrosion resistance and weldability are priorities.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed, maximum ductility for forming
H14	Low–Moderate	Moderate	Good	Excellent	Strain-hardened, limited forming after work hardening
H32	Moderate	Moderate	Good	Excellent	Strain-hardened and stabilized to retain some formability
T5	Moderate–High	Moderate	Fair	Excellent	Cooled from hot working and artificially aged
T6	High	Low–Moderate	Fair	Very Good	Solution heat-treated and artificially aged, common structural temper
T651	High	Low–Moderate	Fair	Very Good	T6 plus stress-relief by stretching or compressive stabilizing
T4	Moderate	Good	Good	Excellent	Solution heat-treated and naturally aged, used when post-forming age hardening is needed

Temper selection controls the trade-off between strength and ductility, with annealed (O) and T4 tempers prioritized for extensive forming operations and T5/T6/T651 chosen for structural applications requiring higher yield and tensile strength. Aging, whether natural (T4) or artificial (T5/T6), precipitates finely dispersed Mg2Si, increasing strength while reducing ductility and altering fatigue response and hardness.

Understanding the temper-specific softening in the heat-affected zone (HAZ) after welding is critical for design; T6 and similar tempers show HAZ softening that often reduces local strength, whereas O and T4 may regain strength through post-weld artificial aging if process constraints allow.

Chemical Composition

Element	% Range	Notes
Si	0.40–0.80	Silicon combines with Mg to form Mg2Si strengthening precipitates.
Fe	0.00–0.70	Iron is an impurity that forms intermetallics, reducing ductility and corrosion resistance.
Mn	0.00–0.15	Manganese refines grain structure and can improve strength slightly.
Mg	0.80–1.20	Primary strengthening element that forms Mg2Si with Si; controls age-hardening response.
Cu	0.15–0.40	Copper raises strength and age-hardening response but can reduce corrosion resistance.
Zn	0.00–0.25	Zinc is a minor impurity; higher levels can affect strength and corrosion behavior.
Cr	0.04–0.35	Chromium inhibits grain growth and improves toughness and resistance to stress-corrosion cracking.
Ti	0.00–0.15	Titanium is used as a grain refiner during casting and primary processing.
Others (each)	≤0.05	Trace elements such as V, Zr, and residuals; Al balance

The Mg and Si levels set the potential for precipitation hardening via Mg2Si; their ratio and distribution control the kinetics and magnitude of age-hardening. Minor additions and residual elements influence grain size, recrystallization, toughness, and susceptibility to intermetallic formation; careful compositional control is essential for consistent mechanical and corrosion behavior.

Mechanical Properties

Tensile behavior in 6061 is strongly temper-dependent. In solution-treated and artificially aged temper (T6), the alloy exhibits high yield and tensile strength with moderate ductility, enabling structural applications where predictable elastic and plastic response are required. Fatigue performance is reasonable for a general-purpose alloy, but highly influenced by surface finish, stress concentration, and tempering state.

Yield and ultimate strengths increase substantially from O/T4 to T6, while elongation and toughness fall correspondingly. Hardness follows the same trend; T6 presents a markedly higher Brinell or Rockwell hardness than O material. Thickness influences achievable properties due to quench sensitivity; thicker sections are more difficult to quench rapidly, which can reduce peak hardness after aging.

Property	O/Annealed	Key Temper (T6/T651)	Notes
Tensile Strength	90–160 MPa	275–350 MPa	T6 typical around 310 MPa; range depends on product form and thickness
Yield Strength	35–100 MPa	240–300 MPa	T6 typical around 275 MPa; yield defined by 0.2% offset
Elongation	18–25%	8–12%	Elongation decreases with increasing strength and reduced ductility
Hardness (Brinell)	35–60 HB	80–110 HB	Hardness correlates with precipitation state; T6 is substantially harder

Mechanical property values vary with product form, processing history, and testing direction. For critical structures designers must account for anisotropy from rolling or extrusion, the effect of weld HAZ softening on local strength, and potential strength reductions in thicker sections due to incomplete solutionizing or quench delays.

Physical Properties

Property	Value	Notes
Density	2.70 g/cm³	Typical for wrought aluminum alloys, used for mass and stiffness calculations
Melting Range (solidus–liquidus)	~582–652 °C	Alloy melting range depends on local composition and intermetallic content
Thermal Conductivity	~150 W/m·K	Lower than pure aluminum but still comparatively high for heat-sinking
Electrical Conductivity	~30–45 % IACS	Conductivity reduced by alloying; expressed as percentage of pure-copper reference (IACS)
Specific Heat	~900 J/kg·K	Typical specific heat for aluminum alloys near room temperature
Coefficient of Thermal Expansion	~23.5 ×10⁻⁶ /K	High thermal expansion relative to steels, important for thermal stress calculations

6061 provides favorable thermal conductivity for many heat-dissipation applications while maintaining a low density that benefits weight-critical designs. The relatively high coefficient of thermal expansion and moderate electrical conductivity must be considered when mating to dissimilar materials or designing thermal management systems. Material selection should account for temperature-dependent changes in modulus and yield in thermal cycling environments.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.2 mm – 6 mm	Good strength in thin gauges after aging	O, T4, T6	Widely used for panels, enclosures, and formed parts
Plate	6 mm – 200 mm	Thickness affects heat-treatment response	O, T6 (limited thickness)	Thick plates often have reduced attainable strength due to quench sensitivity
Extrusion	Complex profiles, lengths to many meters	Good directional strength along profile axis	T5, T6, T651	Extrusions enable complex cross-sections but show anisotropy in properties
Tube	Diameters few mm to 300+ mm	Strength similar to comparable cross-sections	O, T6	Seamless and welded tubes used for structural and hydraulic applications
Bar/Rod	Diameters and cross-sections	High longitudinal strength when age-hardened	T6, T651	Common for machined components and shafts

Sheets and extrusions are readily formed and heat-treated to design requirements; extruded profiles are particularly valuable for long linear components with integrated features. Plate and large-section parts require careful heat treatment and quench strategies to achieve uniform properties. Machining behavior and final mechanical properties are strongly linked to the chosen form and temper, so design specifications must call out both.

Equivalent Grades

Standard	Grade	Region	Notes
AA	A6061	USA	Aluminum Association designation commonly used in North America
EN AW	6061	Europe	Often listed as EN AW-6061 (AlMg1SiCu) under EN standards
JIS	A6061	Japan	Japanese Industrial Standard designation; similar chemical limits but different testing norms
GB/T	6061	China	Chinese standards reference alloy 6061 with comparable composition ranges

Equivalences are broadly consistent in chemistry but can differ in allowable limits for impurities, mechanical property tolerances, and accepted tempers or testing methodologies. Procurement and specification should cite both alloy designation and relevant standard (e.g., ASTM, EN, JIS, GB/T) to ensure conformity with mechanical test requirements, dimensional tolerances, and certification expectations. Minor differences in surface finish, grain structure control, or guaranteed toughness may exist between regional standards.

Corrosion Resistance

6061 exhibits generally good atmospheric corrosion resistance due to the formation of a protective aluminum oxide film that limits uniform corrosion rates in many environments. Localized corrosion such as pitting can occur in chloride-bearing environments; performance is competitive for moderate marine exposure when sacrificial design and coatings are used.

In severe or long-term marine immersion, 5xxx series (Al-Mg) alloys often outperform 6061 in bare environments due to a more robust barrier against localized corrosion; however, 6061 benefits from anodizing and protective coatings that significantly extend service life. Stress-corrosion cracking (SCC) susceptibility is moderate and influenced by temper, with peak-aged tempers (T6) demonstrating higher SCC sensitivity than softer tempers; residual stresses from welding or forming can exacerbate SCC risk.

Galvanic interactions should be managed by insulating interfaces or selecting compatible sacrificial materials; when coupled to more noble metals, 6061 will act anodically and corrode preferentially. Compared with 2xxx series alloys, 6061 offers superior corrosion resistance and weldability, while compared with 5xxx alloys it trades some corrosion performance for higher achievable strength and heat-treatable behavior.

Fabrication Properties

Weldability

6061 welds well with common processes including GMAW (MIG) and GTAW (TIG); the weld metal typically uses filler alloys such as 4043 (Al-Si) or 5356 (Al-Mg) depending on needed strength and corrosion resistance. Heat input must be controlled to limit HAZ softening; T6 material will exhibit reduced strength in the HAZ after welding. Post-weld heat treatment (PWHT) or local re-aging can recover strength in some applications, but distortion and dimensional control must be considered during welding procedures.

Machinability

Machinability of 6061 is considered good to excellent among aluminum alloys; it machines faster than many steels and produces clean chips with appropriate tooling geometry. Carbide or high-speed steel tooling is commonly used with moderate cutting speeds, high feed rates, and generous chip evacuation to avoid built-up edge. Surface finish and tool life are influenced by temper and heat treatment state; T6 material can be slightly more abrasive than O temper due to precipitation-hardened phases.

Formability

Formability is best in annealed or T4 tempers where significant cold forming and complex shaping are required. Bend radii should be selected based on temper and thickness; for T6 sheet, minimum bend radii are larger to avoid cracking, while O/T4 allow tighter radii. Cold work increases strength through strain hardening, but significant springback and reduced ductility in age-hardened tempers must be accounted for in tool design and forming sequences.

Heat Treatment Behavior

Solution treatment for 6061 is typically carried out at temperatures around 520–550 °C to dissolve soluble phases and produce a supersaturated solid solution. Rapid quenching (water quench or controlled quench) from the solution temperature is necessary to retain solute in solid solution prior to aging; quench sensitivity increases with section thickness.

Artificial aging for the T6 temper is commonly performed at temperatures around 160–190 °C for periods typically between 6 and 18 hours depending on section thickness and desired mechanical targets; the treatment precipitates fine Mg2Si that provides the majority of the strength increment. T5 temper involves cooling from elevated temperature followed by artificial aging without solution treatment; T4 is solution-treated and naturally aged at room temperature. T651 indicates T6 with stabilization by stretching to reduce residual stress and distortion.

For non-heat-treatable alloys the response is dominated by work hardening and annealing cycles. In 6061, while heat treatment is the primary strengthening route, local overaging or improper thermal exposure during service can reduce mechanical properties significantly, requiring re-solutioning and re-aging if feasible.

High-Temperature Performance

6061 maintains usable mechanical properties up to moderate elevated temperatures, but significant strength loss occurs as temperature increases above roughly 150 °C. Long-term service at elevated temperatures promotes overaging and coarsening of precipitates, which reduces yield and fatigue strength.

Oxidation at elevated temperatures is limited by the stable aluminum oxide scale; however, dimensional stability and mechanical integrity may deteriorate in cyclic thermal environments. For applications requiring sustained strength above ~120–150 °C, engineers typically select specialized aluminum alloys or high-temperature metals rather than 6061.

Applications

Industry	Example Component	Why A6061 Is Used
Automotive	Chassis components, brackets	Good strength-to-weight ratio and weldability
Marine	Structural fittings, railings	Corrosion resistance and ease of fabrication
Aerospace	Fittings, bulkheads, tubes	Favorable strength, machinability, and weight savings
Electronics	Heat sinks, enclosures	Thermal conductivity and machinability
Recreational Equipment	Bicycle frames, camping gear	Balance of stiffness, strength, and manufacturability

6061's versatility across product forms, its predictable performance after heat treatment, and broad availability make it a default choice for many general-purpose structural applications. Parts that require complex machining, welding, or a combination of strength and corrosion performance benefit from the alloy's balanced mechanical and physical profile.

Selection Insights

Choose 6061 when you need a heat-treatable alloy with a strong combination of weldability, machinability, and corrosion resistance for structural use. It is a middle-ground alloy that delivers higher strength than commercial-purity aluminum (1100) and many work-hardened alloys while being easier to weld and less corrosion-sensitive than many high-strength Al-Cu (2xxx) alloys.

Compared with 1100, 6061 trades higher electrical conductivity and superior formability for significantly higher strength and stiffness, making it better suited to structural applications. Compared with work-hardened alloys such as 3003 or 5052, 6061 offers greater peak strength after aging but slightly reduced corrosion resistance in some chloride-rich environments. Compared with 6063, which is optimized for extrudability and aesthetic finishes, 6061 provides higher structural strength and is preferred when mechanical performance, not surface finish, is the primary requirement.

Closing Summary

6061 remains a widely used engineering aluminum because it offers a practical compromise between strength, corrosion resistance, formability, and cost while being broadly available in many product forms and tempers. Its predictable heat-treatable behavior and good fabrication characteristics keep it relevant for diverse industries where reliable structural performance and manufacturability are required.