Aluminum EN AW-6063: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

EN AW-6063 belongs to the 6xxx series of aluminium alloys, a family defined by the Mg-Si alloying system that enables precipitation hardening. This series sits between the softer 1xxx/3xxx work-hardening alloys and the higher-strength 2xxx/7xxx heat-treatable groups, balancing extrudability, corrosion resistance, and moderate strength.

Major alloying elements in EN AW-6063 are silicon and magnesium, which combine to form Mg2Si precipitates responsible for age hardening. Trace additions of iron, manganese, chromium and titanium influence grain structure, feedstock cleanliness, and response to thermal processing without dramatically altering the basic precipitation mechanism.

EN AW-6063 is a heat-treatable alloy that strengthens by solution treatment and artificial aging (precipitation hardening). Key traits include good extrudability and surface finish, moderate-to-high corrosion resistance in atmospheric environments, excellent weldability in most tempers, and good formability in annealed and partially-hardened states.

Typical industries that use EN AW-6063 include architectural systems (window frames, doorframes), structural extrusions, consumer electronics heat sinks, and light structural components in transportation. Engineers select 6063 when a combination of good surface quality, dimensional stability in extrusion, corrosion resistance, and adequate strength are priorities relative to alternative alloys.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed condition for maximum ductility
H14	Low–Medium	Medium	Good	Excellent	Lightly strain-hardened for improved yield without heat treatment
T5	Medium	Moderate	Good	Excellent	Cooled from elevated temperature and artificially aged
T6	Medium–High	Moderate	Fair–Good	Very Good	Solution heat treated and artificially aged for higher strength
T651	Medium–High	Moderate	Fair–Good	Very Good	T6 with stress-relief by stretching to remove residual stresses

Tempers control the balance between strength and ductility by altering precipitate distribution and dislocation density. Annealed (O) condition is used for forming operations and complex bending, whereas T5/T6 variants are used when dimensional stability and higher load capacity are required.

Artificial aging schedules and work-hardening produce distinct strength profiles and affect subsequent welding and forming steps. Selecting a temper is a trade-off between post-fabrication heat treatments, required surface finish, and in-service mechanical loads.

Chemical Composition

Element	% Range	Notes
Si	0.2–0.6	Primary alloying element; forms Mg2Si with Mg for precipitation hardening
Fe	≤0.35	Impurity element; affects strength and surface finish; promotes intermetallics
Mn	≤0.10	Minor element; refines grain structure, limited in 6063
Mg	0.45–0.9	Combines with Si to form strengthening precipitates; controls hardenability
Cu	≤0.10	Kept low to preserve corrosion resistance; excessive Cu reduces SCC resistance
Zn	≤0.10	Limited content; high Zn not tolerated in 6xxx series
Cr	≤0.10	Grain refiner and control of recrystallization in some tempers
Ti	≤0.10	Used for grain control, especially in cast or billet production
Others	≤0.05 each, ≤0.15 total	Includes trace elements and intentional microalloying

The Mg and Si balance is central to performance because the stoichiometry and distribution of Mg2Si precipitates govern achievable strength and aging kinetics. Iron and other trace elements control casting/extrusion behavior, surface finish, and susceptibility to localized corrosion or intermetallic-induced defects.

Mechanical Properties

Tensile behavior of EN AW-6063 varies strongly with temper; annealed material exhibits a low yield and elongates substantially, while T6/T651 tempers provide a marked increase in yield and ultimate tensile strength with reduced ductility. The alloy shows relatively linear elastic response to yield and a predictable strain-hardening region in higher tempers, making it suitable for design calculations with conservative safety factors.

Yield strength in extruded sections is sensitive to section thickness and cooling rates after solution treatment; thin-section extrusions achieve more uniform properties and better aging response. Fatigue performance is typical for precipitation-hardened Al-Mg-Si alloys, with surface finish, extrusion defects, and residual stresses being primary determinants of fatigue life.

Hardness correlates with temper: O condition gives low hardness, while T6/T651 increase Brinell/Vickers hardness correspondingly due to fine precipitate distributions. Thickness effects are important: thicker sections cool slower after heat treatment leading to coarser precipitates and slightly lower peak strength compared with thin sections which can reach higher property levels under identical processing.

Property	O/Annealed	Key Temper (T6)	Notes
Tensile Strength	100–140 MPa	175–220 MPa	Values depend on section size and specific tempering schedule
Yield Strength	40–80 MPa	120–170 MPa	Measured 0.2% offset; sensitive to aging and cold work
Elongation	12–18%	6–12%	Higher in thinner sections and annealed state
Hardness	25–40 HB	60–85 HB	Hardness correlates with age-hardening and precipitate distribution

Physical Properties

Property	Value	Notes
Density	2.70 g/cm³	Typical for wrought Al alloys; use for mass and stiffness calculations
Melting Range	~605–650 °C	Solidus–liquidus range depends on local composition and impurities
Thermal Conductivity	~160–180 W/m·K	Good thermal conductor compared with steel; depends on temper and alloying
Electrical Conductivity	~30–40 % IACS	Lower than high-purity aluminium due to alloying; influenced by cold work
Specific Heat	~900 J/kg·K	Useful for thermal management and heat-treatment energy calculations
Thermal Expansion	~23–24 µm/m·K (20–100°C)	Typical coefficient for design of assemblies with dissimilar materials

The physical property set makes 6063 attractive for thermal management components and lightweight structural elements. High thermal conductivity and low density deliver favorable specific thermal and stiffness performance compared with steels and higher-strength aluminium alloys.

Thermal properties also influence heat-treatment behavior: thermal conductivity determines quench uniformity in thick sections and can produce gradients if fixtures or insulation are present. Electrical conductivity is sufficient for some conductor applications but is typically traded off against mechanical property requirements.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.5–6 mm	Uniform properties in thin gauge	O, H14, T5	Used for architectural panels, enclosures
Plate	>6 mm	Lower attainable peak strength due to slower quench	O, T6 (limited)	Heavy sections less common for 6063; 6xxx plates used where extrusion not required
Extrusion	Wall thickness 1–20 mm; complex profiles	Excellent surface finish; directional properties	O, T5, T6, T651	Primary product for 6063; tight tolerances and anodizing compatibility
Tube	Thin-walled to thick-walled	Strength varies with wall thickness and cold work	O, T6	Common for frames, rails, and architectural tubing
Bar/Rod	Diameters up to 50 mm	Lower peak strengths for larger diameters	O, H14	Cold drawn bars used for machining or forming

Extruded commercial availability defines the major use case for 6063; complex cross-sections with thin walls can be produced economically while maintaining good surface finish for anodizing. Plate and heavy sections are less common and often replaced by other 6xxx or 7xxx alloys when higher strength in thick sections is required.

Processing differences are important: extruded profiles are often aged on the run or after straightening, whereas sheet and tube production involve different rolling and drawing histories that affect grain structure and mechanical anisotropy. Design for manufacturability should consider minimum bend radii and the anisotropic yield behavior of extrusions.

Equivalent Grades

Standard	Grade	Region	Notes
AA	6063	USA	Common North American designation for the wrought alloy
EN AW	6063	Europe	EN AW-6063 corresponds to the same Mg-Si system with European processing specs
JIS	A6063	Japan	Japanese equivalent commonly used in extrusion industry
GB/T	6063	China	Chinese standard designator with similar compositional envelope

Equivalent grades across regions share the same Mg–Si strengthening chemistry, but there are subtle differences in allowable impurity limits and manufacturing practice that affect surface finish and extrudability. Specifications such as temper designations, testing methods, and acceptance criteria (e.g., permitted porosity, grain size, or surface quality) can vary by standard and producer.

When substituting across standards, verify temper designations and mechanical property tables because a T6 in one standard may be specified with different minimums for yield or tensile strength. Surface finish and anodizing behavior can also be impacted by billet processing and impurity content, so source control is important for architectural applications.

Corrosion Resistance

EN AW-6063 exhibits good general atmospheric corrosion resistance because of its low copper content and the protective nature of the aluminium oxide layer. It anodizes well and develops a consistent, attractive surface that enhances both aesthetics and resistance to localized attack, which is why it is popular in architectural extrusions.

In marine or chloride-containing environments, 6063 is moderately resistant to pitting and crevice corrosion but is not as robust as high-magnesium 5xxx alloys or specially coated stainless steels. Localized attack increases in stagnant seawater or under deposits, so protective coatings, anodizing, or sacrificial design strategies are common in marine use.

Stress corrosion cracking susceptibility for 6xxx alloys is typically low to moderate compared with highly alloyed heat-treatable alloys, but tensile residual stresses combined with corrosive environments and elevated temperatures can promote SCC in susceptible conditions. Galvanic interactions must be considered: when coupled to more noble metals, aluminium will corrode unless electrically insulated or cathodically protected.

Compared with 1xxx and 3xxx series, 6063 trades slightly less intrinsic corrosion resistance for higher strength and better extrudability. Compared with 5xxx series alloys, 6063 offers better anodizing and surface finish but generally lower resistance to long-term immersion in seawater.

Fabrication Properties

EN AW-6063 is straightforward to fabricate using standard shop processes; its combination of formability, weldability, and heat-treatable strength makes it versatile for extrusion-based parts and secondary operations. Control of residual stresses and heat input during joining and straightening is important to maintain dimensional tolerances and avoid overaging.

Weldability

Weldability of 6063 is excellent with common fusion processes such as TIG and MIG. Recommended filler alloys include ER4043 (Al-Si) and ER5356 (Al-Mg) depending on desired post-weld strength and corrosion performance; ER4043 is preferred for improving flow and reducing hot-cracking tendency in Si-containing base metal.

Heat-affected zone (HAZ) softening can occur adjacent to welds in T6 or T651 material because precipitates dissolve and coarsen, reducing local strength; post-weld heat treatment or local stress-relief can restore some properties. Hot-cracking risk is low relative to some high-strength alloys, but good joint design, clean surfaces, and proper filler selection mitigate residual cracking.

Machinability

Machinability is moderate compared with free-cutting aluminium alloys; 6063 machines well when using carbide tools at moderate speeds and with appropriate chip control measures. Use of sharp-edged tooling, positive rake angles, and adequate coolant or air blast reduces built-up edge and produces superior surface finish for anodizing or plating.

Feed and speed should account for section constraints; thin-walled extrusions can vibrate and chatter if unsupported during machining. Drill, mill, and finish operations typically leave surfaces readily anodizable after appropriate cleaning and etching steps.

Formability

Formability in the O and H14 tempers is very good and supports bending, roll forming, and deep drawing in many geometries. Minimum bend radii depend on temper and thickness, but typical design guidance calls for internal radii of 1–3× thickness in annealed material and larger radii in T6.

Cold working (H tempers) increases yield strength at the expense of ductility, so multi-stage processing often uses anneal–form–age or form in O then age to T5/T6 to achieve final properties. For tight bending or severe stretch forming, perform forming in O or low-hardened conditions and apply an artificial aging step only after final geometry is achieved.

Heat Treatment Behavior

EN AW-6063 is a heat-treatable Al-Mg-Si alloy that responds predictably to solution treatment, quenching, and artificial aging. Solution treatment is typically performed in the 520–540 °C range to dissolve Mg2Si into a supersaturated solid solution, followed by rapid quench to retain solute in solid solution.

Artificial aging (precipitation) is commonly performed at 160–185 °C for periods that vary with section thickness and desired temper; T5 describes as-cooled then aged, while T6 refers to solution treated, quenched, and aged to a stable condition. Overaging reduces peak strength but increases thermal stability and toughness; controlled underaging can be used to tailor formability and subsequent strength increases.

Temper transitions are controlled by combinations of mechanical deformation and thermal cycles: H-temper variants leverage work hardening, while T-temper variants use controlled precipitation. Residual stresses can be relieved by stretching (T651) or by low-temperature stress-relief cycles, but significant alteration of mechanical properties requires solution treatment and re-aging.

High-Temperature Performance

Strength of EN AW-6063 degrades progressively with temperature due to precipitate coarsening and reduced matrix strengthening; significant loss of yield strength commonly appears above ~150 °C. For continuous structural applications, keeping service temperature below ~120–150 °C is prudent to avoid creeping or permanent softening over time.

Oxidation at elevated temperatures is limited because aluminium forms a stable oxide, but surface scaling and changes to anodized coatings can occur at sustained high temperatures. HAZ regions around welds can experience accelerated softening when exposed to elevated temperatures, reducing local load-carrying capacity and fatigue life.

For short-term elevated-temperature excursions, 6063 retains useful mechanical integrity, but designers should consider alternative alloys (e.g., 2xxx or 7xxx series) or mechanical design adjustments for high-temperature load-bearing applications. Creep resistance is limited and not a primary design feature of this alloy.

Applications

Industry	Example Component	Why EN AW-6063 Is Used
Architectural	Window and door frames	Excellent extrudability, anodizing finish, and corrosion resistance
Marine	Deck trim and structural extrusions	Good atmospheric corrosion resistance and light weight
Aerospace/Transport	Interior fittings and non-critical structural sections	Favorable strength-to-weight and good surface quality
Electronics	Heat sinks and enclosures	High thermal conductivity and good machinability
Automotive	Trim, cabin structures, and rails	Cost-effective extrusions with adequate strength and finishability

EN AW-6063 is particularly dominant in architectural extrusion markets because its combination of surface finish, anodizing compatibility, and dimensional stability during extrusion fits the needs of façade and framing systems. The alloy provides a pragmatic compromise of manufacturability, cost, and in-service performance for a wide range of light-structural components.

Selection Insights

Use EN AW-6063 when the design calls for high-quality extruded profiles with a good anodized surface, moderate mechanical strength, and excellent extrudability. Choose annealed or low-hardened tempers where forming or bending is primary, and select T5/T6/T651 for components that require higher dimensional stability and load capacity.

Compared with commercially pure aluminium (1100), 6063 offers significantly higher strength at the cost of slightly reduced electrical and thermal conductivity; select 1100 when conductivity or formability is paramount. Compared with work-hardened alloys such as 3003 or 5052, 6063 provides higher achievable precipitation strength and better anodizing behavior, while 3003/5052 may offer superior marine performance and cold-forming where welding or aging is not desired.

Compared with 6061, 6063 has superior extrudability and surface finish for complex profiles but typically lower peak strength; choose 6063 for architectural extrusions and where surface aesthetics and light-to-moderate strength are primary, and prefer 6061 where higher structural strength in larger cross-sections is required.

• Consider cost and availability of extruded profiles: 6063 is widely available for complex sections and often more economical than machining large 6061 components.
• For assemblies joining dissimilar metals, account for galvanic coupling and use coatings, seals, or isolators to protect aluminium surfaces.
• When fatigue life is critical, prioritize surface finish, remove extrusion defects, and consider shot peening or mechanical finishing to improve performance.

Closing Summary

EN AW-6063 remains a mainstay alloy where extrusion quality, surface finish, and balanced mechanical properties are required in a cost-effective package. Its precipitate-based strengthening allows engineers to tailor properties through temper selection and heat treatment, while fabrication and corrosion performance meet the demands of architectural, transport, and thermal-management applications.