Aluminum 6063: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

The alloy 6063 belongs to the 6xxx series of aluminum alloys, which are magnesium-silicon (Mg-Si) heat-treatable alloys designed primarily for extrusion and architectural applications. Magnesium and silicon form Mg2Si precipitates during aging that provide the primary strengthening mechanism, making 6063 a heat-treatable alloy rather than a work-hardened grade. Typical commercial tempers include O (annealed), T5 (cooled from extrusion and artificially aged), and T6 (solution heat-treated and artificially aged), which allow tuning between formability and strength for downstream processing.

6063 exhibits moderate strength, very good corrosion resistance, excellent extrudability and surface finish, and generally good welding characteristics compared with other heat-treatable alloys. Its formability in softer tempers and its ability to produce thin-walled, intricate extrusions with uniform mechanical properties make it a go-to for architectural trim, window frames, and structural profiles. Industries that commonly specify 6063 include building and construction, architectural systems, general-purpose extrusions, light-duty structural components, and some thermal-management hardware.

Engineers choose 6063 over other alloys when an optimized balance of extrudability, surface finish, corrosion resistance, and adequate mechanical performance is required rather than maximum strength. Compared with 6061, 6063 typically extrudes to sharper corners and cleaner finishes at similar manufacturability but with somewhat lower peak strengths. The alloy is favored where tight dimensional tolerances, anodizing quality, and consistent extrusion quality are primary concerns.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High (≈18–28%)	Excellent	Excellent	Fully annealed condition for forming and bending
H14	Low–Medium	Moderate (≈12–18%)	Good	Excellent	Somewhat strain-hardened for intermediate stiffness
T5	Medium	Moderate (≈10–15%)	Good	Very good	Cooled from extrusion and artificially aged; common for extrusions
T6	Medium–High	Lower (≈8–12%)	Fair	Very good	Solution treated and artificially aged for higher strength
T651	Medium–High	Lower (≈8–12%)	Fair	Very good	T6 with stress relief by stretching to reduce residual stresses

Temper has a first-order effect on the microstructure and macroscopic performance because aging precipitates control yield and tensile strength. Softer tempers like O provide maximum ductility and formability for cold bending and complex shaping, while T5/T6 deliver higher tensile and yield strength appropriate for structural use.

Chemical Composition

Element	% Range	Notes
Si	0.2 – 0.6	Key alloying element forming Mg2Si precipitates during aging
Fe	0 – 0.35	Impurity element; increases strength slightly but degrades surface finish
Mn	0 – 0.1	Minor; typically low in 6063 to avoid coarse intermetallics
Mg	0.45 – 0.9	Primary strength contributor together with Si via Mg2Si formation
Cu	0 – 0.1	Low; higher Cu would increase strength but reduce corrosion resistance
Zn	0 – 0.1	Kept low to preserve corrosion resistance and extrusion quality
Cr	0 – 0.1	Trace levels to control grain structure in some specifications
Ti	0 – 0.1	Grain refiner in small additions; improves castability and extrusion start-up
Others	Each ≤0.05, Total ≤0.15	Residuals and trace elements controlled to maintain predictable properties

The Mg and Si contents are balanced to form Mg2Si precipitates during solutionizing and aging, which determines strength and age-hardening kinetics. Low levels of iron and other impurities preserve surface appearance and anodizing response, which is important for architectural and decorative uses.

Mechanical Properties

Tensile behavior of 6063 is strongly temper-dependent. In annealed (O) condition the alloy shows low yield and tensile strengths with high uniform elongation, which favors stamping, bending, and deep drawing. In T5/T6 tempers the alloy achieves higher yield and tensile strengths driven by fine, uniformly distributed Mg2Si precipitates; these precipitates also change work-hardening response and reduce ductility compared with O temper.

Yield and tensile values are also influenced by section thickness and extrusion condition because cooling rates after solution heat treatment and quench affect precipitate distribution. Fatigue performance is moderate; surface finish and extrusion defects are common fatigue initiation sites so anodized or polished finishes can improve fatigue life. Hardness correlates with temper and typically increases substantially from O to T6 as aging precipitates form.

Property	O/Annealed	Key Temper (e.g., T6)	Notes
Tensile Strength	70–110 MPa	170–215 MPa	T6 roughly doubles UTS versus annealed; values depend on section size
Yield Strength	35–55 MPa	120–160 MPa	Yield increases strongly with artificial aging and solution treatment
Elongation	18–28%	8–12%	Ductility reduced in T6 as precipitation hardening progresses
Hardness	20–35 HB	60–75 HB	Brinell hardness rises with temper; depends on aging parameters

Physical Properties

Property	Value	Notes
Density	2.70 g/cm³	Typical for commercial aluminum alloys
Melting Range	~582–652 °C	Solidus/liquidus depend slightly on alloying and impurities
Thermal Conductivity	~170–220 W/m·K	Good thermal conductor; decreases slightly with cold work and alloying
Electrical Conductivity	~34–47 % IACS	Lower than high-purity Al due to solute and precipitate scattering
Specific Heat	~900 J/kg·K	Typical value near room temperature for aluminium alloys
Thermal Expansion	~23.0–24.0 ×10⁻⁶ /K	Moderate coefficient; important for thermal cycling design

6063 retains the advantageous low density and high thermal conductivity of aluminum, making it attractive where weight and heat transfer matter. The thermal expansion coefficient and conductivity must be considered in assemblies that combine dissimilar materials to avoid stress from differential thermal expansion.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.3–6 mm	Strength reduced in thin gages due to quench rates	O, T5	Used for thin-walled panels and trim; anodizes well
Plate	>6 mm	Slightly lower achievable peak strength in thick sections	O, T6	Thick sections need controlled quench for T6 properties
Extrusion	Complex cross-sections, wall thickness 0.7–10 mm	Uniform in continuous profiles; strength affected by cooling	T5, T6, T651	Primary commercial form; excellent surface finish and dimensional control
Tube	Diameters up to 200+ mm	Behavior similar to extrusions; thin walls cool fast	O, T6	Structural tubing and architectural handrails common
Bar/Rod	Φ3–100 mm	Higher section thickness lowers apparent strength	O, T6	Small bars used for machined components and fittings

Processing differences drive the choice of product form: extrusions enable complex, thin-walled cross-sections with tight tolerances, while plate and bar supply bulk stock for fabrication. Quench rate and section thickness strongly influence final mechanical properties for heat-treated tempers, so designers must specify temper and post-heat-treatment operations for consistency.

Equivalent Grades

Standard	Grade	Region	Notes
AA	6063	USA	Aluminum Association designation commonly used in North America
EN AW	AlMgSi0.5 / EN AW-6063	Europe	European EN AW naming links to nominal chemistry and temper notes
JIS	A6063	Japan	Japanese Industrial Standard with similar Mg-Si balance and mechanical targets
GB/T	6063	China	Chinese standard generally equivalent but with some spec tolerance differences

While the generic designation 6063 is consistent across standards, national specifications differ in permitted impurity limits and testing criteria. These small differences can affect guaranteed properties such as minimum elongation or maximum iron content and therefore may matter for tight anodizing or mechanical acceptance criteria.

Corrosion Resistance

In atmospheric environments 6063 provides good general corrosion resistance due to the formation of a protective aluminum oxide film. Its low copper and zinc contents increase resistance to localized corrosion compared with some higher-strength alloys, and anodizing further enhances both appearance and environmental durability. Architectural applications often exploit this combination for long service life with minimal maintenance.

In marine or chloride-rich environments, 6063 performs reasonably well but is not as resistant as some wrought Al-Mg alloys (e.g., 5xxx series) designed specifically for seawater exposure. Pitting initiation can occur in crevices or on rough surfaces where chlorides concentrate, so design for drainage and avoid dissimilar-metal galvanic couples where possible. Stress corrosion cracking susceptibility is low relative to high-strength aluminum alloys but can be exacerbated by tensile stresses, elevated temperatures, and aggressive environments.

Galvanic interactions must be managed in mixed-metal assemblies; 6063 is anodic to stainless steels and copper but cathodic to magnesium. Protective finishes, sealants, and isolating materials mitigate galvanic currents in assemblies. Compared with 2xxx or 7xxx series alloys, 6063 trades peak strength for superior corrosion stability and better anodizing response.

Fabrication Properties

Weldability

6063 welds readily with common fusion processes such as GTAW (TIG) and GMAW (MIG), producing clean weld beads and good fillet appearance in most cases. Preferred filler alloys include 4043 (Al-Si) and 5356 (Al-Mg) depending on base temper and service demands; 4043 reduces cracking risk and yields better color match for anodizing. Weld heat-affected zones experience softening in T6 temper and post-weld artificial aging or re-heat treatment may be required to restore properties.

Machinability

Machinability of 6063 is moderate and generally better than softer pure aluminium but lower than some free-machining alloys with added lead or bismuth. Carbide tooling with positive rake, adequate chip evacuation, and stiff setups produce optimal surface finishes; speeds and feeds should be conservative to avoid built-up edge on aluminum. Chips are typically long and ductile; use flood coolant and chip control strategies for tight tolerance machining.

Formability

Cold-forming performance is excellent in O and H14 tempers where high ductility enables bending and roll-forming with small bend radii. Bending in T6 condition requires larger radii and may produce cracking at sharp edges; designers should specify O or T4/T5 tempers for severe forming then follow with aging if strength is needed. For extruded profiles, controlled designs for wall thickness and corner radii help avoid cracking and maintain dimensional control.

Heat Treatment Behavior

6063 is heat-treatable via solution treatment followed by quenching and aging. Solution treatment is typically performed at temperatures around 535–565 °C to dissolve Mg2Si into solid solution, followed by rapid quench to retain supersaturated solid solution. Artificial aging (T6) uses temperatures in the range of approximately 160–220 °C for times that vary with section size to precipitate fine Mg2Si and achieve peak strength.

T5 temper results when material is cooled from hot working (e.g., extrusion) and then artificially aged without prior solution treatment. T651 denotes T6 with a controlled stretching step to relieve residual stresses. Overaging or prolonged exposure to elevated temperatures coarsens precipitates, reduces yield and tensile strength, and increases ductility, so aging cycles must be optimized for the part geometry and intended service.

High-Temperature Performance

Elevated temperatures reduce the strength of 6063 as precipitates coarsen and the solid-solution strengthening contribution decreases. Useful structural performance is generally limited to service temperatures below roughly 150 °C; above this range significant softening occurs and long-term creep becomes a concern. Oxidation rates are modest because aluminum forms a stable oxide, but protective coatings or anodizing remain important to maintain surface integrity in oxidizing high-temperature atmospheres.

Heat-affected zones adjacent to welds can experience grain coarsening and residual softening that reduce fatigue and static strength in service. For sustained high-temperature applications or cyclic thermal loading, alloys with higher thermal stability or specialized heat treatments should be considered. Design margins and thermal management strategies are essential when using 6063 near its upper service temperature limits.

Applications

Industry	Example Component	Why 6063 Is Used
Building & Construction	Window frames, curtain wall extrusions	Excellent extrudability, surface finish, and anodizing response
Automotive	Trim and decorative profiles	Good balance of formability and adequate strength for non-structural parts
Marine	Non-critical structural components, handrails	Corrosion resistance and good surface finish for exposed environments
Electronics	Heat sinks, enclosures	Good thermal conductivity and ease of machining and extrusion
Consumer Goods	Furniture, sporting goods	Lightweight, aesthetic finishes, and ease of fabrication

6063’s combination of extrudability, surface quality, and moderate mechanical properties make it a staple for architectural and general-purpose extrusions. Designers frequently exploit anodizing and simple mechanical joining to produce economical, high-appearance assemblies.

Selection Insights

For applications where formability, extrudability, and anodizing quality are primary, 6063 is a strong candidate because it delivers reasonable strength while enabling complex thin-walled profiles. Compared with commercially pure aluminum (e.g., 1100), 6063 sacrifices some electrical conductivity and ultimate ductility but gains substantially in yield and tensile strength due to age-hardening precipitates.

When compared with common work-hardened alloys such as 3003 or 5052, 6063 sits higher on the strength scale for heat-treated conditions while offering comparable corrosion resistance in many atmospheric environments; however, 3003/5052 will often outperform 6063 in severe marine chloride exposure and in situations where work hardening is the preferred strengthening route. Versus 6061, 6063 typically extrudes better and produces superior surface finish and more intricate extrusions, so it is preferred for architectural extrusions even though 6061 offers higher peak strength for structural applications.

Closing Summary

Alloy 6063 remains a widely used aluminium grade because it uniquely balances extrudability, surface quality, corrosion resistance, and adequate mechanical properties for a large set of architectural and light structural applications. Its heat-treatable nature provides versatility in production workflows, allowing designers and fabricators to optimize formability or strength through temper selection and post-processing.