Aluminum 6065: Composition, Properties, Temper Guide & Applications
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Table Of Content
Table Of Content
Comprehensive Overview
Alloy 6065 is a member of the 6xxx series of wrought aluminum-magnesium-silicon alloys that are principally strengthened by precipitation of Mg2Si precipitates during heat treatment. Major alloying elements are silicon and magnesium, with trace additions of copper, chromium, titanium and iron that tune strength, grain structure and response to heat treatment. The alloy is heat-treatable rather than primarily work-hardened, and it achieves strength via solution treatment, quenching and artificial aging to precipitate finely dispersed intermetallics. Typical traits include a combination of moderate to high strength, good corrosion resistance, reasonable formability in soft tempers and good weldability when proper filler and procedures are used.
6065 is used in structural and semi-structural components where a balance of extrudability, strength-to-weight and corrosion resistance is required; common industries include transportation, building systems, electrical enclosures and certain aerospace fittings. Compared with other 6xxx alloys, 6065 is selected when designers want an alloy that can be extruded into complex sections and then artificially aged to dimensions with stable mechanical properties. Engineers choose 6065 over softer alloys when a higher design strength is needed without moving to higher-strength but more SCC-prone alloys in the 7xxx series. Availability and specification harmonization vary by region, so procurement should confirm temper-specific properties with suppliers.
In practice, 6065 is favored where the fabrication route (extrusion, bending, welding) must be combined with post-fabrication temper control to reach target mechanical performance. The alloy’s corrosion behavior and anodizing response make it suitable for moderately corrosive environments, and its thermal and electrical conductivities are favorable for heat-dissipating components. Designers must balance trade-offs among peak strength, formability for cold work, and the need for post-weld heat treatment when selecting 6065 over nearby alloys.
Temper Variants
| Temper | Strength Level | Elongation | Formability | Weldability | Notes |
|---|---|---|---|---|---|
| O | Low | High | Excellent | Excellent | Fully annealed; best for forming and machining |
| H14 | Medium | Moderate | Good | Excellent | Strain-hardened and partially tempered for moderate strength |
| T4 | Medium | Good | Good | Excellent | Solution heat-treated and naturally aged; good balance for forming then aging |
| T5 | Medium-High | Moderate | Fair | Good | Cooled from hot working and artificially aged; no solutionizing after forming |
| T6 | High | Moderate-Low | Fair | Good (HAZ softening) | Solution heat-treated and artificially aged for peak strength |
| T651 | High (Stable) | Moderate-Low | Fair | Good (HAZ softening) | T6 with stress relief by stretching or controlled straightening |
| Other H temper combinations | Variable | Variable | Variable | Variable | Tailored strain hardening for specific applications |
Temper selection strongly influences mechanical performance: annealed O tempers maximize ductility and formability but carry the lowest yield and tensile strengths, while T6/T651 provide the highest static strengths at the expense of bendability and elongation. For complex extrusions that require post-extrusion straightening or machining, T5 and T651 tempers are commonly used because they provide dimensional stability and good retained strength after fabrication.
Chemical Composition
| Element | % Range | Notes |
|---|---|---|
| Si | 0.2 – 0.9 | Combines with Mg to form strengthening Mg2Si precipitates |
| Fe | ≤ 0.7 | Impurity element; controls intermetallic particle population and affects toughness |
| Mn | ≤ 0.15 | Minor addition to refine grain structure and improve toughness |
| Mg | 0.6 – 1.2 | Primary strengthening element when combined with Si |
| Cu | 0.15 – 0.4 | Improves strength and machinability but can reduce corrosion resistance |
| Zn | ≤ 0.25 | Generally low; not a primary strengthening contributor in 6xxx alloys |
| Cr | 0.04 – 0.35 | Controls recrystallization and grain structure, improves toughness |
| Ti | ≤ 0.15 | Grain refiner during casting/extrusion; improves as-processed microstructure |
| Others (each) | ≤ 0.05 | Trace elements controlled to maintain consistent aging response |
The composition of 6065 is typical of Mg-Si precipitation-hardening alloys: silicon and magnesium set the potential for peak strength through Mg2Si precipitation, while small amounts of copper and chromium are used to tweak strength and microstructural stability. Iron and other impurities form coarse intermetallics that reduce toughness and fatigue endurance if uncontrolled, so modern production controls these species tightly to achieve predictable aging and mechanical results.
Mechanical Properties
In tensile loading, 6065 behaves like a heat-treatable 6xxx alloy: soft tempers show high ductility and gradual yielding, while T6/T651 temper exhibits well-defined proof strength and higher ultimate tensile strength associated with coherent and semi-coherent precipitates. Yield and tensile strengths increase markedly after solution treatment and artificial aging, but ductility and bendability reduce correspondingly; elongation to failure in T6 may be halved relative to O or T4 tempers. Hardness tracks similarly, with Brinell or Rockwell values increasing substantially after aging, and the material exhibits moderate notch sensitivity relative to 5xxx alloys.
Fatigue strength is influenced by surface finish, residual stresses, and heat treatment; properly aged 6065 offers reasonable high-cycle fatigue performance for structural extrusions but is generally below that of high-strength 2xxx or 7xxx alloys. Section thickness and thermal history critically affect achievable mechanical properties: thick sections cool more slowly during quench and may not fully reach T6-level strength without longer solution treat cycles or modified aging schedules. Post-weld heat-affected zones (HAZ) will typically show local softening, reducing local yield strength unless re-solution and age treatments are applied.
| Property | O/Annealed | Key Temper (e.g., T6/T651) | Notes |
|---|---|---|---|
| Tensile Strength (MPa) | 140 – 220 | 260 – 340 | Values depend on product form and thickness; supplier data should be consulted |
| Yield Strength (0.2% offset, MPa) | 60 – 140 | 200 – 320 | T6 gives most designable yield; O is used where forming dominance exists |
| Elongation (%) | 12 – 25 | 6 – 14 | Elongation falls with increasing strength and thicker sections |
| Hardness (HB) | 40 – 70 | 85 – 120 | Hardness increases with aging; values vary by temper and method |
Physical Properties
| Property | Value | Notes |
|---|---|---|
| Density | 2.70 g/cm³ | Typical for aluminum wrought alloys; used for weight-sensitive design calcs |
| Melting Range | Solidus ~555°C – Liquidus ~650°C | Alloy melting interval; solidus lower than pure Al due to alloying |
| Thermal Conductivity | 140 – 170 W/m·K (typical) | Lower than pure Al but still good for heat-sinking applications |
| Electrical Conductivity | ~28 – 38 % IACS | Reduced from pure Al because of alloying elements; varies with temper |
| Specific Heat | ~0.9 J/g·K (900 J/kg·K) | Useful for thermal mass calculations |
| Thermal Expansion | ~23.0 – 24.5 µm/(m·K) | Comparable to other Al-Mg-Si alloys; important for bimetallic joints |
These physical properties emphasize aluminum’s advantages in lightweight design and thermal management; 6065 retains good conductivity for heat-transfer components while offering higher mechanical performance than purer grades. Electrical conductivity is sufficient for many bus and enclosure applications but is typically lower than 1xxx-series alloys, so designers trading off conductivity for mechanical strength should verify conductor cross-sections. Thermal expansion should be accounted for in assemblies with steel or composites to avoid fatigue from cyclic thermal stresses.
Product Forms
| Form | Typical Thickness/Size | Strength Behavior | Common Tempers | Notes |
|---|---|---|---|---|
| Sheet | 0.4 – 6.0 mm | Good strength in thinner gauges after aging | O, T4, T5, T6 | Common for panels and formed housings; thin gauge response to aging rapid |
| Plate | >6.0 mm up to 150 mm | Strength may be lower after heat treatment due to quench sensitivity | O, T6 (limited) | Thick sections require tailored heat treatment to avoid soft core |
| Extrusion | Cross sections up to several hundred mm | Excellent uniform strength along profile when aged | T5, T6, T651 | Widely used; complex profiles achievable with tight tolerances |
| Tube | OD 10 – 200 mm wall dependent | Similar strength to extrusions; HAZ considered in welded tubes | O, T6 | Used for structural and fluid handling; welded and seamless variants |
| Bar/Rod | Diameters 3 – 100 mm | Good axial properties; response to aging similar to plate | O, T6 | Stock shapes for machining and fabricated fittings |
Extrusions are a principal commercial form for 6065 because the alloy’s Mg-Si chemistry offers good flow and surface finish in complex dies, and subsequent aging provides predictable mechanical properties. Plate and thick sections present quench and aging challenges; designers typically limit thickness or specify modified aging recipes for uniform properties. Sheet forms are common for formed panels and housings where temper choice balances formability and end-use strength.
Equivalent Grades
| Standard | Grade | Region | Notes |
|---|---|---|---|
| AA | 6065 | USA | Aluminum Association designation used in supplier datasheets |
| EN AW | 6065 | Europe | EN AW-6065 commonly used; chemical and mechanical requirements align with AA standards |
| JIS | — | Japan | No widely used direct JIS equivalent; specify AA/EN standards or material chemistry |
| GB/T | 6065 | China | GB variants may exist; verify local standard number and temper specifications |
Cross-referencing between standards is generally straightforward for 6065 because it follows the common Mg‑Si precipitation-hardening chemistry used globally. However, minor compositional tolerances and processing practices differ by region; for critical applications verify the actual chemical and mechanical spec called out in procurement documents. If a JIS direct equivalent is not available, it is common to specify the AA or EN designation and include full composition and mechanical property requirements.
Corrosion Resistance
In atmospheric service, 6065 provides good general corrosion resistance typical of 6xxx alloys, and it can be further improved by anodizing and organic coatings. In marine and chloride-bearing environments it performs reasonably well but is not as inherently resistant as 5xxx magnesium-bearing alloys; protective finishing and design to avoid crevices are recommended. Stress corrosion cracking susceptibility is lower than for many high-strength 7xxx alloys, but 6065 can still experience SCC under tensile stress in aggressive halide environments; avoiding retained tensile stresses and controlling weld-related microstructures reduces risk.
Galvanic interactions follow standard aluminum behavior: 6065 is anodic relative to many stainless steels and copper-based alloys, and anodic protection or sacrificial anodes are common mitigation strategies in dissimilar-metal assemblies. Compared with 1xxx series alloys, 6065 gives far higher strength at the cost of somewhat reduced electrical conductivity and, in some cases, slightly higher susceptibility to localized corrosion if protective coatings are compromised. Proper surface preparation, coatings, and anodizing are effective means to maintain long-term performance in challenging environments.
Fabrication Properties
Weldability
6065 welds readily with common fusion processes such as TIG and MIG, and the weldability is similar to other Mg-Si alloys when appropriate filler metals are chosen. Typical filler alloys are ER4043 (Al-Si) to reduce hot cracking and improve flow, or ER5356 (Al‑Mg) where higher post-weld strength and corrosion resistance are needed; choice depends on required mechanical and corrosion performance. The heat-affected zone will show some softening relative to T6 parent material, and full recovery of T6 strength across the weld generally requires solution heat treatment and re-aging, which is seldom practical for finished assemblies. Careful control of welding parameters, pre- and post-weld treatments, and joint design minimize distortion and HAZ property degradation.
Machinability
Machinability of 6065 is moderate and is comparable to many 6xxx alloys; it machines better than many high-strength aluminum alloys but not as easily as some free-machining alloys. Carbide tooling with positive rake and adequate coolant is recommended to avoid built-up edge and to maintain surface integrity at higher cutting speeds. Typical machining guidelines include moderate to high spindle speeds with increased feed for chip control; fine finishes are achieved with appropriate tool geometry and stable workholding. For tight tolerance components, the temper and prior heat treatment history must be considered since residual stresses and springback affect dimensional stability after machining.
Formability
Cold forming and bending are best performed in soft tempers such as O or T4; these tempers provide the ductility required for tight radii and complex shapes. In T6 temper, formability declines and minimum bend radii must be increased to prevent cracking and edge fracture; typical design rules suggest inside radii of 2–3× thickness for T6 and 0.5–1× thickness for O tempers, but specifics depend on section geometry and tooling. Work hardening from bending operations will increase local yield strength and can complicate subsequent forming or heat treatment. For large-scale forming operations, integrate annealing or solution/age cycles into the process plan to control dimensional stability and final mechanical properties.
Heat Treatment Behavior
6065, as a heat-treatable alloy, responds to classical precipitation hardening sequences: solution treatment, quenching and artificial aging. Typical solution treatment temperatures are in the 520–550°C range, held long enough for uniform dissolution of solute phases, followed by rapid quench to retain supersaturation. Artificial aging to achieve T6 is commonly performed at 160–175°C for several hours; peak hardness is obtained