Aluminum 6085: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

6085 is an aluminum alloy that belongs to the 6xxx series (Al-Mg-Si) family, characterized by magnesium and silicon as its primary alloying elements. This series is heat-treatable by precipitation hardening and combines moderate-to-high strength with good formability and corrosion resistance, targeting structural and extruded components.

Major alloying elements in 6085 are silicon and magnesium, which form Mg2Si precipitates during aging to provide the principal strengthening mechanism. Minor additions such as iron, manganese, chromium and trace elements control grain structure, strength, and surface quality while balancing manufacturability.

Key traits of 6085 include a favorable strength-to-weight ratio, good atmospheric corrosion resistance, and reasonable weldability; formability is generally better in softer tempers and decreases after aging. Typical industries using 6085 are automotive, general structural and architectural extrusions, marine fittings, and electrical enclosures where a combination of extrusion capability and elevated mechanical performance is required.

Engineers choose 6085 when an extrudable 6xxx series alloy is needed with improved mechanical properties relative to softer 6005/6063 grades but with better extrudability or specific surface/processing benefits compared with higher-strength 6082 or 6061. The alloy is selected to balance age-hardening response, surface finish and cost in mid-duty structural applications.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed condition for maximum ductility
H12	Low-Medium	Medium	Good	Excellent	Light work hardening, limited forming
H14	Medium	Medium-Low	Fair	Excellent	Common cold-work temper for moderate strength
T4	Medium	Medium	Good	Very good	Solution heat-treated and naturally aged
T5	Medium-High	Low-Medium	Fair	Good	Cooled from hot working and artificially aged
T6	High	Low	Poor-Fair	Good	Solution treated and artificially peak-aged
T651	High	Low	Poor-Fair	Good	T6 with stress relief by slight stretching

Tempering changes both microstructure and performance by controlling the precipitate size, distribution, and density within the Al-Mg-Si matrix. Soft tempers (O, H1x) favor forming and deep drawing operations, while T-temper variants (T5, T6) maximize strength for structural applications at the expense of elongation and cold formability.

Heat treatment and work hardening combine to create a broad property window for 6085, enabling manufacturers to tailor products from ductile sheet to high-strength extrusions. Choosing an appropriate temper is a trade-off between forming ease, final mechanical demands, and post-fabrication processes such as welding or machining.

Chemical Composition

Element	% Range	Notes
Si	0.6–1.3	Primary alloying element forming Mg2Si precipitates
Fe	0.0–0.5	Impurity element affecting strength and surface finish
Mn	0.0–0.5	Controls grain structure and helps strength stability
Mg	0.4–1.2	Combines with Si to form strengthening precipitates
Cu	0.0–0.2	Small additions increase strength but reduce corrosion resistance
Zn	0.0–0.2	Residual levels; can slightly increase strength
Cr	0.0–0.1	Controls recrystallization and grain size in some variants
Ti	0.0–0.1	Grain refiner for cast or primary products
Others	Balance / max 0.15 each	Residual elements and trace additions; balance Al

The Al-Mg-Si chemistry is tuned so that Mg and Si form Mg2Si precipitates during aging, which are the primary strengthening phases for 6xxx alloys. Trace elements such as Mn, Cr and Ti are used to control recrystallization, grain size and the formation of dispersoids which influence toughness and stress corrosion susceptibility.

Mechanical Properties

Tensile behavior of 6085 is typical for a heat-treatable 6xxx series alloy: in the annealed condition it exhibits good ductility with low yield and tensile strengths, and after solution treatment + artificial aging it reaches significantly higher yield and tensile strengths due to coherent/semi-coherent precipitates. Yield-to-tensile ratios tend to be in the 0.7–0.9 range depending on temper and section size, and elongation falls as hardness increases. Fatigue performance improves with aging up to an optimum temper but is sensitive to surface finish and residual stresses from forming or machining.

Hardness in 6085 follows the aging curve: annealed material is soft and readily formable while T6/T651 tempers register much higher Brinell or Vickers numbers consistent with structural applications. Thickness and section size influence the achievable peak hardness because of quench sensitivity and aging kinetics; thicker sections may age more slowly and show lower peak strengths. Fatigue crack initiation is most affected by surface condition and corrosion pits, while crack propagation rates are comparable to other 6xxx alloys when tested in similar tempers.

Property	O/Annealed	Key Temper (T6)	Notes
Tensile Strength	~90–140 MPa	~280–340 MPa	Values depend on section, exact chemistry and processing
Yield Strength	~35–80 MPa	~240–300 MPa	Yield increases substantially after aging
Elongation	~20–30%	~8–12%	Elongation reduces with age-hardening and increasing thickness
Hardness	~30–55 HB	~85–120 HB	Hardness correlates with precipitate distribution and tempers

Physical Properties

Property	Value	Notes
Density	2.70 g/cm³	Typical for Al-Mg-Si alloys
Melting Range	~555–650 °C	Solidus-liquidus range influenced by alloying and traces
Thermal Conductivity	~140–170 W/m·K	Lower than pure Al; depends on temp and alloy content
Electrical Conductivity	~28–40 % IACS	Reduced from pure Al due to solutes and precipitates
Specific Heat	~0.9 J/g·K (900 J/kg·K)	Typical room-temperature value
Thermal Expansion	~23–24 µm/m·K (20–100 °C)	Typical coefficient for 6xxx series alloys

Physical properties of 6085 make it attractive for components requiring good thermal transfer and low weight. Thermal conductivity and electrical conductivity are lower than pure aluminum and tend to decline modestly with increasing alloying and aging, but remain adequate for many heat sink and enclosure applications.

Thermal expansion and specific heat are typical for aluminum alloys, so designers must accommodate relatively large dimensional changes with temperature in assemblies combining dissimilar materials. The alloy’s melting range and phase behavior guide acceptable soldering, brazing and joining processes.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.3–6 mm	Uniform properties; limited thickness for peak T6	O, H14, T4, T6	Widely used for panels and enclosures
Plate	6–50+ mm	Strength may be reduced in thick sections due to quench	O, T4, T6	Used where higher section modulus is required
Extrusion	Profile-dependent	High strength in T6 after aging; continuous shapes	T5, T6, T651	6xxx alloys optimized for extrusion and dimensional stability
Tube	Ø small-large, wall 1–10 mm	Similar to extrusions; weld or seamless options	O, T6	Structural/pressure tubes are common
Bar/Rod	Ø 5–200 mm	Solid sections show quench and aging gradients	O, T6	Used for machined parts and fittings

Sheet and plate production emphasizes surface quality and control of thickness to minimize quench gradients during solution treatment. Extrusions are a major application for 6085 where the alloy’s combination of flow, weldability and age-hardening response is exploited to produce complex cross-sections.

Processing differences (rolling, extrusion, forging) affect final mechanical anisotropy, grain structure and residual stresses. Designers must choose form and temper together to ensure performance after downstream operations like bending, stamping or welding.

Equivalent Grades

Standard	Grade	Region	Notes
AA	6085	USA	Recognized as an Al-Mg-Si structural alloy in some supplier catalogs
EN AW	6085	Europe	Common European designation (EN AW-6085) for wrought products
JIS	A6063/A6061 (approx)	Japan	No exact one-to-one; approximate equivalents are in the 6xxx family
GB/T	6085 (approx)	China	Chinese standards may list similar chemistries under 6xxx series

Direct cross-references for 6085 can vary between standards because regional specifications emphasize different impurity limits, tempers and permitted mechanical properties. Small composition or processing differences between standards can alter quench sensitivity, achievable peak strength and surface quality, so material certificates and supplier data must be reviewed before substitution.

When substituting between similar 6xxx alloys, consider differences in response to heat treatment and as-extruded mechanical anisotropy; a nominally equivalent chemistry does not guarantee identical aged properties or formability.

Corrosion Resistance

6085 offers good atmospheric corrosion resistance typical of Al-Mg-Si alloys due to the protective aluminum oxide layer and limited active galvanic driving force with many environments. In industrial and urban atmospheres it performs well; the finer precipitate structure in peak-aged tempers can slightly increase susceptibility to localized corrosion if coupled with aggressive environments or chloride contamination.

In marine environments, 6085 demonstrates reasonable behavior for moderately exposed components but is not a first choice for continuously immersed or splash-zone hardware without protective coatings or anodizing. Chloride-induced pitting and crevice corrosion are the primary failure modes in aggressive saltwater conditions and are accelerated by tensile stresses and surface defects.

Stress corrosion cracking (SCC) susceptibility is lower than in some high-strength 7xxx or 2xxx alloys, but high-strength tempers combined with residual tensile stresses can promote SCC under severe environmental conditions. Galvanic interactions with more noble metals (copper, stainless steels) will favor corrosion of the 6085 alloy if electrical contact and electrolyte are present, so insulating or protective design measures are recommended.

Compared with 5xxx magnesium-bearing work-hardened alloys, 6085 trades slightly reduced cathodic protection for improved aging strength and better weldability. Compared with 6xxx alloys of different chemistries, surface finish, temper and heat treatment history are often the dominant factors controlling real-world corrosion performance.

Fabrication Properties

Weldability
6085 generally welds well with common fusion processes (TIG/MIG/GMAW) when appropriate procedures and filler wires are used. Recommended fillers are Al-Mg-Si and general-purpose 4043 or 5356 series depending on required post-weld strength and corrosion performance; 4043 provides better crack resistance and surface finish while 5356 yields higher strength but can reduce corrosion resistance in some environments.

Hot-cracking risk is moderate and is controlled through joint design, preheat when necessary, and using compatible filler alloys; HAZ softening is an expected outcome of welding peak-aged tempers and may necessitate post-weld artificial aging to restore strength. Weld parameters should minimize dilution and avoid excessive heat input to reduce the depth of HAZ softening and distortion.

Machinability
Machinability of 6085 is rated medium compared with free-cutting aluminum alloys; the alloy machines readily but does not reach the very high speeds of leaded or specially alloyed grades. Carbide tooling with positive geometry and adequate coolant is recommended to manage chip formation and tool wear, and feed rates should be set to avoid built-up edge and chatter on thin-wall sections.

Surface finishes achievable by machining are good, and post-machining heat treatment can be used to optimize strength if machining is performed in softer tempers. Threading, tapping and fine detail machining benefit from pre-aging to stabilize dimension and hardness where thermal softening could otherwise occur.

Formability
Formability in 6085 depends strongly on temper and section thickness; in annealed and lightly worked tempers sheet can be deep drawn and bent to small radii, while T6 material will crack under severe forming. Typical recommended minimum inside bend radii for sheet in softer tempers are on the order of 1–2× thickness, increasing to 3–6× thickness for peak-aged tempers to avoid edge cracking.

Cold-work response is predictable and consistent, with springback behavior similar to other 6xxx alloys, so tool compensation is standard practice. For complex forming, using T4 or O tempers with final aging after forming yields the best combination of formability and final mechanical properties.

Heat Treatment Behavior

As a heat-treatable alloy, 6085 responds to solution heat treatment followed by quenching and artificial aging to develop strength. Solution treatment temperatures commonly used for 6xxx series alloys are in the range of ~520–550 °C, held long enough to dissolve Mg2Si and homogenize the microstructure; rapid quenching is critical to retain supersaturated solid solution before aging.

Artificial aging (T5/T6) is typically performed at temperatures between ~160–200 °C with time adjusted to reach desired precipitate size and strength, generating GP zones and β″/β′ precipitates that confer peak hardness. Overaging at higher temperatures or longer times coarsens precipitates and lowers strength while improving toughness and stress-corrosion resistance; manufacturers use tailored aging cycles to balance properties.

T temper transitions are well-established for design control: material can be supplied as T4 (naturally aged) for good formability with moderate strength or as T6/T651 for peak-aged structural service. For non-heat-treated product forms, work hardening is used to raise strength and temper classification H1x/H2x indicates the level of cold work applied.

High-Temperature Performance

6085 begins to show significant strength reduction at elevated service temperatures as precipitates coarsen and solute atoms become mobile; above roughly 150–175 °C long-term strength is reduced and creep or relaxation becomes a design concern. Short-term exposure to higher temperatures for welding or brazing must be managed to avoid excessive softening or distortion.

Oxidation is modest at typical elevated service temperatures encountered in most applications, but prolonged exposure to high temperature can alter surface oxide characteristics and accelerate intergranular degradation in certain atmospheres. The HAZ adjacent to welds behaves similarly to other 6xxx alloys, with peak-aged zones softening and requiring re-aging treatment if original strength levels are needed.

For thermal cycling applications, designers should consider thermal expansion mismatch and the potential for fatigue acceleration due to elevated-temperature creep and microstructural changes. When continuous strength above ~150 °C is required, alternative alloy systems or additional design margins should be considered.

Applications

Industry	Example Component	Why 6085 Is Used
Automotive	Extruded chassis rails, structural profiles	Good combination of extrudability, strength and corrosion resistance
Marine	Deck fittings, non-critical structural extrusions	Adequate corrosion resistance with good formability and finish
Aerospace	Secondary fittings, trim and brackets	Favorable strength-to-weight for non-primary structure parts
Electronics	Enclosures, heat spreaders	Good thermal conductivity and machinability for housings
Construction	Window frames, curtain wall extrusions	Surface finish, extrudability and dimensional stability

6085 fits applications where extruded geometries and mid-to-high strength are required without the cost or processing complexity of premium aerospace alloys. The alloy’s versatility in tempers and forms makes it useful across industries for both structural and aesthetic components.

Selection Insights

6085 is a good choice when you need an extrudable 6xxx alloy that delivers higher strength than common architectural grades while retaining good surface quality and extrusion flow. Choose annealed or T4 tempers for forming operations and T5/T6/T651 for structural components where stiffness and yield are critical.

Compared with commercially pure aluminum (1100), 6085 trades higher strength and better stiffness for somewhat reduced electrical conductivity and formability; use 6085 when mechanical performance is prioritized over maximum conductivity. Compared with work-hardened alloys such as 3003 or 5052, 6085 provides higher age-hardened strength with comparable corrosion resistance, but it can be less tolerant of extreme cold forming without prior anneal.

Compared with common heat-treatable alloys like 6061 or 6063, 6085 may be preferred for specific extrusion performance or surface finish requirements despite similar or slightly lower peak strength. When selecting 6085, weigh availability, required temper, and downstream processing (forming, welding, machining) against the slightly higher material cost versus basic 6xxx grades.

Closing Summary

6085 remains relevant because it provides a balanced platform within the 6xxx family: extrudable geometries, tailored tempers from highly formable to structurally strong, and dependable corrosion resistance for many engineered assemblies. Its chemistry and processing window allow manufacturers to optimize mechanical, surface, and fabrication traits for mid-to-high duty applications where weight, cost and manufacturability must be balanced.