Aluminum 7085: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

7085 is a high-strength aluminum alloy belonging to the 7xxx series, which are primarily Zn–Mg–Cu containing alloys optimized for aerospace structural applications. The alloy emphasizes high yield and tensile strength with an alloy chemistry tailored to balance strength, fracture toughness, and resistance to stress-corrosion cracking compared with legacy 7xxx alloys.

Major alloying elements are zinc as the principal strengthener, magnesium which forms MgZn2 strengthening precipitates, and copper which raises as-quenched strength and alters aging kinetics. Minor additions of zirconium, chromium or titanium are commonly used to control grain structure, inhibit recrystallization, and refine recrystallized microstructures in heavy-section plate or extrusions.

7085 is a heat-treatable alloy that derives peak strength from solution heat treatment, quenching, and artificial aging to form dense, coherent Mg–Zn rich precipitates. Key traits include very high static strength and good fracture toughness for the level of strength, moderate-to-poor weldability with conventional fusion methods, and limited formability in peak-aged tempers but superior performance in controlled overaged tempers.

Typical industries are aerospace primary and secondary structures, high-performance defense components, and other sectors where strength-to-weight and damage-tolerance are critical. Engineers choose 7085 over other alloys when a combination of thick-section strength, improved crack-initiation resistance, and aerospace-qualified product forms are required, often preferring 7085 when 7075 or 7050 cannot meet toughness or SCC performance targets in large plate.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed, maximum ductility for cold forming
H111	Low–Medium	Medium	Good	Fair	Partially strain-hardened, limited forming for small bends
T5	Medium–High	Medium	Fair	Poor	Cooled from elevated temperature and artificially aged
T6	High	Low–Medium	Poor	Poor	Peak aged for maximum strength; common for static structures
T651	High	Low–Medium	Poor	Poor	T6 plus stress-relief by stretching to reduce residual stress
T73 / T76	Medium–High	Medium	Fair	Poor	Overaged tempers for improved SCC resistance and fracture toughness
H14	Medium	Medium	Fair	Fair	Work-hardened with limited forming ability, used in sheet form

Temper has a primary role in tuning the strength/toughness/formability triad; annealed conditions enable significant cold forming but sacrifice strength, while T6 and T651 provide maximum static strength with reduced ductility. Overaged tempers such as T73 or T76 intentionally lower peak strength to improve resistance to stress-corrosion cracking and increase fracture toughness, making them popular for thick-section aerospace plates.

Chemical Composition

Element	% Range	Notes
Si	0.10 max	Impurity; limited effect on strength
Fe	0.20 max	Common impurity; excessive Fe can form intermetallics that affect toughness
Mn	0.05 max	Typically low in 7xxx alloys; limited role
Mg	2.0–3.0	Key precipitate-former (MgZn2) driving age-hardening
Cu	1.5–2.5	Raises strength and influences aging kinetics and toughness
Zn	6.5–8.5	Principal strengthening element; level tuned for peak strength and SCC behavior
Cr	0.05–0.25	Microstructure control additive to inhibit recrystallization
Ti	0.02–0.10	Grain refiner in cast or wrought forms
Others (Zr, Ag, B)	Trace additions	Zr or other trace additions may be used to control grain growth and improve toughness; exact levels vary by mill product

The alloy’s performance is dominated by the Zn–Mg–Cu system that defines aging kinetics and precipitate structure; higher Zn and Mg promote a dense distribution of strengthening precipitates while Cu modifies their composition and coherency strain. Small additions of Zr or Cr are deliberate to produce a sub-grain structure in thick plate, which reduces recovery and grain-boundary precipitate formation, thereby improving fracture toughness and reducing susceptibility to intergranular corrosion.

Mechanical Properties

7085 displays high tensile and yield strengths in peak-aged tempers with reduced elongation compared with lower-strength aluminum alloys. Yield behavior shows limited yield drop but significant dependence on section thickness and aging condition; thick sections typically exhibit lower yield and tensile values due to slower quench rates. Elongation varies substantially with temper and thickness, with O or annealed material showing elongation in the mid-double digits while T6/T651 is frequently in the single-to-low double digits.

Hardness in peak-aged tempers is high and correlates with tensile strength; Brinell hardness values for T6/T651 plate typically fall into a range significantly above common 6xxx alloys and similar to other high-strength 7xxx alloys. Fatigue performance is generally favorable for the strength class when careful attention is paid to surface finish and residual stresses; however, fatigue-crack growth and initiation can be worsened by localized corrosion or machining marks. Section thickness and heat-treatment path strongly affect both static and fatigue properties because of sensitivity to quench and aging conditions which control precipitate distribution and residual stress.

Property	O/Annealed	Key Temper (e.g., T6/T651)	Notes
Tensile Strength	~300–380 MPa	~540–620 MPa	Tensile decreases with section thickness; T6 provides peak strength
Yield Strength	~140–250 MPa	~470–560 MPa	Yield-to-tensile ratios vary with temper and aging state
Elongation	~20–30%	~6–12%	Annealed material is much more formable than peak-aged tempers
Hardness	~70–95 HB	~150–190 HB	Hardness correlates with precipitate density and temper

Physical Properties

Property	Value	Notes
Density	2.78–2.82 g/cm³	Typical for Zn–Mg–Cu alloyed aluminum; slightly denser than pure Al
Melting Range	≈ 480–635 °C	Solidus and liquidus depend on alloying; melting range wider than pure Al
Thermal Conductivity	120–150 W/m·K (approx)	Lower than pure aluminum due to solute scattering
Electrical Conductivity	~30–40 % IACS	Reduced compared with low-alloyed aluminum because of solute content
Specific Heat	~0.88–0.90 J/g·K	Typical aluminum specific heat at ambient
Thermal Expansion	~23–24 ×10⁻⁶ /K	Typical linear coefficient for wrought Al alloys at room temperature

The physical property set places 7085 within the expected bounds for high-strength wrought aluminum alloys; density remains low relative to steels, enabling excellent strength-to-weight. Thermal and electrical conductivities are reduced by alloying elements that scatter electrons and phonons, so designers should not expect heat-sink performance equal to commercially pure or 1xxx series alloys.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.5–6 mm	Strength consistent in thin gauges; less sensitivity to quench	O, H111, T5	Common for secondary structures where forming is needed
Plate	6–200+ mm	Strength decreases with thickness if quenched slowly	T6, T651, T73/T76	Heavy plate often processed to control quench and overage for SCC resistance
Extrusion	Up to large cross-sections	Strength depends on section size and controlled precipitation	T6/T651, T5	Less common than plate; extrusions used for complex stiffeners
Tube	Custom diameters/walls	Mechanical properties influenced by forming and heat-treatment	T6/T651	Used in high-strength structural tubing where welding is restricted
Bar/Rod	Diameters up to 150 mm	Properties vary with cross-section and subsequent aging	T6, T651	Used for forgings, fittings and machined components

Processing differences drive application choices: sheet and thin gauges are chosen for formability and light-weight structures, while plate is specified when thick-section strength and fracture toughness are required. Extrusions and forgings of 7085 are less common and typically reserved for components that require the alloy’s high strength and fracture resistance combined with specific cross-sectional shapes.

Equivalent Grades

Standard	Grade	Region	Notes
AA	7085	USA	Primary designation used by North American producers for aerospace plate
EN AW	—	Europe	No single direct EN standard equivalent; many European mills supply proprietary 7xxx variants
JIS	—	Japan	No widely adopted direct JIS equivalent; usage often relies on AA or proprietary designations
GB/T	—	China	Chinese mills produce similar high-Zn alloys but direct standard equivalence to AA7085 is limited

7085 is largely a proprietary aerospace plate alloy and does not have broad one-to-one equivalents in national standards that are openly interchangeable; suppliers often provide mill specifications that must be matched against mechanical, chemical, and fracture-toughness requirements. When cross-referencing, engineers should compare detailed composition ranges, temper definitions, and fracture-toughness data rather than relying solely on nominal grade numbers.

Corrosion Resistance

In atmospheric environments 7085 provides reasonable resistance to general corrosion but is more susceptible to localized attack than 5xxx or 6xxx series alloys because of higher zinc and copper content. Surface treatments, cladding, and protective coatings are commonly specified for exterior or aggressive environments to mitigate pitting and exfoliation tendencies. When properly overaged (T73/T76) the alloy shows improved resistance to stress-corrosion cracking compared to peak-aged tempers.

Marine behavior is mixed: 7085 will perform acceptably in mildly corrosive environments if protected, but in unprotected salt-spray or splash zones the alloy requires coatings or cladding to achieve long-term durability. Galvanic interactions with common fasteners and mating materials must be considered; pairing 7085 with stainless steel will create a galvanic couple where aluminum is the anodic member, accelerating corrosion unless insulated or cathodically protected.

Stress-corrosion cracking is a key design concern with 7xxx alloys: peak-strength tempers are more vulnerable, particularly when tensile residual stresses and corrosive electrolytes are present. Overaging and controlled microstructure (grain boundary precipitate control via Zr/Cr additions) are standard mitigation strategies. Compared with 5xxx and 6xxx families, 7085 trades corrosion resistance for high strength; compared with 7075/7050, 7085 aims for a favorable trade-off—often offering improved toughness and SCC resistance in thick sections.

Fabrication Properties

Weldability

Conventional fusion welding of 7085 is generally discouraged for primary structural applications because of severe HAZ softening, loss of strength, and susceptibility to hot cracking and porosity. If joining is required, friction stir welding (FSW) or solid-state processes are preferred; these reduce melting-related defects and preserve more of the parent-metal properties. When fusion welding is performed for non-critical joints, specialized filler wires and pre/post-heat controls are necessary, but designers should account for HAZ soft zones and reduced fatigue life.

Machinability

Machinability of 7085 in T6/T651 is moderate to good relative to other high-strength 7xxx alloys, benefiting from a reasonably uniform microstructure in wrought forms; however, tool wear is higher than for 6xxx alloys. Carbide tooling with sharp geometries, positive rake, rigid setups, and abundant coolant are recommended to manage chip formation and heat. Surface finish and residual stresses from machining directly influence fatigue life and crack initiation, so final finishing and stress-relief practices are important for critical aerospace parts.

Formability

Forming performance depends strongly on temper and thickness; O and H111 tempers offer the best cold-forming ability and tight bend radii, while T6/T651 are poor candidates for bending without risk of cracking. Recommended minimum bend radii increase with strength and decrease with thickness; designers often use warm forming or pre-heat plus subsequent re-aging to achieve complex shapes in thicker sections. For sheet forming, appropriate temper selection and tool design reduce springback and edge cracking tendencies.

Heat Treatment Behavior

7085 is heat-treatable: solution treatment typically occurs at temperatures near 470–480 °C to dissolve soluble phases followed by rapid quenching to retain a supersaturated solid solution. Artificial aging schedules vary by desired property balance; typical peak-aging (T6) may use temperatures around 120–130 °C for durations on the order of 16–24 hours, while overaging (T73/T76) uses higher temperatures or longer times to coarsen precipitates and improve SCC resistance. T651 denotes T6 with a controlled stretch to reduce residual stresses and is common for aerospace plate.

T temper transitions include natural aging effects immediately after quench and the ability to obtain intermediate properties with interrupted aging or retrogression and re-aging (RRA) processes to recover toughness and SCC resistance without large strength penalties. Careful control of quench rate, aging temperature, and solution-treatment time is essential in thick sections to avoid local soft zones and inconsistent mechanical properties.

High-Temperature Performance

Strength retention of 7085 degrades with increasing temperature as precipitates coarsen and become less effective; service limits for retaining room-temperature static properties are typically under 100–120 °C depending on time and load. Prolonged exposure above aging temperatures may reduce strength and promote overaging, so designers must account for transient exposures during service or processing. Oxidation is minimal at typical service temperatures for aluminum alloys, but elevated-temperature exposure combined with moisture can accelerate localized attack.

In welded joints the HAZ is particularly vulnerable because of precipitate dissolution and coarsening; this yields soft bands that reduce load-carrying capacity and fatigue resistance. For components exposed to heat or thermal cycling, stress-relief treatments and careful temper selection help mitigate long-term property loss.

Applications

Industry	Example Component	Why 7085 Is Used
Aerospace	Wing skins and structural ribs	High strength-to-weight and fracture toughness in thick plate
Marine / Defense	High-strength structural fittings	Damage tolerance and high static strength where weight matters
Transportation	Lightweight chassis fittings for high-performance vehicles	Superior strength allowing thinner sections and mass savings
Electronics / Thermal Management	Structural heat spreaders for rugged electronics	Moderate thermal conductivity combined with structural performance

7085 is typically selected for high-value, safety-critical components where a premium is paid for the alloy’s combination of high tensile/yield strength and improved toughness in thick sections. Its use is concentrated in aerospace and defense where specification-level validation, plate availability, and traceable processing are required.

Selection Insights

7085 is the natural choice when high strength and improved fracture toughness in thick sections are required and when designers accept limitations in weldability and formability. For applications where forming or joining by fusion welding is a priority, lower-strength alloys or specialized tempers are likely better choices.

Compared with commercially pure aluminum (1100), 7085 trades electrical and thermal conductivity and formability for much higher strength and stiffness, making it unsuitable where conductivity or deep drawing is required. Compared with work-hardened alloys such as 3003 or 5052, 7085 offers far higher strength but generally less corrosion immunity and ductility; choose 7085 when structural performance outweighs corrosion-driven maintenance concerns. Compared with common heat-treatable alloys like 6061, 7085 provides substantially higher peak strength and often better fracture toughness in plate, but at higher material cost and reduced ease of welding; 7085 is preferred for primary structural members where that extra strength and damage tolerance are required.

Closing Summary

7085 occupies a high-performance niche within the 7xxx family by delivering very high strength in thick-section plate while balancing fracture toughness and SCC resistance through controlled chemistry and tempers. Its adoption in aerospace and defense components reflects the alloy’s capability to reduce structural weight without sacrificing damage tolerance, making it a relevant choice for demanding structural applications where material performance justifies its cost and fabrication constraints.