Aluminum 7068: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

7068 is a 7xxx-series aluminum alloy, placed within the high-strength Al-Zn-Mg-Cu family. It is developed to deliver the highest strength possible for wrought aluminum alloys through a carefully balanced Zn–Mg–Cu chemistry and microalloying additions that control recrystallization and precipitate distribution.

The major alloying elements are zinc (primary strengthening element), magnesium (forms MgZn2 precipitates with Zn), copper (increases strength and enables age-hardening response), and microalloying elements such as zirconium and chromium to refine grain structure and limit recrystallization. The alloy is heat-treatable; peak strength is achieved by solutionizing, quenching and artificial aging (T‑tempers), with secondary strengthening from controlled dispersoids that provide creep and fracture resistance.

Key traits include extremely high tensile and yield strengths relative to other commercial alloys, competitive fatigue performance for a high-strength aluminum when properly aged, and reasonable machinability. Corrosion resistance is moderate—better than some very high-strength Zn-rich alloys when overaged, but inferior to 5xxx-series Mg alloys and many stainless steels; weldability is limited due to HAZ softening and susceptibility to hot cracking unless special procedures and fillers are used. Typical industries include aerospace, defense, high-performance sporting goods, and specialty automotive applications where ultimate strength-to-weight ratio is critical.

Engineers select 7068 when component design demands the maximum usable yield and tensile strength from an aluminum alloy while still retaining the advantages of a lightweight, non-ferrous material. It is chosen over alloys such as 7075 where a small absolute increase in strength and tighter microstructural control deliver performance gains for fasteners, fittings, or structural parts under high static or cyclic loads.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High (≥15%)	Excellent	Excellent	Fully annealed; easiest to form and machine
T6 / T651	Very High	Moderate (6–10%)	Limited	Poor to Moderate	Solution-treated and artificially aged; T651 includes stress relief by stretching
T6511 / T651A	Very High	Moderate (6–10%)	Limited	Poor to Moderate	Variation of T651 with controlled stress-relief or additional straightening
T7 (overaged)	High	Moderate to Higher (8–12%)	Better than T6	Moderate	Overaging trades peak strength for improved SCC and corrosion resistance
Hx (strain-hardened)	Moderate	Variable	Moderate	Moderate	Less commonly used; lower peak strength than T‑tempers but improved formability

The temper has a dominant influence on 7068 properties because the alloy is strongly heat-treatable. Solutionizing and artificial aging produce fine, coherent MgZn2-rich precipitates that raise yield and ultimate strength, while overaging coarsens these precipitates and improves resistance to stress-corrosion cracking at the cost of peak strength.

In practice, T6/T651 variants are specified when absolute strength and stiffness are primary, while T7 or intermediate tempers are chosen where corrosion resistance, fracture toughness and in-service durability are more important. Annealed (O) or strain-hardened tempers are used for forming and machining prior to final heat treatment.

Chemical Composition

Element	% Range	Notes
Si	≤0.12	Impurity; controlled to avoid brittle intermetallics
Fe	≤0.30	Impurity; higher Fe forms coarse phases that reduce toughness
Mn	≤0.10	Minor; can slightly improve grain structure
Mg	2.0–3.0	Primary co-strengthening with Zn to form MgZn2 precipitates
Cu	1.6–2.4	Increases strength and hardness, affects corrosion and toughness
Zn	7.0–8.5	Principal strengthening element; key to high peak strength
Cr	≤0.20	Grain refinement and recrystallization control
Ti / Zr	0.05–0.25 (combined)	Microalloying to form dispersoids, control grain growth and improve toughness
Others (each)	≤0.05	Trace elements controlled for cleanliness; balance Al

The alloying balance is optimized to maximize the volume fraction and stability of fine Mg–Zn precipitates that provide primary age-hardening, while Cu tailors the precipitate structure and provides secondary strengthening. Microalloying elements such as Zr and Cr form fine dispersoids that inhibit grain growth during solution treatment and quenching, improving toughness, reducing quench sensitivity, and controlling recrystallization during thermomechanical processing.

Mechanical Properties

7068 shows a marked difference between annealed and peak-aged conditions. In T6/T651 tempers the alloy achieves among the highest tensile and yield strengths available in commercial wrought aluminum, with UTS and yield values that enable significant weight reduction in structural designs. Elongation in peak tempers is moderate, and fracture toughness is typically lower than lower-strength Al alloys but acceptable when component geometry and stress concentrators are controlled.

Fatigue performance of 7068 can be very good for an Al–Zn–Mg–Cu system when the microstructure is optimized and surface finish is controlled; however, high-strength aluminum alloys remain sensitive to surface defects and corrosive environments that can nucleate fatigue cracks. Thickness and section size affect achievable properties due to quench sensitivity and precipitation kinetics; thin sections reach peak strength more readily after quenching than thick sections, which may require slower cooling or modified heat-treatment cycles.

Hardness follows strength trends: annealed material shows low Brinell/Vickers values consistent with soft Al, while T6-type tempers produce high hardness values that correspond to the high yield strength. Localized HAZ softening during welding and the potential for residual stresses must be accounted for in design.

Property	O/Annealed	Key Temper (T6 / T651)	Notes
Tensile Strength	200–300 MPa (typical)	700–780 MPa (typical range)	Peak-aged strengths among the highest for wrought Al; values depend on section thickness and exact aging
Yield Strength	100–250 MPa	640–700 MPa	Yield approaches values typically associated with some steels in specific tempers
Elongation	≥15%	6–10%	Ductility reduced in peak-aged states; fracture mode becomes more transgranular/intergranular depending on aging
Hardness (HB)	~60–90 HB	~150–180 HB	Hardness correlates with precipitate volume fraction and distribution

Physical Properties

Property	Value	Notes
Density	~2.78–2.81 g/cm³	Slightly higher than some low-alloyed Al but still low for high strength
Melting Range	~475–635 °C (solidus/liquidus range typical for Al–Zn–Mg–Cu)	Exact solidus/liquidus depend on composition and minor elements
Thermal Conductivity	~120–150 W/m·K (at 20 °C, typical alloyed value)	Lower than pure Al due to alloying scatterers; varies with temper and composition
Electrical Conductivity	~30–45 %IACS	Alloying reduces conductivity relative to pure Al
Specific Heat	~0.88–0.90 J/g·K	Similar to other Al alloys
Thermal Expansion	~23–25 ×10⁻⁶ /K	Comparable to other wrought Al alloys; design for thermal mismatch required with composites/steel

The physical properties of 7068 are generally similar to other high-strength aluminum alloys; the alloy retains the favorable density and specific heat of aluminum while sacrificing some thermal and electrical conductivity because of the high solute content. Thermal expansion and conductivity must be considered in thermal management and joining scenarios, particularly when paired with dissimilar materials.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.5–6 mm typical; up to ~12 mm	Thin sheets reach peak properties more uniformly	T6, T651, O	Used for highly stressed panels and machined parts after aging
Plate	6–100+ mm	Thick plates are quench-sensitive; may show reduced peak properties unless process controlled	T6/T7 variants; T651 for stress-relief	Often requires specialized heat-treatment and quench fixtures
Extrusion	Variable cross-sections	Extruded sections can achieve high properties if solution-treated and aged	T6/T651	Complex profiles used for structural members and fittings
Tube	OD/ID variable	Wall thickness impacts quench and aging response	T6/T651	Used in weight-sensitive structural tubing; care in welding and joining
Bar/Rod	Diameters up to several inches	Bar stock can be produced and age-hardened to high strength	T6, T651	Common for fasteners, pins and high-strength machined components

Wrought forms differ in quenchability and residual stress behavior. Thin items are easier to heat treat to peak properties; thick plates and large sections require controlled quenching or modified alloy tempers (T7 or multi-step aging) to avoid a strong center-line underage and to reduce distortion. Extrusions and forgings are often solution-treated after shaping to produce a homogeneous precipitation state.

Equivalent Grades

Standard	Grade	Region	Notes
AA	7068	USA	Primary designation for this high-strength alloy in aluminum associations
EN AW	7068	Europe	Often referenced as EN AW-7068 with similar composition; differences may exist in allowable impurities
JIS	A7068 (approx.)	Japan	Local standards may carry similar chemistries under different designations and heat-treatment specifications
GB/T	7068	China	Chinese standardized variants exist; exact chemistries and mechanical property guarantees can vary

Standards and designations are broadly similar, but manufacturing and testing practices differ between regions. Minor differences in maximum impurity levels, microalloying additions, and qualification test procedures can create variation in properties and fracture behavior—engineers should verify specification sheets and certificates of conformity for critical components to ensure interchangeability.

Corrosion Resistance

7068 is an Al–Zn–Mg–Cu alloy and inherits the family’s sensitivity to localized corrosion in chloride-containing environments. In atmospheric conditions with low chloride exposure, properly overaged or surface-treated 7068 performs acceptably; however, bare T6 material can be susceptible to pitting and intergranular attack, particularly at stressed locations.

In marine or high-chloride environments, 7068 requires protective coatings, anodizing, or selection of an overaged (T7-style) temper to improve corrosion resistance. Even then, it generally underperforms compared with 5xxx-series magnesium-bearing marine alloys and stainless steels for long-term immersion or splash-zone service without robust protection.

Stress corrosion cracking is a concern for high-strength Al–Zn–Mg alloys. Peak-aged T6 tempers have higher SCC susceptibility; overaging and microalloying dispersoids reduce susceptibility but at the expense of peak strength. Galvanic coupling with cathodic materials (copper, stainless steel) will accelerate local attack; coupling to steel should be insulated and design should avoid crevices and retained salts.

Compared with other alloy families, 7068 trades corrosion performance for strength: it commonly outstrips 6xxx-series alloys in strength but is generally less corrosion-resistant than many 5xxx-series alloys and certain 3xxx-series alloys used in marine applications. Proper temper selection and surface protection are essential design levers.

Fabrication Properties

Weldability

Welding 7068 is challenging due to HAZ softening and a significant loss of strength in the fusion zone; the precipitation-hardening microstructure is disrupted by heat input. TIG and MIG welding may be performed for non-critical, localized joints using low-heat procedures, but post-weld heat treatment cannot always restore base-metal properties for large structures. If welding is required, matching filler alloys designed for strength and SCC resistance (e.g., special Al‑Zn‑Mg filler alloys or lower-strength Al‑Si fillers) and procedures minimizing heat input are recommended.

Machinability

Machinability of 7068 in peak-aged temper is generally good compared with high-strength steels due to its lower density and good chip-breaking behavior, but high hardness increases tool wear. Carbide tooling, positive rake geometry and high-speed machining with ample coolant produce the best results. Machining in a softer temper (O) before final aging is a common practice to reduce tool wear and distortion during complex machining operations.

Formability

Forming is best performed in annealed (O) or soft tempers; T6/T651 material exhibits limited cold formability and higher springback. Bend radii should be conservative (e.g., larger multiples of thickness) in peak tempers to avoid cracking at stress concentrators. Where significant forming is required, perform operations in an annealed condition followed by solution treatment and artificial aging to achieve final strength.

Heat Treatment Behavior

As a heat-treatable alloy, 7068 follows classical precipitation-hardening metallurgy. Solution treatment is typically performed at temperatures in the range required to bring alloying elements into solid solution (commonly ~470–500 °C depending on section size and furnace practices) followed by rapid quenching to retain a supersaturated solid solution. Artificial aging (e.g., T6 aging) is commonly performed at temperatures roughly between 120–160 °C for times tailored to achieve peak hardness and strength; times vary with section size and overaging tolerance.

Overaging to produce T7-style tempers involves higher aging temperatures or longer times to coarsen precipitates; this reduces peak strength while improving stress corrosion cracking resistance and fracture toughness. T651 designations indicate a controlled straightening or stretching operation after quench to reduce residual stresses and distortion. Because of quench sensitivity, thick sections may require modified cycles or interrupted quench protocols and the use of microalloying dispersoids (Zr, Ti) to reduce recoverable heat-treat dependence.

High-Temperature Performance

7068 retains elevated strength relative to lower-alloyed aluminum at modest elevated temperatures, but significant strength reduction occurs as temperature approaches and exceeds ~120–150 °C. Long-term exposure above ~100–120 °C leads to microstructural evolution (coarsening of strengthening precipitates) and measurable loss of yield and hardness; design service limits are usually set well below these temperatures for critical load-bearing applications.

Oxidation is minimal compared with ferrous alloys, but elevated temperature exposure can change surface oxide characteristics and may influence corrosion resistance. In welded joints, HAZ regions are especially vulnerable; localized softening and precipitate dissolution/reprecipitation reduce local load capacity and contribute to creep or stress-rupture under sustained high-temperature loading.

Applications

Industry	Example Component	Why 7068 Is Used
Aerospace	Structural fittings and high-load pins	Exceptional strength-to-weight and high yield allow lightweight designs
Defense / Firearms	Receivers, bolt carriers, high-strength components	High static strength and machinability for precision parts
Motorsports / Automotive	Suspension links, roll-cage connectors	High strength enables lighter components under dynamic loads
Sporting Goods	High-performance bicycle frames, hardware	Competitive weight reduction with high stiffness
Electronics	Structural frames and brackets	High stiffness-to-weight and machinability for compact assemblies

7068 is selected for applications where peak strength and yield allow lighter, stiffer designs and where the manufacturing supply chain can support controlled heat-treatment and protective finishing. The alloy is most compelling where weight saving translates to performance or fuel efficiency gains, and where protective coatings or design choices manage corrosion and fatigue risks.

Selection Insights

When selecting 7068, prioritize it for designs requiring the highest possible yield and tensile strengths in a wrought aluminum, and when the design and manufacturing processes can accommodate controlled heat treatment and protective finishes. Expect higher material cost and tighter handling requirements than common Al alloys.

Compared with commercially pure aluminum (1100), 7068 trades electrical and thermal conductivity and room-temperature formability for a multiple-fold increase in strength and stiffness; choose 7068 when structural performance is the main driver. Compared with work-hardened alloys such as 3003 or 5052, 7068 provides much higher static strength but typically lower intrinsic corrosion resistance in chloride environments and poorer cold formability. Compared with common heat-treatable alloys like 6061 or 6063, 7068 substantially outperforms them in yield and tensile strength; select 7068 when higher strength justifies increased cost and when weld/joining constraints can be managed.

Closing Summary

7068 remains relevant where the highest practical strength in a wrought aluminum is required and where weight-sensitive designs benefit from the improved strength-to-weight ratio. Its specialized chemistry and heat-treatment response permit structural solutions not achievable with lower-strength alloys, provided design, fabrication and corrosion-protection strategies are applied to mitigate the alloy’s sensitivities.