Aluminum 7056: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

7056 is a high-strength aluminum alloy in the 7xxx series (Al-Zn-Mg-Cu) family, formulated for applications that require very high static and fatigue strength combined with aerospace-quality toughness. The alloy’s primary strengthening elements are zinc and magnesium, with appreciable copper additions and microalloying trace elements such as chromium, zirconium and titanium to control grain structure and recrystallization.

7056 is a heat-treatable alloy that attains its mechanical performance through solution treatment, quenching and precipitation (age) hardening; the alloy can also be overaged for improved fracture toughness and stress-corrosion resistance. Key traits include very high strength-to-weight ratio, relatively poor intrinsic weldability compared with 5xxx and 6xxx series alloys, limited room-temperature formability in peak-aged tempers, and moderate corrosion resistance that can be significantly improved by temper selection and surface treatments.

Typical industries that use 7056 are aerospace (structural forgings, fittings, and landing gear components), high-performance motorsport, and defense hardware where high static and fatigue strengths are essential. The alloy is selected over other grades when maximum strength and fatigue performance are prioritized while keeping component weight low, especially when mechanical fastening or controlled fabrication processes are feasible.

Engineers choose 7056 instead of other 7xxx alloys when a specific balance of toughness versus peak strength is required, or when fine-grain microalloying (e.g., Zr/Ti) and tailored aging practices are used to mitigate stress-corrosion cracking while retaining a high yield and tensile strength.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed, maximum ductility for forming
H12 / H14	Low–Medium	Medium–High	Good	Good	Light strain-hardened for shaping with some strength
T5	Medium	Medium	Limited	Poor–Fair	Cooled from elevated temperature and artificially aged
T6	High	Low–Medium	Limited	Poor	Peak-aged to maximize strength; common structural temper
T651	High	Low–Medium	Limited	Poor	T6 with a straightening (stress-relief) operation; common for aerospace
T76 / T7451	Medium–High	Medium	Improved	Poor–Fair	Overaged tempers to improve SCC resistance and toughness
Hxxx (cold-worked)	Variable	Variable	Moderate	Good	Combination tempers used for tailored strength/formability

Tempers strongly govern 7056 performance: annealed (O) plate and sheet are the most formable and easiest to machine, while T6/T651 supplies the maximum static strength at the expense of elongation and bending behavior. Overaged tempers such as T76/T7451 trade some peak strength for substantially improved stress-corrosion cracking resistance and fracture toughness, which is critical for safety-critical aerospace components.

Chemical Composition

Element	% Range	Notes
Si	≤ 0.40	Typical impurity; excessive Si may affect melting behavior
Fe	≤ 0.50	Impurity that forms intermetallics; controlled to limit embrittlement
Cu	1.4–2.4	Increases strength and hardenability; affects corrosion behavior
Mn	≤ 0.10	Minor, controls recrystallization when present
Mg	2.0–2.8	Major strengthening element via MgZn2 precipitates
Zn	7.0–8.8	Primary strength contributor; high Zn increases hardenability
Cr	0.04–0.20	Controls grain structure and reduces recrystallization
Ti	0.05–0.20	Grain refiner for forgings and castings
Zr / Other microalloying	0.05–0.25	Zr and similar elements form dispersoids to limit grain growth
Others / Residuals	≤ 0.15 each	Includes trace elements and unspecified residuals; balance Al

The high Zn/Mg combination produces the MgZn2-type precipitates that are responsible for peak strength after artificial aging. Copper promotes higher strength and fracture toughness but can lower corrosion resistance; therefore, Cu and Zn levels are balanced and microalloying additions (Zr/Cr/Ti) are employed to produce a fine, stable grain structure and to control recrystallization during thermomechanical processing.

Mechanical Properties

7056 exhibits a wide range of tensile and yield strengths depending on temper and product form; peak-aged tempers (T6/T651) are among the highest for aluminum alloys and provide excellent static strength but reduced ductility and bendability. Yield strength in T6-like tempers can approach or exceed other high-strength 7xxx alloys, with tensile strength and yield diminishing with increasing section thickness due to quench-rate sensitivity.

Elongation to failure is substantially higher in annealed condition and decreases as strength increases; typical elongations in T6 are sufficient for machining and light forming but not for severe cold forming. Hardness correlates with aging state and is useful for quality control; fatigue strength is favorable for forged and thick-section parts but is sensitive to surface condition and heat-treatment homogeneity.

Thickness effects are significant for 7056 because the ability to reach peak age during quench and aging is reduced as section thickens; designers must account for lower properties in heavy forgings and plates or use modified heat treatments and alloy variants to compensate.

Property	O/Annealed	Key Temper (e.g., T6/T651)	Notes
Tensile Strength	220–300 MPa (typ.)	540–640 MPa (typ.)	Wide range depending on temper, section thickness and aging
Yield Strength	110–200 MPa (typ.)	470–560 MPa (typ.)	Yield is strongly quench- and temper-dependent
Elongation	18–28%	6–12%	Peak-aged tempers show reduced ductility
Hardness (HV)	60–90	150–200	Vickers hardness correlates with tensile properties

Physical Properties

Property	Value	Notes
Density	~2.78 g/cm³	Typical for high-strength Al-Zn-Mg-Cu alloys
Melting Range	~500–635 °C (solidus to liquidus approx.)	Solidification range depends on exact composition and impurities
Thermal Conductivity	~120–140 W/m·K	Lower than pure aluminum but adequate for many thermal applications
Electrical Conductivity	~30–45% IACS	Reduced relative to purer alloys due to alloying elements
Specific Heat	~880–910 J/kg·K	Near that of common aluminum alloys at ambient temperature
Thermal Expansion	~23–24 µm/m·K	Typical linear expansion coefficient for Al alloys at room temperature

The physical constants reflect a balance between metallic conductivity and alloying content; thermal conductivity and electrical conductivity are reduced by the substantial Zn/Mg/Cu additions compared with 1xxx alloys. Designers should expect the alloy to behave thermally like other 7xxx系 alloys with fast heat-sinking capability but somewhat diminished conductivity for high-frequency electrical applications.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.5–6 mm	Lower as thickness increases	O, T6, T76	Used in aerospace skins and precision panels; forming limited in peak age
Plate	6–200+ mm	Property gradient with thickness	T6, T651, T76	Thick plates require controlled quench; heavy sections see reduced properties
Extrusion	Variable cross-sections	Strength similar to plate for similar temper	T6, T651	Complex extrusions possible but require careful direct-aging control
Tube	OD 10–300 mm	Strength depends on wall thickness	T6, T76	Used for structural tubing where fatigue performance is required
Bar/Rod	Dia. 5–200 mm	Good machinability in O; high strength in T6	O, T6	Forged bar commonly heat treated for critical components

Forming and processing routes determine achievable properties: thin-sheet parts can be solution-treated and quenched quickly to achieve near-peak ages, while thick plates and forgings are more quench-sensitive and often require modified aging cycles. Extrusions and forgings benefit from microalloying to control grain growth and improve structural homogeneity in large cross sections.

Equivalent Grades

Standard	Grade	Region	Notes
AA	7056	USA	Principal designation under the Aluminum Association
EN AW	AlZn7.5MgCu?*	Europe	Broadly equivalent compositions exist but require verification for specific tempers
JIS	A7056 (approx.)*	Japan	Local catalogues may list close equivalents with different limits
GB/T	Al-Zn-Mg-Cu series (7056-like)*	China	Chinese standards have near-equivalent high-strength Zn-Mg-Cu alloys

Direct one-to-one equivalents for 7056 are limited because compositions and processing windows differ across standards; the asterisked entries indicate that local designations often approximate 7056 but can have different trace element limits, microalloying additions and temper availability. Engineers must verify chemical and mechanical specification sheets rather than relying solely on nominal grade names when sourcing internationally.

Corrosion Resistance

7056 has moderate general corrosion resistance in atmospheric environments, but like other high-Zn 7xxx alloys it can be susceptible to pitting and exfoliation corrosion in aggressive chloride environments if left untreated. Overaged tempers (T76/T7451) and cladding or anodizing significantly improve resistance to stress-corrosion cracking and intergranular attack.

In marine environments, 7056 without proper surface treatment or sacrificial protection is less durable than 5xxx or coated 6xxx alloys; localized attack and SCC are the primary concerns. Application-level mitigation includes protective coatings, sealants at joints, cathodic protection, and tight control of design to avoid crevices that trap saltwater.

Stress-corrosion cracking is an important failure mode for high-strength 7xxx alloys; 7056’s microalloying (Zr/Cr) and careful temper selection can reduce SCC susceptibility, but designers should apply conservative design factors and consider overaged tempers for critical components. Galvanic interaction with more noble materials (e.g., stainless steels or titanium) is typically unfavorable for aluminum; isolation and fastener selection are important to avoid accelerated anodic dissolution.

Fabrication Properties

Weldability

Welding 7056 is generally challenging; fusion welding methods (TIG/MIG) risk hot cracking, porosity and pronounced HAZ softening that can reduce local strength by a significant fraction. When welding is unavoidable, filler alloys with higher Mg content (e.g., 5356) or specially formulated 7xxx fillers are sometimes used, but welds frequently remain weaker than base metal and require post-weld heat treatment where feasible.

Electron beam and friction stir welding are preferred for critical applications because they can reduce HAZ size and avoid liquid-phase cracking; however, process control and post-weld solution/aging are needed to regain acceptable mechanical properties. For many aerospace use-cases, mechanical fastening or adhesive bonding is preferred to welding.

Machinability

7056 exhibits reasonably good machinability in both annealed and peak-aged conditions compared with other high-strength alloys, but tool selection and clamping rigidity are critical to avoid chatter and work-hardening at the cut face. Carbide tooling with positive rake geometry, adequate coolant, and moderate cutting speeds are recommended; feed rates should be chosen to produce continuous chips and minimize workpiece heating.

Because 7056 can be produced with tight tolerances, machining is a common final-stage operation for fittings and fasteners; pre-aging or stress-relief operations can improve dimensional stability during heavy machining. Surface finish and chip control are important for fatigue-critical components.

Formability

Forming is best conducted in annealed (O) or partially softened tempers; T6/T651 exhibits limited cold formability and requires larger bend radii and incremental forming techniques. Typical minimum internal bend radii for thin sheet in peak-aged tempers are in the range of 3–6 times material thickness, but designers should validate radii with prototypes and consider local springback.

For stampings and complex shapes, solution treat-and-form or warm-forming approaches followed by artificial aging can be used to obtain near-net shapes with acceptable final properties. Cold working (H-tempers) provides intermediate strength/formability trade-offs for parts that require some shaping without full anneal.

Heat Treatment Behavior

7056 is heat-treatable via conventional solution treatment, quenching and artificial aging sequences. Solution treatments are typically performed near the solvus temperature for Zn/Mg/Cu systems (approximately 470–480 °C) to dissolve solute-rich phases, followed by rapid quenching to retain solute in supersaturated solid solution.

Artificial aging for T6-type conditions commonly uses intermediate temperatures (typically 120–160 °C) for times tuned to balance peak strength and toughness; faster aging yields higher peak strength but can increase SCC susceptibility. Overaging treatments (T76/T7451) use higher temperatures and/or longer times to coarsen precipitates, reducing yield and tensile strength modestly while substantially improving fracture toughness and SCC resistance.

T temper transitions are predictable: T4 (naturally aged) to T6 (artificial aging) increases strength; T73/T76 reduce peak strength but improve corrosion and toughness. Control of quench rate and aging cycle is crucial for thick sections to avoid property gradients and soft internal zones.

High-Temperature Performance

7056 loses strength relatively rapidly with increasing temperature; usable static strength declines above approximately 100–125 °C and significant property degradation occurs above 150 °C. Creep resistance is limited compared with heat-resistant alloys, so long-term high-temperature service is not recommended for load-bearing components.

Surface oxidation is minimal up to elevated service temperatures typical of aircraft environments, but prolonged exposure at elevated temperatures can alter precipitate distributions and reduce fatigue life. Designers should limit continuous service temperatures and consider alternative alloys for sustained thermal loads or provide shielding and thermal management to keep component temperatures within safe limits.

Applications

Industry	Example Component	Why 7056 Is Used
Aerospace	Structural fittings, wing ribs, lug forgings	Highest practical strength-to-weight and fatigue performance for critical fittings
Marine / Defense	Missile and weapon housings, high-strength connectors	High specific strength and tailored toughness; microalloying helps SCC resistance
Motorsport / Automotive	Roll-cage components, structural cross-members (limited)	Weight-critical structural parts where welding/fabrication method allows
Electronics / Thermal Management	Small heat spreaders, brackets	Good thermal conductivity coupled with high stiffness for compact, load-bearing parts

7056 is typically reserved for components where maximum specific strength and fatigue resistance are essential and where fabrication routes can avoid the deleterious effects of fusion welding. Its combination of high strength, controllable toughness and available tempers makes it a staple in safety-critical aerospace subcomponents.

Selection Insights

7056 is selected when strength-to-weight and fatigue performance are prioritized over ease of fabrication or raw-material cost. Compared with commercially pure aluminum (1100), 7056 trades far higher tensile and yield strengths for lower electrical conductivity and reduced formability; use 7056 when structural performance outweighs conductivity and forming ease.

Compared with common work-hardened alloys such as 3003 or 5052, 7056 sits well above them in strength while offering similar or slightly reduced corrosion resistance depending on temper; choose 7056 for load-bearing structures where 3xxx/5xxx cannot meet required strength. Compared with widely used heat-treatable alloys like 6061/6063, 7056 offers superior peak strength and fatigue life, though it may be more expensive and more difficult to weld; select 7056 when its higher specific strength justifies increased fabrication control and possible specialty joining processes.

When choosing 7056, weigh trade-offs: it delivers aerospace-grade strength and fatigue properties but requires careful heat treatment, surface protection and often alternative joining techniques. Consider availability and cost premium relative to 6xxx and 5xxx alloys and validate temper and thickness impacts on final properties before final selection.

Closing Summary

7056 remains relevant because it delivers one of the highest strength-to-weight combinations available in wrought aluminum while allowing metallurgical tailoring to improve toughness and SCC resistance; this makes it ideal for safety-critical, weight-sensitive components in aerospace and defense. Proper attention to temper selection, heat treatment and fabrication methods unlocks its performance advantages while mitigating typical 7xxx-series limitations.