Aluminum 7077: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

Alloy 7077 is a member of the 7xxx series aluminum alloys, a family primarily strengthened by zinc with significant contributions from magnesium and copper. It belongs to the precipitation‑hardening, heat‑treatable class of Al‑Zn‑Mg‑Cu alloys that are engineered to deliver very high strength combined with reasonable toughness for demanding structural applications.

The primary alloying strategy in 7077 is age hardening (solution heat treat, quench, and artificial aging) which produces a fine dispersion of Guinier‑Preston zones and eta (MgZn2)-type precipitates. Microalloying elements and controlled thermal/mechanical processing are used to optimize toughness and resistance to cracking while pushing tensile and yield strengths above many competing alloys.

Key traits of 7077 include very high static strength, good fatigue resistance when properly processed, and moderate corrosion resistance that can be improved by temper selection and surface treatments. Its weldability and cold formability are limited compared with softer aluminum alloys, so it is typically used where strength‑to‑weight ratio is the primary design driver in aerospace, defense, high‑performance automotive, and specialty industrial structures.

Engineers choose 7077 when peak strength and fatigue performance are required in thin sections or forgings and when weight savings justify higher material and processing cost. It is selected over 6xxx series alloys where higher static and fatigue strength are essential, and over 7075 in some applications where tailored chemistries or better SCC/fatigue balance are needed.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed condition for forming and machining
H14	Medium	Moderate	Fair	Poor	Strain‑hardened, non‑heat treated; limited use for 7xxx alloys
T5	High	Low–Moderate	Limited	Poor	Cooled from elevated temperature shaping and artificially aged
T6	High	Low	Limited	Poor	Solution heat treated and artificially aged; common high‑strength temper
T651	High	Low	Limited	Poor	T6 with stress relief stretching; common for aerospace forgings
T7651 / T77x	High	Low–Moderate	Limited	Poor	Overaged or specially aged tempers to improve SCC and fracture toughness

Temper has a primary impact on strength, ductility, and residual stress state of 7077. Annealed O‑tempers provide the best formability for stamping and deep drawing, while T6/T651 deliver the highest static strengths at the expense of elongation and cold formability.

Aged and overaged tempers (e.g., T7651) are often specified where stress corrosion cracking resistance and fracture toughness are critical, trading off some peak yield and tensile strengths. Welding is generally deleterious to age‑hardened tempers because the heat‑affected zone (HAZ) will soften unless specialized welding processes and postweld treatments are used.

Chemical Composition

Element	% Range	Notes
Si	0.10 max	Typical impurity that influences casting characteristics and grain structure
Fe	0.30 max	Impurity that forms intermetallics and can reduce ductility
Mn	0.05 max	Minor alloying to control grain structure and improve toughness
Mg	2.0–3.5	Major strengthening element that forms MgZn2 precipitates with Zn
Cu	1.2–2.2	Adds strength but increases susceptibility to corrosion and SCC
Zn	5.5–8.5	Principal strengthening element; governs peak age hardening response
Cr	0.05–0.25	Microalloying for recrystallization control and grain refinement
Ti	0.02–0.10	Grain refiner for improved ingot and as‑cast structure
Others	Balance / trace	Trace additions (e.g., Zr, Ni) may be used for property tuning

The alloy chemistry for 7077 places it among the high‑Zn, Mg‑Cu precipitation‑hardenable family where Zn and Mg concentrations set the achievable peak strengths through controlled precipitation of Mg‑Zn phases. Copper increases strength and offsets some of the ductility loss, but it also tends to increase susceptibility to localized corrosion and stress corrosion cracking if not mitigated by tempering and microalloying.

Minor additions such as Cr, Ti, Zr or other microalloying elements are used to pin recrystallization, control grain growth during thermomechanical processing, and improve fracture toughness and fatigue crack growth resistance. Manufacturing tolerances and national standards impose ranges and limits that can shift the optimal aging response slightly between suppliers.

Mechanical Properties

7077 exhibits a wide mechanical property envelope depending on temper and processing, from relatively soft, ductile O‑condition material to very high‑strength T6/T651 and specialty overaged tempers. Under T6/T651 processing, tensile strengths commonly exceed 500–650 MPa and yield strengths approach 450–600 MPa, with corresponding reductions in uniform elongation. Annealed (O) material typically shows tensile strengths in the 180–300 MPa range with elongations above 10–20%.

Hardness in peak‑aged tempers is substantially higher than in annealed conditions; typical Brinell or Vickers hardness values reflect the precipitation state and will drop precipitously in the HAZ after welding. Fatigue performance of 7077 can be excellent if the microstructure and surface condition are controlled; fatigue life is sensitive to surface defects, residual tensile stress, and temper‑related microstructural features.

Thickness and form factor affect achievable properties because solution heat treatment and quench rates vary with section size, and coarse grains or retained solute gradients in thick sections can reduce peak hardness and strength. Forgings and thick plate require controlled solution treatments and quench strategies to approach the properties achieved in thinner wrought product.

Property	O/Annealed	Key Temper (e.g., T6/T651)	Notes
Tensile Strength	180–300 MPa	520–680 MPa	Wide range dependent on aging, section thickness, and supplier processing
Yield Strength	80–180 MPa	450–600 MPa	Yield is highly temper dependent; T651 widely specified for aerospace
Elongation	12–25%	5–12%	Ductility decreases as strength increases; thickness also affects elongation
Hardness	40–70 HB	150–190 HV (~150–180 HB)	Hardness correlates with precipitation state and is reduced in HAZ

Physical Properties

Property	Value	Notes
Density	~2.78–2.81 g/cm³	Typical for high‑strength Al‑Zn‑Mg‑Cu alloys; lighter than steels
Melting Range	~500–640 °C	Solidus/liquidus vary with chemistry; aluminum base melts near 660 °C
Thermal Conductivity	~120–160 W/(m·K)	Lower than pure Al due to alloying; good for heat dissipation relative to steels
Electrical Conductivity	~30–45 % IACS	Reduced from commercial‑pure aluminum by alloying elements
Specific Heat	~875–910 J/(kg·K)	Typical aluminum family specific heat at ambient
Thermal Expansion	~23–24 ×10⁻⁶ /K	Coefficient similar to other Al alloys; important for thermal design

Density and thermal properties make 7077 attractive where high specific strength and reasonable thermal conduction are required. Thermal conductivity and specific heat are sufficient for many structural and thermal management roles, but the conductivity is notably lower than nearly pure aluminum or low‑alloy series.

Electrical conductivity is reduced by the high alloy content and should be considered when electrical pathways are required; designers commonly choose lower alloy series for conductivity‑critical parts. The alloy’s thermal expansion is similar to other aluminum alloys and must be accommodated in multi‑material assemblies to avoid thermal stresses.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.5–6.0 mm	Good in thin gauges with proper aging	O, T5, T6, T651	Used for aerospace skins and high‑strength panels
Plate	6–150+ mm	Strength reduced in thick plate due to quench sensitivity	T6, T651, overaged	Thick sections require special quench practice and may be used for forgings
Extrusion	Variable cross sections	Property control depends on T‑process and quench	T6, T5	Complex profiles possible but pay attention to quench rates
Tube	1–25 mm wall	Similar behavior to sheet when thin walls	T6/T651, O	Often used in structural and aerospace tubing
Bar/Rod	Diameters to 200+ mm	Forged bars maintain good through‑thickness properties if processed	T6, T651	For machined structural fittings and high‑strength components

Sheets and thin extrusions can achieve near‑peak age‑hardening responses due to favorable quench rates, making them suitable for aerospace skins and panels. Plate and large forgings are more challenging because slower cooling promotes local softening and heterogeneous precipitate distributions, requiring rigorous process control.

Commercial forms are selected based on the intended final operation: sheet for forming and light structural work, plate and forged bar for high‑load fittings, and extrusions for structural members with complex cross sections. Each form requires adapted heat treatment and possibly post‑machining aging to meet dimensional and mechanical specifications.

Equivalent Grades

Standard	Grade	Region	Notes
AA	7077	USA	Aluminum Association designation for the alloy family
EN AW	7077	Europe	EN AW‑7077 commonly used; chemical tolerances and tempers may differ
JIS	A7077	Japan	JIS designation; processing and temper codes follow JIS conventions
GB/T	7077	China	GB/T grades often track AA chemistries but may have supplier‑specific limits

National and regional standards typically adopt the 7077 designation, but chemical tolerances, impurity limits, and temper definitions can vary slightly between standards. For critical aerospace or safety components, engineers must confirm the exact standard, mill certificates, and mechanical property test results from the supplier.

Cross‑referencing must include temper codes and any additional processing notes (e.g., T651 vs. T6511) because small differences in stress‑relief stretching, aging times, or allowable impurity levels can have meaningful impacts on SCC resistance, fatigue, and fracture toughness.

Corrosion Resistance

Atmospheric corrosion resistance for 7077 is moderate and is poorer than many 5xxx and 6xxx series alloys due to the high Zn and Cu content which promote localized corrosion mechanisms. Proper surface protection such as conversion coatings, anodizing, or paint systems is commonly specified for outdoor or aggressive environments to control pitting and exfoliation.

In marine or chloride‑rich environments, 7077 is more susceptible to pitting and stress corrosion cracking than Al‑Mg (5xxx) alloys and some 6xxx alloys unless an overaged temper with improved SCC resistance is used. Overaging and tailored microalloying can reduce SCC susceptibility, but protective coatings and cathodic isolation are frequently required for long‑term service in seawater exposures.

Stress corrosion cracking remains a concern for high‑strength 7xxx alloys and can be activated by tensile residual stresses combined with corrosive agents; design and manufacturing practices such as controlled aging, residual stress relief (stretching), and avoidance of tensile surface stresses are used to mitigate risk. Galvanic interaction with more noble materials (e.g., stainless steel) can accelerate localized corrosion; insulating interfaces and appropriate fastener choices are recommended.

Compared with 6xxx and 5xxx families, 7077 trades corrosion resistance for substantially higher strength and fatigue capability. Engineers must balance protective treatments and temper selection against required mechanical performance and life‑cycle maintenance expectations.

Fabrication Properties

Weldability

Welding 7077 by fusion methods is challenging because the HAZ experiences marked softening and the alloy family is prone to hot‑cracking and loss of strength in welded joints. Conventional TIG/MIG welding typically produces joints with significantly reduced strength compared with base metal, and recommended practices often avoid fusion welding for critical structural parts. Friction stir welding and solid‑state techniques are preferred where welding is necessary, and filler alloys (e.g., certain 5xxx or 6xxx series fillers) are selected to reduce hot‑cracking risk and adjust corrosion behavior.

Machinability

Machinability of 7077 is generally good in the peak‑aged condition thanks to its high strength and stable chips, but tool wear can be higher than for softer alloys due to abrasives and higher cutting forces. Carbide tooling with positive rake and ample cooling is recommended to control built‑up edge and preserve surface integrity. Feed rates and speeds should be selected considering the temper, with heavier cuts requiring conservative parameters to avoid chatter and part distortion.

Formability

Cold formability is limited in age‑hardened tempers; forming operations are best done in O‑temper or in specially solutionized and partially aged conditions to avoid cracking. Typical recommended minimum inside bend radii depend on temper and thickness, but designers should expect larger radii than for 5xxx and 3xxx series alloys to prevent fracture. Where tight bends are required, perform forming in annealed condition followed by appropriate solution treatment and aging, or consider incremental forming and warm forming techniques.

Heat Treatment Behavior

As a heat‑treatable alloy, 7077 responds to solution treatment followed by rapid quenching and controlled artificial aging to precipitate strengthening phases. Typical solution treatment temperatures for Al‑Zn‑Mg‑Cu alloys are in the 470–500 °C range followed by quench in water, though exact temperatures and times depend on section size and supplier recommendations to avoid incipient melting or overaging.

Artificial aging (T6 style) uses intermediate temperatures (e.g., 120–180 °C) for several hours to develop peak strength, while overaging (T7x styles) uses higher temperatures or extended times to coarsen precipitates and improve SCC resistance and toughness at the expense of peak hardness. T‑temper transitions are used to tune the balance among yield, toughness, and environmental crack resistance; post‑weld or post‑form aging can partially restore properties if quench and aging are properly controlled.

For non‑heat‑treatable operations such as final shaping without aging, work hardening is not a practical route to high strength in 7077 due to the alloy class; annealing to O condition is used for forming and machining, and then heat treatment is applied to reach design properties. Control of quench rates and immediate water quenching is critical for thick sections to avoid soft zones and heterogeneous microstructures.

High-Temperature Performance

7077 loses a significant fraction of its room‑temperature strength as temperature increases; service temperatures above ~120 °C begin to compromise long‑term mechanical stability and precipitate distribution. Creep resistance at elevated temperatures is limited, so 7077 is not recommended for sustained high‑temperature load bearing applications; thermal exposure can promote overaging and strength degradation.

Oxidation of aluminum is self‑limiting and forms a protective Al2O3 film, so surface corrosion due to oxidation is typically minor compared with other mechanisms, but elevated temperatures combined with stress can accelerate environmental damage. The heat‑affected zone from high‑temperature processes (e.g., welding, brazing) shows distinct softening and coarsened precipitate structures, which influences part design and postheat treatment requirements.

Designers should limit continuous exposure to elevated temperatures and consider alternative alloys or protective coatings when operating environments approach the aging or overaging thresholds. For intermittent elevated‑temperature cycles, re‑aging treatments may partially recover some mechanical properties but will not fully restore the original microstructure in all cases.

Applications

Industry	Example Component	Why 7077 Is Used
Aerospace	Structural fittings, forgings, stringers	Very high strength‑to‑weight and good fatigue performance
Defense	Missile and launch vehicle components	Strength, tight tolerances, and weight criticality
High‑Performance Automotive	Suspension components, roll cages	Reduced mass with high static and fatigue strength
Industrial / Machinery	High‑load shafts and bars	Machinability to tight tolerances with high strength
Electronics / Thermal Management	Structural heat spreaders (limited)	Reasonable thermal conductivity and stiffness

7077 is used where structural weight savings and high load capacity are decisive, particularly in aerospace and defense applications where the manufacturing cost is justified by performance gains. Its combination of high static strength, fatigue resistance, and ability to be produced in forgings and precision machined parts makes it attractive for fittings and highly stressed components.

Because of its limited weldability and corrosion behavior, 7077 is paired with protective finishes and carefully controlled joining strategies, and it is often specified when alternative alloys cannot meet load or fatigue requirements without a weight penalty.

Selection Insights

Use 7077 when maximum static and fatigue strength per unit weight is the primary requirement and when the manufacturing supply chain can provide controlled heat treatment and surface protection. It is most appropriate for structural forgings, high‑load fittings, and thin‑section aerospace components where performance justifies higher material and processing cost.

Compared with commercially pure aluminum (e.g., 1100), 7077 sacrifices electrical and thermal conductivity and formability in exchange for dramatically higher strength. Compared with work‑hardened alloys such as 3003 or 5052, 7077 provides far greater strength but generally worse corrosion resistance and formability; choose 7077 for structural strength, not for ease of forming or marine corrosion resistance without coatings.

Compared with common heat‑treatable alloys like 6061 or 6063, 7077 offers significantly higher peak strength and often better fatigue life, but at the cost of more challenging fabrication, increased sensitivity to SCC, and typically higher material cost. Select 7077 when load, weight, and fatigue performance are driving criteria and when the design can accommodate temper‑specific limitations.

Closing Summary

Alloy 7077 remains a niche but critical material for high‑performance structural applications where exceptional strength‑to‑weight and tailored fatigue behavior are required. With careful temper selection, process control, and corrosion protection, 7077 enables components that would be impractical with lower‑strength aluminum alloys, keeping it relevant in aerospace, defense, and other demanding engineering domains.