Aluminum 7050: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

7050 is a member of the 7xxx series aluminum alloys, characterized by zinc as the principal alloying element and engineered primarily as a heat-treatable, precipitation-hardening aluminum. It was developed for high-strength structural applications where a combination of high static strength, fracture toughness and improved stress-corrosion resistance is required relative to early high-strength Zn–Mg–Cu alloys.

Major alloying elements in 7050 are zinc, magnesium and copper, with small additions of zirconium or titanium used to control grain structure and inhibit recrystallization during thermomechanical processing. The strengthening mechanism is classical age hardening: solution heat treatment, rapid quench to retain a supersaturated solid solution, and controlled artificial aging to precipitate fine MgZn2 (η′/η) phases that provide precipitate strengthening.

Key traits include very high yield and tensile strength in peak-aged tempers, good fracture toughness in thick-section tempers, and improved resistance to stress-corrosion cracking (SCC) when processed and aged to SCC-resistant tempers (e.g., T7451, T76). Limitations include reduced ductility and formability compared with 5xxx and 6xxx series alloys, and more limited weldability in peak-aged conditions. Typical industries are aerospace and defense (primary airframe structures, wing skins, spars, fuselage webs), specialty transportation, and high-performance components where strength-to-weight and damage tolerance drive material choice.

Engineers select 7050 over other alloys when a combination of very high static strength, good fracture toughness in thick sections, and improved SCC resistance are required; it is often preferred to 7075 when SCC resistance and fracture-toughness balance are more important than absolute peak strength. Cost and supply chain factors also influence selection, since 7050 is a specialty, higher-cost alloy compared with more common structural alloys.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed condition used for forming and deep drawing
T5	Medium	Moderate	Fair	Limited	Cooled from elevated temperature and artificially aged; used for extrusions
T6	Very High	Low–Moderate	Poor–Fair	Poor	Peak strength achieved by artificial aging after solution treatment
T651	Very High	Low–Moderate	Poor–Fair	Poor	T6 with stress-relief by stretching; common for plates to reduce distortion
T7451	High	Moderate	Fair	Poor	Overaged temper designed for improved SCC resistance and toughness
T76 / T77	Moderate–High	Moderate	Fair	Better than T6	Overaged tempers that trade some strength for improved corrosion/SCC resistance
H14	Medium	Moderate	Fair	Limited	Strain-hardened then partially annealed; less common for 7050

The temper chosen for 7050 has a strong, predictable influence on mechanical behavior and corrosion performance. Peak-strength tempers (T6/T651) maximize yield and tensile strength but reduce ductility and formability and increase sensitivity to corrosion and SCC; overaged tempers (T7451, T76) lower peak strength slightly in exchange for better SCC resistance and fracture toughness.

Forming operations are usually performed in O or soft tempers followed by solution heat treatment and age—this sequence preserves formability and still enables high final-strength states. Welding is generally discouraged for peak-aged 7050 because of significant HAZ softening; if welded, post-weld heat-treatment or selection of softer tempers and appropriate filler alloys may be required.

Chemical Composition

Element	% Range	Notes
Si	≤ 0.12	Typical impurity; low level to maintain toughness
Fe	≤ 0.12	Iron limits are kept low to minimize intermetallics and anisotropy
Cu	2.0–2.6	Raises strength and influences precipitation behavior; affects corrosion
Mn	≤ 0.10	Low; minor role in grain structure control
Mg	2.3–2.6	Active in MgZn2 precipitate formation, key for strength
Zn	6.0–6.8	Principal strengthening element; high levels provide age-hardening capacity
Cr	≤ 0.04	Not a primary alloying element in standard 7050; small amounts may appear
Ti	≤ 0.05	Grain refiner in cast forms or trace in wrought products
Zr / Others	0.04–0.20 Zr typical	Zr is commonly added to control recrystallization and improve grain structure in plate and extrusion stocks

The balance of Zn, Mg and Cu controls the volume fraction and morphology of η′/η (MgZn2) precipitates that are responsible for the high strength of 7050. Small additions of Zr act as grain refiners and retard recrystallization during thermomechanical processing, improving toughness and providing more stable mechanical properties in thick sections. Tight control of impurities such as Fe and Si is necessary to avoid coarse intermetallic particles that degrade fatigue, fracture toughness and corrosion resistance.

Mechanical Properties

7050 exhibits high tensile strength and yield strength in peak-aged tempers, with a relatively narrow yield-point-to-ultimate difference due to the strong precipitation hardening. Elongation is reduced in high-strength tempers, particularly in thick sections where constraint and manufacturing history (e.g., rolling, quenching) further limit ductility. Hardness correlates with temper: peak-aged states show high hardness (indicative of dense precipitate populations), while overaged tempers reduce hardness but improve toughness and SCC resistance.

Fatigue performance of 7050 is generally very good when the microstructure is fine and homogeneous, and when surfaces are finished and free of corrosion pits. However, fatigue life is sensitive to thickness, residual stresses and heat-treatment homogeneity; thick sections require careful control of quench and aging to avoid soft zones and reduced fatigue strength. Thermal and thickness effects alter achievable strength: thicker plates cool more slowly after solutionizing, which can cause heterogeneous precipitation and lower properties; controlled thermomechanical processing and specialized tempers (T7451, T76) are used to manage these effects.

Property	O/Annealed	Key Temper (T6 / T651 / T7451)	Notes
Tensile Strength (UTS)	~240–320 MPa	~500–570 MPa	UTS depends on temper and thickness; T6/T651 are peak strength ranges, T7451 slightly lower
Yield Strength (0.2% offset)	~120–200 MPa	~430–510 MPa	Yield values vary with temper; T651 commonly specified for structural plates
Elongation (pct)	~20–30%	~6–12%	Higher in O condition; elongation decreases with increasing strength and thickness
Hardness (Brinell)	~40–70 HB	~120–155 HB	Hardness approximations; conversion from tensile depends on microstructure and temper

Values given are representative ranges for wrought 7050 products and will vary with exact chemistry, processing route, section thickness and heat-treatment schedule. Designers should consult mill certificates and perform application-specific testing for critical structural components.

Physical Properties

Property	Value	Notes
Density	2.83 g/cm³	Typical density for high-strength Al–Zn–Mg–Cu wrought alloys
Melting Range	~477–635 °C	Solidus–liquidus range varies slightly with composition; avoid overheating during thermal processing
Thermal Conductivity	~120–150 W/m·K	Lower than pure aluminum; thermal conductivity decreases with alloying and aging
Electrical Conductivity	~30–40 % IACS	Alloying reduces conductivity significantly relative to pure Al
Specific Heat	~0.90 kJ/kg·K	Approximate value near room temperature
Thermal Expansion	~23–24 µm/m·K (20–100 °C)	Comparable to other high-strength aluminum alloys; important for fit-up and stress design

The physical properties make 7050 attractive for lightweight structures where thermal management is less demanding than in electronic heat-sink applications. Thermal conductivity and electrical conductivity are reduced relative to pure aluminum because of the high solute content and dense precipitate dispersions. The melting/solidus window and thermal expansion coefficient are important controls during welding, brazing and heat treatment to prevent distortion and thermal cracking.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.5–6.4 mm	Strength influenced by temper and rolling; thinner gauges can achieve near-peak properties	T6, T651, T7451, O	Widely used for aerospace skins and panels in aerospace-tempers for high strength
Plate	6.4–200+ mm	Strength and toughness vary with thickness; special processing for thick plates to control cooling	T651, T7451, T76	Primary use: thick wing skins, spars, structural plates requiring high toughness
Extrusion	Varies by profile	Can be age-hardened after shaping; mechanical anisotropy must be managed	T5, T6	Extrusions used for complex structural profiles; heat treatment route impacts distortion
Tube	Diameters from small to large	Similar behavior to bar/extrusion; wall thickness influences property gradients	T6, T651	Used where high strength-to-weight is needed; joining techniques and forming options differ
Bar/Rod	Diameters up to ~200 mm	Homogeneous properties when hot-worked; size affects quench efficiency	T6, T651	Forgings and bars used for fittings, machined structural components

Processing differences drive end-use selection: sheet and plate production require controlled rolling, quenching and aging to achieve homogeneous mechanical properties across thickness. Extrusions and forged shapes often undergo T5 or T6 treatments tailored to the geometry to manage distortion and residual stress. Plate production for aerospace frequently includes Zr additions and special quench-and-age cycles to achieve stable microstructures in thick sections.

Equivalent Grades

Standard	Grade	Region	Notes
AA	7050	USA	Primary designation under Aluminum Association standards for wrought alloy
EN AW	7050 (AlZn6.2MgCu)	Europe	EN designation commonly mirrors AA chemistry; material specifications align for aerospace use
JIS	No direct equivalent	Japan	No single direct JIS grade; A7075 and similar high-strength alloys are sometimes referenced for comparable properties
GB/T	7050	China	Chinese national standards often reference 7050 as a direct equivalent; chemical and mechanical specs are closely matched

Although several international standards list 7050 or chemically equivalent designations, small variations in allowable impurity levels, trace element additions (Zr, Ti) and process requirements can create measurable differences in toughness, SCC resistance and aging response. Engineers should compare specific mill certificates and applicable standard revisions when substituting material sources across regions.

Corrosion Resistance

Atmospheric corrosion resistance of 7050 is moderate for a high-strength Al–Zn–Mg–Cu alloy; the alloy shows acceptable performance in many environments but is more susceptible to localized corrosion (pitting) than 5xxx and many 6xxx series alloys. Overaged tempers (T76, T7451) and appropriate surface treatments (chromate conversion, anodizing, cladding where applicable) improve general corrosion performance and long-term durability in service.

In marine or high-salinity environments, 7050 requires careful temper selection and often protective coatings because chloride-induced pitting and intergranular attack can initiate fatigue cracks. The alloy shows better resistance to SCC than older 7xxx series formulations when aged to SCC-resistant tempers, but it still remains more SCC-prone than many 5xxx alloys; designers must consider environment, stress levels and protective strategies.

Galvanic coupling with dissimilar metals (e.g., stainless steel, carbon steel) can accelerate localized corrosion of aluminum—proper isolation, coatings and joint design reduce galvanic current flow. Compared with 6xxx series alloys, 7050 trades corrosion resistance for higher strength; compared with 7075, 7050 typically offers improved SCC resistance and toughness, making it preferable in primary structural aerospace applications where corrosion and fracture behaviour are critical.

Fabrication Properties

Weldability

Welding 7050 is challenging, particularly in peak-aged tempers, because heat input produces a heat-affected zone (HAZ) where precipitates overage and strength is locally reduced. Fusion welding (TIG/MIG) risks hot cracking and significant loss of mechanical properties in the HAZ; filler alloys with compatible strength and protection against liquation cracking (such as Al–Zn–Mg–Cu fillers or specially developed 7xxx-series fillers) are sometimes used but full restoration of peak properties by post-weld heat treatment is difficult in large assemblies.

Resistance welding and friction stir welding (FSW) are commonly used alternatives: FSW produces a more favorable local microstructure and reduced softening compared with fusion welding and is frequently employed for large structural components. When fusion welding is unavoidable, designers should plan for localized mechanical property reduction, apply post-weld heat treatments if geometry permits, and use rivets or mechanical fasteners where necessary.

Machinability

7050 is considered reasonably machinable for high-strength aluminum alloys, but machinability indices are lower than softer aluminum alloys because of high strength and work-hardening tendencies. Carbide tooling with positive rake angles, rigid setups, and moderate to high cutting speeds with ample coolant are recommended to control built-up edge and chip formation. Surface finish and dimensional stability are excellent when sharp tooling and optimized feeds are used; however, heavy interrupted cuts or thin-walled sections require attention to chatter and fixture design.

Drilling and tapping high-strength tempers may generate work hardening around holes; pre-drilling in softer tempers or using peck drilling cycles can improve hole quality. Post-machining stress relief may be needed for fatigue-critical components.

Formability

Forming 7050 is best performed in soft tempers (O) or by using processes that allow post-form heat treatment to reach the final aged condition. Cold-forming in higher-strength tempers leads to springback and potential cracking; minimal bend radii are larger than for 5xxx and 6xxx alloys due to lower ductility. Typical recommended inside bend radii for aerospace sheet are several times the sheet thickness depending on temper; for critical components, dies and forming sequences are designed to limit local strain concentrations.

Hot-forming or preheating can enhance formability in some profiles, but subsequent solutionizing, quenching and aging steps must be engineered to avoid distortion and to achieve target mechanical properties. When complex forming is required, form in O condition and follow with appropriate solution/age cycle to restore strength.

Heat Treatment Behavior

Solution treatment of 7050 is typically carried out around 470–480 °C to dissolve strengthening precipitates into a supersaturated solid solution; exact temperatures and times depend on section thickness and product form. Rapid quenching from solution temperature is critical to retain solute in solution and enable effective aging; insufficient quench rates in thick sections can result in soft zones and reduced strength.

Artificial aging schedules vary by desired balance of strength and SCC resistance. Peak-age schedules (T6) achieve the highest strength via aging at temperatures typically in the range of 120–135 °C for many hours; overaging treatments (T7451, T76) use higher aging temperatures or multi-step aging sequences to coarsen precipitates slightly, reducing internal stresses and improving SCC performance. Transitioning between T tempers (e.g., T6 to T7451) is achievable by re-aging but requires controlled heating to ensure uniform response.

Achieving consistent properties in thick plate requires attention to thermomechanical history: Zr-containing variants, controlled quench media, and temperature monitoring during aging help reduce through-thickness gradients. For non-heat-treatable alloys the primary strengthening path is work hardening, but 7050 is intentionally heat-treatable and should be processed accordingly.

High-Temperature Performance

At elevated service temperatures (above ~150–200 °C), 7050 experiences progressive loss of yield and tensile strength as precipitate distributions coarsen and overage. The long-term static strength and creep resistance at moderate temperatures are inferior to specialized high-temperature alloys and designers should limit continuous service temperatures where dimensional stability and strength retention are required.

Oxidation is limited under typical atmospheric conditions up to moderate temperatures due to the protective alumina layer; however, at high temperatures or under cyclic thermal exposure the alloy can suffer from scaling and changes in microstructure that reduce mechanical performance. HAZ behavior in welded joints is especially sensitive to thermal exposure; temper and post-weld processing must mitigate softening and embrittlement risks.

Applications

Industry	Example Component	Why 7050 Is Used
Aerospace	Wing skins, spars, fuselage webs	High strength-to-weight, good fracture toughness and SCC-resistant tempers for primary structures
Defense	Missile and weapon system structural parts	High static strength and toughness for dynamic loads
Marine	High-performance structural fittings	Favorable strength and overaged tempers provide improved corrosion/SCC behavior
Automotive	High-performance chassis components (