Aluminum 7076: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

7076 is a high-strength member of the 7xxx-series aluminum alloys, a family primarily alloyed with zinc and grouped with other high-strength, heat-treatable aerospace alloys. Its metallurgy is based on a zinc-magnesium-copper system that produces high strength by precipitation hardening, placing it among the upper tier of commercially available Al-Zn-Mg(-Cu) compositions.

The major alloying elements are zinc and magnesium, with copper and trace additions (Cr, Ti, Zr) used to control grain structure, aging response, and resistance to localized corrosion. Strengthening is achieved through solution heat treatment, quenching and subsequent artificial aging to precipitate finely dispersed MgZn2 and related phases; work hardening plays a secondary role in certain H-tempers.

Key traits include very high tensile and yield strengths for a wrought aluminum, moderate-to-poor inherent corrosion resistance relative to 5xxx and 6xxx series, limited weldability without strength loss in the heat-affected zone (HAZ), and fair formability in softer tempers. Typical industries that use 7076 are aerospace structural components, defense hardware, high-performance sporting goods, and specialized transportation components where high specific strength and stiffness are required.

Engineers choose 7076 over other alloys when maximum strength-to-weight ratio is critical and when post-fabrication heat treatment and corrosion protection strategies (cladding, coatings, or sacrificial alloys) are acceptable. It is selected over 6xxx-series alloys when higher peak strength is required, and over 7075 when slight differences in toughness, processing behaviors, or proprietary composition tweaks yield application benefits.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High (10–25%)	Excellent	Excellent (requires pre/post-treatment)	Fully annealed condition for forming
T4	Medium	Medium (8–15%)	Good	Limited	Solution-treated and naturally aged
T6	High	Low–Medium (5–11%)	Moderate	Poor (significant HAZ softening)	Solution-treated and artificially aged for peak strength
T73	Medium-High (improved SCC resistance)	Moderate (6–12%)	Moderate	Poor	Overaged to improve corrosion/SCC resistance
T651	High (residual stress relieved)	Low–Medium (5–11%)	Moderate	Poor	T6 with stress relief by stretching
H2X / H3X (strain-hardened variants)	Variable	Variable	Variable	Limited	Strain-hardened and partially annealed forms for specific characteristics

Temper choice strongly modifies performance: solution treating and artificial aging (T6 family) maximize tensile and yield strengths at the expense of ductility and weldability. Overaged tempers such as T73 trade some peak strength for markedly improved resistance to stress-corrosion cracking and better performance in aggressive environments.

For forming and operations that require high plastic strain (deep drawing, severe bending), annealed O or lightly aged T4 tempers are preferred; final strength can be restored by full heat treatment if the design allows.

Chemical Composition

Element	% Range	Notes
Si	≤ 0.40	Impurity; controlled to reduce brittleness and casting defects
Fe	≤ 0.50	Controlled; high Fe can form intermetallics that reduce toughness
Mn	≤ 0.30	Minor; can aid grain structure control in some variants
Mg	2.0–3.0	Principal strengthening element that forms MgZn2 precipitates
Cu	1.2–1.9	Enhances strength and affects ageing response; increases SCC susceptibility
Zn	5.6–7.0	Primary strength-providing element in 7xxx alloys
Cr	0.18–0.35	Microalloying for grain control and recrystallization inhibition
Ti	≤ 0.20	Grain refiner in cast/wrought processing
Others (Zr, Sc, Ni, Pb)	≤ 0.05 each, balance Al	Minor additions used in specialty heats to tailor properties

The alloy’s mechanical and corrosion performance is governed by the relative amounts of Zn, Mg and Cu: Zn and Mg form the strengthening MgZn2 precipitates after ageing, while Cu enhances peak strength and influences precipitation sequences. Grain refiners (Ti, Zr) and dispersoid formers (Cr, Zr) are often used to stabilize microstructure during thermomechanical processing and to reduce recrystallization, which in turn affects toughness and SCC resistance.

Mechanical Properties

The tensile behavior of 7076 is typical of high-strength 7xxx-series alloys: steeply rising yield and ultimate tensile strengths after artificial aging with relatively low uniform elongation. In peak-aged tempers the fracture mode tends to be a mix of transgranular ductile tearing and intergranular features where coarse precipitates and grain boundary phases are present; such microstructural tendencies influence fatigue crack initiation and propagation.

Yield strength depends strongly on temper and section thickness: thin-sheet T6 material reaches near-peak precipitation hardening, while thicker sections or weld-affected zones show lower retained strength. Fatigue performance is good for the alloy family when surfaces are well-finished and corrosion pits are avoided; surface treatments and shot peening significantly improve high-cycle fatigue life.

Hardness correlates with tensile/yield: annealed O material is relatively soft and machinable, while T6/T651 reaches high hardness values but suffers from reduced ductility and increased machining tool wear. Thickness effects are significant: the achievable peak-aged properties decrease with increasing cross-section due to slower cooling rates and coarse precipitate formation.

Property	O/Annealed	Key Temper (e.g., T6/T651)	Notes
Tensile Strength	~240–320 MPa	~540–620 MPa	T6 values typical for thin-section wrought product; specific heat/processing affects range
Yield Strength	~120–200 MPa	~480–560 MPa	Yield increases substantially with artificial aging
Elongation	~10–25%	~5–11%	Elongation drops with higher strength tempers
Hardness (HB)	~60–95 HB	~150–190 HB	Hardness scales with precipitate density; measures vary with cross-section and test method

Physical Properties

Property	Value	Notes
Density	~2.78 g/cm³	Typical for high-strength Al-Zn-Mg-Cu alloys; lower density than steels
Melting Range	Solidus ~470–490 °C; Liquidus ~635–650 °C	Broad melting interval due to alloying elements
Thermal Conductivity	~120–150 W/m·K	Reduced from pure Al but still favorable for heat-sinking compared with many metals
Electrical Conductivity	~28–38 % IACS	Lower conductivity compared with 1xxx and 6xxx series due to alloying
Specific Heat	~0.88–0.90 J/g·K	Typical for aluminum alloys at room temperature
Thermal Expansion	~23–24.5 µm/m·K (20–100 °C)	Similar to other aluminum alloys; design considerations for thermal cycling

7076 offers a favorable combination of low density and reasonable thermal conductivity, making it attractive where mass-critical thermal management is required. The alloy’s thermal expansion and conductivity should be accounted for in assemblies where dissimilar materials are joined, especially at elevated temperatures, because differential thermal strain can induce stress concentrations.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.5 mm – 6 mm	Achieves near-peak T6 properties in thinner gauges	O, T4, T6, T651, T73	Common for aerospace skins and panels; formability depends on temper
Plate	6 mm – 150 mm+	Peak properties reduced in thick sections; requires controlled quench	T6, T651, T73	Thick plate needs process controls to avoid soft core or coarse precipitates
Extrusion	Complex profiles, diameters up to several hundred mm	Properties influenced by cooling and homogenization	T6, T651	Used for structural profiles; microstructure depends on billet chemistry and extrusion speed
Tube	Thin- to thick-wall	Similar age-hardening trends; welding/joint design critical	T6, T651	Drawn or extruded tubes for structural components; annealing common before forming
Bar/Rod	Diameters 3 mm – 200 mm	Machinability good in O; strength increases after ageing	O, T6, T651	Used for fasteners, fittings, and machined parts

Forming route and product form strongly influence achievable properties: sheet and thin extrusions can be brought to full T6 strength reliably, while thick plates and large sections often require specialized quenching and aging cycles to avoid property gradients. Processing choices—such as pre-aging, controlled quench media, and stress-relief stretching—are critical to ensuring dimensional stability and mechanical consistency across product forms.

Equivalent Grades

Standard	Grade	Region	Notes
AA	7076	USA	Aluminum Association designation; base reference for composition and tempers
EN AW	7076 (approx)	Europe	EN designation commonly aligns but exact limits and temper codes can differ
JIS	A7076 (approx)	Japan	JIS may not have a direct one-to-one for all heats; check local material certificates
GB/T	7076 (approx)	China	Chinese standards often provide near-equivalent compositions; verify mechanical spec differences

Equivalent-grade mapping must be done with care: chemical limit bands and temper definitions in EN, JIS and GB/T standards do not always match AA tables exactly, and subvariants with microalloying (Zr, Sc) or modified Cu/Mg ratios can lead to materially different processing and performance. Engineers should compare certified chemical and mechanical test reports rather than relying solely on nominal grade names when substituting material sources across regions.

Corrosion Resistance

7076, like other high-Zn 7xxx-series alloys, exhibits moderate atmospheric corrosion resistance but is more susceptible to localized corrosion and stress-corrosion cracking (SCC) than 5xxx and many 6xxx alloys. In neutral atmospheres the unprotected alloy performs adequately, but in industrial or marine environments it requires protective coatings, cladding (e.g., Alclad), or cathodic protection to achieve long life.

In marine and chloride-rich service, pitting and intergranular attack can initiate at precipitate-depleted zones adjacent to grain boundaries, especially in peak-aged tempers. Overaging (T73/T76 equivalent treatments) and microalloying (Cr, Zr additions) are common mitigation strategies to reduce SCC susceptibility and improve resistance to chloride-induced corrosion.

Galvanic interactions follow typical aluminum behavior: when coupled to more noble metals (stainless steel, copper), 7076 will corrode preferentially and thus requires electrical isolation or sacrificial anodes in mixed-metal assemblies. Compared to 3xxx/5xxx alloys, 7076 trades corrosion performance for strength; compared to 6xxx alloys it is generally stronger but more sensitive to SCC unless specially processed.

Fabrication Properties

Weldability

Welding high-strength 7xxx alloys is challenging: fusion welding methods (GMAW/MIG, GTAW/TIG) typically produce HAZ softening and loss of strength due to dissolution or coarsening of precipitates. Pre- and post-weld thermal treatments are often impractical for assemblies, so riveted or mechanically fastened joints are commonly used in critical structural applications. When welding is required, lower-strength filler alloys (e.g., 5356 or 4043) and controlled procedures can produce acceptable joints for secondary structures, but designers must account for reduced joint strength and increased susceptibility to SCC.

Machinability

Machinability in annealed (O) condition is good: the alloy machines similar to other high-strength Al alloys, producing short, broken chips with proper tooling. In peak-aged conditions tool wear increases due to higher strength and hardness; carbide tooling with high positive rake and heavy coolant application is recommended. Typical machinability index is moderate; speeds and feeds should be adjusted to maintain surface finish and tool life.

Formability

Formability is highly temper-dependent: O and T4 tempers exhibit good bendability and drawability, enabling typical sheet forming operations with reasonable minimum bend radii (e.g., 2–4× thickness for air bending depending on tooling). T6/T651 material has limited cold formability and is prone to cracking if bent without stress relief; warm forming and solution-anneal plus re-age cycles are used when complex shapes are required with high final strength.

Heat Treatment Behavior

7076 is firmly a heat-treatable alloy family: solution heat treatment dissolves alloying elements into a supersaturated solid solution, typically performed in the 470–480 °C range with adequate soak time for section thickness. Rapid quench (water quench or controlled polymer quench) is required to retain a high supersaturation, followed by artificial aging cycles to precipitate strengthening phases.

Artificial aging to T6 typically occurs at ~120–125 °C for durations tuned to target mechanical properties; higher temperature overaging (T73/T76 treatments) reduces peak strength but substantially improves resistance to stress-corrosion cracking and overaged stability at elevated temperature. The T651 temper adds a controlled stretch to relieve residual quench stresses while maintaining peak-aged properties.

For operations relying on work hardening, such as H-tempers, strain aging and partial annealing can be used to tailor intermediate properties; however, the dominant design route for 7076 is via solution treat/age sequences rather than cold-work strengthening.

High-Temperature Performance

Strength of 7076 decreases with temperature: significant softening occurs above ~120–150 °C, and long-term exposure above ~100–120 °C accelerates overaging and loss of yield/tensile properties. Creep resistance is limited compared with high-temperature alloys; short-term elevated-temperature exposure may be tolerated but cyclic thermal excursions can reduce fatigue life and dimensional stability.

Oxidation is minimal in the temperatures typical for structural service, but high-temperature exposure can exacerbate precipitate coarsening and grain boundary phase evolution, increasing SCC risk and reducing toughness. HAZ regions created during welding or localized heating are particularly susceptible to property degradation and should be minimized or post-treated when possible.

Applications

Industry	Example Component	Why 7076 Is Used
Aerospace	Wing fittings, hardpoints, and structural forgings	High strength-to-weight and fatigue performance for load-bearing parts
Marine	High-performance craft structural members	Strength combined with appropriate corrosion mitigation strategies
Defense	Small arms and ordnance components	High strength and toughness for critical hardware
Automotive	High-performance suspension components	Enables lightweight, stiff components where weight saving is premium
Sports/Leisure	High-end bicycle frames and racing equipment	Maximal specific strength and stiffness at the top end of alloy choices
Electronics	Structural frames and some thermal management parts	Balance of thermal conductivity and low density for weight-sensitive assemblies

7076 is selected where very high static and fatigue strength per unit mass is required and where appropriate fabrication and corrosion protection measures can be specified. It is particularly common in aerospace primary and secondary structures where its mechanical advantages outweigh additional processing costs.

Selection Insights

7076 is appropriate when strength-to-weight ratio is a primary design driver and when users can accept more restrictive fabrication and corrosion-protection procedures. Choose 7076 for heavily loaded structural parts that will be heat-treated after forming or where post-processing for corrosion protection is routine.

Compared with commercially pure aluminum (1100), 7076 trades much higher strength for lower electrical and thermal conductivity and reduced cold formability; use 1100 when conductivity or deep-draw formability is the priority. Compared with work-hardened alloys such as 3003 or 5052, 7076 offers far higher peak strength but requires stricter corrosion mitigation and is less tolerant of welding and cold-forming. Compared with common heat-treatable alloys such as 6061/6063, 7076 provides higher ultimate and yield strength in peak tempers but often at higher cost, lower corrosion resistance and more challenging weldability; prefer 7076 when the extra strength justifies trade-offs in processing and protection.

Closing Summary

7076 remains a relevant high-performance aluminum alloy where superior strength-to-weight is required and manufacturing processes can control heat treatment, welding and corrosion protection; its niche is in demanding structural applications where the engineering trade-offs—reduced weldability and elevated corrosion management—are acceptable for the performance gains.