Aluminum 7071: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

7071 is a member of the 7xxx series aluminum alloys, a family characterized by zinc as the principal alloying element supplemented by magnesium and copper to obtain very high strength. Like other 7xxx alloys, 7071 is primarily a heat-treatable aluminum alloy that derives its strength from solution heat treatment followed by quenching and artificial aging to precipitate fine, dispersed strengthening phases.

Major alloying elements in 7071 are zinc (Zn), magnesium (Mg) and copper (Cu), with trace additions of chromium (Cr) or zirconium (Zr) to control grain structure and recrystallization during processing. These elements combine to give 7071 a high strength-to-weight ratio, moderate fatigue resistance, and reasonable machinability, while typically trading off some formability and weldability compared with softer aluminum families.

Key traits of 7071 include peak tensile strength and yield strength that place it among the higher-strength aluminum alloys, moderate to low atmospheric corrosion resistance relative to 5xxx and 6xxx series, and limited direct-weldability in peak tempers due to heat-affected zone (HAZ) softening and risk of cracking. Typical industries using 7071 include aerospace, high-performance automotive, defense, and specialty sporting goods where high specific strength and stiffness are prioritized.

Engineers choose 7071 over other alloys when the application demands high static strength and stiffness with tight dimensional control and where localized machining or high-rate forming is minimal. The alloy is selected over steels when weight savings are critical and over lower-strength aluminum grades when higher allowable stresses or reduced cross-sections are required.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed condition; maximum ductility for forming
H14	Moderate	Moderate	Good	Good	Strain-hardened; improved yield over O with limited cold formability
T5	High	Moderate	Fair	Limited	Cooled from hot working and artificially aged; commonly used for extrusions
T6	Very High	Low–Moderate	Limited	Poor (increases cracking risk)	Solution heat-treated and artificially peak aged; highest strength in common use
T651	Very High	Low–Moderate	Limited	Poor	T6 with stress-relief by stretching; retains high strength with reduced residual stress
T73	High (overaged)	Improved	Improved	Better than T6	Overaged temper to improve SCC resistance at cost of peak strength
T76	Moderate–High	Moderate	Better	Better	Controlled overaging to balance strength and stress corrosion resistance

Temper has a first-order effect on 7071 performance: solution treatment and aging (T tempers) control the size and distribution of Zn–Mg–Cu precipitates, which directly determine yield and tensile strength. Overaged tempers (T73/T76) trade peak strength for improved resistance to stress-corrosion cracking and better toughness, while O and H tempers provide the ductility needed for forming operations.

Chemical Composition

Element	% Range	Notes
Si	0.10 max	Impurity-level silicon; minimizes low-melting phases
Fe	0.50 max	Iron is a residual element; can form intermetallics that affect toughness
Mn	0.10 max	Minor; controls grain structure when present
Mg	2.0 – 2.8	Major strengthening partner to Zn; forms MgZn2 precipitates with Zn
Cu	1.0 – 2.0	Raises strength and hardness but can reduce corrosion resistance
Zn	5.5 – 7.0	Primary strength element in 7xxx series; critical for precipitation hardening
Cr	0.04 – 0.20	Microalloying to control recrystallization and grain size
Ti	0.02 – 0.10	Grain refiner added in cast or wrought products
Others	Balance Al with traces	Includes residuals (V, Zr) and deliberate microalloying elements

Zinc and magnesium form the primary precipitation-strengthening phase (MgZn2), with copper modifying precipitate chemistry and kinetics to improve peak strength. Chromium and minor elements pin grain boundaries and suppress uncontrolled recrystallization during thermomechanical processing, improving fracture toughness and stability during aging.

Mechanical Properties

Tensile behavior of 7071 is characterized by a high ultimate tensile strength and a correspondingly high 0.2% offset yield when in peak-aged tempers. The alloy shows relatively low uniform elongation in T6/T651 tempers and a reduction in ductility compared with softer Al alloys; in annealed and H-tempers elongation is significantly higher and forming is feasible. Hardness follows the same pattern: low in O, increasing dramatically after solution and artificial aging.

Fatigue behavior of 7071 is good for a high-strength aluminum alloy but is sensitive to surface finish, residual stresses, and the presence of corrosion or damage. Thinner sections can generally be aged to higher hardness uniformly, but thickness effects on quench rate during solution treatment will influence achievable strength and may require modified aging cycles for thick sections. Yield-to-tensile ratio is typically lower than that of steels but favorable among aluminum alloys used for structural applications.

Fracture modes depend on temper and processing: coarse intermetallic particles act as crack initiation sites under cyclic loading, while overaged tempers can improve fatigue crack growth resistance and stress-corrosion cracking (SCC) performance. Control of inclusion content, tight process control during heat treatment, and surface treatments are often required to obtain consistent long-life performance in critical applications.

Property	O/Annealed	Key Temper (T6/T651)	Notes
Tensile Strength	220–280 MPa	540–610 MPa	T6 provides peak tensile; range depends on section thickness and aging schedule
Yield Strength	95–150 MPa	480–540 MPa	Large increase on aging; yield dependent on precipitate distribution
Elongation	12–20%	6–12%	Elongation reduced markedly in peak tempers
Hardness (Brinell)	35–70 HB	145–185 HB	Hardness correlates with precipitation state and microstructural homogeneity

Physical Properties

Property	Value	Notes
Density	2.78 g/cm3	Typical for high-strength Al–Zn–Mg–Cu alloys; excellent specific strength
Melting Range	~477–635 °C	Wide melting range due to alloying; watch for low-melting eutectics during welding
Thermal Conductivity	~120–140 W/m·K (25 °C)	Lower than pure Al but adequate for many thermal management uses
Electrical Conductivity	~30–40 %IACS	Lower than lower-alloyed aluminum grades; conductivity reduces after aging
Specific Heat	~0.90 J/g·K	Near typical aluminum base metal value
Thermal Expansion	23.0–24.5 µm/m·K (20–100 °C)	Moderate coefficient; design compensation required when joining to dissimilar materials

7071 shows typical thermal and electrical behaviour of high-strength 7xxx alloys: thermal conductivity and electrical conductivity are reduced relative to purer aluminum grades because of the high alloy content. The density advantage remains a principal driver; strength-to-weight ratios are favorable for structural design where mass reduction is critical.

Thermal treatment windows are constrained by the low-melting compounds that form from residual elements; manufacturing operations such as welding, brazing, and local heating must be controlled to avoid incipient melting and detrimental microstructural changes. Thermal expansion is similar to other wrought alloys so differential thermal strain considerations apply when assembling with composites or steels.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.2 mm – 6 mm	Thin gauge achieves more uniform aging	O, H14, T6, T73	Used where light gauge high strength needed; careful control of surface defects
Plate	6 mm – 100 mm	Thick sections show quench sensitivity; may require T73	T6, T651, T73	Thicker plates may not reach full T6 properties without modified processes
Extrusion	Profiles up to meters long	Good directional properties; age hardenable	T5, T6	Extruded shapes used for high-strength structural members
Tube	Ø small to large, wall dependent	Similar to bar/extrusion behavior	T6, T651	Welded or drawn tubes require controlled heat treatment to avoid distortion
Bar/Rod	Diameters to 200 mm	Homogeneity critical; high residual stress if cold worked	O, T6	Bars used for machined components and fasteners

Sheets are typically produced with surface finishes and temper controls suitable for secondary machining and forming; plates require thicker-section thermal treatments and often use T73 to mitigate residual stress and cracking. Extrusions and tubes benefit from T5/T6 processing routes for dimensional stability and high strength; however, long profiles need consistent cooling to avoid property gradients. Bars and forgings are commonly solution-treated and either artificially aged or mechanically stabilized (T651) for precision machining and structural use.

Equivalent Grades

Standard	Grade	Region	Notes
AA	7071	USA	Proprietary alloy designation within the 7xxx family; check mill certifications for exact chemistry
EN AW	7071	Europe	EN AW-7071 may be referenced; European specs can vary in trace element limits
JIS	A7071	Japan	Japanese designation sometimes used for similar Zn–Mg–Cu alloys; compare tensile/yield data
GB/T	7071	China	Chinese standards provide local chemistries and processing practices; cross-check for interchangeability

Equivalent grade listings for 7071 are indicative: because 7xxx alloys vary in Zn/Mg/Cu ratios and microalloy additions, direct interchangeability between regions requires verification of both chemical composition and mandated mechanical properties. Specifications can differ in allowable impurities, heat-treatment procedures, and testing requirements, so cross-referencing mill certificates and mechanical test reports is essential before substitution.

Corrosion Resistance

Atmospheric corrosion resistance of 7071 is moderate; the high zinc and copper content reduces natural corrosion resistance compared with 5xxx and 6xxx series alloys. In typical atmospheres the alloy forms an oxide film, but pitting and intergranular attack are more likely in chloride-rich or industrial environments unless protective coatings or appropriate tempers (e.g., T73) are used.

In marine environments 7071 is less resistant than 5xxx (Mg-rich) alloys and certain coated 6xxx alloys; prolonged exposure, splash zones, and salt spray accelerate localized corrosion and can lead to embrittlement or loss of cross-section. Corrosion allowances or sacrificial coatings are often employed for long-term marine service, and the use of overaged tempers improves SCC resistance.

Stress-corrosion cracking is a known risk for high-strength 7xxx alloys, particularly in peak-aged conditions with high tensile residual stresses and in environments containing chlorides or caustic species. Overaging (T73/T76) and careful control of residual stresses via stretching or annealing mitigate SCC susceptibility. When joining to galvanically dissimilar metals, 7071 tends to be anodic relative to stainless steels but cathodic to more noble metals; isolating coatings or insulating fasteners are commonly used to prevent galvanic degradation.

Compared against other alloy families, 7071 offers higher strength at the expense of corrosion robustness; designers often move to 6xxx series where corrosion and weldability take precedence, or to 5xxx series for superior marine performance at lower strength.

Fabrication Properties

Weldability

Welding 7071 in peak tempers is challenging: TIG and MIG welds commonly suffer from HAZ softening, loss of strength, and increased susceptibility to hot and cold cracking due to low-melting grain boundary phases. Recommended practice is to avoid welding in critical-stress locations or to apply pre- and post-weld heat treatments when feasible; use of filler alloys that match target mechanical properties and lower melting phases can reduce hot cracking risk. Resistance welding techniques and mechanical fastening are often preferred where structural integrity must be preserved.

Machinability

7071 has fair to good machinability for a high-strength aluminum alloy; it machines more readily than steels but requires rigid setups, sharp carbide tools, and optimized feed/speed parameters to avoid built-up edge and chatter. Cutting speeds are typically higher than for steels but lower than for softer aluminums; coolant and chip evacuation are important because the alloy produces tough, sometimes stringy chips. Tool life can be shortened by high hardness in T6 states, so roughing in softer tempers or stabilized T651 conditions is a common approach.

Formability

Cold formability of 7071 is limited in aged tempers owing to low ductility and higher yield strength; minimum bend radii are larger than for 5xxx or 3xxx alloys and springback is significant. Forming is best carried out in O or H tempers, or by warm-forming processes that allow subsequent solution treatment and aging to restore strength. Deep drawing and severe stamping are generally avoided in T6; designers use tailored tempers (e.g., T73) or segmented forming strategies to combine shaping with final aging cycles.

Heat Treatment Behavior

7071 is heat-treatable via the classical solutionizing–quench–age sequence. Solution treatment temperature is typically in the 470–480 °C range to dissolve Zn and Mg into supersaturated solid solution, followed by rapid quenching to retain solute in a supersaturated state. Artificial aging (e.g., T6: ~120–135 °C for 24 hours, depending on alloy specifics) precipitates fine metastable phases that maximize strength; aging profiles must be adjusted for section thickness and initial quench rate.

Overaging treatments (T73/T76) employ higher temperature or longer-duration aging cycles to coarsen precipitates and reduce residual stresses and SCC sensitivity, accepting a reduction in peak strength. T651 involves solution treatment, quenching and a controlled stretch to relieve residual stresses, followed by aging to reach near T6 strength with better dimensional stability.

For non-heat-treatable variants or for temporary formability, cold work hardening (H tempers) is used to increase yield strength without aging. Annealing returns the alloy to O condition with recrystallization and recovery of ductility; however, multiple full solution cycles are required to fully reestablish precipitation hardening after annealing.

High-Temperature Performance

7071 loses strength with increasing temperature, with practical upper service limits generally below 150 °C for load-bearing applications where significant strength retention is required. Elevated temperatures accelerate precipitate coarsening, reducing yield and tensile strength and degrading fatigue and creep resistance compared with room-temperature properties.

Oxidation of the surface is not severe for short-term exposures, but prolonged high-temperature service can lead to intermetallic coarsening and grain boundary weakening that increases susceptibility to creep and intergranular failure. The heat-affected zone from welding is particularly vulnerable to softening and embrittlement when exposed to elevated temperatures; designs requiring heat or high-temperature stability typically specify alternate alloys or apply protective thermal barriers.

Applications

Industry	Example Component	Why 7071 Is Used
Aerospace	Structural fittings, bulkhead frames	High strength-to-weight and good machinability for critical geometry parts
Automotive	High-performance chassis brackets, suspension components	Allows lightweighting with high static strength
Marine	High-strength structural elements, fittings	Used where strength is needed and corrosion can be mitigated by coatings
Electronics	Heat spreader housings, rigid frames	Combination of stiffness and thermal conductivity for compact assemblies

7071 is often selected for precision machined parts where a combination of high strength, dimensional stability, and acceptable fatigue properties enable reduced section sizes and weight savings. Where corrosion protection can be engineered and welds are minimized, 7071 enables performance that is difficult to match with lower-strength aluminum grades.

Selection Insights

For engineers choosing a material, prefer 7071 when high specific strength and stiffness are primary requirements and when post-processing (machining, heat treatment) can be tightly controlled. Use T6/T651 for maximum static strength, and select T73/T76 when stress-corrosion cracking resistance is required despite some loss in peak strength.

Compared with commercially pure aluminum (1100), 7071 sacrifices electrical and thermal conductivity as well as formability in exchange for a much higher tensile and yield strength. Compared with work-hardened alloys such as 3003 or 5052, 7071 offers substantially higher static strength but typically reduced corrosion resistance and weldability; choose 7071 when structural performance outweighs forming and surface durability priorities. Compared with heat-treatable 6xxx alloys such as 6061/6063, 7071 provides higher peak strength at comparable densities but can be more sensitive to SCC and welding; 7071 is selected when strength-to-weight is the decisive metric and when appropriate protective measures for corrosion and joining are in place.

Closing Summary

7071 remains relevant as a high-performance member of the 7xxx family for applications that demand elevated strength and stiffness at low mass, particularly when machining and controlled heat treatment are part of the manufacturing flow. Its use requires mindful mitigation of corrosion, welding, and forming limitations, but when specified appropriately 7071 enables optimized lightweight designs across aerospace, automotive and specialty engineering sectors.