Aluminum A7075: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

A7075 is a member of the 7xxx series aluminium alloys, which are zinc–magnesium–copper strengthened compositions developed for high specific strength applications. The alloy’s primary alloying elements are zinc (major), magnesium and copper, with minor additions of chromium and often trace titanium or zirconium for grain control. Strengthening is achieved primarily through precipitation hardening (age hardening) following solution heat treatment and quenching, making A7075 a classic heat-treatable high-strength aluminium alloy rather than a work-hardened alloy.

The hallmark traits of A7075 are very high tensile and yield strength for an aluminium alloy, good fatigue strength, and relatively low density, producing a high strength-to-weight ratio. Corrosion resistance is moderate and typically inferior to 5xxx or 6xxx series alloys without protective surface treatment or cladding, and conventional fusion welding is problematic due to hot cracking and severe softening in the heat-affected zone. Typical industries using A7075 include aerospace structural components, high-performance sporting goods, defense and ordnance, and high-stress mechanical parts where strength-to-weight is critical.

Engineers choose A7075 when maximum static and fatigue strength are primary design drivers and when part geometry and joining methods can accommodate its limitations in formability and weldability. It is selected over lower-strength alloys when mass reduction and stiffness at low-to-moderate temperatures are paramount, and over titanium or steel when cost, machinability, or corrosion-protection strategies favor aluminium systems.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed, best for forming and machining
H14	Moderate	Moderate	Fair	Poor	Strain-hardened, limited for 7xxx series; used for thin-sheet parts
T5	High	Low–Moderate	Poor–Fair	Poor	Cooled from elevated temperature shaping and artificially aged
T6	Very High	Low	Poor	Poor	Solution treated, quenched and artificially aged; peak strength condition
T651	Very High	Low	Poor	Poor	T6 with stress relief by stretching to minimize residual stresses
T73	Moderate–High	Moderate	Fair	Poor	Overaged temper optimized for improved corrosion resistance and SCC mitigation

The temper selected for A7075 fundamentally changes its performance envelope. O or annealed tempers allow extensive cold forming and provide high ductility and reduced strength, while T6/T651 offers maximum static and fatigue strengths with correspondingly low ductility and poor room-temperature formability.

Overaging to T73 or similar tempers trades off a portion of peak strength to substantially improve resistance to stress-corrosion cracking and corrosion-induced exfoliation. For manufacturing, this means designers must balance forming and joining operations against final mechanical property targets and corrosion durability requirements.

Chemical Composition

Element	% Range	Notes
Si	0.4 max	Typical impurity; controlled to limit intermetallics that affect toughness
Fe	0.5 max	Iron forms hard intermetallics; excess reduces toughness and increases porosity risk
Mn	0.3 max	Small effect; not a primary alloying addition in 7075
Mg	2.1–2.9	Key precipitate former (MgZn2) that contributes to age hardening
Cu	1.2–2.0	Raises strength by stabilizing precipitates but tends to reduce corrosion resistance
Zn	5.1–6.1	Principal strength alloying element; forms strengthening Mg–Zn precipitates
Cr	0.18–0.28	Grain structure control; reduces recrystallization and improves toughness
Ti	0.2 max	Grain refiner in cast or wrought processing when added in small amounts
Others	Balance Al ± small traces (Zr, V)	Aluminium comprises the balance; trace elements may be included for grain/toughness control

The alloy chemistry is tuned to maximize the precipitation of Mg–Zn (MgZn2 and associated phases) and copper-containing complex precipitates during artificial aging. Zinc and magnesium drive the primary strengthening reactions, while copper enhances peak-aged strength but tends to increase susceptibility to localized corrosion and stress-corrosion cracking if not mitigated by temper selection or surface protection. Chromium and trace additions help stabilize the as-processed microstructure and reduce grain-boundary precipitate continuity, benefiting toughness and fatigue life.

Mechanical Properties

The tensile behavior of A7075 is characterized by high ultimate and yield strengths in peak-aged tempers, with relatively low elongation values compared with softer aluminium alloys. In T6/T651 conditions, the material exhibits a high initial elastic modulus consistent with aluminium but a high yield level that allows thinner sections for equivalent load-carrying capacity; fatigue strength is also strong relative to other aluminium alloys when surface finish and stress concentrators are properly controlled. Annealed or O temper A7075 shows much lower tensile strength but significantly improved ductility and formability, making it suitable for operations that require shaping prior to final heat treatment.

Yield strength is sensitive to temper and thickness, with heavy sections showing lower through-thickness mechanical properties due to quench-rate limitations during solution treatment. Elongation-to-failure varies from the mid-single digits in peak tempers to well over 10–20% in annealed material, which must be considered for crashworthiness and forming scenarios. Hardness correlates closely with temper and precipitation state; peak-aged conditions produce high hardness and wear resistance for sliding or bearing applications, while annealed conditions yield much lower hardness for machining ease.

Fatigue resistance of 7075 is generally excellent for a wrought aluminium alloy, but it is highly dependent on surface condition, presence of corrosion pits, and temper state; T6 exhibits high fatigue limit but can be vulnerable to corrosion-assisted fatigue and stress-corrosion cracking. Thickness and section size influence achievable properties because the solution treatment and quench rates required to develop the optimum precipitation microstructure are more difficult to realize in thicker sections, typically necessitating modified heat-treatment schedules or acceptance of reduced peak properties.

Property	O/Annealed	Key Temper (T6/T651)	Notes
Tensile Strength	200–300 MPa	480–570 MPa	Range varies by temper, thickness, and supplier; T6 is peak-strength typical range
Yield Strength	80–200 MPa	350–525 MPa	Yield increases dramatically with aging; values depend on product form and thickness
Elongation	12–25%	5–11%	Annealed high-ductility, T6 reduced elongation; depends on section size and test orientation
Hardness	35–70 HB	140–180 HB	Hardness mirrors yield/tensile trends; reported values vary with testing method

Physical Properties

Property	Value	Notes
Density	~2.81 g/cm³	Slightly higher than some other aluminium alloys due to Zn and Cu content
Melting Range	~477–635 °C	Solidus and liquidus range typical for 7xxx series alloys
Thermal Conductivity	~120–150 W/m·K	Lower than pure Al, reduced by alloying and precipitates
Electrical Conductivity	~30–40 % IACS	Reduced relative to pure aluminium; depends on temper and solute content
Specific Heat	~870–910 J/kg·K	Typical aluminium specific heat; varies slightly with temperature
Thermal Expansion	~23–24 ×10^-6 /K	Coefficient of thermal expansion similar to other aluminium alloys

The density and thermal properties make A7075 attractive where high stiffness and lower mass are required along with moderate thermal transport capability. Thermal conductivity is good compared to many structural metals but lower than pure aluminium and certain 6xxx alloys due to alloying solutes and precipitates that scatter phonons and electrons. Electrical conductivity is significantly compromised relative to pure aluminium and should not be relied upon for current-carrying applications where low resistivity is critical.

Thermal expansion is consistent with other aluminium alloys and must be accommodated where A7075 components are mated to dissimilar materials with differing expansion coefficients. The melting range informs heat-treatment windows and welding temperature limitations, emphasizing the need for controlled processes to avoid incipient melting of low-melting eutectics in the microstructure.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.5–6 mm	Good in T6/T651; thinner gauge allows more uniform quench	O, T6, T651, T73	Widely used for thin structural panels and aerospace skins; cladding sometimes applied
Plate	6–100+ mm	Strength reduced in thick plate due to slower quench	T6, T651, T73	Thick plate requires special quench or post-aging to approach peak properties
Extrusion	Up to large cross-sections	Property gradients may occur; best in smaller profiles	T6 (after quench-age), T73	Used for high-strength profiles where complex geometry is needed
Tube	Custom diameters, wall thicknesses	Mechanical properties similar to plate/extrusion; welds can be an issue	O, T6	Formed from extrusions or rolled-welded tube; careful processing required for thin walls
Bar/Rod	Diameters up to several inches	Good machinability in many tempers; strength scales with temper	O, T6	Common for high-strength fasteners, shafts, and machined parts

Processing route and product form determine achievable properties because solution-treatment quench rates and subsequent ageing control precipitate size, distribution, and therefore strength and toughness. Thin sheets and small sections more readily achieve T6 properties after quench and artificial aging, while thick plate and large extrusions may require modified heat-treatment cycles, interrupted quenching strategies, or acceptance of lower peak properties due to slower cooling.

Applications and joining strategies differ by form: sheets are commonly clad and used where surface finish and corrosion protection are important, plates provide bulk structural capability, and extrusions or bars are favored where complex cross-sections or precision-machined parts are required.

Equivalent Grades

Standard	Grade	Region	Notes
AA	A7075	USA	Common designation in American Aluminium Association standards
EN AW	7075	Europe	European EN designation; broadly equivalent chemistry and properties
JIS	A7075	Japan	Japanese standard often aligns closely with AA/JIS alloys but may have different property specs
GB/T	7075	China	Chinese standard equivalent with localized production and specification tolerances

While the numeric designation 7075 is widely used across standards, subtle differences arise in maximum impurity limits, permitted trace elements, and specified mechanical-property acceptance criteria. Procurement requires checking the specific standard referenced (AA, EN, JIS, GB/T) to ensure that required limits for elements such as Cu, Zn, and Cr, and mechanical property acceptance values are met for the intended application. Cladding, tempers, and authorized product forms may also vary by regional standard and mill practice.

Corrosion Resistance

A7075 exhibits moderate atmospheric corrosion resistance in benign environments but is more susceptible to localized corrosion, such as pitting and exfoliation, than many 5xxx and 6xxx series alloys. The high zinc and copper content that provide superior strength also promote galvanic and intergranular corrosion tendencies, particularly in marine chloride-rich environments if protective coatings or anodic treatments are not applied. Cladding with purer aluminium (Alclad) or conversion coatings and sealants is a common mitigation strategy for elevated-corrosion environments.

Stress corrosion cracking (SCC) is a notable concern for peak-aged temper A7075, particularly in T6 where high tensile residual or applied stresses combine with corrosive agents to initiate brittle-like cracking. Overaged tempers such as T73 or design strategies to reduce applied stress levels are standard practices to reduce SCC risk in critical components. In galvanic couples, A7075 is anodic relative to many steels but cathodic to more noble metals; when coupled with stainless steel or carbon steels in the presence of an electrolyte, galvanic corrosion and localized attack can be exacerbated unless electrically insulating joints or protective coatings are used.

Compared with 5xxx (Mg-rich) alloys, A7075 trades corrosion resistance for higher strength; compared with 6xxx series, 7075 typically delivers higher static strength but lower general corrosion resistance. Long-term service in harsh marine or chemical-exposure environments generally requires protective metallo-chemical surface treatments or selection of a more corrosion-tolerant alloy.

Fabrication Properties

Weldability

Fusion welding of A7075 is challenging and generally discouraged for load-bearing structural applications because fusion welds tend to crack and the heat-affected zone experiences significant softening, often losing a large portion of peak-aged strength. Friction stir welding (FSW) is the preferred joining method for many A7075 applications because it produces a refined microstructure with reduced susceptibility to hot cracking and better retention of mechanical properties, although the weld zone still exhibits different strength and fatigue behavior compared with parent T6 material. When fusion welding is necessary for non-critical parts, specialized filler wires and post weld solution treatment and aging (if geometry permits) are required, and acceptance testing must verify performance.

Machinability

A7075 is regarded as one of the better-machining high-strength aluminium alloys due to its relatively low ductility in peak tempers and high strength that facilitate chip breaking, allowing good surface finishes and tight tolerances with standard carbide tooling. Recommended tooling includes high-positive carbide inserts with sharp geometry, rigid fixturing, and adequate coolant or lubrication to minimize built-up edge and thermal softening. Cutting speeds can be high relative to steels, but feeds must be controlled to avoid chatter and to manage the thin, continuous chips typical of aluminium alloys; tool coatings designed for aluminium reduce galling and prolong tool life.

Formability

Cold forming of A7075 is limited in peak tempers; springback is significant and the material tends to fracture at tight radii. The O/annealed temper is the preferred condition for stamping, deep drawing, and extensive bending, and parts are frequently formed in annealed condition then solution treated and artificially aged to reach the specified tempered strength where geometry allows. Minimum bend radii are dependent on temper and thickness; as a general guideline, peak-aged T6 sheet often requires radii several times the material thickness, while annealed material can be formed with much tighter radii.

Heat Treatment Behavior

For heat-treatable alloys such as A7075, the standard sequence to obtain peak properties is solution treatment, quenching, and artificial aging. Solution treatment is typically performed near the solidus/solvus temperature for sufficient time to place alloying elements in solid solution, followed by rapid quenching to retain a supersaturated solid solution. Artificial aging (precipitation heat treatment) is then conducted—T6 commonly uses an aging schedule such as 120°C for many hours to nucleate fine Mg–Zn precipitates that deliver high strength.

Overaging treatments (T73, T7451, etc.) intentionally coarsen precipitates to improve resistance to stress-corrosion cracking and exfoliation at the cost of some peak strength. T651 and similar designations indicate T6 aging plus a stress-relief operation such as controlled stretching or mechanical straightening to reduce residual stress from quenching or forming. The effectiveness of heat treatment is thickness-limited; heavy sections may not achieve the same quench rate and therefore do not attain identical peak-aged properties without specialized processing or quench media.

Non-heat-treatable routes are not applicable for achieving the primary strengthening mechanism in 7xxx series alloys beyond limited strain hardening; annealing is used to restore ductility prior to forming, but subsequent age hardening is necessary to recover design strength.

High-Temperature Performance

A7075 exhibits significant strength loss as temperature increases above typical ambient service temperatures; useful structural strength is typically limited to roughly room temperature up to about 120°C for sustained service. Above approximately 150–200°C the precipitation microstructure coarsens and the alloy rapidly loses yield and tensile strength, making it unsuitable for high-temperature load-bearing components. Oxidation is not severe at moderate temperatures because aluminium rapidly forms a protective oxide, but elevated temperatures can accelerate microstructural changes and soften the alloy.

Heat-affected zones from welding or localized heating may experience incipient melting of low-melting eutectics or dissolution of strengthening phases if temperatures locally exceed solution-treatment thresholds, resulting in permanent strength loss and a need for post-process heat treatment where geometry permits. For applications approaching the upper temperature limits, alternative materials engineered for elevated-temperature performance or careful thermal management strategies should be considered.

Applications

Industry	Example Component	Why A7075 Is Used
Aerospace	Wing spars, fittings, landing gear components	Exceptional strength-to-weight and fatigue performance for critical structural parts
Marine	High-strength stanchions, rigging components	High static strength where protective coatings or cladding mitigate corrosion
Aerospace/Defense	Missile airframes, ordnance components	High strength, machinability, and stiffness for dynamic and high-load parts
Sporting Goods	Bicycle frames, climbing gear, aerospace-grade hardware	Combines low mass with high strength for performance products
Electronics	Structural housings and heat-spread components (limited)	Good thermal conductivity and stiffness, used where mechanical strength dominates

A7075 is chosen where maximizing load capacity for a given mass is required and where designs can manage corrosion and joining limitations. The alloy is particularly dominant in aerospace primary and secondary structural parts, defense applications, and select high-performance consumer equipment where machining, finishing, and protective surface treatments are practical and justified by performance gains.

Selection Insights

Select A7075 when strength-to-weight ratio and fatigue strength are decisive and when manufacturing methods (machining, FSW, or mechanical fastening) can avoid the limitations of fusion welding and poor formability in peak tempers. Use annealed material for forming operations and plan for subsequent heat treatment if final high strength is required.

Compared with commercially pure aluminium (e.g., 1100), A7075 sacrifices electrical and thermal conductivity and formability for a substantially higher tensile and yield strength. Compared with common work-hardened alloys (e.g., 3003, 5052), A7075 offers far superior strength but reduced general corrosion resistance and poorer room-temperature formability. Compared with common heat-treatable alloys (e.g., 6061/6063), A7075 provides higher peak strength and superior fatigue properties, though at the expense of increased susceptibility to stress-corrosion cracking and generally higher cost and fabrication constraints.

Use A7075 when the design priority is minimal mass and maximal strength and when procurement, processing, and surface protection strategies can be deployed to manage corrosion, joining, and heat-treatment limitations. For general-purpose structural parts with easier fabrication and better corrosion tolerance, consider alloys like 6061; for maximum strength in highly critical components, A7075 remains a top candidate.

Closing Summary

A7075 remains a cornerstone high-strength aluminium alloy where exceptional strength-to-weight and fatigue performance are required and where manufacturing processes and corrosion protection can be tailored to its temper-dependent limitations. Its combination of precipitation-hardened strength, machinability, and aerospace pedigree makes it a durable choice for demanding structural applications despite the trade-offs in weldability and corrosion susceptibility.