Aluminum 7075: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

7075 is a member of the 7xxx series aluminum alloys, which are Zn-Mg-Cu based high-strength alloys designed primarily for structural applications. Its principal alloying elements are zinc (Zn) as the primary strengthener, magnesium (Mg) to form precipitation-strengthening phases with zinc, and copper (Cu) to increase strength and hardenability; trace additions of chromium (Cr) and titanium (Ti) control grain structure and recrystallization. The strengthening mechanism is heat-treatable precipitation hardening (age hardening) rather than work hardening, producing very high yield and tensile strengths after solution treatment and artificial aging.

7075 is characterized by very high strength-to-weight ratio, moderate fatigue performance, limited intrinsic corrosion resistance relative to 5xxx and 6xxx families, and poor fusion weldability without special procedures; formability is limited in peak tempers but improves in annealed or lightly aged conditions. Typical industries include aerospace primary and secondary structures, high-performance automotive components, defense hardware, tooling, and high-strength sporting goods. Designers select 7075 when strength and stiffness per unit mass are the primary drivers and when designer-controlled fabrication and corrosion protection can mitigate its weaknesses.

7075 is chosen over other aluminum alloys when the application demands near-steel static strengths while maintaining significant weight savings. It competes with titanium and high-strength steels in high-performance applications where machining to tight tolerances and post-process heat treatment are acceptable. The alloy is avoided where field welding, high-formability stamping, or unprotected long-term marine exposure are dominant requirements.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed for forming and machining
H14	Moderate	Moderate	Fair	Poor	Strain-hardened; used for extrusions and cold work
T4	Moderate	Good	Good	Poor	Solution heat-treated and naturally aged
T5	High	Moderate	Fair	Poor	Cooled from hot working and artificially aged
T6	Very High	Moderate-Low	Limited	Poor	Solution heat-treated and artificially aged (peak strength)
T73	High (overaged)	Moderate	Improved	Poor	Overaged for improved SCC resistance and toughness
T651	Very High	Moderate-Low	Limited	Poor	T6 with stress relief by stretching (dimensional stability)

Temper has a first-order effect on mechanical performance and practical processability for 7075. Annealed (O) and solution-treated variants are preferred for forming and cold stretching, while T6/T651 provide maximum static strength at the expense of ductility and formability. Overaged tempers like T73 trade peak strength for improved resistance to stress-corrosion cracking and slightly better toughness, making them candidates for corrosive or critical fatigue environments.

Chemical Composition

Element	% Range	Notes
Si	0.40 max	Impurity; affects casting and high-temperature behavior
Fe	0.50 max	Impurity that can form intermetallics and reduce toughness
Mn	0.30 max	Minor; sometimes added for grain structure control
Mg	2.1–2.9	Essential for MgZn2 precipitates that provide age hardening
Cu	1.2–2.0	Raises strength and hardenability but reduces corrosion resistance
Zn	5.1–6.1	Primary strengthening element forming MgZn2 precipitates
Cr	0.18–0.28	Controls recrystallization and contributes to toughness
Ti	0.20 max	Grain refiner used in castings and primary ingots
Others	0.15 total max	Includes residuals like Zr, Sr; kept low to control properties

The performance of 7075 is governed by the Zn–Mg–Cu ternary system where MgZn2 (eta-phase) precipitates are the primary hardening phases when properly aged. Copper raises strength and contributes to the hardening response but also accelerates localized corrosion and susceptibility to stress-corrosion cracking. Chromium and trace elements refine grain structure and help maintain toughness and stability during thermomechanical processing.

Mechanical Properties

Tensile behavior of 7075 is highly temper-dependent, with aged tempers showing high ultimate tensile strengths and high yield strengths due to finely dispersed precipitates. In T6/T651 conditions the stress–strain response is characterized by a comparatively high elastic limit and limited uniform elongation, leading to relatively low total elongation compared with 5xxx and 6xxx alloys. Hardness levels follow the same trend, with peak-aged conditions producing the highest hardness values corresponding to the strongest precipitation state.

Fatigue performance is generally good in properly treated and shot-peened components but is sensitive to surface condition, residual stresses, and corrosion. The alloy exhibits thickness-dependent properties: larger cross-sections can show lower properties due to slower quench rates and coarser precipitate distributions. Yield and tensile stress concentrations can promote stress-corrosion cracking, particularly in peak-aged tempers exposed to moist chloride environments.

Processing and temper selection strongly affect failure modes; overaged tempers improve SCC resistance and toughness at the cost of ultimate strength. Design allowances for reduced ductility and notch sensitivity should be made when using T6 or related tempers in dynamic or fracture-critical components.

Property	O/Annealed	Key Temper (T6/T651)	Notes
Tensile Strength	~170–280 MPa (25–40 ksi)	~540–620 MPa (78–90 ksi)	Peak-aged T6/T651 values vary with thickness and supplier
Yield Strength	~60–150 MPa (9–22 ksi)	~470–540 MPa (68–78 ksi)	Yield rises dramatically after aging
Elongation	~20–35%	~5–12%	Elongation drops in peak tempers and with increased thickness
Hardness	~45–70 HB	~150–190 HB	Brinell hardness correlates with tensile strength after aging

Physical Properties

Property	Value	Notes
Density	2.81 g/cm³	Typical for high-strength Al–Zn–Mg–Cu alloys
Melting Range	~477–635 °C	Solidus–liquidus ranges vary with composition and impurities
Thermal Conductivity	~130–150 W/m·K	Lower than pure Al and some 6xxx alloys due to alloying
Electrical Conductivity	~30–40% IACS	Reduced relative to 1100 or 6061 because of alloying additions
Specific Heat	~0.96 kJ/kg·K	Typical for aluminum alloys near room temperature
Thermal Expansion	~23–24 ×10⁻⁶ /K	Similar coefficient to other wrought Al alloys

7075’s physical properties reflect its alloy content: density is only marginally higher than other series, while conductivity and thermal diffusivity are reduced by alloying elements. Thermal and electrical characteristics remain adequate for many structural applications but are inferior to pure aluminum for heat-sink or conductor roles where maximum conductivity is required.

Thermal processing windows are constrained by the melting/solidus temperatures and the precipitation kinetics; careful control of solution treatment temperature and quench severity is required to obtain target mechanical properties. The alloy’s moderate thermal expansion must be accounted for in multi-material assemblies.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.2–6 mm	Good when T6/T651; formability limited in peak tempers	O, T4, T5, T6, T73	Widely used for machined and formed components after aging
Plate	6–100+ mm	Strength decreases with thickness due to quench sensitivity	O, T6, T651, T73	Thick plate requires special heat treatment and quench fixtures
Extrusion	Variable cross-sections	Mechanical properties vary with section thickness	O, H14, T6 (limited)	Complex profiles produced but age-hardening can cause distortion
Tube	Thin to thick-walled	Similar behavior to sheet; welded tube has HAZ concerns	O, T6	Seam-welded tubes require post-weld heat treatment options
Bar/Rod	Ø3–200 mm / billets	High strength in T6; susceptibility to quench gradients	O, T6, T651	Common for machined structural parts and fasteners

Processing differences between forms are rooted in quenchability and section size. Thin sections and small bars quench rapidly and reach peak T6 properties reliably, while thick plates and large forgings require specialized quench media and fixtures to avoid property gradients. Extrusions and welded products introduce HAZ and residual stress considerations that may necessitate post-fabrication heat treatment or selection of overaged tempers.

Equivalent Grades

Standard	Grade	Region	Notes
AA	7075	USA	Aluminum Association designation commonly referenced in supplier data sheets
EN AW	7075 (AlZn5.5MgCu)	Europe	Similar chemistry; EN tempers align with AA tempers but differ in designation conventions
JIS	A7075	Japan	Equivalent alloy with JIS-defined impurity limits and temper codes
GB/T	7075	China	Chinese standard grade with comparable composition but potential differences in allowed impurities and testing

Subtle differences between regions arise from permitted impurity ceilings, temper designation conventions, and certified mechanical property limits for specific product forms and thicknesses. Procurement should reference the applicable national standard and inspection documents; cross-certification may be required for critical aerospace or defense applications. Suppliers often provide supplier-specific designations (e.g., 7075-T6511) that require attention to the exact processing history.

Corrosion Resistance

7075 offers only moderate atmospheric corrosion resistance compared with 5xxx and 6xxx aluminum families. The presence of copper increases susceptibility to localized corrosion such as pitting and intergranular attack in chloride-containing environments. Protective measures such as organic coatings, anodizing, cladding, or cathodic protection are commonly employed for exterior exposure and marine services.

Stress-corrosion cracking (SCC) is a critical concern for 7075, particularly in peak-aged T6 and similar tempers under sustained tensile stress in moist chloride environments. Overaging to T73 or selecting slightly lower-strength tempers reduces SCC susceptibility at the expense of ultimate strength. Galvanic interactions with dissimilar metals must be managed because 7075's electrochemical potential can accelerate corrosion of less noble metals while 7075 itself may localize attack at contact points if coatings fail.

Compared with 6xxx (e.g., 6061) and 5xxx (e.g., 5052) series alloys, 7075 is less tolerant to aggressive environments; however, when appropriately protected and maintained, its high strength often justifies the additional corrosion-control measures in aerospace and high-performance applications.

Fabrication Properties

Weldability

Welding 7075 by conventional fusion methods is generally discouraged because the alloy exhibits significant hot-cracking, loss of strength in the heat-affected zone, and poor restoration of original properties. Friction stir welding can produce acceptable joints in some tempers, but the welded region typically requires post-weld solution treatment and aging to recover mechanical properties, which is often impractical for assembled structures. When welding is unavoidable, use of specialized filler alloys, pre- and post-heat treatments, and strict process controls are required to minimize embrittlement and SCC risk.

Machinability

7075 is considered a readily machinable high-strength aluminum; it machines faster and with better surface finish than many steels due to aluminum’s low density and chip-forming behavior. Tooling of carbide or high-speed steel with positive rake geometry and high coolant flow yield long tool life, and feeds/speeds are generally higher than for 6061. Chips tend to be continuous; chip control and evacuation must be managed to avoid tool re-cutting and heat build-up that can affect surface integrity.

Formability

Formability is good in O and T4 tempers but becomes limited in peak-aged tempers where ductility is reduced. Recommended minimum bend radii depend on temper and thickness but are typically larger than for softer Al-Mg alloys, and springback is significant due to high yield strength. For complex shapes, form in annealed condition followed by solution treatment and age hardening where feasible, or select alternative alloys if extensive cold forming is required.

Heat Treatment Behavior

7075 is a classic heat-treatable alloy where the typical route is solution treatment, rapid quench, and artificial aging. Solution treatment is generally performed near 475–480 °C to dissolve the MgZn2 and related phases into the matrix, followed by rapid quenching to retain a supersaturated solid solution. Artificial aging (T6) commonly uses temperatures around 120 °C for periods such as 12–24 hours to precipitate fine MgZn2 particles and achieve near-peak strength.

Overaging treatments (T7x family, e.g., T73) use higher aging temperatures or longer times to coarsen precipitates, decreasing peak strength but improving stress-corrosion cracking resistance and fracture toughness. T651 denotes the T6 condition followed by a controlled stretching to relieve residual stresses; this is often specified for aerospace plate and extrusions to stabilize dimensions. Control of quench rate is critical: inadequate quenching yields coarser precipitates, lower strength, and heterogeneous properties through section thickness.

Non-heat-treatable strengthening via work hardening is of limited relevance for 7075 because its primary strengthening derives from precipitation; some Hxx tempers exist but are generally less common or provide inferior strength compared with heat treatment.

High-Temperature Performance

7075 loses its elevated strength rapidly as service temperature increases beyond typical room-temperature aging stability; significant softening occurs above approximately 100–120 °C as precipitates overage. Long-term exposure at moderately elevated temperatures can reduce yield and ultimate strengths due to coarsening of strengthening precipitates and potential recovery phenomena. Consequently, 7075 is not a preferred alloy for sustained high-temperature structural applications.

Oxidation resistance is similar to other aluminum alloys; aluminum forms a thin protective oxide layer but this does not prevent the thermally-activated precipitate evolution that degrades mechanical properties. In welded or thermally cycled parts, HAZ softening and local loss of strength can be aggravated by thermal exposure, making post-weld treatments or alternative joining strategies advisable for components exposed to elevated temperatures.

For short-term or intermittent elevated-temperature service where strength retention is required, designers should quantify allowable temperature–time exposures and consider alternate alloys or protective heat treatment schedules. Creep resistance in 7075 is limited compared to high-temperature aluminum alloys and is usually negligible at typical application stresses.

Applications

Industry	Example Component	Why 7075 Is Used
Aerospace	Wing fittings, structural forgings	Exceptional strength-to-weight and fatigue properties when properly treated
Marine	High-strength shafts, fittings (protected)	High strength for weight-critical parts with applied corrosion protection
Automotive	High-performance suspension and chassis components	High static strength for lightweight performance parts
Defense	Weapon components, mounts	High tensile strength and machinability for precision parts
Sporting Goods	Bicycle frames, climbing equipment	High strength and fatigue resistance for weight-sensitive gear
Electronics	Structural mounts, some heat spreaders	Combination of stiffness and machinability for structural supports

7075 remains the alloy of choice for applications where maximum static and fatigue strength per mass are the dominant design drivers and where fabrication and corrosion mitigation strategies can be implemented. Its machinability and capacity for producing high-precision parts make it suitable for components where tight tolerances and surface finish are required.

Selection Insights

Use 7075 when strength-to-weight is paramount and when manufacturing processes (heat treatment, machining, coatings) can be tightly controlled. It is ideal for aerospace fittings, defense hardware, and precision machined parts where the cost premium and corrosion-control measures are justified by performance gains.

Compared with commercially pure aluminum (e.g., 1100), 7075 trades electrical and thermal conductivity plus excellent formability for an order-of-magnitude increase in strength; choose 1100 only when conductivity or deep drawing is the priority. Compared with work-hardened alloys like 3003 or 5052, 7075 provides much higher static strength but reduced corrosion resistance and formability, so those alloys are preferred for marine sheetwork, fuel tanks, or welded structures. Compared with heat-treatable 6xxx alloys (e.g., 6061), 7075 offers substantially higher peak strength but worse weldability and corrosion performance; choose 7075 for ultimate strength and 6061 when weldability, anodizing quality, or general corrosion resistance is more important.

Consider cost, supply chain availability, and required post-fabrication treatments in selection; if welding or extensive forming in-service is expected, evaluate 6061 or 5052 as alternatives despite lower strength.

Closing Summary

7075 remains a cornerstone high-strength aluminum alloy where designers demand near-steel static strength with significant weight savings, balanced by careful fabrication and corrosion-control strategies. Its heat-treatable precipitation-hardening response enables engineered combinations of strength and toughness across tempers, making it indispensable in aerospace, defense, and high-performance applications. Proper temper selection, surface protection, and process control are essential to fully exploit 7075’s capabilities while managing its limitations.