Aluminum 8075: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

Alloy 8075 is a high-strength, heat-treatable aluminum alloy that sits functionally alongside the high-strength Zn‑Mg‑Cu family rather than the common 1xxx–6xxx mainstream families. It is typically classified in the aluminum 8xxx series, where the chemistry is tuned to maximize strength while attempting to retain acceptable toughness and corrosion behavior for structural applications.

The major alloying elements in 8075 are zinc and magnesium, with controlled additions of copper and micro-alloying elements such as chromium, zirconium or titanium to refine grain structure and control recrystallization. Strengthening is achieved primarily through precipitation hardening (solution treatment followed by quench and artificial aging), producing fine η-phase (MgZn2) precipitates that provide high yield and tensile strength.

Key traits of 8075 include high specific strength, moderate-to-poor weldability in fusion processes, reduced electrical and thermal conductivity compared with pure aluminum, and limited cold formability in peak-aged tempers. Its targeted industries include aerospace structures, high-performance transportation components, and certain marine or rail structural parts where a high strength-to-weight ratio is required.

Engineers choose 8075 when a combination of high strength, damage tolerance, and optimized corrosion performance (relative to older 7xxx alloys) is needed and when weight savings justify the additional material and processing cost. It is selected over lower-strength alloys when peak structural performance is required and over some 7xxx-series alloys when specific manufacturability or corrosion performance trade-offs are favorable.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed, used for complex forming and joining prior to strengthening
H14	Low–Medium	Medium	Good	Fair	Strain-hardened and partially stabilized for moderate strength and good formability
T5	Medium–High	Low–Medium	Fair	Poor–Fair	Cooled from an elevated temperature and artificially aged; convenient for extrusions
T6	High	Low	Poor	Poor	Solution heat-treated, quenched and artificially aged; gives near-maximum strength
T651	High	Low	Poor	Poor	T6 with stress-relief by stretching to minimize residual stresses after quench
T76 / T77	Medium–High	Medium	Better than T6	Poor	Overaged or modified aging to improve SCC resistance at some cost in peak strength

Temper has a primary effect on the trade-off between strength and ductility: annealed and strain-hardened tempers give the best formability while T6/T651 provide the highest static strengths. Overaging (T76/T77) is a common production choice when improved resistance to stress corrosion cracking is required at the expense of some peak strength.

Chemical Composition

Element	% Range	Notes
Si	0.10–0.50	Deoxidizer and grain-boundary phase former; too much reduces toughness
Fe	≤0.50	Impurity element; contributes to intermetallics that can reduce ductility
Mn	≤0.30	Controls grain structure and improves toughness marginally
Mg	1.8–2.6	Major strengthening element; forms MgZn2 precipitates with Zn
Cu	0.8–1.9	Raises strength and hardness but can reduce corrosion resistance if excessive
Zn	5.0–6.5	Primary strength contributor by forming Mg‑Zn precipitates; key for high strength
Cr	0.05–0.25	Micro-alloying for recrystallization control and improved toughness
Ti	≤0.20	Grain refiner when added in small amounts during casting/extrusion
Others / Al balance	Balance	Trace amounts of Zr, V or other elements may be present to control precipitation and grain growth

The balance of zinc, magnesium and copper sets the fundamental precipitation chemistry that establishes peak strength after solution treatment and aging. Trace micro-alloying elements such as Cr, Zr and Ti are used deliberately to control grain size, limit recrystallization, and stabilize the microstructure during thermomechanical processing, which improves toughness and resistance to quench-induced cracking.

Mechanical Properties

In tensile behavior 8075 behaves like other high‑Zn precipitation‑hardening alloys: yield and tensile strengths rise sharply after solution treatment and artificial aging but ductility is reduced. Peak-aged tempers (T6/T651) deliver high yield strength and good elastic modulus retention, while annealed or H‑tempers provide superior elongation for forming operations. Fatigue strength is influenced heavily by surface condition, thickness, and residual stresses, with shot peening and careful surface finish able to significantly extend fatigue life.

Yield strength in engineering practice for peak tempers can approach values typical of high‑strength 7xxx alloys; however, fatigue crack growth rates and damage tolerance are sensitive to microstructure and manufacturing history. Hardness scales closely with tensile strength and is used in production to control aging, where Rockwell or Vickers hardness measurements provide rapid assessment of temper state. Thickness effects are significant: thicker sections cool more slowly after quench and may show lower precipitate density and consequently reduced strength unless managed with controlled processing or overaging schedules.

Property	O/Annealed	Key Temper (T6/T651)	Notes
Tensile Strength	~200–320 MPa (typical for heavy anneal)	~470–540 MPa (typical peak-aged)	Wide range depends on thickness, aging, and exact chemistry
Yield Strength	~70–180 MPa	~400–480 MPa	Yield varies with aging sequence; T6/T651 yields are high for structural use
Elongation	15–25%	6–12%	Elongation drops substantially in peak-aged conditions
Hardness	~40–75 HV	~150–185 HV	Hardness correlates with age-hardening and is used for QC during heat treatment

Physical Properties

Property	Value	Notes
Density	~2.78 g/cm³	Typical for high‑Zn aluminium alloys; used for mass calculations
Melting Range	Solidus ~480–510 °C; Liquidus ~640–655 °C	Alloying broadens melting range relative to pure Al
Thermal Conductivity	~120–150 W/m·K (depending on temper)	Lower than high-purity aluminum due to alloying elements
Electrical Conductivity	~28–40 % IACS	Reduced with higher Zn and Cu content; varies with temper and processing
Specific Heat	~0.88–0.92 kJ/kg·K	Typical for aluminium alloys in structural applications
Thermal Expansion	~23–24 µm/m·K (20–100 °C)	Standard aluminium coefficient for structural design

The physical properties reflect the alloy’s high alloy content: thermal and electrical conductivities are penalized compared with low-alloyed aluminum but remain favorable versus steel on a mass-specific basis. The melting/solidus temperatures are important for welding and heat-treatment windows; the relatively wide melting range and alloying-related low-melting intermetallics increase the risk of hot cracking during fusion welding.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.5–6.0 mm	Thin gauges achieve close-to-peak strengths after aging	O, H14, T5, T6, T651	Widely used for skin and thin structural panels
Plate	6–200+ mm	Thicker sections require careful quench and may have lower achievable strength	O, T6, T651	Thick plates need controlled quenching or can be used in overaged conditions
Extrusion	Variable cross-sections	Strength depends on section thickness and T‑tempers	T5, T6, T651	Extrusions are age-hardenable; complex profiles possible with controlled homogenization
Tube	OD range varies	Seamless or welded; mechanical properties depend on wall thickness and heat treatment	O, T6	Common for high-strength structural tubing and chassis parts
Bar/Rod	Diameters up to 200 mm	Bars require solution treatment and controlled quench for peak properties	O, T6	Used where high section modulus and localized strength are needed

Processing differences are significant between thin and thick products because quench rate controls precipitate nucleation during aging. Sheets and extrusions quench rapidly and achieve higher strengths after standard aging; plate and large bars often require modified heat treatments or sacrifice some peak strength to avoid quench-induced cracking or inhomogeneous properties. Designers must select form and temper to match the balance of formability, final strength, and fabrication route.

Equivalent Grades

Standard	Grade	Region	Notes
AA	8075	USA	Common designation used by manufacturers and suppliers
EN AW	Not widely standardized	Europe	No direct 1:1 European EN equivalent; designers often reference EN AW‑7075 or EN AW‑7020 as functional analogues with careful cross-checking
JIS	Not directly standardized	Japan	Equivalent not commonly listed; local specifications and supplier data sheets are used
GB/T	Not widely standardized	China	No direct GB/T standard; Chinese mills may supply similar chemistries under proprietary designations

There is no universally accepted 1:1 equivalent across all standards for 8075; the alloy is controlled primarily by supplier specifications and aerospace OEM requirements. When substituting in international projects, engineers should compare detailed chemistry, heat-treatment response, and mechanical property sheets rather than rely solely on grade labels, because small differences in Cu/Mg/Zn or micro-alloy elements can materially affect aging response and corrosion performance.

Corrosion Resistance

Atmospheric corrosion resistance for 8075 is typical for high‑Zn, precipitation‑hardened alloys: fair in benign environments but sensitive to high‑chloride or polluted atmospheres without protective coatings. The risk of exfoliation corrosion and intergranular attack increases when high peak strength microstructures are present, especially on thicker sections or after improper processing, so cladding, conversion coatings, anodizing, or organic coatings are commonly used in exposed applications.

In marine environments 8075 requires design and protection measures because chloride-induced pitting and localized corrosion can initiate fatigue cracks; however, when properly coated and detailed it can be used in marine superstructures where weight savings are essential. Stress corrosion cracking (SCC) susceptibility is a key design consideration: peak-aged conditions (T6/T651) show higher SCC sensitivity and overaging strategies (T76/T77) or thermomechanical processing are used to improve SCC resistance at some strength cost.

Galvanic interactions should be managed by design: 8075 is anodic to many stainless steels and copper alloys, and care is needed when coupling with dissimilar metals. Compared with 5xxx‑series alloys (e.g., 5052) it offers higher strength but lower intrinsic corrosion resistance; compared with older 7xxx alloys, 8075 variants are often tuned to improve exfoliation resistance via microalloying and modified aging practices.

Fabrication Properties

Weldability

Fusion welding of 8075 is challenging due to the alloy’s high Zn and Mg content, which promotes hot-cracking and produces a soft HAZ with significant strength loss. Friction stir welding (FSW) is the preferred joining method for structural applications because it preserves fine precipitate distributions and minimizes HAZ softening. If fusion welding is required, use low-strength fillers, pre- and post-weld heat treatments or mechanical fasteners, and expect a welded joint to have substantially lower strength than the base metal unless specialized processes are employed.

Machinability

Machinability of 8075 is generally rated moderate; the alloy machines better in tempers closer to annealed condition and becomes more demanding in peak-aged tempers where hardness increases tool wear. Carbide tooling with high positive rake angles and stiff setups is recommended, and cutting parameters should favor higher speeds with copious flood cooling to prevent built-up edge. Chip control tends to be discontinuous for thin sections and continuous for ductile annealed tempers, so tooling geometry and coolant strategy should be chosen to manage evacuation and surface finish.

Formability

Forming operations are easiest in O and lightly work‑hardened tempers where elongation and bendability are high; peak tempers like T6 are poor candidates for complex cold forming without intermediate anneals. Minimum bend radii should be conservative in T6 (typically ≥3–6 × thickness depending on tooling and radius), and stretch/forming is feasible in pre‑annealed conditions followed by post‑form heat treatment to regain strength. For tight radius or deep drawing applications, order material in O temper and plan for subsequent solution and aging steps if final strength is required.

Heat Treatment Behavior

As a heat‑treatable alloy, 8075 responds to classical solution treatment, quench and aging sequences. Solution treatment is typically performed at temperatures near the alloy’s solidus margin (approximately 475–500 °C depending on section size) to dissolve soluble phases, followed by an immediate quench to retain a supersaturated solid solution. Artificial aging follows, with T5 representing direct artificial aging without prior solution treatment, and T6 representing solution treatment plus artificial aging; aging temperatures typically range from 120 °C to 180 °C depending on the desired strength/toughness balance.

T651 indicates a T6 temper with a controlled stretch or stress-relief after quenching to minimize residual distortion in structural parts, which is common for aerospace plates. Overaging (T76/T77) uses higher or extended aging to coarsen precipitates and reduce susceptibility to SCC and exfoliation, producing a lower peak strength but improved environmental performance. Non-heat-treatable behavior is limited to pre-age cold working and annealing operations used to restore ductility prior to final heat treatment.

High-Temperature Performance

8075 experiences appreciable strength loss as temperature increases above ambient; most structural strength is degraded above ~100–150 °C and is not suitable for sustained service at elevated temperatures encountered in engine or hot-structure applications. Oxidation in air is limited (aluminum forms a protective oxide), but elevated temperatures accelerate temper evolution and precipitate coarsening, which reduces mechanical properties and can alter corrosion resistance.

The HAZ produced during welding will also show localized overaging and softening, compounding the loss of strength near welds and making hot-structure design details critical. For short-term exposures or processes like brazing, careful thermal management and pre/post-heat treatments are required to avoid detrimental microstructural change.

Applications

Industry	Example Component	Why 8075 Is Used
Aerospace	Fuselage skins, structural fittings	High strength-to-weight and good fatigue/finish characteristics for airframe structures
Marine	Lightweight structural members	Weight-saving and good coated corrosion performance when properly detailed
Automotive / Transport	High-performance chassis and suspension components	High specific strength reduces mass and improves dynamic response
Electronics	Structural supports and brackets	Combination of strength and thermal conductivity for structural thermal paths

In summary, 8075’s application portfolio is focused on situations where high static and fatigue strength are required and where designers can justify specialized fabrication or protective treatments. Its use is most impactful in weight-sensitive structures where traditional aluminium alloys cannot meet strength targets without excessive thickness.

Selection Insights

For quick selection guidance, choose 8075 when you need a high-strength, precipitation-hardenable alloy with aerospace-grade mechanical performance and are able to accommodate restricted weldability and protective corrosion measures. It is best specified when weight-critical stiffness and high fatigue performance are design drivers and when processing capabilities (FSW, controlled quench, specialized aging) are available.

Compared with commercially pure aluminum (1100) 8075 trades off electrical and thermal conductivity as well as formability in favor of dramatically higher strength and fatigue resistance. Compared with common work-hardened alloys (3003 / 5052), 8075 sits significantly higher on strength but typically requires coatings and careful corrosion control to match 5xxx-series environmental robustness. Compared with common heat‑treatable alloys like 6061 or 6063, 8075 provides higher peak strength for structural applications; choose 8075 when ultimate strength-to-weight is more important than the broader manufacturability and weld-friendliness of the 6xxx family.

Closing Summary

Alloy 8075 remains relevant for modern engineering where high specific strength and tailored fatigue performance are essential and where manufacturing processes and protective measures are in place to manage weldability and corrosion trade-offs. Its heat‑treatable nature and adaptable aging strategies make it a useful material for high‑performance, weight‑sensitive structural applications.