Aluminum 7079: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

7079 is a high-strength, heat-treatable aluminum alloy in the 7xxx series, characterized by zinc as the primary alloying element with significant additions of magnesium and copper. It sits in the high-strength end of wrought aluminum alloys and is engineered for structural applications where strength-to-weight ratio is critical.

The alloy achieves its strength through solution heat treatment followed by artificial aging (precipitation hardening), producing fine MgZn2 and Cu-containing precipitates that impede dislocation motion. Key traits include very high strength, moderate-to-poor intrinsic corrosion resistance relative to 5xxx and 6xxx alloys, limited weldability in peak-aged conditions, and variable formability that improves when in softer tempers.

Typical industries using 7079 include aerospace primary and secondary structures, high-performance sporting goods, defense components, and specialty automotive and marine applications where high static strength is required. Engineers choose 7079 over other alloys when an exceptional combination of yield and tensile strength is required while still retaining weldability or formability with process controls, or when specific temper/aging treatments can be used to balance SCC resistance.

7079 is often selected instead of 7075 or 7050 when particular chemistries or processing routes produce improved through-thickness properties or when specific temper variants (e.g., controlled stretching, overaging) yield desirable combinations of resistance to stress corrosion cracking and retained strength. The alloy is chosen over more common 6xxx series when peak structural strength is prioritized over conductivity or ease of forming.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed, maximum ductility for forming
H12	Low-Medium	Moderate	Good	Good	Partial strain hardening, limited increase in strength
H14	Medium	Moderate	Fair	Fair	Light work hardening for thin sections
T5	Medium-High	Moderate	Fair	Poor (strength loss after welding)	Cooled from elevated-temperature shaping and artificially aged
T6	High	Low-Moderate	Poor	Poor	Peak-aged condition, highest common strength
T651	High	Low-Moderate	Poor	Poor	Solution heat-treated, stress relieved by stretching, artificially aged
T76	Medium-High	Moderate	Fair	Poor	Overaged temper for improved SCC resistance
H112	Medium-High	Moderate	Fair	Poor	Stabilized temper after thermal processing

Temper selection exerts a large influence on the final mechanical and corrosion properties of 7079; annealed O condition enables deep forming and bending while T6/T651 delivers maximum structural performance. Overaged tempers such as T76 reduce susceptibility to stress corrosion cracking at the cost of some tensile/yield strength, which makes them valuable for hostile environments.

Chemical Composition

Element	% Range	Notes
Si	0.10 max	Impurity; small amounts acceptable for casting, limited hardening effect
Fe	0.50 max	Intermetallic formers; elevated Fe reduces toughness and fatigue life
Cu	1.0–2.0	Increases strength, influences precipitation behavior and toughness
Mn	0.30 max	Can modify grain structure, limited strengthening
Mg	2.0–3.0	Principal hardening partner with Zn forming MgZn2 precipitates
Zn	6.0–7.5	Primary strengthening element; controls precipitate chemistry and peak strength
Cr	0.18–0.35	Grain structure control and improved recrystallization resistance
Ti	0.10–0.25	Grain refiner, used in small quantities to control cast/ingot grain size
Others (each)	Residuals	Trace elements and residuals are controlled to maintain toughness and processability

The performance of 7079 is controlled primarily by the Zn–Mg–Cu system; Zn and Mg combine to form the primary strengthening precipitate MgZn2, while Cu alters precipitate morphology and shifts ageing kinetics. Chromium and titanium are added in small amounts to refine grain structure and resist recrystallization during processing, which improves toughness and through-thickness properties.

Mechanical Properties

In tension, 7079 displays a strong dependence on temper and thickness. In annealed (O) condition tensile strength is relatively low and elongation is high, suitable for forming and cold working. In peak-aged tempers (T6/T651) tensile and yield strengths reach values characteristic of high-strength 7xxx alloys but ductility is reduced; elongation typically falls into the single-digit to low double-digit percent range for structural thicknesses.

Hardness tracks strength with marked increases from O to T6; typical hardness in T6 approaches the range used for structural aluminum components and correlates with fatigue performance that is generally good in well-processed materials. Fatigue behavior is sensitive to surface finish, residual stress state, and the presence of coarse intermetallic particles or porosity introduced during processing; shot peening and surface treatments are commonly used to extend fatigue life.

Thickness influences both achievable strength and fracture behavior because heat-treating and quenching effectiveness decline with increasing cross-section, and because residual stresses and through-thickness metallurgy vary with section size. Thick plates may show lower mechanical properties and higher susceptibility to exfoliation and intergranular corrosion compared with thin sheet.

Property	O/Annealed	Key Temper (e.g., T6/T651)	Notes
Tensile Strength	200–320 MPa	520–640 MPa	T6 yields peak tensile strength; ranges depend on thickness and temper control
Yield Strength	90–160 MPa	430–560 MPa	Yield increases dramatically with age hardening and stretching
Elongation	12–22%	6–12%	Annealed is highly ductile; peak-aged has limited ductility for bending
Hardness	~50–80 HB	~150–190 HB	Hardness correlates with precipitation state and overaging reduces hardness modestly

Physical Properties

Property	Value	Notes
Density	2.78–2.82 g/cm³	Typical for high-strength Al–Zn–Mg–Cu alloys; value depends on exact composition
Melting Range	~480–640 °C	Solidus/liquidus range influenced by Zn/Cu; careful thermal control required during casting/welding
Thermal Conductivity	120–150 W/m·K	Lower than pure aluminum; alloying and precipitates reduce conductivity
Electrical Conductivity	~30–35 %IACS	Reduced compared with pure aluminum because of solute and precipitation scattering
Specific Heat	~0.88–0.90 J/g·K	Similar to other aluminum alloys at room temperature
Thermal Expansion	23–24 x10^-6 /K	Comparable to other 7xxx series alloys; relevant for joint design with dissimilar materials

7079's physical properties reflect the balance between metallic aluminum matrix and dense precipitate populations. Thermal conductivity and electrical conductivity are moderate and decrease with increasing alloying and precipitation; designers should account for reduced heat-sinking compared with pure aluminum or low-alloyed 1xxx/3xxx alloys.

Thermal expansion and specific heat are close to typical aluminum values, and thermal management strategies should consider the alloy’s lower conductivity when used for heat-sinking applications or in high thermal gradient environments.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.5–6.0 mm	Full range from low (O) to high (T6/T651)	O, T5, T6, T651, T76	Widely used for skin and secondary structural parts
Plate	6–150 mm	Strength diminished in thick sections; quench sensitivity	T6, T651, T76	Thick plates require heavy-section processing and controlled quench
Extrusion	Cross-sections up to ~200 mm	Good longitudinal strength, temper-dependent	T5, T6, T651	Extrusion alloys require optimized die and quench to avoid T‑phase inhomogeneity
Tube	Diameters typical for structural tubing	Strength similar to sheet in thin-walled tube	T5, T6	Cold drawing and heat treatment used for final properties
Bar/Rod	Diameters/sections for fasteners and fittings	High axial strength achievable	O, T6	Machinable in O and peak strengthened in T6 after aging

Form and processing route significantly change achievable properties: extrusions and drawn tubing develop strong directional textures that influence anisotropy and fracture behavior. Plate thickness poses a practical limit to achieving full T6 properties due to slower cooling rates and increased risk of quench-induced residual stresses and distortion.

Different product forms also determine secondary processing steps: plate often requires solutionizing and aging in large furnaces with careful quench and straightening, while extrusions are commonly aged from the as-extruded condition to achieve desired temper with minimal distortion.

Equivalent Grades

Standard	Grade	Region	Notes
AA	7079	USA	Primary designation under Aluminum Association standards
EN AW	7079	Europe	Equivalent EN designation, commonly used for wrought products
JIS	A7079	Japan	JIS nomenclature aligns with AA chemical and mechanical specifications
GB/T	7079	China	Chinese standard often references similar chemistries and tempers

Equivalency tables reflect broadly similar chemistry and temper designations but subtle differences in impurity limits, processing requirements, and property assurance may exist across standards. When specifying 7079 components internationally, engineers should verify the exact standard, allowable tolerances, and acceptance tests to ensure interchangeability.

Corrosion Resistance

7079 exhibits lower general and pitting corrosion resistance compared with 5xxx and many 6xxx series alloys due to the high Zn and Cu contents that promote anodic dissolution and intergranular attack under certain conditions. In neutral atmospheres the alloy performs acceptably, but marine and chloride-containing environments accelerate localized corrosion mechanisms.

Stress corrosion cracking (SCC) is a notable concern for high-strength 7xxx alloys, and susceptibility increases with higher strength tempers like T6; overaging (e.g., T76) and controlled residual stress reduction can significantly reduce SCC risk. Protective strategies include cladding, anodizing, chromate conversion coatings, cathodic protection, and careful temper selection and post-forming stress relief.

Galvanic interaction against more noble materials (stainless steel, titanium) will cause accelerated anodic dissolution of 7079 in electrolytes; designers should isolate dissimilar metals or provide coatings and insulation to avoid galvanic corrosion. Comparatively, 7xxx alloys offer higher strength but worse corrosion behavior than 5xxx and many 6xxx alloys, which trade strength for improved corrosion resistance.

Fabrication Properties

Weldability

Welding 7079 is challenging: fusion welding (TIG/MIG) typically causes severe strength loss in the heat-affected zone and introduces risk of hot cracking and porosity. Filler selection is critical and welders often use Al–Si or Al–Mg fillers (e.g., 4043 or 5356 families) based on service requirements, but welded joints rarely approach the parent material strength, and post-weld age treatments seldom fully restore peak properties. Mechanical fastening, adhesive bonding, or friction stir welding are often preferred; friction stir welding yields superior joint properties and lower SCC susceptibility in many cases.

Machinability

Machinability of 7079 is moderate; peak-aged tempers can be harder on tools and produce shorter broken chips while annealed material machines more easily and produces long chips. Carbide tooling with positive rake geometry and high-pressure coolant is recommended to maintain tool life and surface finish, and feeds/speeds should be tuned to temper and section size. Surface residuals and trapped intermetallic particles influence finish and fatigue-critical components require careful post-machining stress-relief.

Formability

Forming is best performed in soft tempers (O or H1x) where elongation and bendability are maximized; T6 and T651 conditions have limited cold formability and require larger bend radii and special presses. Incremental forming, warm forming, or pre-annealing may be used to obtain complex shapes. Designers should adhere to minimum bend radii and avoid sharp features in T6 condition to prevent cracking; post-forming solution treatment and aging are options if geometry tolerances and distortion allowance permit.

Heat Treatment Behavior

As a heat-treatable alloy, 7079 responds strongly to solution treatment, quenching, and artificial aging cycles. Typical solution treatment temperatures lie in the 470–480 °C range, held long enough to homogenize solute-rich phases, and followed by rapid quenching to retain a supersaturated solid solution. The subsequent artificial aging at temperatures typically between 120–170 °C precipitates fine MgZn2 and Cu-containing phases for peak strength (T6).

Overaging cycles (e.g., T76) intentionally coarsen precipitates to improve resistance to stress corrosion cracking and exfoliation, albeit with a reduction in peak strength. T651 denotes that the material was solution treated, artificially aged to T6, and then stress relieved by stretching; stretching relieves quench-induced residual stresses and reduces distortion for precision parts.

High-Temperature Performance

7079 loses substantial strength as temperature increases; significant softening occurs above approximately 120–150 °C, and designers should limit continuous service temperatures accordingly. For short-term elevated-temperature exposures the alloy retains some load-bearing capability, but creep resistance is poor compared with high-temperature alloys and declines rapidly with temperature and stress.

Oxidation is generally controlled by aluminum’s native oxide, but high temperature exposure accelerates environmental attack and can aggravate grain-boundary related degradation. Heat-affected zones from welding can show localized property reductions and long-term stability issues if exposed to cyclic thermal or mechanical loading.

Applications

Industry	Example Component	Why 7079 Is Used
Aerospace	Fittings, brackets, critical fittings	High strength-to-weight, good fracture toughness when processed
Marine	Structural frames and spars	High static strength and ability to be overaged for SCC resistance
Automotive	High-performance chassis and suspension components	Weight savings with high yield strength for safety-critical parts
Defense	Weapon mounts, structural components	High strength and ballistic/impact resistance in engineered forms
Sporting Goods	Bicycle frames, high-performance components	Lightweight high-strength solution for competitive equipment

7079 is applied where designers need an optimized combination of high static strength and acceptable toughness with the option to tailor corrosion resistance via tempering and surface treatments. The alloy’s role is most pronounced in components where weight reduction cannot compromise structural integrity.

Selection Insights

7079 is a high-strength choice when yield and tensile performance are primary; expect trade-offs in corrosion resistance, weldability, and formability. Use annealed tempers for forming and peak-aged or overaged tempers for finished structural components, balancing SCC resistance against peak strength requirements.

Compared with commercially pure aluminum (1100), 7079 trades conductivity and formability for much higher strength and stiffness. Compared with work-hardened alloys such as 3003 or 5052, 7079 provides substantially higher static strength but generally worse corrosion performance and poorer cold formability. Compared with common heat-treatable alloys like 6061/6063, 7079 delivers higher peak strength but usually at higher cost, greater SCC susceptibility, and more restrictive welding and forming practices.

When selecting 7079, consider availability, cost of tempers and heat treatment cycles, and downstream fabrication needs; if ease of welding or superior corrosion resistance is required, a 6xxx or 5xxx alternative may be more appropriate. Use 7079 when structural demands and specific performance-per-weight requirements justify the additional processing and protective measures.

Closing Summary

7079 remains relevant as a specialist high-strength aluminum alloy that enables weight-critical structural designs where tensile and yield performance are paramount. Its value lies in the ability to tailor strength and corrosion resistance through temper selection and controlled heat treatment, making it a go-to alloy for demanding aerospace, defense, and high-performance engineering applications.