Aluminum 7015: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

Alloy 7015 is a member of the 7xxx series of aluminum alloys, a family dominated by zinc as the principal alloying element and typically augmented with magnesium and copper for precipitation strengthening. As a heat-treatable, precipitation-hardenable alloy, 7015 uses a Zn-Mg-Cu chemistry to achieve high strength through solution heat treatment, quenching and artificial aging rather than by cold work.

Key traits of 7015 include high tensile and yield strength, moderate-to-good fatigue properties when properly treated and inspected, and serviceable corrosion resistance that can be improved by overaging or cladding. The alloy is less weldable than most 5xxx and 6xxx alloys and requires careful thermal and mechanical control during fabrication; formability is adequate in annealed and certain H-tempers but reduces markedly in peak-aged tempers.

7015 finds use in aerospace structural components, high-strength fasteners, and applications where strength-to-weight is prioritized over raw corrosion resistance or maximum conductivity. Engineers select 7015 when a higher specific strength than 6061/6063 is required and when design life and stiffness benefit from a heat-treatable solution-aging route rather than work hardening.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High (18–30%)	Excellent	Excellent	Fully annealed, best for forming and machining
F	Very low–low	High	Excellent	Good	As fabricated, no controlled tempers
H12	Medium	Low–Medium (6–10%)	Fair	Limited	Partial strain-hardened, limited bendability
H14	Medium	Low (6–8%)	Fair	Limited	Light strain hardening for moderate strength increase
H114	Medium	Medium (8–12%)	Good	Limited	Stabilized temper for improved SCC resistance
T6	High	Low–Medium (6–10%)	Poor–Fair	Difficult	Peak-aged for maximum strength, susceptible to SCC
T651	High	Low–Medium (6–10%)	Poor–Fair	Difficult	Solution treated, stress-relieved by stretching, common aerospace temper
T73	Medium–High	Medium (8–12%)	Fair	Moderate	Overaged for improved corrosion and SCC resistance
T76 / T77	Medium	Medium (8–13%)	Fair	Moderate	Modified aging for better fracture toughness or stress corrosion behavior

Temper selection dominates final performance: T6/T651 tempers deliver maximum strength at the expense of ductility and susceptibility to stress-corrosion cracking, while overaged tempers (T73/T76) give up some peak strength to improve corrosion and SCC resistance. Cold work (H‑tempers) allows intermediate strength without full solution heat treatment but reduces formability and can leave heterogeneous properties through thickness.

Chemical Composition

Element	% Range	Notes
Si	≤ 0.40	Impurity; controlled to limit casting and grain boundary phases
Fe	≤ 0.50	Controlled to minimize intermetallics that reduce toughness
Cu	1.0–2.0	Contributes to strength and age-hardening kinetics; increases susceptibility to SCC
Mn	≤ 0.10	Minor; can modify grain structure and improve toughness slightly
Mg	1.6–2.6	Major strengthening element with Zn through MgZn2 precipitates
Zn	5.0–6.8	Principal strengthening element; controls peak-aged strength
Cr	0.05–0.25	Microalloying to control grain structure and recrystallization
Ti	≤ 0.10	Grain refiner in cast/extruded products
Others (Zr, V, trace)	≤ 0.20 combined	Microalloying additions to control recrystallization and improve fatigue life

The performance of 7015 is governed by the relative balance of Zn, Mg and Cu which determine the volume fraction, chemistry and coherency of strengthening precipitates after aging. Minor additions such as Cr, Zr or Ti act to control recrystallization and grain size during thermomechanical processing, improving toughness and reducing exfoliation or intergranular corrosion tendencies.

Mechanical Properties

In tensile behavior, 7015 in peak-aged conditions (T6/T651) exhibits high ultimate and yield strengths comparable with other high-strength 7xxx-series alloys, showing relatively linear-elastic response up to yield and limited uniform elongation prior to plastic flow. Annealed (O) condition displays much lower strength but substantially higher ductility, making it useful for cold forming or deep drawing prior to final heat treatment.

Hardness follows the same trend as tensile properties, with Brinell or Vickers hardness values rising sharply after aging and peaking in the T6 condition; hardness data must be interpreted in conjunction with temper, thickness and specific heat-treatment schedule. Fatigue behavior is generally favorable for a high-strength aluminum if surface finish is controlled and corrosion is mitigated; however, fatigue and fracture toughness deteriorate with increasing strength and with the presence of stress-corrosion pits or intermetallic inclusions.

Thickness has a strong effect on attainable properties because solution heat treatment and quenching effectiveness drop off with plate thickness; thick sections are more difficult to quench uniformly and can show lower yield and tensile strengths as a result. Residual stresses from quenching and subsequent straightening or stretch relief (T651) also impact dimensional stability and fatigue life in structural applications.

Property	O/Annealed	Key Temper (e.g., T6/T651)	Notes
Tensile Strength	230–320 MPa (typical)	520–570 MPa (typical)	Values vary with thickness and aging; T6 gives peak strength
Yield Strength	110–200 MPa (typical)	470–520 MPa (typical)	Yield increases markedly after solution and aging
Elongation	18–30%	6–10%	Elongation decreases as strength increases; depends on temper and thickness
Hardness	60–90 HB	140–160 HB	Approximate Brinell ranges, dependent on heat treatment and microstructure

Physical Properties

Property	Value	Notes
Density	≈ 2.80 g/cm³	Slightly higher than pure Al due to alloying elements
Melting Range	≈ 475–635 °C	Solidus and liquidus vary with composition and impurities
Thermal Conductivity	≈ 120–140 W/(m·K)	Lower than pure Al; depends on temper and cold work
Electrical Conductivity	≈ 30–40 %IACS	Reduced relative to pure aluminum due to alloying; varies with temper
Specific Heat	≈ 880–910 J/(kg·K)	Typical for aluminum alloys near room temperature
Thermal Expansion	≈ 23–25 µm/(m·K)	Comparable across Al alloys; important for thermal cycling design

These physical properties underline trade-offs in thermal management and joining: thermal conductivity remains sufficient for many heat-sinking roles but is lower than pure aluminum and some 6xxx alloys. Electrical conductivity is reduced by alloying and should be considered when 7015 is selected for electrical applications or where contact resistance matters.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.5–6 mm	Uniform through-thickness up to moderate gauges	O, H1x, T6, T73	Common for lightweight panels and aerospace skins; limited deep drawability in T6
Plate	6–200+ mm	Strength can drop with increasing thickness due to quench limits	O, T6, T651, T73	Thick plate requires controlled quenching and often T73 for corrosion-critical parts
Extrusion	Wall thicknesses variable	Directional properties; strength depends on heat treatment	O, T6, T651	Complex profiles possible but quench sensitivity limits very large cross-sections
Tube	0.5–20 mm wall	Good longitudinal strength; ends and joints require careful heat treatment	O, T6	Used for high-strength structural tubing after appropriate heat treatment
Bar/Rod	6–200 mm diam.	Homogeneous if processed and solution treated correctly	O, T6, T651	Used for fittings, fasteners, and machined components

Processing differences substantially affect final properties: sheet and thin extrusions are easier to quench and age to peak strength, while thick plate and large sections often require special heat sinks or overaging to ensure dimensional stability and corrosion resistance. Applications vary with form factor: extrusions for complex profiles, plate for structural components, and bar for machined high-strength parts.

Equivalent Grades

Standard	Grade	Region	Notes
AA	7015	USA	American Aluminum Association designation commonly used in aerospace specs
EN AW	7015	Europe	European EN standard designation often paired with specific temper suffixes
JIS	A7015 (approx.)	Japan	Japanese standards may reference similar Zn-Mg-Cu alloys with local temper codes
GB/T	7015 (approx.)	China	Chinese standard equivalents exist but chemistry/tolerances can vary by mill

Subtle differences between regional specifications usually concern permitted impurity levels, exact ranges for Zn/Mg/Cu and the allowed microalloy additions (Zr/Cr/Ti), plus defined mechanical property limits at specific thicknesses. When substituting a grade from another region, engineers must compare the detailed chemical and mechanical tables, aging practices and certification requirements rather than relying solely on the designation.

Corrosion Resistance

Atmospheric corrosion resistance for 7015 is moderate; in benign environments the alloy performs acceptably, but in chloride-containing or marine atmospheres it is more susceptible to pitting and intergranular corrosion than most 5xxx or 6xxx series alloys. Protective measures such as anodizing, cladding with pure aluminum, chromate conversion coatings or use of overaged tempers (T73/T76) markedly improve surface durability.

Stress corrosion cracking (SCC) is a critical consideration for 7015 in highly stressed, corrosive service when in peak-aged tempers (T6/T651), because the combination of high strength and certain grain-boundary precipitate conditions promotes SCC initiation. Overaged tempers and controlled thermomechanical processing reduce SCC susceptibility by coarsening or redistributing precipitates and reducing internal stresses.

Galvanic interactions are typical for aluminum alloys: 7015 is anodic to stainless steels and some copper-based alloys, so isolation or sacrificial protection is recommended in mixed-metal assemblies. Compared with 5xxx work-hardened alloys (e.g., 5052), 7015 yields higher strength but typically worse corrosion performance unless appropriately protected or overaged.

Fabrication Properties

Weldability

Welding 7015 is challenging due to its high zinc/magnesium content and precipitation-hardening nature; fusion welding (TIG/MIG) often causes loss of temper in the HAZ and a softened zone that can drop strength significantly. Recommended practices include using specialized fillers with compatible chemistry, applying post-weld solution treatment and aging if feasible, or preferring mechanical fasteners and adhesive bonding for critical structures. Hot-cracking and porosity risk are elevated in thick sections and when contamination or improper heat inputs occur.

Machinability

Machinability of 7015 in the annealed state is good to very good, with stable chip formation and favorable cutting forces; in peak-aged tempers machinability worsens and tool wear increases. Carbide tooling and rigid setups are recommended, with moderate to high cutting speeds for finishing and lower speeds for heavy stock removal. Surface finish and fatigue-critical features should be machined in controlled tempers to avoid inducing residual damage.

Formability

Forming is easiest in O and some H1x tempers where ductility is high and bend radii can be tight; in peak-aged T6 conditions formability is poor and springback is significant. Typical recommended minimum bend radii for T6 condition are 2–4× thickness for simple bends, with smaller radii possible in O or H14 tempers; warm forming or solution-treat-and-age cycles are used to form complex shapes before final aging. Designers should plan forming before final heat treatment or use post-forming stabilization treatments to control distortions.

Heat Treatment Behavior

7015 is a classic heat-treatable alloy that responds strongly to solution heat treatment followed by rapid quench and artificial aging. Typical solution treatment temperatures range from about 470–480 °C to dissolve the primary alloying elements into a supersaturated matrix; rapid quenching (water quench) is required to retain a supersaturated solid solution.

Artificial aging schedules vary depending on targeted properties: T6 typically uses lower-temperature aging (e.g., 120–145 °C) for several hours to achieve peak strength, while T73/T76 overaging uses higher temperatures or longer times to coarsen precipitates and improve corrosion/SCC resistance. Transitioning between tempers requires controlled cooling, possible straightening/stretching (T651), and precise process control to achieve repeatable mechanical properties.

For completeness, non-heat-treatable behavior is limited because 7015 is primarily designed for precipitation hardening; work hardening can provide modest strength increases but cannot match the benefits of solution and aging. Annealing (O) fully softens the material and is used for forming or machining prior to final heat treatment.

High-Temperature Performance

At elevated temperatures 7015 exhibits a significant reduction in yield and tensile strength, with useful structural performance typically limited to temperatures below approximately 120–150 °C. Creep resistance is limited compared with high-temperature alloys; sustained loads at elevated temperatures accelerate overaging and precipitate coarsening, reducing both strength and fatigue life.

Oxidation of aluminum at these service temperatures is generally self-limiting due to protective oxide formation, but high-temperature environments that are chemically aggressive or contain chlorides can accelerate corrosion of both bulk material and protective coatings. The HAZ in welded parts is especially vulnerable to strength loss and microstructural change under subsequent thermal exposure.

Applications

Industry	Example Component	Why 7015 Is Used
Aerospace	Fuselage and wing fittings, structural forgings	High specific strength and fatigue performance after appropriate tempers
Marine	High-strength structural members, fittings	Good damage tolerance when overaged and coated; strength-to-weight benefits
Defense	Armor components, weapon mounts	High strength and stiffness with relatively low density
Automotive	High-performance chassis components	Offers weight savings where strength is paramount and low-volume manufacturing is feasible
Electronics	Structural frames, heat spreaders (limited)	Thermal conductivity adequate and stiffness useful in compact assemblies

7015 is chosen when designers need an alloy that combines aerospace-grade specific strength with acceptable fatigue performance and the ability to be tailored through aging to favor strength or corrosion resistance. Its processing complexity and cost usually confine use to applications where those properties justify tighter manufacturing control.

Selection Insights

Choose 7015 when high strength-to-weight ratio and controlled fatigue performance are higher priority than ease of welding or peak corrosion resistance. It is appropriate for aerospace and high-performance structural parts where thermomechanical processing and post-weld heat treatment can be applied.

Compared with commercially pure aluminum (e.g., 1100), 7015 trades conductivity and formability for substantially higher strength and stiffness, making it unsuitable where electrical conductivity or extreme formability are primary requirements. Compared with work-hardened alloys such as 3003 or 5052, 7015 offers much higher strength but generally worse forming in peak tempers and requires aging control; it also tends to be more sensitive to chloride-induced corrosion. Compared with common heat-treatable alloys like 6061 or 6063, 7015 delivers higher peak strength and stiffness, but often at increased cost, lower weldability and higher SCC risk; select 7015 when those extra strength margins and fatigue characteristics are decisive despite trade-offs.

Closing Summary

Alloy 7015 remains a relevant high-strength aluminum solution where aerospace-grade specific strength and fatigue performance are required and where manufacturing routes can control heat treatment and surface protection. Its chemistry and temper flexibility allow engineers to tune strength versus corrosion resistance, making it a specialist material for demanding structural applications.