Aluminum 7072: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

Alloy 7072 belongs to the 7xxx series family of aluminum alloys and is best described as an aluminum–zinc-bearing cladding alloy developed to provide enhanced corrosion protection for high-strength 7xxx series substrates. Unlike the primary structural 7xxx alloys (such as 7075), 7072 is produced with a chemistry tuned for surface corrosion resistance and workability rather than for high bulk strength.

The major alloying element in 7072 is zinc at modest levels, with the remainder being essentially commercially pure aluminum and trace additions of elements such as silicon, iron and small residuals of magnesium and copper. The alloy is not designed for precipitation hardening of the substrate; 7072 is effectively non-heat-treatable in the sense of developing significant age-hardening response and instead relies on metallurgical purity and cold-workable tempers to control mechanical behavior.

Key traits of 7072 include excellent atmospheric and marine corrosion resistance when used as a cladding layer, high formability in annealed condition, very good surface finish and brazeability, and generally excellent weldability as aluminum metal; however, it delivers relatively low intrinsic tensile strength compared with structural heat-treatable alloys. Typical industries and product sectors include aerospace cladding for structural 7xxx-series plates and sheets, marine and coastal structural panels, architectural claddings, and certain electrical and thermal applications where a clean aluminum surface is required.

Engineers choose 7072 primarily where corrosion protection of a high-strength substrate is required without significantly altering the core alloy’s mechanical response; it is selected over other cladding or coating approaches because it metallurgically bonds well to 7xxx-series cores, preserves fatigue performance better than many organic coatings, and provides a ductile, sacrificial surface layer that resists pitting and exfoliation.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High (>20%)	Excellent	Excellent	Fully annealed, maximum ductility for cladding and forming
H12	Low–Medium	Moderate (10–18%)	Very Good	Very Good	Light cold work; retains good formability for complex shapes
H14	Medium	Moderate (8–15%)	Good	Very Good	Typical commercial cold-worked temper for clad sheets
H18	Medium–High	Lower (5–10%)	Fair	Good	Higher strength from cold work, reduced formability
H24	Medium	Moderate	Good	Good	Stabilized hard temper through partial anneal after work
T6	Not applicable	N/A	Poor	N/A	7072 is not a precipitation-hardening alloy; T6 not generally used

7072 tempering is dominated by anneal and strain-hardening routes rather than age-hardening cycles. The O temper offers the best formability and is the most common for cladding operations, while H-series tempers are used where some strengthening of the cladding is desired at the expense of ductility.

In practice the cladding thickness and core alloy temper interact: thin clad layers in O condition provide excellent conformability during downstream forming of 7xxx cores, whereas harder H tempers can reduce surface fracture risk during rolling and handling but may reduce the sacrificial corrosion-protection effectiveness.

Chemical Composition

Element	% Range	Notes
Si	≤ 0.25	Impurity; controls casting/rolling behavior and inclusions
Fe	≤ 0.40	Residual; affects grain structure and dispersoids
Cu	≤ 0.05	Kept low to avoid localized anodic activity with cladding
Mn	≤ 0.10	Minor impurity; influences grain refinement slightly
Mg	≤ 0.15	Very low; not intended to provide age-hardening
Zn	0.6–1.3	Primary purposeful alloying element to adjust corrosion behavior
Cr	≤ 0.05	Trace; limits recrystallization in some tempers
Ti	≤ 0.05	Grain refiner additions possible in cast products
Others	Balance Al, each ≤ 0.05 total	Residual and trace elements per specification

The composition of 7072 centers on achieving a high-purity aluminum matrix with a controlled zinc content sufficient to alter surface electrochemistry yet low enough to avoid significant age-hardening or hydrogen embrittlement. Trace iron and silicon are managed to reduce coarse intermetallics that would degrade surface quality and fatigue life.

Because the alloy is used primarily as a sacrificial or protective cladding, its chemistry is optimized to form a stable, adherent oxide and to minimize galvanic potential differences with common cores; minimal copper and magnesium help avoid creating local anodic/cathodic couples that would accelerate corrosion.

Mechanical Properties

As a cladding alloy 7072 exhibits tensile and yield strengths closer to commercially pure aluminum than to structural 7xxx alloys; its tensile curve is characterized by low yield, modest ultimate tensile strength, and good uniform elongation in annealed condition. The O temper typically shows the highest ductility and lowest yield, making it suitable for severe forming operations. Cold-working to H tempers increases yield and tensile values through strain hardening while reducing elongation and notch toughness modestly.

Hardness of 7072 is low in O and rises with H-series cold work; typical Vickers or Rockwell readings are within the range of soft aluminum alloys and are not comparable to the high values seen in heat-treated aerospace aluminums. Fatigue performance for 7072 as a thin cladding depends heavily on substrate condition and effective bonding; a ductile, well-bonded cladding can improve initiation resistance for pitting-driven fatigue but contributes little to bulk load-carrying. Thickness of the cladding layer controls its mechanical contribution: thin foils provide surface protection with negligible strength effect, while heavier coatings can slightly raise section stiffness but will still be mechanically subordinate to core alloys.

Property	O/Annealed	Key Temper (H14)	Notes
Tensile Strength	60–120 MPa	90–150 MPa	Tensile increases with cold work; values depend on thickness and processing
Yield Strength	25–50 MPa	55–95 MPa	Low yield in O; H tempers approach mid-range Al yields
Elongation	20–35%	8–18%	Annealed condition gives high uniform elongation for forming
Hardness	25–40 HV	35–55 HV	Low absolute hardness compared with structural heat-treated alloys

Physical Properties

Property	Value	Notes
Density	2.70 g/cm³	Typical for aluminum alloys; useful for weight calculations
Melting Range	643–658 °C	Narrow melting interval; solidus close to pure Al
Thermal Conductivity	~210 W/m·K	Slightly below pure Al due to alloying; high for heat-sinking
Electrical Conductivity	~30–40 % IACS	Lower than pure Al owing to Zn and residual impurities
Specific Heat	~900 J/kg·K	Typical for aluminum alloys across moderate temperature ranges
Thermal Expansion	23.5–24.5 µm/m·K	Coefficient of thermal expansion similar to other Al alloys

The physical property set confirms 7072’s suitability where a light, conductive, and thermally compliant surface is desirable; the conductivity values permit its use in heat-transfer and electrical contact applications where the cladding also must protect against corrosion. Thermal expansion closely matches common aluminum core alloys, minimizing thermally induced interface stresses during service and thermal cycling.

The melting and thermal conductivity figures are relevant to processing: forging, brazing and welding behaviors are influenced by the relatively high thermal conductivity and the narrow melting range that is close to pure aluminum.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.1–5.0 mm	Thin, low-strength surface layer	O, H14, H18	Most common format for cladding of 7xxx series sheet and plate
Plate	5–50 mm (clad thickness 0.05–0.5 mm)	Surface protection; minimal core strength effect	O, H12	Used as cladding on structural plates in aerospace
Extrusion	Limited use, small sections	Lower structural contribution	O, H14	Rare; available for specialized profiles and overlays
Tube	Thin-wall clad tube	Surface-corrosion protection	O	Specialty applications for corrosion-resistant conduit
Bar/Rod	Small diameters	Low bulk strength	O, H14	Typically in metallurgical or brazing stock forms

Sheets and thin plates are the dominant commercial forms for 7072 because the alloy’s primary role is surface protection rather than bulk structure. Cladding is typically produced by roll bonding, hot rolling or continuous casting onto a 7xxx-series core; the interface metallurgical bond quality is a critical parameter controlled by temperature, reduction, and surface condition.

Extrusions and bar/rod forms are uncommon and generally reserved for specialty applications that require a corrosion-resistant surface on small profiles; these products are produced with controlled chemistries and tempers to maintain ductility for forming and joining.

Equivalent Grades

Standard	Grade	Region	Notes
AA	7072	USA	Recognized aluminum association designation for cladding alloy
EN AW	7072	Europe	EN AW-7072 used in European trade and standards for cladding
JIS	A7072	Japan	Japanese standard designation generally aligns chemistry and usage
GB/T	7072	China	Chinese standard often used for cladding and surface alloys

Equivalent designations across standards are largely consistent because 7072’s use as a cladding alloy imposes narrow compositional and processing requirements. Differences that do exist are typically in maximum impurity limits, surface quality specification, or permitted cladding thickness ranges rather than fundamental metallurgy.

When sourcing from different regions it is important to compare the specific standard’s tolerances for elements such as iron and silicon, and to confirm approval for bondability and cladding thickness if the material will be roll-bonded to a structural core.

Corrosion Resistance

7072 provides excellent atmospheric corrosion resistance and is often selected specifically for its ability to form a tenacious oxide film that resists pitting and general corrosion in both rural and marine atmospheres. When used as a cladding layer on high-strength 7xxx substrates it acts sacrificially and delays exfoliation and intergranular attack in aggressive environments. Surface continuity and absence of through-thickness defects are critical; any breaches in the cladding will expose the substrate and can lead to localized accelerated attack.

In marine environments 7072 performs well as the exposed surface layer, offering good resistance to salt-spray and cyclic wetting that would otherwise accelerate anodic dissolution of high-strength cores. Galvanic interactions between 7072 and common cores are generally favorable because the cladding is intended to be slightly anodic relative to the core, protecting the substrate; however, designers must still consider fasteners, mating materials and crevice conditions that can localize corrosion.

Stress-corrosion cracking (SCC) risk for 7072 itself is negligible because its strength is low; the primary SCC concern is the underlying 7xxx-series substrate, and a continuous 7072 cladding can significantly reduce the susceptibility of high-strength cores by controlling surface chemistry and hindering wetting of intermetallic-rich grain boundaries. Compared to 5xxx and 6xxx family alloys, 7072 provides superior sacrificial protection when paired with 7xxx cores but does not confer the mechanical advantages of those families.

Fabrication Properties

Weldability

7072 welds readily as an aluminum alloy, but welding must consider the thin cladding layer and potential dilution with substrate material when used as a clad system. In fusion welding of clad/substrate combinations, filler alloys such as 4043 or 5356 are commonly used depending on required ductility and corrosion resistance; selection should minimize galvanic mismatch and avoid introducing brittle intermetallics. Hot-cracking risk is low for 7072 alone but increases when welding high-strength 7xxx cores due to their susceptibility; proper welding procedures and post-weld treatments for the core may be necessary to restore resistance.

Machinability

Machining of 7072 is similar to commercially pure aluminum; the alloy machines easily with good chip formation and low cutting forces, though its ductility can produce long, continuous chips in soft tempers. Recommended tooling is carbide or high-speed steel with moderately high cutting speeds and positive rake geometries; coolant is typically used to control built-up edge and to maintain surface finish. The machinability index is modest relative to free-cutting aluminum alloys that contain lead or bismuth; 7072 is preferred where surface integrity and corrosion resistance are priorities over maximum material removal rates.

Formability

Formability of 7072 in O temper is excellent, enabling deep drawing, bending and complex stamping with small bend radii when appropriate lubrication and tool radii are used. Bend radius recommendations typically mirror those for soft aluminum sheet—minimum inside radii on the order of 0.5–1.0× thickness for many operations—while higher H tempers require larger radii and may need intermediate anneals to avoid surface cracking. Cold-work response is predictable: ductility diminishes with accumulated strain and the alloy can be re-annealed to restore formability for multi-stage forming sequences.

Heat Treatment Behavior

7072 is effectively non-heat-treatable for precipitation hardening purposes; attempts to apply typical solution-and-aging cycles used for 7xxx structural alloys will not develop significant age-hardening because the alloy chemistry lacks sufficient magnesium and copper. Solution treatment is therefore not a productive route for strengthening 7072 and can risk distortion or excessive grain growth without benefit. Artificial aging transitions (T tempers) are not standard for 7072 and the alloy is normally controlled via mechanical temper (H) and anneal (O) cycles.

Work-hardening and annealing are the principal metallurgical controls: cold working increases strength and hardness through dislocation accumulation while annealing at appropriate temperatures (typically in the range used for commercial pure Al anneals) reduces hardness and restores ductility. For clad products, annealing schedules must be coordinated with the substrate to avoid compromising the structural core’s temper or mechanical properties.

High-Temperature Performance

7072 loses strength rapidly with increasing temperature, similarly to other low-alloyed aluminum products, and should not be used for load-bearing applications above approximately 150–200 °C for extended periods. Oxidation of aluminum at elevated temperatures is generally limited to the formation of a protective oxide, but prolonged high-temperature exposure can change surface appearance and can alter mechanical bonding to certain substrates. The heat-affected zone (HAZ) during welding of clad-to-core systems can locally soften or embrittle substrate material depending on the core composition; 7072 itself does not retain significant elevated-temperature strength and cannot protect a core subjected to high thermal loads.

Designs requiring sustained elevated-temperature performance should consider alternative alloys or protective systems; where brief thermal excursions occur, 7072 will retain dimensional stability and protective characteristics but will not provide mechanical reinforcement.

Applications

Industry	Example Component	Why 7072 Is Used
Aerospace	Clad skins and aluminum plate for fuselage and wing panels	Provides sacrificial corrosion protection and maintains surface quality for high-strength cores
Marine	Deck panels, superstructure cladding	Excellent atmospheric and salt-spray resistance for exposed surfaces
Aerospace/Defense	Fittings and thin overlays	Good formability and bonding for precision-shaped protective layers
Electronics	Heat spreader faces, enclosures	High thermal conductivity and corrosion-resistant finish
Architecture	Facade panels and louvers	Durable appearance with good metalworking properties

7072 is favored where a high-quality aluminum surface is required atop a strong structural substrate: it is the classic cladding choice for protecting 7xxx-series aerospace plates and for marine or architectural panels where both appearance and corrosion resistance are critical. In many cases the thin protective layer allows designers to exploit the strength of a 7xxx core while mitigating environmental degradation without adding significant weight or changing the jointing strategy.

Selection Insights

Use 7072 when the principal design objective is corrosion protection of a high-strength substrate combined with good formability and surface finish. It is particularly appropriate for aerospace and marine systems where maintaining fatigue life and avoiding pitting are priorities, and where metallurgical bonding to a 7xxx core is required. Cost and availability are typically favorable because production is concentrated on sheet and clad-plate forms for established supply chains.

Compared with commercially pure aluminum (1100), 7072 sacrifices some electrical conductivity and absolute formability in exchange for improved corrosion resistance and better compatibility as a cladding for 7xxx cores; 1100 may be chosen when maximum conductivity or deep drawability is the overriding requirement. Compared with work-hardened alloys such as 3003 or 5052, 7072 sits lower in intrinsic mechanical strength but offers superior sacrificial protection when used as a cladding on high-strength substrates; choose 3003/5052 when higher bulk strength or specific forming behaviors dominate. Compared with heat-treatable structural alloys like 6061/6063, 7072 cannot match peak strength, but it is selected when surface corrosion protection and metallurgical compatibility with 7xxx cores are the decisive factors rather than maximum tensile performance.

Closing Summary

Alloy 7072 remains a specialized but essential material in modern engineering where protective, ductile aluminum cladding is required to preserve the performance of high-strength substrates. Its combination of good formability, excellent corrosion resistance, and compatibility with 7xxx-series cores keeps it relevant in aerospace, marine and architectural applications where surface integrity and fatigue protection are critical.