Aluminum 7055: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

7055 is a 7xxx series aluminum alloy, placing it squarely in the high-strength Al-Zn-Mg-Cu family that is widely used in aerospace applications. The alloy is deliberately formulated with high zinc and magnesium levels plus copper and microalloying elements to enable precipitation strengthening via heat treatment rather than by work-hardening.

Major alloying elements include zinc (primary strength contributor), magnesium and copper (promote formation of MgZn2 and other strengthening precipitates), and microalloying with zirconium and/or chromium for grain structure control. Strengthening is achieved through solution heat treatment, rapid quenching, and controlled artificial aging to precipitate fine, coherent intermetallic phases that provide high yield and tensile strength.

Key traits include very high static strength and good fracture toughness for a 7xxx alloy, with moderate corrosion resistance that can be improved by overaging and microalloying. Weldability is limited with traditional fusion welding methods, formability is moderate to poor in peak-aged tempers, and machinability is fair when using carbide tooling and optimized feeds/speeds.

Typical industries are aerospace primary and secondary structures, high-performance sporting goods, and specialized structural components where weight-critical strength is paramount. Engineers choose 7055 over other alloys when the design demands the highest specific strength combined with reasonable toughness and a controlled balance of corrosion resistance through proper temper selection.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High (20–30%)	Excellent	Excellent	Fully annealed, best for forming and joining prior to heat treatment
H14	Medium	Moderate (10–18%)	Good	Poor (in HL states)	Strain-hardened variant for moderate strength and improved form stability
T5	Medium-High	Moderate (8–15%)	Fair	Poor	Cooled from elevated temperature and artificially aged; fast processing option
T6	High	Low (5–12%)	Limited	Poor	Peak artificial aging for maximum strength; reduced ductility and formability
T7 (e.g., T76)	Medium-High	Moderate (8–14%)	Better than T6	Poor	Overaged/controlled aging for improved SCC resistance and dimensional stability
T7451 / T7452	High	Low-Moderate (6–12%)	Limited	Poor	Stress-relieved and artificially aged variants optimized for aerospace forgings and plates

Temper significantly alters the balance between strength, ductility, and corrosion performance. Annealed (O) material provides the best formability and is commonly used for complex shaping before final precipitation heat treatment, while T6 delivers the highest static strength at the expense of elongation and bendability.

Overaging variants such as T7 and stabilized tempers like T7451 are used to trade a small amount of peak strength for improved resistance to stress-corrosion cracking and better in-service dimensional stability; these tempers are common for structural aerospace components where long-term durability is key.

Chemical Composition

Element	% Range	Notes
Si	0.4 max	Impurity; controls casting/processing behavior
Fe	0.5 max	Intermetallic-former; excess reduces toughness
Mn	0.05–0.3	Minor; aids grain structure when present
Mg	2.3–2.9	Works with Zn to form strengthening precipitates
Cu	1.9–2.6	Boosts strength and fracture toughness; worsens SCC if not controlled
Zn	7.3–8.4	Primary strengthening element in 7xxx alloys
Cr	0.04–0.2	Grain structure control and recrystallization inhibitor
Ti	0.02–0.12	Grain refiner for cast/forged feedstock
Others (Zr, traces)	0.08–0.25 (Zr typical)	Microalloying for dispersoid control and toughness; balance Al

The high zinc content combined with magnesium and copper produces the fine, metastable MgZn2 and related precipitates responsible for the alloy’s very high strength after solution treatment and aging. Microalloying with zirconium/chromium controls recrystallization and grain size, improving toughness and enabling thicker sections to be produced with acceptable properties. Trace impurities like iron and silicon are kept low to avoid coarse intermetallics that reduce fatigue life and formability.

Mechanical Properties

7055 exhibits marked contrasts between annealed and peak-aged conditions: in O-temper it is ductile and easy to form, while in T6/T7451 tempers it achieves some of the highest tensile and yield strengths available in wrought aluminum alloys. Yield and tensile strengths increase dramatically during artificial aging as coherent precipitates nucleate and grow; however, elongation and notch toughness trade off against that peak strength. Fatigue behavior is strongly influenced by microstructure, cold work, and surface condition, with small intermetallic particles or machining damage acting as crack initiation sites.

Thickness and quench rate also influence mechanical response significantly; thicker sections are more prone to residual soft zones and require microalloying and process controls to maintain uniform properties. Hardness correlates closely with tensile properties and will typically drop in the weld heat-affected zone or after overaging. Designers must balance temper selection, part geometry, and post-processing to achieve required static and cyclic performance.

Property	O/Annealed	Key Temper (T6 / T7451)	Notes
Tensile Strength	220–280 MPa	540–640 MPa	Peak-aged strengths depend on section thickness and precise tempers; values are typical for sheet/plate
Yield Strength	100–170 MPa	470–580 MPa	High yield in peak tempers makes 7055 attractive for highly stressed components
Elongation	20–30%	6–12%	Ductility drops with increasing strength and aging intensity
Hardness	40–70 HB	140–180 HB	Brinell hardness increases with precipitation; HAZ softening occurs with fusion welding

Physical Properties

Property	Value	Notes
Density	~2.81 g/cm³	Typical for high-strength aluminum alloys; contributes to excellent specific strength
Melting Range	Solidus ~475–500°C; Liquidus up to ~640–650°C	Alloying lowers the melting interval compared with pure Al; consult supplier data for precise numbers
Thermal Conductivity	~120–140 W/m·K	Lower than pure Al but acceptable for many structural and thermal management roles
Electrical Conductivity	~30–36 %IACS	Significantly reduced relative to pure Al due to alloying additions
Specific Heat	~0.96 J/g·K (960 J/kg·K)	Typical aluminum-range value; affects thermal soak and quench behavior
Thermal Expansion	~23–24 ×10⁻⁶ K⁻¹	Similar to other aluminum alloys; consider in multi-material assemblies

The density and thermal properties give 7055 an attractive strength-to-weight ratio and reasonable thermal management capabilities for structural parts. Thermal conductivity and electrical conductivity are reduced relative to pure aluminum and to lower-alloyed families, so designers should not select 7055 for primary heat-sink applications without confirming thermal requirements.

Specific heat and expansion characteristics influence heat-treatment scheduling and dimensional control; quenching from solution temperature requires rapid heat extraction to develop desired precipitation states, and residual thermal gradients can induce distortion in complex parts.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.5–6 mm	Responds well to aging; thin sections reach peak more uniformly	O, T6, T7451	Used for skin panels, stiffened components after aging
Plate	>6 mm up to ~200 mm	Thicker sections require microalloying and tailored quench to avoid soft cores	T6, T7451, T7	Aerospace forgings and machined structural parts often use plate
Extrusion	Complex cross-sections, varying lengths	Properties depend on extrusion ratio and subsequent heat treatment	O, T6	Extruded shapes allow integrated stiffeners but require precise aging
Tube	OD/ID per spec; thin- to thick-walled	Geometry affects quench uniformity and mechanical property gradients	O, T6	Used for high-strength structural tubing where weight saving is critical
Bar/Rod	Diameters up to forgings	Machinable in various tempers; forged bar feeds large parts	O, T6, T7451	Used for fittings, pins, and machined structural components

Processing differences (rolling, forging, extrusion) change as-received microstructures and the alloy’s response to solution and aging steps. Sheets and thin extrusions quench quickly and achieve uniform precipitation, while thick plates need controlled quench paths, microalloying (Zr/Cr), or furnace homogenization to avoid soft interior zones. Applications are selected by form based on achievable tolerances, required mechanical gradients, and downstream machining or forming operations.

Equivalent Grades

Standard	Grade	Region	Notes
AA	7055	USA	Common UNS designation A97055 for wrought 7055 products
EN AW	7055	Europe	EN AW-7055 is commonly used but exact chemical limits and temper codes may differ slightly
JIS	A97055 / Comparable	Japan	Local standards often list a comparable composition rather than identical designation
GB/T	7055	China	Chinese standard grades generally follow similar chemistries but processing variants and tolerances differ

Equivalent grade labels vary by standards body and sometimes by supplier processing history; chemistries are similar but tolerances, allowable impurities, and specified mechanical values can differ. Users should always check the specific mill certificate, temper code, and specification (e.g., AMS, ASTM, EN) for the lot being purchased, especially for critical aerospace or fatigue-prone components.

Corrosion Resistance

7055, as a 7xxx-series alloy, is more susceptible to localized corrosion and stress-corrosion cracking (SCC) than 5xxx and 6xxx families in naturally aged or peak-aged conditions. Overaging and temper choices such as T7, plus microalloying like Zr, are commonly used to improve SCC resistance and to stabilize the grain-boundary precipitate structure for long-term service in aggressive environments.

In atmospheric and mildly marine environments, properly overaged and coated 7055 demonstrates acceptable behavior; however, direct saltwater immersion or splash-zone exposure requires corrosion protection strategies such as anodizing, conversion coatings, and sealants. Galvanic interactions are a concern when mating 7055 to dissimilar metals; anodized layers and isolation methods are recommended to prevent accelerated local corrosion.

Compared to 6xxx alloys (e.g., 6061), 7055 offers higher strength but generally lower inherent corrosion resistance, requiring additional surface treatment or temper selection. Compared to 7075, 7055 is often formulated to provide a better balance of fracture toughness and SCC resistance, but both families need prudent corrosion mitigation in marine or high-humidity applications.

Fabrication Properties

Weldability

Conventional fusion welding of 7055 typically results in significant loss of mechanical properties in the fusion zone and HAZ because the precipitate structure is destroyed and re-precipitation is difficult to recover fully by localized heat input. Friction stir welding is the preferred joining technique for structural applications, producing refined microstructures and improved retention of strength when post-weld aging is applied. When fusion welding is unavoidable, extensive post-weld heat treatment and the correct filler or interlayer strategy are required; however, many aerospace specifications avoid fusion welds in critical 7055 components.

Machinability

Machinability of 7055 is moderate; the alloy machines better than some high-copper alloys but worse than more ductile 6xxx family alloys. Carbide tooling with rigid setups and high positive rake geometry are recommended, along with high-pressure coolant to control chip formation and heat. Typical chip behavior ranges from short segmented to long continuous depending on feed and temper; optimized feeds and speeds reduce tool wear and improve surface integrity for fatigue-critical parts.

Formability

Forming is best performed in annealed (O) or light work-hardened tempers; peak-aged tempers such as T6 have limited ductility and are prone to cracking during bending or stretch forming. Minimum bend radii are generally larger than for 5xxx/6xxx alloys; a conservative rule of thumb is a minimum inside radius of 3–4× thickness for annealed material, increasing for stronger tempers. Warm forming and subsequent solution treatment/ageing can be used to produce complex shapes while retaining high final properties.

Heat Treatment Behavior

7055 is a heat-treatable alloy that follows the classic solution-treatment and aging pathway: solution treat at typical temperatures near 470–485°C to dissolve soluble phases, followed by rapid quench to retain solute in a supersaturated solid solution. Artificial aging (e.g., T6: ~120–130°C for several hours) nucleates fine Mg-Zn precipitates that drive strength to peak levels. Overaging treatments (T7 variants) at higher temperatures or longer times coarsen precipitates to improve stress-corrosion resistance and toughness at a modest strength cost.

Temper transitions such as T6 → T7 are used deliberately to enhance long-term service behavior; likewise, stabilized tempers like T7451 incorporate a stress-relief step and controlled aging to meet dimensional stability and fracture toughness requirements for aerospace forgings and thick plates. Precise soak times, quench medium, and aging cycles must be tailored to section size and intended microstructure and are typically specified in supplier and industry heat-treatment standards.

High-Temperature Performance

7055 loses significant strength as temperature rises; above roughly 120–150°C the precipitate structure that provides peak strength begins to coarsen and properties degrade. Long-term exposure above ~150°C accelerates overaging and should be avoided for structural applications that require high static strength. Oxidation is moderate and typical of aluminum alloys; protective coatings or anodizing can mitigate surface oxidation for elevated-temperature exposure.

The heat-affected zones from welding show locally reduced strength and altered microstructures that are particularly sensitive to elevated service temperatures. For high-temperature or creep-prone applications, engineers typically select different alloys designed for thermal stability rather than 7055.

Applications

Industry	Example Component	Why 7055 Is Used
Aerospace	Wing skins, fuselage stiffeners, landing-gear fittings	Very high strength-to-weight and good fracture toughness for primary/secondary structures
Marine	High-performance hull fittings and spars	High specific strength combined with tailored corrosion mitigation
Automotive / Motorsport	Structural crash elements, roll cages (specialty)	Reduced weight and high static strength for performance components
Sporting Goods	High-end bicycle frames, racket frames	Excellent stiffness-to-weight and fatigue performance when properly treated
Electronics / Thermals	Structural heat-spreader frames	Good thermal conductivity relative to specific strength needs

7055 is favored where the design requires exceptional static strength and stiffness at minimum weight, with sufficient toughness and fatigue life for safety-critical applications. It is often constrained to applications where manufacturing controls and corrosion protection can be strictly applied.

Selection Insights

7055 is selected when maximum specific strength and good fracture toughness are required and when the manufacturing chain can support precise heat treatment, protective coatings, and controlled forming or joining. It is most appropriate for aerospace and high-performance structural parts rather than commodity or low-cost applications.

Compared with commercially pure aluminum (1100), 7055 trades much higher strength for lower electrical/thermal conductivity and reduced formability; choose 7055 when structural strength dominates functional conductivity or ease of forming. Compared with work-hardened alloys like 3003/5052, 7055 is far stronger but less formable and more sensitive to corrosion; it is preferable when strength outweighs simple forming and cost. Compared with heat-treatable 6xxx series alloys like 6061, 7055 delivers significantly higher peak strength and often better fracture toughness for aerospace uses, but at the expense of weldability and intrinsic corrosion resistance; choose 7055 when the highest strength-to-weight ratio is essential and fabrication constraints can be managed.

Closing Summary

7055 remains a top-tier wrought aluminum alloy for applications demanding extreme specific strength and balanced toughness, particularly in aerospace and high-performance structural domains. Its utility depends on careful temper selection, controlled processing, and appropriate corrosion protection to fully leverage its engineered microstructure and mechanical capabilities.