Aluminum 7020: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

7020 is a 7xxx-series aluminum alloy (Al-Zn-Mg family) engineered for high strength with a focus on improved toughness and stress-corrosion performance compared with traditional 7xxx alloys. Its nominal chemistry centers on zinc as the principal strengthening element with magnesium as the secondary element and low levels of copper and chromium to control grain structure and recrystallization.

The alloy is heat-treatable and gains strength principally through solution treatment, quenching and artificial aging (precipitation hardening of Zn-Mg phases), although work-hardening has limited effect compared with non-heat-treatable series. Key traits include high specific strength, reasonably good fatigue resistance for high-strength Al alloys, moderate corrosion resistance (improved vs high-Cu 7xxx alloys), limited room-temperature formability in peak tempers, and careful weldability due to HAZ softening.

7020 is commonly used in aerospace fittings, structural components, transport and marine applications where a combination of elevated strength, good fracture toughness and reasonable corrosion resistance is required. Engineers select 7020 when a higher strength-to-weight ratio and better SCC resistance are needed compared with conventional 6xxx series alloys, or when 7xxx-series strength is required but 7075’s susceptibility to corrosion and lower fracture toughness is unacceptable.

7020 is chosen over other alloys when designers require a balance of high static and fatigue strength with improved resistance to stress-corrosion cracking and better aging stability. It competes with 6061 and 7075 in many structural niches, often preferred where weldability or higher ductility in certain tempers is a consideration. Availability in extrusion, plate and sheet forms plus well-established heat-treatment schedules make 7020 attractive for production parts with predictable mechanical performance.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed, highest ductility for forming
T4	Moderate (naturally aged)	Moderate-High	Good	Good	Solution treated and naturally aged; good formability for moderate strength
T6	High	Moderate	Fair-Poor	Limited	Solution treated + artificial aging; peak strength for static loading
T651	High (stress-relieved)	Moderate	Fair-Poor	Limited	T6 with controlled stretching to reduce residual stress
H14	Moderate-High	Low-Moderate	Limited	Good	Strain-hardened by partial cold working; intermediate strength without heat treatment
T5	Moderate-High	Moderate	Limited	Limited	Cooled from elevated temperature and artificially aged; used for extrusions

Temper significantly controls the balance between strength and ductility in 7020. Annealed (O) or T4 conditions give the best formability for stamping or deep forming, whereas T6/T651 provide the highest static strength but suffer reduced bendability and require care to prevent springback and cracking.

Heat-treatable tempers exhibit pronounced HAZ softening in welded joints; designers often select T651 for critical structural parts to manage residual stress and stability. Intermediate H and T5 tempers are used where partial cold work or on-line aging of extrusions yields sufficient strength while keeping forming or joining operations feasible.

Chemical Composition

Element	% Range	Notes
Si	≤ 0.12	Impurity; limits casting defects and reduces effect on strength
Fe	≤ 0.50	Impurity; high levels reduce toughness and machinability
Mn	0.03 – 0.20	Microalloying to control grain structure and recrystallization
Mg	1.0 – 1.8	Primary strengthening partner with Zn (MgZn2 precipitates)
Cu	≤ 0.10 – 0.25	Low to moderate; reduces SCC risk relative to high-Cu 7xxx alloys
Zn	3.8 – 4.8	Principal strengthening element; controls precipitation hardening
Cr	0.04 – 0.20	Grain refiner; improves toughness and controls recrystallization
Ti	≤ 0.05	Fine grain nucleant in ingot processing
Others (each)	≤ 0.05	Includes V, Zr traces; balance Al

Alloying additions tune 7020’s mechanical and corrosion behavior: Zn and Mg form coherent and semi-coherent precipitates during aging that provide the primary strengthening mechanism. Chromium and small Mn/Ti additions refine grain structure and reduce susceptibility to recrystallization and intergranular fracture, while low copper minimizes stress-corrosion cracking risk compared with higher-Cu 7xxx alloys.

Impurity elements such as Fe and Si are tightly controlled because they form intermetallic particles that reduce fracture toughness and may act as fatigue crack nucleation sites. Controlled chemistry enables stable response to heat treatment and consistent mechanical performance across product forms.

Mechanical Properties

In T6/T651 conditions 7020 displays a high tensile strength suitable for structural applications, with a characteristic combination of yield and ultimate strength that supports high load-bearing components. Yield strength in peak tempers is substantially higher than 6xxx series alloys while offering improved toughness versus higher-strength 7xxx alloys; elongation in peak tempers is moderate and sufficient for many machined and structural parts.

Under annealed (O) or solution-treated (T4) conditions elongation rises significantly and tensile strength falls, making these tempers preferable for forming operations. Hardness correlates strongly with artificial aging: T6 gives the highest hardness and static load resistance, while the annealed condition shows low hardness and superior dent resistance.

Fatigue performance of 7020 is generally good for a high-strength aluminum, benefitting from controlled grain structure and lower Cu; however, fatigue life is sensitive to surface finish, residual stresses and local notches. Thickness and product form influence mechanical properties because cooling rates and recrystallization during processing alter precipitation kinetics and grain morphology; thicker plates may exhibit slightly lower peak hardness and toughness than thin extrusions processed with faster quench rates.

Property	O/Annealed	Key Temper (T6 / T651)	Notes
Tensile Strength (MPa)	160 – 240	360 – 420	T6 provides roughly 2–2.5× strength of O; values depend on product form and thickness
Yield Strength (MPa)	55 – 110	320 – 370	Yield rises steeply after aging; T651 includes stress-relief stretch treatment
Elongation (A%)	18 – 30	8 – 14	Ductility decreases with increasing strength; fracture toughness trade-off
Hardness (HB)	40 – 70	110 – 140	Brinell hardness increases with aging; hardness correlates with strength and wear resistance

Physical Properties

Property	Value	Notes
Density	~2.78 g/cm³	Typical for Al-Zn-Mg alloys; good strength-to-weight ratio
Melting Range	Solidus ~475–490°C; Liquidus ~635–645°C	Alloy solidus/liquidus depend on exact composition and impurities
Thermal Conductivity	~130 – 160 W/m·K	Lower than pure Al but adequate for heat-sinking compared with steels
Electrical Conductivity	~28 – 36 % IACS	Lower than 1xxx and 6xxx series due to alloying; typical for high-strength Al
Specific Heat	~880 J/kg·K	Useful in thermal design and transient heat calculations
Thermal Expansion	~23 – 24 µm/m·K (20–100°C)	Similar to other Al alloys; relevant for differential expansion design

7020 retains aluminum’s low density and favorable thermal conductivity, making it attractive where mass savings and heat dissipation matter. Reduced electrical and thermal conductivity versus pure aluminum are trade-offs for increased strength from precipitation-hardening phases.

Thermal characteristics dictate heat-treatment windows and service limits; designers should allow for significant loss of precipitation strengthening when components operate at elevated temperatures approaching or exceeding typical aging temperatures.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.5 – 6 mm	Best quench and aging response in thinner gauges	O, T4, T6	Widely used for light structural panels and machined parts
Plate	6 – 100+ mm	Thicker sections may have slightly reduced peak strength	T6, T651	Requires controlled quenching to achieve uniform properties
Extrusion	Profiles up to large cross-sections	Good directional strength; aging can be performed on-line	T5, T6, T651	Popular for structural frames and complex cross-sections
Tube	Diameters varied; seamless/welded	Similar to extrusions; wall thickness affects aging	T6, T651	Used for high-strength tubing and structural members
Bar/Rod	Diameters up to 200 mm	Machinability and uniformity depend on solid section size	O, T6	Used for fittings, machined components and forgings

Sheets and thin extrusions typically achieve peak properties more readily due to faster quench rates, while thick plate sections need careful processing to prevent soft cores. Extruded profiles allow tailored cross-sections and can be age-hardened immediately after quench (T5) or after stress relieving (T651) for dimensional stability.

Manufacturing choices are driven by required mechanical performance and geometry complexity: form-first heat treat cycles are common for parts requiring significant bending, whereas machine-from-bar strategies favor T6 condition for dimensional control and fatigue resistance.

Equivalent Grades

Standard	Grade	Region	Notes
AA	7020	USA	Common alloy designation under Aluminum Association listings
EN AW	7020	Europe	EN AW-7020 commonly used; chemical and mechanical specs follow EN standards
JIS	A7020	Japan	JIS variants keep composition limits similar but with regional tolerances
GB/T	7020	China	Chinese GB/T grade aligns with international 7020 chemistries and applications

Regional specifications for 7020 are broadly consistent in elemental ranges and temper definitions, but tolerances on impurity elements and mechanical verification tests can vary. European EN AW-7020 standards emphasize tight control of recrystallization-inhibiting elements for plate and extrusion quality.

Users should consult specific standards/certificates for dimensional tolerances, permitted inclusions, and supplier process controls since those influence fatigue life, SCC resistance and allowable defect levels for critical components.

Corrosion Resistance

In atmospheric environments 7020 exhibits moderate corrosion resistance with better performance than high-copper 7xxx alloys due to its relatively low Cu content. Natural anodizing and chromate or modern organic coatings significantly enhance resistance to pitting and general corrosion, making 7020 suitable for many outdoor structural applications.

Marine exposure accelerates localized corrosion; 7020 can be used in marine structures when additional protection (anodizing, conversion coatings, sealing joints and protective paints) is applied. Avoiding stagnant seawater retention and insulating dissimilar metals are essential design practices to reduce galvanic attack.

Stress-corrosion cracking susceptibility in 7020 is lower than in high-Cu 7xxx alloys but remains a design consideration for heavily stressed, high-strength tempers (T6). Joint design, temper selection (favoring T4/T651 where applicable), and post-weld heat treatment strategies are typically used to mitigate SCC risk.

Galvanic interaction with steels, copper or stainless alloys can be significant in chloride environments; employ insulating barriers, sacrificial coatings or cathodic protection at joint interfaces. Compared with 5xxx (Mg series) and 6xxx (Mg-Si) aluminum families, 7020 offers higher strength at the cost of slightly more demanding corrosion control measures.

Fabrication Properties

Weldability

7020 can be welded using common fusion techniques (TIG, MIG), but welds in high-strength tempers experience significant HAZ softening; post-weld heat treatment is often required to restore strength in critical applications. Filler alloys such as 5356 or other Al-Mg fillers are commonly used to reduce hot-cracking susceptibility and improve ductility of the weld metal. Careful joint design, pre- and post-weld mechanical stress relief, and control of heat input reduce porosity and HAZ issues; fusion welding of load-bearing components is performed with qualification and often followed by local aging.

Machinability

Machinability of 7020 is generally rated as moderate to good for a high-strength aluminum, with solid sections providing consistent chip formation when using sharp carbide tools. Recommended tooling includes coated carbide inserts with positive rake geometry and abundant coolant or lubricant to control built-up edge and improve surface finish. Cutting speeds are higher than for steels but lower than for soft wrought aluminum with feeds and depths optimized to avoid vibration and to manage heat in the cutting zone.

Formability

Formability is highly temper-dependent: O and T4 conditions provide the best bendability, deep drawing and stamping characteristics, while T6 and T651 are substantially less formable and prone to cracking at tight radii. Typical minimum inside bend radii for annealed 7020 sheet are on the order of 1× thickness, whereas T6 parts often require 2–4× thickness or use of specialized tooling and elevated temperature forming to avoid fracture. Springback is pronounced in higher strength tempers, so tooling compensation and trials are essential for precision formed parts.

Heat Treatment Behavior

7020 is a classic heat-treatable alloy: solution treatment is typically performed at approximately 470–480°C to dissolve the Zn-Mg rich phases into solid solution, followed by rapid quenching to retain supersaturation. Artificial aging (T6) is commonly carried out at temperatures in the 120–160°C range for several hours to precipitate strengthening phases and reach peak hardness; aging curves must be tailored to section size and desired balance of strength and toughness.

T651 temper indicates T6 with a controlled stretching operation to minimize residual stresses and distortion; this temper is preferred for structural parts where dimensional stability and fatigue resistance are required. Unlike non-heat-treatable alloys, 7020’s strength is dominated by precipitate size and distribution rather than cold work, so careful control of time-temperature profiles and quench rates is critical to achieving specified mechanical properties.

High-Temperature Performance

7020 loses a significant portion of its precipitation-strength at elevated service temperatures; long-term exposure above ~120°C progressively coarsens precipitates and reduces yield and ultimate strength. Short-term excursions to moderately higher temperatures can be tolerated but repeated cycling or prolonged exposure will shorten fatigue life and reduce load-bearing capability. Oxidation is minimal for aluminum at typical service temperatures, but protective coatings may degrade at high temperatures and expose bare metal to corrosive environments.

Heat-affected zones adjacent to welds are particularly vulnerable because localized thermal exposure alters precipitate distributions and can create soft bands that concentrate strain under mechanical or thermal cycling. For applications requiring elevated-temperature retention of mechanical properties, alternative alloys designed for sustained high-temperature use should be considered.

Applications

Industry	Example Component	Why 7020 Is Used
Aerospace	Structural fittings, bulkhead components	High strength-to-weight with good fracture toughness and SCC resistance
Marine	Deck support members, frames	Improved corrosion resistance vs high-Cu 7xxx alloys and good strength
Automotive / Rail	High-strength extruded profiles, chassis components	Strength and fatigue performance for lightweight structural members
Sports / Recreation	High-performance bicycle frames, structural tube	Good strength-to-weight and machinability for precision parts
Electronics / Thermal	Structural heat spreaders, housings	Balance of stiffness, thermal conductivity and machinability

7020 is deployed where designers need a premium combination of strength, toughness and reasonably good corrosion behavior in both fabricated and machined components. Its availability in multiple product forms and established heat-treatment recipes make it a versatile choice for engineered parts where performance consistency and lifecycle durability are needed.

Selection Insights

Choose 7020 when high static and fatigue strength is required along with improved fracture toughness and reduced SCC risk relative to higher-Cu 7xxx alloys. It is well suited for structural, aerospace and marine parts where weight savings and predictable aging behavior are priorities.

Compared with commercially pure aluminum (e.g., 1100), 7020 trades significant electrical and thermal conductivity and formability for greatly increased strength; use 1100 where conductivity or formability dominates and 7020 where load-bearing capability is essential. Compared with work-hardened alloys such as 3003 or 5052, 7020 offers much higher strength but requires heat treatment control and corrosion protection; choose 3003/5052 when forming or corrosion resistance in chloride environments without heat treatment is central. Compared with common heat-treatable 6xxx alloys (6061/6063), 7020 typically provides higher strength and better fatigue performance but may have higher material cost and stricter welding/heat-treatment requirements; prefer 7020 when its superior strength-to-weight and toughness justify the additional processing constraints.

Closing Summary

7020 remains a relevant high-strength aluminum alloy for modern engineering due to its favorable balance of strength, toughness and managed corrosion behavior, combined with versatile product-form availability and well-understood heat-treatment routes. Its position between conventional 6xxx alloys and higher-strength but more corrosion-prone 7xxx alloys makes it a practical choice for structural applications demanding reliable, repeatable performance.