Aluminum 7012: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

7012 belongs to the 7xxx series of aluminum alloys, a family defined by zinc as the principal alloying element with magnesium and copper as secondary constituents. These alloys are generally formulated for high strength through precipitation hardening and are classified among heat-treatable aluminum alloys rather than purely work-hardened grades.

Major alloying elements in 7012 are zinc (Zn), magnesium (Mg), and copper (Cu), often accompanied by controlled additions of chromium (Cr), titanium (Ti) and trace levels of iron (Fe) and silicon (Si) for process control. The strengthening mechanism is predominantly age-hardening (precipitation of MgZn2 and related phases) following solution treatment and controlled aging cycles; grain control and dispersoids from trace elements assist in damage tolerance and recrystallisation control.

Key traits of 7012 include high specific strength, moderate-to-good fatigue performance, and achievable toughness when processed correctly; corrosion resistance is moderate and sensitive to temper and local metallurgy, while weldability can be limited due to HAZ softening and susceptibility to hot cracking in some conditions. Typical industries using 7xxx-series alloys like 7012 are aerospace structural fittings, military and defense components, high-performance sporting goods, and niche automotive or marine components where high strength-to-weight ratio is critical.

Engineers select 7012 over other alloys when a balance of high static strength, good fatigue resistance, and tailored toughness is needed and when design demands outweigh the penalties in formability and simplified welding that come with lower-strength alloys. It is chosen instead of higher-strength but more SCC-prone 7075 variants when improved corrosion performance and ductility retention in specific tempers are desired.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High (20–30%)	Excellent	Excellent	Fully annealed, best for forming and joining before final heat treatment
H14	Moderate	Moderate (10–18%)	Good (limited drawing)	Good	Strain-hardened, used for work-strengthened components
T5	Moderate-High	Moderate (8–14%)	Fair	Limited	Cooled from an elevated temperature and artificially aged; quicker processing
T6	High	Modest (6–12%)	Limited	Limited (weld HAZ softening)	Solution heat-treated and artificially aged to peak strength
T651	High	Modest (6–12%)	Limited	Limited	T6 condition with stress relief by stretching after quench; used in critical structural parts

Temper has a major effect on the trade-off between strength and ductility for 7012, with annealed (O) product offering maximum formability and T6/T651 providing peak mechanical strength at the expense of elongation. Practical processing chains often sequence O forming followed by solution treating and aging, or apply controlled pre-aging (T5) when dimensional stability is required without full solution treatment.

Chemical Composition

Element	% Range	Notes
Si	0.10–0.40	Typical impurity control limits to avoid brittle intermetallics
Fe	0.10–0.50	Impurity level; promotes coarse intermetallic particles if uncontrolled
Mn	0.05–0.30	Minor addition to improve grain structure and toughness
Mg	1.0–2.5	Principal strengthening component together with Zn through Mg-Zn precipitates
Cu	0.2–2.0	Enhances peak strength and hardness but can reduce SCC resistance
Zn	3.5–6.5	Primary strength contributor via MgZn2 precipitates during aging
Cr	0.05–0.25	Microstructure control to inhibit recrystallization and improve toughness
Ti	0.02–0.15	Grain refiner used in cast and wrought products
Others	Balance Al, trace impurities	Aluminum balance with tight control on elements that form low-melting phases

The relative proportions of Zn, Mg, and Cu determine precipitation kinetics and the attainable peak strength versus toughness and corrosion resistance. Trace elements and impurities influence grain size, recrystallisation behavior, dispersoid formation and susceptibility to localized corrosion or hot cracking during processing.

Mechanical Properties

In tensile service, 7012 exhibits high ultimate tensile strength in properly aged tempers, with yield strength typically following closely due to the precipitation-strengthened matrix. Elongation-to-failure decreases as strength increases; typical T6-type tempers show moderate ductility adequate for many structural components but require careful design for high-strain applications.

Hardness correlates with the degree of aging; peak-aged states deliver maximum hardness and static strength, while overaging trades strength for improved fracture toughness and corrosion resistance. Fatigue performance is generally good for 7xxx-style alloys when microstructure is optimized and surface condition is controlled, but fatigue life is sensitive to local metallurgical discontinuities and surface scratches.

Thickness has a strong influence on achievable mechanical properties because quench rates and residual stress vary with section thickness; thicker sections are harder to fully solution-treat and quench, which reduces attainable strength and can increase susceptibility to quench-induced distortion.

Property	O/Annealed	Key Temper (e.g., T6/T651)	Notes
Tensile Strength	~120–200 MPa	~450–560 MPa	T6-type peak-aged strengths typical for high-zinc 7xxx alloys
Yield Strength	~40–110 MPa	~380–500 MPa	Yield approaches tensile in high-strength tempers; design accordingly
Elongation	20–30%	6–12%	Ductility reduced in peak-aged conditions; thickness-dependent
Hardness (HB)	30–60 HB	120–170 HB	Hardness mirrors precipitation state; overaging reduces hardness but can improve toughness

Physical Properties

Property	Value	Notes
Density	~2.78 g/cm³	Slightly higher than pure aluminum due to alloying elements
Melting Range	~475–635 °C	Typical for 7xxx series; solidus/liquidus depend on local composition
Thermal Conductivity	~120–160 W/m·K	Lower than pure Al; conductivity decreases with higher alloying
Electrical Conductivity	~30–45% IACS	Reduced due to alloy scatter; varies with temper and composition
Specific Heat	~0.88–0.95 J/g·K	Comparable to other Al alloys; useful in thermal mass calculations
Thermal Expansion	~23.5 ×10⁻⁶ /K	Coefficient similar to other wrought aluminum alloys in ambient range

Physical behavior of 7012 makes it attractive where high strength-to-weight is required while still retaining useful thermal conductivity for certain thermal management components. The combination of moderate thermal conductivity and relatively low density is beneficial for weight-sensitive thermal and structural applications.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.3–6.0 mm	Good uniformity in thin gauges	O, T5, T6	Common for panels and formed components; thin-gauge quenching is effective
Plate	6–200 mm	Lower attainable peak strength in thick sections	T6 (limited), T651	Thick sections may be temper-limited by quench rates and distortion
Extrusion	Profiles up to several meters	Good along-extrusion strength; section-dependent	T6, T5	Complex cross-sections achievable; quench management critical
Tube	OD 6–200 mm	Strength depends on wall thickness and processing	T6, T651	Used for high-strength structural tubing; welding/ERW options possible
Bar/Rod	Diameters 5–200 mm	Homogeneous properties if properly processed	O, T6	Used for machined fittings and fasteners; age-hardening applied post-forming

Sheets and thin extrusions are most commonly used for achieving high peak strength after rapid quenching; plates and thick extrusions require careful process design to minimize quench-related loss of strength. Product form selection is driven by required mechanical properties, dimensional tolerances, and post-processing (machining, welding, heat treatment).

Equivalent Grades

Standard	Grade	Region	Notes
AA	7012	USA	Recognized as a 7xxx-series wrought alloy in some supplier lists
EN AW	No direct equivalent	Europe	No exact EN AW equivalant; similar behavior to higher-strength Al-Zn-Mg alloys
JIS	No direct equivalent	Japan	Localized specifications vary; design by composition rather than direct grade swap
GB/T	No direct equivalent	China	Chinese standards may offer functional equivalents in commercial 7xxx families

Direct one-to-one equivalents are uncommon for 7012; engineers normally cross-reference by chemical composition and property matrix rather than exact grade labels. When specifying for international procurement, validate composition ranges and mechanical property guarantees rather than relying solely on grade name.

Corrosion Resistance

Atmospheric corrosion resistance of 7012 is moderate and highly dependent on temper, surface condition, and alloy chemistry. In peak-aged states the combination of Zn and Cu can increase susceptibility to localized corrosion compared with low-alloyed 5xxx or 6xxx series, especially if surface film integrity is compromised.

In marine environments 7012 requires protective measures such as cladding, anodizing, or specialized coatings to approach the long-term performance of more corrosion-resistant alloys; without protection, pitting and intergranular attack can occur in aggressive chloride environments. Stress corrosion cracking (SCC) risk exists for high-strength tempers and is influenced by Cu content, heat treatment, residual stresses, and service environment; mitigation includes overaging, cathodic protection, and careful design to reduce tensile residual stresses.

Galvanic interactions with more noble metals (stainless steel, copper) can accelerate local corrosion; 7012 should be electrically insulated when coupled with such materials in marine or wet environments. Compared with 5xxx series (Mg-rich) alloys, 7012 usually offers higher static strength but inferior general corrosion resistance and requires more aggressive corrosion protection strategies in chloride-rich service.

Fabrication Properties

Weldability

Welding of 7012 is challenging in high-strength tempers because the heat-affected zone (HAZ) will soften due to dissolution and coarsening of strengthening precipitates. Gas tungsten arc (TIG) or gas metal arc (MIG) welding is possible with appropriate filler alloys (e.g., lower-strength 5xxx or specially formulated 7xxx fillers), but joint design must account for reduced HAZ strength and potential for hot cracking; pre- and post-weld treatments can mitigate some issues.

Machinability

Machinability of 7012 is generally good in overaged or annealed conditions but becomes more challenging in peak-aged tempers due to increased hardness and strength. Carbide tooling, rigid fixturing, and conservative feed rates are recommended to control tool wear; chip formation tends toward short segmented chips if feed rates and tool geometry are optimized.

Formability

Formability is best in annealed (O) tempers and diminishes rapidly with increased tempering. Minimum bend radii and draw limits should reference supplier data; when forming is required for parts that will be strength-treated, perform forming in the O condition followed by solution treatment and age hardening, or use pre-aged tempers (T5) for moderate forming with less property loss.

Heat Treatment Behavior

7012 is heat-treatable and follows classical precipitation hardening steps: solution treatment, quench, and artificial aging. Typical solution treatment temperatures are in the range of approximately 470–500 °C depending on section size and composition, held long enough to dissolve soluble phases and homogenize the microstructure.

Quenching must be rapid to retain supersaturated solid solution; water quenching or polymer quenches are common for thin sections, while thicker sections require careful control to avoid quench-induced distortion and variation in properties. Artificial aging is performed at moderate temperatures (typically 120–170 °C) to precipitate strengthening MgZn2-type phases; peak-aged conditions (T6) deliver maximum strength while overaging (T7) increases toughness and corrosion resistance.

T temper transitions involve the balance between applying strain hardening (H tempers) and thermal aging; T651 specifically denotes a T6 temper with stress relief by stretching after quench and before aging to reduce residual distortion. The heat-treatment window is narrower than many 6xxx alloys, requiring tighter process control for repeatable results.

High-Temperature Performance

Mechanical strength of 7012 deteriorates with temperature, with noticeable reductions above approximately 100 °C and more pronounced losses approaching 150–200 °C. Creep resistance at elevated temperatures is limited compared with specialized high-temperature alloys, so continuous operation is typically restricted to moderate temperatures where adequate strength retention is maintained.

Oxidation is not generally a limiting factor at common service temperatures, but microstructural changes during prolonged thermal exposure (overaging and coarsening of precipitates) reduce static and fatigue strength. The HAZ from welding can be particularly susceptible to property degradation when exposed to elevated temperatures, demanding caution for any service involving thermal cycling or sustained heat.

Applications

Industry	Example Component	Why 7012 Is Used
Aerospace	Fittings, brackets	High strength-to-weight and good fatigue performance
Marine	Structural brackets	Balance of strength and reparable corrosion practices
Automotive	Lightweight structural components	Enhanced static strength for weight-sensitive parts
Defense	Weapon mounts, small structural parts	High strength with tailored toughness
Electronics	Structural frames, heat spreaders	Structural stiffness and acceptable thermal conductivity

7012 is applied where designers require a combination of high static strength and good fatigue properties while accepting trade-offs in formability and weldability. Its use is often targeted to components where weight reduction drives performance and where post-forming heat treatment can be economically applied.

Selection Insights

7012 should be selected when a high-strength, heat-treatable aluminum with reasonable fatigue resistance is required and when designers can accommodate controlled processing and corrosion protection. It is a choice for components that benefit from age-hardening and where dimensional stability can be achieved via T651-style treatments.

Compared with commercially pure aluminum (e.g., 1100), 7012 trades significantly reduced electrical and thermal conductivity and lower formability for far higher static strength and fatigue capability. Against common work-hardened alloys (e.g., 3003, 5052), 7012 provides much higher strength but often needs coatings or cladding to match corrosion performance. Versus widely used heat-treatable alloys like 6061 or 6063, 7012 offers higher peak strength in many tempers but may be chosen less often when maximum corrosion resistance, weldability, or simple extrudability are primary concerns.

Engineers should weigh strength needs, fatigue life, corrosion mitigation strategies, production capability for heat treatment, and unit cost/availability when choosing 7012 over neighboring alloy families.

Closing Summary

7012 remains relevant as a specialized high-strength aluminum alloy that delivers an attractive strength-to-weight ratio and solid fatigue behavior when processed under controlled heat-treatment and fabrication practices. Its use is justified in applications where structural performance outweighs the penalties in formability, weldability and corrosion exposure, and where careful metallurgical control can be applied to optimize both mechanical and durability outcomes.