Aluminum 7049: Composition, Properties, Temper Guide & Applications
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Table Of Content
Table Of Content
Comprehensive Overview
7049 is a high-strength aluminum alloy in the 7xxx series, which are Al-Zn-Mg(-Cu) alloys primarily used where high specific strength is required. Its chemistry centers on zinc as the primary alloying element with significant magnesium and copper to enable precipitation hardening.
The strengthening mechanism for 7049 is heat-treatable precipitation hardening (solution heat treatment, quench and age), with microstructural control via trace additions (Zr, Ti) and thermomechanical processing to refine grain structure and retard recrystallization. Key traits include very high ultimate and yield strengths in peak-aged tempers, moderate to low ductility in peak strength conditions, limited weldability with significant HAZ softening risk, and reduced forming ease relative to 5xxx and 6xxx series.
7049 is commonly used in aerospace and defense primary and secondary structures, high-strength fittings, and other applications where a high strength-to-weight ratio and fracture toughness are crucial. Designers choose 7049 over other alloys when a combination of high static strength and improved SCC/exfoliation resistance in overaged tempers is required, while accepting trade-offs in formability and ease of welding.
Temper Variants
| Temper | Strength Level | Elongation | Formability | Weldability | Notes |
|---|---|---|---|---|---|
| O | Low | High | Excellent | Excellent | Fully annealed, best formability |
| T4 | Moderate | Moderate | Good | Poor-Moderate | Naturally aged after solution treatment |
| T6 / T651 | High | Low-Moderate | Poor | Poor | Peak-aged for maximum strength; T651 stress-relieved |
| T7 / T76 / T7651 | Moderate-High | Moderate | Fair | Poor | Overaged for improved SCC and exfoliation resistance |
| H14 / H24 | Moderate | Low-Moderate | Fair | Poor | Strain-hardened or strain-hardened + partially annealed variants for sheet products |
Temper strongly governs the trade-off between strength and toughness versus ductility and corrosion resistance. Peak-aged tempers such as T6/T651 deliver maximum tensile and yield strength but at the cost of elongation, formability and higher susceptibility to stress corrosion cracking in some conditions.
Overaged tempers (T7, T76 family) intentionally trade a portion of peak strength for a measurable improvement in resistance to stress-corrosion cracking and exfoliation, and these tempers are commonly specified for structural aerospace components where durability in service environments is a priority.
Chemical Composition
| Element | % Range | Notes |
|---|---|---|
| Si | ≤ 0.30 (typ) | Impurity; helps fluidity in castings, usually low |
| Fe | ≤ 0.40 (typ) | Impurity; can form intermetallics that affect toughness |
| Mn | ≤ 0.10 (typ) | Minor; controls grain structure in some variants |
| Mg | 2.0 – 3.0 (approx) | Major strengthening partner with Zn via MgZn2 precipitates |
| Cu | 1.4 – 2.6 (approx) | Improves strength and hardenability; may reduce corrosion resistance |
| Zn | 6.5 – 9.0 (approx) | Principal alloying element for high strength (Zn-rich precipitates) |
| Cr | ≤ 0.25 (typ) | Adds recrystallization control, improves toughness |
| Ti | ≤ 0.10 (typ) | Grain refiner in cast/extruded products |
| Others (incl. Zr, B) | 0.05 – 0.25 total (typ) | Zr typical as dispersoid former to refine grain and limit recrystallization |
Elements in 7049 are balanced to maximize precipitation hardening (Zn-Mg ± Cu) while minimizing deleterious coarse intermetallics. Trace additions such as Zr or Cr produce fine dispersoids that pin grain boundaries and reduce grain growth during solution treatment, which improves toughness and fatigue resistance in thick sections.
Mechanical Properties
7049 shows a pronounced dependence of tensile and yield values on temper, section thickness and processing history. In peak-aged tempers the alloy attains very high ultimate and yield strengths due to the dense population of MgZn2-type precipitates, while annealed or naturally aged conditions exhibit much lower strengths and much higher elongation.
Fatigue performance is generally very good for the alloy family when produced with controlled grain structure and minimized surface defects. However, fatigue strength is sensitive to damage in the HAZ after welding and to surface corrosion; therefore surface finish and protective coatings strongly influence endurance performance in service.
| Property | O/Annealed | Key Temper (e.g., T6/T651) | Notes |
|---|---|---|---|
| Tensile Strength | ~220–300 MPa (typical) | ~540–600 MPa (typical) | Peak-aged condition delivers >2× strength vs annealed |
| Yield Strength | ~110–180 MPa (typical) | ~470–520 MPa (typical) | Yield shows similar temper sensitivity as UTS |
| Elongation | ~14–22% | ~6–12% | Ductility reduced in high-strength tempers |
| Hardness (HB) | ~40–85 HB | ~140–165 HB | Brinell hardness is a practical proxy for temper level |
When designing with 7049, account for thickness-dependent strength loss in heavy sections due to slower quench rates and coarse precipitate distributions. Engineers should also factor in that stress-relief operations (T651, stretching) and controlled aging schedules are commonly used to tailor residual stress and dimensional stability.
Physical Properties
| Property | Value | Notes |
|---|---|---|
| Density | ~2.78–2.82 g/cm³ | Typical for high-strength Al-Zn-Mg alloys |
| Melting Range | ~480–635 °C (solidus–liquidus region) | Alloying broadens melting range vs pure Al |
| Thermal Conductivity | ~120–140 W/m·K (approx) | Lower than pure Al; varies with temper and composition |
| Electrical Conductivity | ~28–36 % IACS (approx) | Reduced compared with commercial-purity Al |
| Specific Heat | ~0.88–0.92 J/g·K | Typical aluminum alloy specific heat at ambient |
| Thermal Expansion | ~23.5 – 24.5 µm/m·K | Coefficient of thermal expansion similar to other Al alloys |
The alloy retains high thermal conductivity relative to steels and many engineering metals, which makes 7049 acceptable for structural components that also need some heat-dissipation capability. Electrical and thermal conductivities are lower than 1xxx and some 6xxx family alloys due to the higher solute content and precipitate population.
Product Forms
| Form | Typical Thickness/Size | Strength Behavior | Common Tempers | Notes |
|---|---|---|---|---|
| Sheet | 0.5 – 6.0 mm | Strength limited by cold work and temper | O, T4, T6, T7 | Used for skins, panels; requires careful forming and temper selection |
| Plate | 6 – 250 mm | Thickness-dependent strength and toughness | T6, T651, T76 | Thick plate needs controlled quenching to avoid soft cores |
| Extrusion | Variable cross-sections | Strength varies with section size and cooling | T6, T651 | Complex extrusions require homogenization and solution treatment |
| Tube | OD comparable to bar | Good hoop strength in peak tempers | T6, T76 | Machined and cold-finished tubes used in structural applications |
| Bar/Rod | Diameter 6 – 200 mm | Strength depends on diameter and aging | T6, T651 | Common for machined fittings and fasteners |
Processing route strongly affects final properties: plates and thick extrusions are more susceptible to quench-induced softening in the center and typically require specialized solution/quench fixtures and aging recipes. Sheet and thin products can be cold-formed in softer tempers and then solution treated and aged to achieve near-peak properties when appropriate.
Equivalent Grades
| Standard | Grade | Region | Notes |
|---|---|---|---|
| AA | 7049 | USA | Standard American designation for this high-strength Al-Zn-Mg(-Cu) alloy |
| EN AW | 7049 | Europe | EN AW-7049 designates the same compositional family; European specifications cover tempers and product forms |
| JIS | A7049 (approx) | Japan | Japanese standards often use a similar numeric designation; finishing and testing details may differ |
| GB/T | AlZn7.5MgCu (approx) | China | Chinese GB/T nomenclature typically describes key alloying content (Zn, Mg, Cu) rather than exact AA number |
Equivalent designations across standards map chemistry and product specifications but can differ in permitted impurity limits, mechanical property qualification methods, and temper definitions. Engineers should always reference the specific standard sheet (AA, EN, JIS, GB/T) and verify that temper, mechanical and inspection requirements match the application rather than relying solely on alloy number equivalency.
Corrosion Resistance
7049 exhibits moderate atmospheric corrosion resistance in overaged tempers, but peak-aged conditions can be more susceptible to localized corrosion and stress-corrosion cracking (SCC) in aggressive environments. The alloy family is prone to exfoliation corrosion in plate forms unless carefully processed and overaged or coated.
In marine environments, 7049 requires protective measures such as cladding, anodizing or organic coatings to perform acceptably. Salt spray exposure accelerates pitting and intergranular attack unless the alloy is provided in a temper optimized for SCC resistance (T76/T7 family) or protected by barrier layers.
Galvanic interaction with dissimilar metals can be severe because 7049 is a cathodic material relative to steels and many copper alloys; careful design of insulating barriers or sacrificial anodes is necessary in assemblies. Compared with 5xxx series (e.g., 5052) 7049 trades sacrificial corrosion resistance for higher strength, and compared with many 6xxx alloys it can be more sensitive to localized attack unless overaged.
Fabrication Properties
Weldability
Welding conventional fusion processes (TIG/MIG) generally produces significant property loss in 7049 due to dissolution of strengthening precipitates and HAZ softening. Hot-cracking risk is elevated with high-strength Zn-Mg-Cu alloys; conventional filler alloys rarely restore base-metal strength and fatigue performance.
Friction stir welding (FSW) is often the preferred joining method because it minimizes melting, reduces hot cracking risk, and produces a more favorable microstructure in the weld zone. When fusion welding is unavoidable, specialized filler and post-weld heat treatment strategies and acceptance testing are required.
Machinability
Machinability of 7049 is moderate to good in overaged or stress-relieved tempers; peak-aged states can be tougher on tools due to higher strength and work-hardening. Carbide tooling with positive geometries, rigid machines and appropriate high-pressure coolant produce the best surface finishes and tool life.
Cutting speeds are lower than for softer 6xxx or 1xxx alloys, and chip control requires attention because chips can be stringy in softer tempers or break into abrasive particulates in harder tempers. Pre-machining in a softer temper followed by final heat-treatment is a common production strategy.
Formability
Forming is feasible in annealed (O) or solution-treated-and-partially-aged tempers but is limited in peak-aged conditions. Minimum bend radii are larger for T6 than for O temper; springback is significant and must be anticipated in tooling.
Cold working followed by solution treatment and aging is a common route to complex shapes with high final strength, but this requires careful control of distortion and dimensional stability during heat processing.
Heat Treatment Behavior
As a heat-treatable Al-Zn-Mg-Cu alloy, 7049 follows the classical solutionize-quench-age sequence with process windows that must be tailored to section thickness and desired properties. Typical solution treatment temperatures are in the ~470–480 °C range to dissolve soluble phases, followed by rapid quenching to retain a supersaturated solid solution.
Artificial aging is performed at moderate temperatures (typically 120–160 °C) to precipitate age-hardening phases; aging time and temperature determine the peak strength and the degree of overaging. Overaged (T7/T76 family) conditions use higher temperatures or longer times to promote coarsening of precipitates and improve resistance to SCC and exfoliation at the expense of some peak strength.
High-Temperature Performance
7049 loses a significant portion of its room-temperature strength as service temperature increases beyond typical aging temperatures, with noticeable softening beginning above ~120 °C. Continuous service at elevated temperatures (>125–150 °C) is not recommended for applications requiring high strength, as coarsening of precipitates reduces yield and fatigue resistance.
Oxidation of aluminum alloys occurs slowly compared to steels; however, the mechanical degradation due to precipitate coarsening and relaxation of residual stresses in the HAZ is the principal concern at temperature. Designers should limit high-temperature exposure or select alternative alloys specifically designed for elevated temperature service when necessary.
Applications
| Industry | Example Component | Why 7049 Is Used |
|---|---|---|
| Aerospace | Structural fittings, landing-gear components | High strength-to-weight and fracture toughness in optimized tempers |
| Defense | Missile bodies, high-performance structural members | Elevated static strength and tailored toughness |
| Marine | High-strength brackets and fittings | Improved strength with overaged tempers for corrosion resistance |
| Electronics | Structural frames, heat spreader housings | Good thermal conductivity combined with high stiffness |
7049 is selected where high static strength, reasonable fatigue performance and tailored corrosion resistance are required, particularly in aerospace and defense where weight savings are critical. The alloy is less common in commodity markets because of cost, weldability limits and forming constraints, but it remains a go-to material for demanding structural parts.
Selection Insights
7049 is appropriate when maximum specific strength and optimized fracture toughness are priorities and when design can accommodate limited formability and challenging welding. Choose overaged tempers (T7/T76) when stress-corrosion resistance and long-term durability in aggressive environments are needed, accepting some loss of peak strength.
Compared with commercially pure aluminum (1100), 7049 offers dramatically higher strength at the expense of electrical and thermal conductivity and substantially reduced formability. Compared with work-hardened alloys such as 3003 and 5052, 7049 provides much higher strength but typically worse forming characteristics and similar or slightly worse corrosion performance in marine conditions unless overaged.
Compared with common heat-treatable alloys like 6061, 7049 delivers higher peak strength and fracture toughness in many tempers, which justifies its use in aerospace fittings despite higher material cost and lower weldability. Choose 7049 when structural performance outweighs joining and forming convenience.
Closing Summary
7049 remains a high-performance aluminum choice for aerospace, defense and other demanding structural applications where a superior strength-to-weight ratio and tailored resistance to stress-corrosion cracking are required. Its selection demands careful attention to temper, section size, joining method and protective treatments, but when processed correctly it provides a combination of properties that few other aluminum alloys can match.