Aluminum 6070: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

Aluminum alloy 6070 is a member of the 6xxx series of aluminum alloys, which are characterized by magnesium and silicon as their principal alloying additions. The alloying balance in 6070 places it among heat-treatable, age-hardenable compositions that respond to solution treatment and artificial aging to develop useful strength while retaining good extrudability and surface finish.

The primary strengthening mechanism for 6070 is precipitation hardening via Mg2Si (magnesium silicide) formation during controlled aging cycles. This gives 6070 a combination of moderate-to-high strength, good ductility in softer tempers, and predictable thermal response that is attractive for structural extrusions and machined parts.

Key traits of 6070 include a favorable strength-to-weight ratio, competent corrosion resistance in atmospheric environments, and good weldability when appropriate filler metals and post-weld treatments are used. Formability in annealed and partially work-hardened tempers is strong, enabling bending and drawing operations; however, peak-aged tempers reduce ductility and require consideration for forming operations.

Typical industries using 6070 include automotive (structural and chassis components), rail and mass transit (extruded framing), industrial machinery (profiles and fittings), and some marine applications where a balance of strength, fabrication ease, and corrosion performance is required. Engineers select 6070 when they need a 6xxx-series alloy that offers extrusion-friendly metallurgy with competitive peak properties and dimensional stability compared with other 6xxx alloys.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High (20–35%)	Excellent	Excellent	Fully annealed condition for forming and joining
H14	Moderate	Moderate (10–18%)	Good	Good	Strain-hardened, limited by work-hardening capability
T4	Moderate	Moderate-High (12–25%)	Good	Good	Solution heat-treated and naturally aged; good balance of formability and strength
T5	Moderate-High	Moderate (8–15%)	Fair-Good	Good	Cooled from elevated temperature shaping and artificially aged
T6	High	Low-Moderate (8–12%)	Limited	Good	Solution treated and artificially aged for peak strength
T651	High	Low-Moderate (8–12%)	Limited	Good	T6 variant with stress relief by stretching to reduce residual stresses

Tempers in 6070 control the precipitation state of Mg2Si and any microstructural recovery after cold work, which directly governs the tensile and yield response. Designers pick O or T4 for forming operations and T6/T651 for finished structural components where dimensional stability and peak strength are required.

Chemical Composition

Element	% Range	Notes
Si	0.2–0.8	Silicon combines with magnesium to form Mg2Si precipitates, controlling age-hardening response.
Fe	0.05–0.40	Iron is a common impurity; it forms intermetallics that can reduce ductility and surface finish.
Mn	0.00–0.10	Manganese refines grain structure and improves strength slightly; typically low in 6070.
Mg	0.35–0.9	Magnesium is the primary strengthening element with Si to produce Mg2Si precipitates.
Cu	0.05–0.25	Copper may be present in small amounts to tweak strength and aging kinetics, but high Cu compromises corrosion resistance.
Zn	0.00–0.20	Zinc is typically low; elevated Zn can raise strength but increase sensitivity to stress corrosion.
Cr	0.00–0.10	Chromium assists in controlling grain growth and can reduce recrystallization during heat treatment.
Ti	0.00–0.10	Titanium is used in trace amounts as a grain refiner for improved mechanical properties and surface quality.
Others	Balance to 100 (each ≤0.05)	Small controlled additions and residuals (e.g., Zr, V) can be present to optimize properties for extrusion and aging.

The Mg–Si ratio and the absolute content of Mg and Si determine the volume fraction and coherency of precipitates formed during aging, which sets the achievable peak strength. Trace elements such as Cr, Ti, and small amounts of Cu or Zn are used to tailor recrystallization behavior, grain size, and corrosion response for specific processing routes and applications.

Mechanical Properties

Tensile behavior for 6070 is typical of heat-treatable 6xxx alloys: it shows a pronounced increase in both yield and ultimate tensile strength with artificial aging, accompanied by a decrease in ductility. In annealed or T4 conditions the alloy exhibits good uniform elongation and energy absorption suitable for forming and crash energy management; in T6/T651 peak conditions the alloy provides higher stiffness and load-carrying capability with lowered elongation.

Yield strength and tensile strength are sensitive to section thickness and thermal history; thin extrusions or rolled sections can be brought to near-peak properties more quickly than thicker plates because of faster cooling and more uniform heat treatment. Hardness correlates with the precipitation state and is a convenient proxy for strength during process control; overaging will reduce hardness and tensile properties but can improve toughness and reduce susceptibility to stress-corrosion cracking.

Fatigue resistance of 6070 in peak-aged conditions is moderate and benefits from smooth surface finishes, controlled residual stresses, and proper shot peening or stress-relief treatments. The presence of intermetallic particles (iron-rich phases) can be initiation sites for fatigue cracks, so control of impurity levels and extrusion parameters is important for high-cycle applications.

Property	O/Annealed	Key Temper (e.g., T6/T651)	Notes
Tensile Strength	100–150 MPa	250–320 MPa	Wide ranges reflect section size and aging treatment; quoted values are typical engineering ranges.
Yield Strength	40–70 MPa	200–280 MPa	Yield varies strongly with temper and prior cold work; T651 provides improved residual stress state.
Elongation	20–35%	8–12%	Ductility decreases as strength increases; elongation also depends on section thickness.
Hardness	30–60 HB	80–120 HB	Hardness tracks tensile properties; instrumental for QC during aging and fabrication.

Physical Properties

Property	Value	Notes
Density	~2.70 g/cm³	Typical aluminum alloy density; useful for mass and stiffness calculations.
Melting Range	~555–650 °C	Solidus–liquidus ranges vary with alloying and impurities; provides process windows for casting and welding.
Thermal Conductivity	~130–160 W/m·K	Lower than pure aluminum due to alloying; still good for heat-dissipation applications.
Electrical Conductivity	~28–38 %IACS	Reduced from pure Al by alloying; acceptable for structural-electrical combined components.
Specific Heat	~0.88–0.92 J/g·K	Typical for aluminum alloys; relevant for thermal transient analysis.
Thermal Expansion	~23–24 µm/m·K (20–100 °C)	Coefficient of thermal expansion similar to other Al–Mg–Si alloys; important for assembly tolerances.

The physical properties make 6070 attractive where lightweight combined with reasonable thermal conductivity is needed, such as heat-dissipating structural parts. The relatively high thermal expansion coefficient must be considered for assemblies with dissimilar materials to avoid dimensional drift or stress during temperature cycles.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.5–6 mm	Uniform through-thickness when cold-rolled	O, T4, T5, T6	Common for panels, cover plates, and shallow-draw parts
Plate	6–50+ mm	May show lower homogeneity in thick sections	O, T4, T6	Thicker sections require adjusted heat treatment for uniform aging
Extrusion	Profile-dependent (thin webs to thick ribs)	Often heat-treated after extrusion to achieve T5/T6	T5, T6, T651	Widely used for complex cross-sections and framing
Tube	Ø 10–200+ mm	Welding or extrusion method affects grain structure	O, T4, T6	Used for structural tubing and hydraulic manifolds
Bar/Rod	Ø 3–100 mm	Machinability varies with temper; drawn bars may be stronger	O, H14, T6	Stock for machined components and fasteners

Sheets and extrusions are the dominant product forms for 6070, with extrusions exploiting the alloy’s extrusion-friendly chemistry for long, complex profiles. Plate and thick sections require careful thermal processing to ensure through-thickness solutionizing and aging, and bar/rod are preferred for components requiring subsequent machining or cold work.

Equivalent Grades

Standard	Grade	Region	Notes
AA	6070	USA	ANSI/AA designation for the commercial alloy; primary reference in supplier datasheets.
EN AW	6070	Europe	EN AW-6070 designation is commonly used for extruded profiles and wrought products.
JIS	—	Japan	No exact 1:1 JIS counterpart; comparable to certain Al–Mg–Si wrought alloys used for extrusions.
GB/T	—	China	China may list a close equivalent within Al–Mg–Si alloy family, often matched by composition and temper.

Subtle differences between regional standards can arise from slightly different allowable impurity levels, designated tempers, and testing requirements. When substituting across standards, engineers should verify composition limits, mechanical property requirements at specified tempers, and any mandated heat-treatment or testing protocols.

Corrosion Resistance

In atmospheric environments 6070 exhibits corrosion resistance typical of 6xxx series alloys, providing good resistance to general oxidation and pitting under normal service conditions. The presence of Mg and Si confers a stable protective oxide film that limits uniform corrosion rates; however, localized attack can initiate at mechanical damage or at sites with intermetallic particles.

Marine exposure accelerates corrosion challenges; while 6070 performs reasonably well in mildly saline atmospheres, long-term immersion or splash zones can promote pitting and crevice corrosion if protective coatings or anodizing are not used. Proper surface treatments, anodic coatings, and cathodic isolation from more noble materials are common mitigation strategies for marine applications.

Stress corrosion cracking (SCC) susceptibility in heat-treatable Mg–Si alloys is moderate and tends to increase with higher strength tempers and with the presence of tensile residual stresses. Galvanic interactions with stainless steels and copper alloys can be significant due to aluminum’s electrochemical potential; insulating layers or sacrificial cathodic protection is often required in mixed-metal assemblies.

Compared with 5xxx series (Al–Mg) alloys, 6070 generally has slightly lower innate SCC resistance in peak-aged conditions but better strength and surface finish. Compared with 2xxx series (Al–Cu) alloys, 6070 offers superior corrosion resistance but lower ultimate strength, making it a preferred choice where corrosion performance and fabrication ease are priorities.

Fabrication Properties

Weldability

6070 welds well with common fusion welding processes such as TIG and MIG when using appropriate filler metals designed for Al–Mg–Si alloys. Recommended fillers are typically 4043 (Al–Si) or 5356 (Al–Mg) depending on required strength, ductility, and corrosion considerations; 4043 provides excellent fluidity and reduced hot-cracking tendency, while 5356 yields higher strength in the weld deposit. Hot-cracking risk is moderate for 6xxx alloys; controlling joint design, restraint, heat input, and filler selection minimizes solidification cracking. Heat-affected zone (HAZ) softening occurs locally in peak-aged tempers, so post-weld artificial aging or mechanical stress-relief may be required to restore uniform properties.

Machinability

Machinability of 6070 is typical for wrought Al–Mg–Si alloys and is generally good to excellent in annealed and partially aged tempers. Carbide tooling with positive rake, high-speed steel, or PVD-coated tools perform well at moderate cutting speeds while maintaining finish; recommended surface speeds often range from 200–600 m/min depending on tool geometry and coolant. Chips tend to be continuous and ductile; careful chip evacuation and control of feed rates are necessary to prevent built-up edge and ensure dimensional stability. For tight-tolerance parts, final machining in the T4 condition followed by aging can control distortion.

Formability

Formability in O and T4 tempers is strong, enabling bending with relatively small internal radii and conventional stamping operations without excessive cracking. For drawn or deep-formed parts, using annealed or mildly aged tempers and progressive forming steps preserves surface integrity and formability. Bend radius recommendations typically follow R/t ratios comparable to other 6xxx alloys; sharp bends in peak-aged tempers often require preheating or post-forming stress relief. Cold work increases strength via strain hardening but reduces ductility, so designers should plan forming sequences that keep final forming in softer tempers when possible.

Heat Treatment Behavior

As a heat-treatable 6xxx series alloy, 6070 responds predictably to solution treatment, quenching, and artificial aging to develop strength via controlled precipitation. Typical solution treatment temperatures are in the range of 510–540 °C to dissolve Mg2Si into solid solution, followed by rapid quenching to retain a supersaturated solid solution. Subsequent artificial aging at temperatures in the range 160–200 °C promotes controlled precipitation of fine, coherent Mg2Si particles that raise strength to peak values.

T temper transitions follow the canonical 6xxx pattern: T4 denotes solution treated and naturally aged, T5 indicates cooled from elevated temperature and artificially aged, and T6 represents solution treated and artificially aged to a stable peak condition. Overaging at higher temperatures or longer times coarsens precipitates, lowering strength but improving toughness and reducing susceptibility to stress-corrosion cracking. For critical components, process windows for solutionizing and aging should be validated with hardness and tensile testing to ensure targeted property envelopes.

For non-heat-treatable processing routes such as cold work, 6070 can be strain-hardened (H-line tempers), but the ultimate achievable strength via work hardening is lower than peak precipitated strengths; therefore, heat treatment remains the primary route for high-strength applications. Full annealing returns the alloy to a recrystallized, ductile state suitable for forming operations.

High-Temperature Performance

6070 exhibits progressive strength loss with increasing temperature, like other Al–Mg–Si alloys, with useful structural stiffness and load-bearing capacity typically limited to service temperatures below approximately 150–175 °C. Above these temperatures the stability of fine Mg2Si precipitates decreases, leading to softening and reduced yield strength; long-term exposure at elevated temperatures can accelerate overaging and coarsening effects.

Oxidation at typical service temperatures is minimal due to the protective aluminum oxide film; however, prolonged high-temperature exposure in oxidizing atmospheres can affect surface finish and dimensional stability. In welded zones, HAZ overaging is a key concern at elevated temperature excursions during fabrication; designers should consider post-weld heat treatments or conservative allowable stresses for service temperature rises.

Applications

Industry	Example Component	Why 6070 Is Used
Automotive	Extruded chassis rails, cross-members	Good extrusion properties, balanced strength and weight savings
Marine	Structural profiles and framing	Acceptable corrosion resistance with proper coatings and good fabrication ease
Aerospace	Secondary fittings, interior structural members	Favorable strength-to-weight and predictable heat-treatment response
Electronics	Structural heat-spreading frames	Combination of mechanical strength and thermal conductivity for enclosures and mounts

6070 is used where the combination of extrudability, finishing quality, and age-hardened strength enables complex profiles that are also machine- or weld-ready. Its balance of physical and mechanical properties makes it a versatile choice for mid-tier structural and fabrication applications.

Selection Insights

Choose 6070 when you need a heat-treatable Al–Mg–Si alloy that offers good extrudability, surface finish, and a predictable route to peak strength without the higher cost or machining difficulty of high-strength 2xxx or 7xxx alloys. It is particularly attractive for long extrusions and structural profiles that require post-forming heat treatments.

Compared with commercially pure aluminum (e.g., 1100), 6070 trades some electrical and thermal conductivity and slightly reduced formability for substantially higher yield and tensile strength. Compared with common work-hardened alloys such as 3003 or 5052, 6070 delivers superior peak strength after aging at the expense of slightly lower corrosion resistance in certain marine conditions and somewhat more complex thermal processing.

Compared with common heat-treatable alloys such as 6061 or 6063, 6070 can be preferred when specific extrusion profiles, surface finish, or slightly different aging kinetics are required; it may offer better extrudability or surface appearance for some profiles despite yielding similar or marginally lower peak strength, so selection often depends on supplier availability and specific process control.

Closing Summary

Aluminum 6070 remains a relevant 6xxx-series alloy for engineers seeking a middle ground between formability, extrudability, and age-hardened strength for structural profiles and fabricated components. Its predictable precipitation-hardening behavior, acceptable corrosion resistance, and compatibility with standard fabrication techniques make it a practical choice across automotive, marine, and industrial applications where balanced performance and manufacturability are key.