Aluminum 6020: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

Alloy 6020 belongs to the 6xxx series of aluminium alloys, which are aluminium‑magnesium‑silicon (Al‑Mg‑Si) heat‑treatable alloys. The 6xxx family is characterized by Mg2Si precipitation hardening; 6020 is formulated for a balance of extrusion performance, moderate strength and good surface finish, placing it alongside alloys such as 6060 and 6063 in application space.

Major alloying elements in 6020 are silicon and magnesium as the strengthening pair, with controlled levels of iron, copper, manganese, chromium and trace additions (titanium or zirconium in some mill variants) to control grain structure and improve processing. Strengthening is achieved primarily through solution heat treatment, quenching and artificial aging (precipitation hardening), although final properties can be modified by cold work in some tempers.

Key traits of 6020 include moderate-to-good strength for a formable alloy, good corrosion resistance in atmospheric environments, excellent extrudability and surface finish, and generally good weldability with appropriate filler choices. Its formability and surface quality make it attractive where complex extrusions or formed profiles are required and where a combination of finish and dimensional stability is needed.

Typical industries using 6020 are automotive structural extrusions, architectural profiles, light‑weight marine structures, and certain electronics housings where extrusions or formed sections with moderate strength and good cosmetic finish are required. Engineers choose 6020 over higher‑strength 6xxx alloys when better extrudability, surface appearance, or dimensional tolerance in extrusion and finishing steps are priorities, and over non‑heat‑treatable alloys when an intermediate strength increase via aging is desirable.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High (20–30%+)	Excellent	Excellent	Fully annealed, best for severe forming
T1	Low–Moderate	Moderate	Very Good	Very Good	Cooled from hot working with natural aging
T4	Moderate	Moderate–High	Very Good	Very Good	Solution treated and naturally aged
T5	Moderate–High	Lower	Good	Good	Cooled from hot working and artificially aged
T6	High	Lower (6–15%)	Fair–Good	Good	Solution treated and artificially aged to peak strength
T651	High	Lower (6–15%)	Fair–Good	Good	Stress‑relieved by stretching after solution treat

Tempers strongly affect mechanical performance and forming behavior. Annealed (O) and naturally aged (T4) tempers give the best ductility and are preferred for severe forming, while artificially aged tempers (T5, T6) provide higher tensile and yield strength at the expense of elongation.

For extrusions and structural sections, temper selection is a trade‑off between final mechanical requirements and downstream forming or joining operations; T6/T651 are chosen for strength and stability, whereas O or T4 are chosen to maximize formability and minimize cracking during forming.

Chemical Composition

Element	% Range	Notes
Si	0.3–0.9	Primary alloying element for Mg2Si precipitation
Fe	0.2–0.7	Impurity; controlled to maintain extrudability and toughness
Mn	0.0–0.15	Trace, improves grain structure when present
Mg	0.3–0.7	Combines with Si to form strengthening precipitates
Cu	0.0–0.15	Often minimal; increases strength but can reduce corrosion resistance
Zn	0.0–0.2	Typically low; large amounts are not intentional
Cr	0.0–0.1	Microalloying for grain control and to limit recrystallization
Ti	0.0–0.05	Grain refiner in cast/extruded billets
Others	Balance Al; total of other elements ≤0.15	Small additions/impurities such as Zr, V depending on mill practice

The Si and Mg contents determine the volume fraction and composition of Mg2Si precipitates, which set the precipitation hardening response during artificial aging. Low levels of Fe and Cu are important to preserve corrosion resistance and surface finish, while Cr/Ti additions are used to control grain structure during billet casting and extrusion.

Because composition windows vary by standard and mill practices, final material certs should be consulted for exact limits; small differences in Mg and Si significantly change aging kinetics and peak properties.

Mechanical Properties

Tensile behavior for 6020 is typical of medium‑strength 6xxx alloys: in peak‑aged tempers (T6/T651) it exhibits elevated yield and ultimate tensile strengths with reduced elongation compared with annealed tempers. The alloy demonstrates a relatively linear elastic region followed by moderate strain hardening prior to stable necking; fatigue strength is governed by surface condition and residual stress state from extrusion/aging.

Yield strength and elongation vary strongly with temper and section thickness; thin extrusions and sheet in T6 can show higher yield but lower ductility than thicker plate or annealed sections. Hardness correlates with the degree of artificial aging and typically rises from low values in the O condition to significantly higher Brinell or Vickers numbers in T6, reflecting precipitation hardening.

Fatigue resistance is sensitive to surface finish, machining marks and weld quality; fatigue performance is often improved by surface treatments and careful design to avoid stress concentrations. Thickness effects matter: thicker sections cool slower during quench, which can reduce supersaturation and aging response, yielding slightly lower peak strength than thin sections treated with identical cycles.

Property	O/Annealed	Key Temper (T6/T651)	Notes
Tensile Strength	~120–180 MPa	~180–260 MPa	Range depends on cross‑section, aging schedule and supplier control
Yield Strength	~40–90 MPa	~140–220 MPa	Yield increases markedly after solution + artificial aging
Elongation	20–35%	6–15%	Ductility reduced with higher strength tempers
Hardness	~30–50 HB	~60–95 HB	Hardness increases with precipitate volume fraction and aging time

Values above are representative ranges for typical commercial product forms; specific supplier datasheets and standards provide precise certified values for given tempers and sections.

Physical Properties

Property	Value	Notes
Density	2.70 g/cm³	Typical for Al‑Mg‑Si alloys; used for weight calculations
Melting Range	~555–650 °C	Solidus/liquidus depend on minor constituents; consult standard for exact values
Thermal Conductivity	~140–170 W/m·K (20 °C)	Lower than pure Al due to alloying; thickness and temper have small effects
Electrical Conductivity	~30–45 %IACS	Moderately conductive; reduced vs commercial‑pure Al
Specific Heat	~880–900 J/kg·K	Near that of pure aluminium; small alloy dependence
Thermal Expansion	23–24 µm/m·K (20–100 °C)	Typical linear thermal expansion for Al alloys

Physically, 6020 offers the lightweight characteristics and relatively high thermal/electrical conductivities typical of aluminium alloys, with modest reductions from pure aluminium due to solute scattering and precipitates. Thermal conduction and expansion are key design inputs in heat‑sensitive assemblies; 6020 behaves similarly to other 6xxx alloys in thermomechanical systems.

Melting range and solidus temperatures are relevant for welding and casting/brazing operations; judicious control of heat input and cooling rates during welding is necessary to avoid localized overaging or softening in HAZ regions.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.5–6.0 mm	Good, sensitive to temper	O, T4, T6	Used for panels and formed components
Plate	>6 mm up to 50 mm	Lower peak strength in thick sections	O, T4, T6	Thick sections may exhibit reduced aging efficiency
Extrusion	Thin‑wall to large complex profiles	Good, extrusion conditions control properties	O, T5, T6, T651	Widely used for architectural and automotive profiles
Tube	Ø10 mm–500 mm	Similar to extrusions; wall thickness affects properties	O, T4, T6	Common for structural and fluid handling uses
Bar/Rod	Ø2 mm–200 mm	Machinable forms; properties vary with section	O, T4, T6	Used for machined components and fasteners

Sheets and thin extrusions allow rapid quench and efficient aging, achieving higher peak strengths than very thick plates. Extrusion processing brings billet chemistry, die design and cooling strategy into the final microstructure; manufacturers often specify slightly different alloy chemistries for billet quality and surface finish control.

Choosing product form is often driven by geometry and surface requirements: extrusions enable complex cross‑sections and integral stiffeners, plate offers simpler shapes at larger thicknesses, and sheet balances formability and surface finish for painted or anodized components.

Equivalent Grades

Standard	Grade	Region	Notes
AA	6020	USA/International	Recognized alloy designation in many supplier lists
EN AW	6020	Europe	EN AW‑6020 used for extrusions and drawn sections
JIS	A6020	Japan	JIS variants exist with similar chemistry and properties
GB/T	6020	China	Chinese standardized variants often aligned to EN/AA chemistries

Equivalent grade labels are often similar across regions, but processing specifications and allowable tolerances can differ by standard and mill practice. Subtle differences in impurity limits or trace microalloying (Zr, V) can alter recrystallization behavior, surface quality and aging kinetics, so cross‑referencing material certifications is essential when substituting suppliers.

When exact interchangeability is required for qualified components, request mill certificates and heat treatment records to verify that mechanical and chemical limits meet the receiving standard.

Corrosion Resistance

Atmospheric corrosion resistance of 6020 is generally good for a 6xxx series alloy due to relatively low copper and controlled iron; it resists general atmospheric attack and forms a protective oxide film comparable to 6060/6063. Surface finish and anodizing quality are favorable, making 6020 suitable for architectural and exterior applications where appearance and longevity are important.

In marine or chloride‑rich environments 6020 performs acceptably for many structural uses but is not as corrosion‑resistant as certain 5xxx (Al‑Mg) alloys; attention to galvanic coupling and protective coatings is crucial for long service life near salt water. Stress corrosion cracking (SCC) susceptibility is moderate: higher strength tempers and tensile stresses combined with corrosive environments can increase SCC risk, so design and temper selection must consider chloride exposure and residual stresses.

Galvanic interactions follow standard aluminium behavior: 6020 in contact with more noble metals (stainless steel, copper) will tend to corrode preferentially unless electrically insulated. Compared with 1xxx series, 6020 trades slightly reduced pure‑metal conductivity for improved strength and comparable corrosion resistance; compared with 5xxx series, it trades some SCC resistance for improved paintability and extrusion quality.

Fabrication Properties

Weldability

6020 welds well by common fusion processes (TIG/MIG) when standard practices are followed; pre‑weld cleaning and appropriate filler selection minimize porosity and cracking. Recommended fillers are Al‑Si types (e.g., 4043) for good wetting and reduced hot cracking, or Al‑Mg‑Si fillers (e.g., 5356/5183 variants) where mechanical strength of the weld metal is prioritized, acknowledging some differences in post‑weld corrosion behavior.

Heat‑affected zone (HAZ) softening is typical in precipitation‑hardening alloys: localized reduction of strength occurs adjacent to welds due to dissolution or overaging of precipitates. Post‑weld solution heat treatment and re‑aging are rarely practical for large assemblies; design compensation and weld sequence control are common mitigation strategies.

Machinability

Machinability of 6020 is moderate; it machines better than many high‑strength alloys but worse than certain free‑machining aluminium grades. Carbide cutting tools with TiN or AlTiN coatings and rigid setups give best results, with conservative feeds and speeds for larger sections to avoid built‑up edge. Coolant application and sharp tooling reduce surface smearing and improve finish; chip control is generally manageable with recommended grooves and tool geometries.

Typical machinability indices place 6xxx alloys in the mid‑range; feed and speed selection should account for temper and product form, with harder tempers requiring slower cutting and heavier tooling.

Formability

Formability is excellent in annealed (O) and T4 tempers, allowing tight bends and deep draws with reduced cracking risk. In T6/T5 tempers, minimum bend radii increase and springback is higher; typical internal bend radius recommendations are 1–2× thickness in annealed tempers and 2–3× thickness in peak‑aged tempers for sheet operations.

Cold‑work response is predictable: work hardening increases strength but decreases ductility; where significant forming is required, perform forming in O or T4 then solution/age to desired final temper where feasible.

Heat Treatment Behavior

6020 is a heat‑treatable Al‑Mg‑Si alloy and follows conventional 6xxx heat treatment routes: solution treatment, quench and artificial aging are the primary thermal processes for strength control. Typical solution treatment temperatures are in the range of 510–540 °C (dependent on section size and supplier recommendations) with rapid quenching to retain a supersaturated solid solution.

Artificial aging (T6/T5) is typically carried out at 160–200 °C for several hours to develop Mg2Si precipitates; aging schedules control the balance between peak strength and toughness/stress‑corrosion resistance. Overaging lowers strength but can improve ductility and SCC resistance; therefore aging is a tuning parameter based on expected service conditions.

T temper transitions follow standard nomenclature: T4 (solution treated + natural aging) may be used where forming is required after solution treatment, while T6 (solution + artificial aging) is used for peak strength. For non‑heat‑treatable processing steps such as work hardening, annealing to O is used to restore ductility.

High-Temperature Performance

Above room temperature the strength of 6020 falls off progressively as precipitates coarsen and dissolution kinetics change; significant strength reduction is observed above ~150 °C for extended service. Short‑term exposure up to ~200 °C may be tolerated without catastrophic loss of properties, but long‑term creep and softening make 6020 unsuited for sustained high‑temperature structural duty.

Oxidation of aluminium is limited to a protective Al2O3 layer and is not typically a limiting factor for 6020 in air up to elevated temperatures. In welded assemblies, HAZ regions are particularly vulnerable to softening under elevated temperature excursions, and post‑exposure properties depend on peak temperature and time at temperature.

Designers should treat service temperatures above 100–120 °C with caution, and consider alloys specifically tailored for elevated temperature strength or apply mechanical design margins where thermal exposure is expected.

Applications

Industry	Example Component	Why 6020 Is Used
Automotive	Window frames, structural extrusions	Good extrudability, surface finish and moderate strength
Marine	Non‑critical structural members and profiles	Corrosion resistance and light weight for secondary structures
Aerospace	Interior fittings, non‑primary fittings	Good strength‑to‑weight and excellent surface finish
Electronics	Housings and heatsinks	Thermal conductivity and good cosmetic finish
Architecture	Curtain wall profiles, trim	Extrudability, anodizing quality and dimensional stability

6020 is commonly used where a combination of extrusion quality, surface appearance, and moderate structural performance is needed rather than the highest possible strength. Its balance of properties makes it especially valuable for visible architectural trims, automotive extruded components with complex cross‑sections, and lightweight structural profiles.

When finish and dimensional stability are priorities, 6020 is favored over certain higher‑strength 6xxx alloys because of its improved extrusion surface quality and consistent aging response.

Selection Insights

When selecting 6020, prioritize applications that need good extrudability, surface finish and moderate precipitation‑hardened strength; it is particularly attractive for complex profiles that will be anodized or painted. Consider T4/O tempers where forming is required, and T5/T6 when elevated strength is necessary, remembering trade‑offs in ductility and SCC resistance.

Compared with commercially pure aluminium (e.g., 1100), 6020 trades off a portion of electrical and thermal conductivity and slightly reduced formability for substantially higher strength and better structural performance. Compared with work‑hardened alloys such as 3003 or 5052, 6020 provides higher age‑hardening strength with comparable paintability but can exhibit lower ductility in aged tempers; choice depends on whether post‑forming strengthening or maximum ductility is the priority.

Compared with common heat‑treatable alloys like 6061 or 6063, 6020 is often chosen where extrusion surface finish or specific billet processing yields are more important than achieving the absolute highest peak strength; 6061 may offer higher peak strength, but 6020 can provide improved extrudability and cosmetic surface characteristics for architectural or complex profiles.

Closing Summary

Aluminium 6020 remains a relevant engineering alloy where balanced strength, excellent extrudability and high‑quality surface finish are required; its heat‑treatable nature allows designers to tailor properties via temper selection, making it a practical choice for automotive, architectural and light structural applications.