Aluminum 3A18: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

3A18 is a member of the 3xxx series aluminum alloys, which are principally manganese-containing, non-heat-treatable alloys based on aluminum with Mn as the primary strengthening addition. The numeric suffix indicates that manganese content is higher than typical 3000-series commercial grades, positioning 3A18 between conventional 3003 and higher-Mn specialty alloys in terms of strength and work-hardening response.

The dominant alloying element is manganese, with controlled levels of silicon, iron and trace elements; magnesium and copper are deliberately limited to keep the alloy non-heat-treatable and to preserve corrosion resistance. Strengthening is achieved predominantly through solid-solution effects and strain hardening (cold work); there is negligible age-hardening response because precipitate-forming solutes are kept low.

Key traits of 3A18 include good baseline strength for an Al–Mn alloy, robust atmospheric corrosion resistance, good cold formability in annealed conditions, and straightforward weldability with standard Al filler metals. Its combination of formability, corrosion resistance and modest strength makes it attractive for industries where fabricability and longevity in service environments matter more than peak, heat-treatable strengths.

Typical industries using alloys of this family include building and construction (architectural panels and trim), transportation (interior automotive components and lightweight structural sections), marine (non-critical structures and fittings), and consumer appliances. Engineers select 3A18 over purer aluminum grades when an improved yield and tensile baseline is needed without sacrificing formability and corrosion resistance, and over heat-treatable alloys when complex forming operations or cost-effective fabrication must be prioritized.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed condition; best for deep drawing and complex forming
H14	Medium-High	Low-Medium	Fair	Good	Light work-hardening; common for sheet applications needing higher yield
H18	High	Low	Limited	Good	Heavily cold-worked; high strength with reduced ductility
T4	Medium	Medium	Good	Good	Solutionized and naturally aged where applicable; uncommon for non-heat-treatable alloys
T6 (if present)	Not typical	N/A	Poor	Good	Not a standard temper for Al–Mn non-heat-treatable alloys; listed for completeness
H24/H26	Medium	Medium-Low	Fair	Good	Partial anneal after work hardening to balance strength and formability

Temper has a direct and predictable effect on mechanical and forming performance. Annealed (O) temper delivers the best formability and highest elongation, which is essential for deep drawing and complex stamping, whereas H-series work-hardened tempers trade ductility for yield and tensile strength, improving permanent load capacity at the expense of bendability.

Manufacturers use intermediate tempers (e.g., H24) to balance stamping survivability with required in-service strength; selecting the correct temper requires matching anticipated forming strain, desired springback characteristics, and post-form weld or join operations.

Chemical Composition

Element	% Range	Notes
Si	≤ 0.6	Controlled to limit brittle intermetallics and maintain ductility
Fe	≤ 0.7	Common impurity; higher Fe increases strength but can reduce toughness
Mn	1.6–2.0	Primary alloying element for strengthening by solid solution and dispersoids
Mg	≤ 0.10	Kept low to avoid age-hardening and retain corrosion resistance
Cu	≤ 0.10	Minimised to prevent susceptibility to localized corrosion and SCC
Zn	≤ 0.2	Low level to avoid galvanic penalties; not a strengthening contributor here
Cr	≤ 0.10	Small additions can control grain structure during processing
Ti	≤ 0.15	Grain refiner in cast/processed stocks; controlled for cleanliness
Others	≤ 0.15 total	Trace residuals including Zr, Ni, Sr; balance Al

The composition emphasizes manganese as the the deliberate strengthening solute, with tight controls on copper, zinc and magnesium to prevent precipitation hardening and to preserve corrosion resistance. Silicon and iron are limited to acceptable impurity levels that allow cost-effective melting while avoiding significant degradation of ductility and surface appearance.

Mechanical Properties

3A18 shows classic Al–Mn tensile behavior: in the fully annealed state it has modest yield and moderate tensile strength with high elongation, enabling forming operations without extensive cracking. As the material is cold worked into H tempers, yield and tensile strengths increase substantially at the expense of elongation; ductility drops predictably and springback increases, which must be compensated for in tool design.

Hardness follows the same trend, from low Brinell numbers in O temper to substantially higher hardness after work-hardening; this correlates with improved wear resistance and higher fatigue endurance limits at moderate cyclic stresses. Fatigue performance is generally good for components run in the corrosion-resistant state, but can be sensitive to surface condition, notches and weld-induced local softening or residual stresses.

Thickness affects mechanical response through constraint on strain distribution: thinner gauges will accept higher uniform elongation and formability but may have lower absolute load-carrying capacity; thicker sections show improved static stiffness and can support greater post-forming residual loads but are harder to cold-form without springback compensation.

Property	O/Annealed	Key Temper (H14 / H18)	Notes
Tensile Strength	110–160 MPa	200–260 MPa	H14/H18 values depend on degree of cold work and final gauge
Yield Strength	40–80 MPa	140–220 MPa	Yield rises rapidly with minor cold work; yield point can be broad in Al–Mn alloys
Elongation	20–35%	6–15%	Elongation drops sharply with increasing temper designation
Hardness (HB)	30–45 HB	65–95 HB	Correlates with tensile increase; hardness is gauge- and work-hardening dependent

Physical Properties

Property	Value	Notes
Density	2.70 g/cm³	Typical for most commercial Al–Mn alloys
Melting Range	645–655 °C	Solidus–liquidus range is narrow; casting behavior not the primary use
Thermal Conductivity	≈ 140–170 W/m·K	Alloying reduces conductivity relative to pure Al; useful for moderate heat-sink needs
Electrical Conductivity	≈ 30–40 %IACS	Lower than high-purity Al; varies slightly with temper and impurity content
Specific Heat	≈ 880–910 J/kg·K	Typical aluminum specific heat near ambient temperature
Thermal Expansion	23–24 µm/m·K (20–100 °C)	Considerable expansion; design must account for thermal growth in assemblies

Aluminum 3A18 retains the advantageous thermal conductivity and specific heat of aluminum alloys, which makes it suitable for moderate thermal management tasks where weight and corrosion resistance are also priorities. Density and expansion figures make it attractive for lightweight structural parts but require attention to thermal mismatch when joined to steels or composites.

Electrical conductivity is reduced relative to commercially pure aluminum, so 3A18 is not typically chosen for primary electrical conductors; instead, it is selected where a balance of mechanical performance and軽weight corrosion resistance is paramount.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.2–6.0 mm	Conforms well to O/H series behavior	O, H14, H18	Most common form for architectural and appliance panels
Plate	6–50 mm	Higher section stiffness; limited cold forming	O, H24	Used where greater thickness and stiffness are needed
Extrusion	Profiles up to 200 mm	Strength varies with section and temper	O, H12	Extrusions used for frames and structural sections; dimensional control important
Tube	0.5–10 mm wall	Good formability for drawn/seamed tubes	O, H14	Used in heat exchanger housings and non-pressurized marine tubing
Bar/Rod	3–50 mm dia.	Strength depends on cold work/aging history	O, H18	Common for machined components and fittings

Sheet stock is the most widely produced product form and benefits from consistent surface quality for architectural and appliance uses, while plate is produced for structural panels and is normally sold in softer tempers to enable limited forming. Extrusions and tubes are produced with attention to grain flow and surface finish; extruded sections often undergo light post-extrusion stretching or cold working to stabilize dimensions and increase yield strength.

Forming routes differ by product: sheet is typically roll-formed, stamped or deep-drawn; extrusions are pushed and stretched, then age-stabilized or work-hardened as needed; heavy plate is normally fabricated by mechanical shaping and welding rather than deep drawing.

Equivalent Grades

Standard	Grade	Region	Notes
AA	3A18	China / Regional	Chinese standard designation used in domestic supply chains
EN AW	3003 (similar)	Europe	EN AW-3003 is compositionally close; not an exact cross but useful for specification comparison
JIS	A3003 (approx.)	Japan	JIS Al–Mn grades provide a functional analog for design equivalence
GB/T	3A18	China	National standard mapping typically uses the 3A18 designation directly

Exact one-to-one equivalents between regional standards do not always exist because of small but important differences in permitted impurity levels and specified temper practices. When converting specifications, engineers should compare certified composition and mechanical data rather than relying solely on grade names, and include acceptance testing clauses to capture critical differences in Mn content, Fe limits and surface quality.

Corrosion Resistance

3A18 demonstrates strong general atmospheric corrosion resistance typical of Al–Mn alloys due to the formation of a protective, adherent alumina film; this film limits uniform corrosion and preserves surface appearance in outdoor environments. The low copper and zinc content reduces susceptibility to localized pitting and intergranular attack compared with copper-bearing alloys.

In marine and chloride-laden environments 3A18 performs well relative to many other non-heat-treatable alloys, though prolonged immersion and stray-current conditions will accelerate degradation; proper design detailing, coatings and isolation from dissimilar metals are recommended for long-term service. Stress corrosion cracking (SCC) is not a major concern for Al–Mn alloys compared with high-strength, heat-treatable aluminum alloys; however, elevated residual tensile stresses combined with corrosive chloride environments can still promote crack initiation in poorly detailed components.

Galvanic interactions should be considered when joining 3A18 to more noble metals such as stainless steel or copper; using insulating barriers, protective coatings, or compatible fasteners mitigates galvanic attack. Compared with 5xxx (Al–Mg) series alloys, 3A18 offers similar atmospheric performance but typically better surface appearance and similar resistance to exfoliation; compared with 6xxx (Al–Mg–Si) alloys, corrosion resistance is comparable but processing and formability advantages may favor 3A18 for complex shapes.

Fabrication Properties

Weldability

Welding behavior for 3A18 is favorable with conventional TIG (GTAW) and MIG (GMAW) processes; weld pools flow well and porosity is manageable with proper cleaning. Recommended filler alloys include Al–Mn variants and common commercially available filler metals such as 4043 (Al–Si) or 5356 (Al–Mg) depending on desired post-weld corrosion resistance and mechanical match; 5356 offers higher strength but may modestly reduce corrosion resistance in some environments.

Hot-cracking risk is low relative to certain 2xxx or 7xxx series alloys because of the alloy’s chemistry and solidification characteristics, but good joint design and fit-up are still required to minimize stress concentrators. The heat-affected zone will experience some softening only insofar as cold-worked tempers are locally annealed; because strengthening is not precipitation based, post-weld strength recovery through heat treatment is not applicable.

Machinability

As a relatively ductile Al–Mn alloy, 3A18 exhibits fair machinability but is not a 'free-cutting' grade; chip control and tool life benefit from sharp tooling and appropriate feeds. Carbide or coated high-speed steel tools with high positive rake angles and good coolant application yield the best surface finish; speeds should be moderate to avoid built-up edge typical of aluminum machining.

Work-hardening at the tool interface can occur if feed or chip evacuation is insufficient, so tooling and fixturing should minimize rubbing and enable continuous chip clearance. For production machining, use of backstops, brush-like chip breakers and periodic tool inspection improves cycle stability.

Formability

Formability is excellent in annealed condition, enabling deep drawing, complex stamping and stretch forming with tight radii; typical recommended minimum inside bend radius in O temper is 1–2× thickness for mild curvature and 2–3× thickness for tight bends, depending on tooling and surface finish. Cold-worked H tempers have sharply reduced elongation; forming should either be done prior to hardening or compensated with larger radii and incremental bending.

Springback is higher in H tempers and in thicker sections; die compensation and incremental forming strategies are commonly used to meet dimensional tolerances. For drawn or embossed parts, lubrication and surface treatment selection have a large effect on tool life, frictions and final surface appearance.

Heat Treatment Behavior

3A18 is classified as a non-heat-treatable alloy where mechanical properties are adjusted primarily by cold working and annealing rather than by solution treatment and precipitation aging. Conventional solution treat/age cycles typical for 6xxx or 7xxx alloys are ineffective here because the principal alloying element (Mn) does not form strengthening metastable precipitates that respond to artificial aging.

Annealing is achieved by heating into the range of approximately 300–415 °C (dependant on section thickness and mill practice) to restore ductility, recrystallize the microstructure and reduce internal strains introduced by cold work. Controlled cooling after anneal is used to avoid distortion; full annealing will reduce work-hardened strength to near-O temper levels.

Work hardening (cold rolling, drawing, or stamping) is the practical route to increase yield and tensile strength; subsequent partial anneals (intermediate tempers such as H24) allow suppliers and fabricators to tailor a balance of formability and strength by tempering the cold-worked structure.

High-Temperature Performance

Like most Al–Mn alloys, 3A18 experiences a progressive loss of mechanical strength at elevated temperatures; above approximately 150 °C to 200 °C significant reductions in yield and tensile strength occur, limiting load-bearing service in high-temperature applications. Creep resistance at sustained elevated temperatures is limited; for furnace-exposed or high-ambient-temperature structural applications, engineers should select alloys specifically designed for elevated-temperature service.

Oxidation is limited to a thin protective alumina layer that forms quickly and retards further attack; there is no significant scale formation as seen in steels, but prolonged exposure to high temperatures can affect surface appearance and mechanical integrity. The heat-affected zone in welded assemblies can show localized softening if service temperatures approach those used for annealing, so designers must consider combined thermal and mechanical load cases.

For intermittent exposures or applications up to ~100–120 °C, 3A18 retains much of its room-temperature ductility and strength, making it suitable for engine bay components, housings and enclosures where temperature excursions are moderate and transient.

Applications

Industry	Example Component	Why 3A18 Is Used
Automotive	Interior panels; decorative trim	Good formability and improved strength vs pure Al for stamped parts
Marine	Non-structural deck fittings; housing panels	Corrosion resistance in wet and splash environments
Aerospace	Secondary fittings; brackets	Favorable strength-to-weight and ease of fabrication for non-critical hardware
Consumer Appliances	Refrigerator panels; dryer drums	Excellent surface finish potential and formability for stamped enclosures
Electronics	Enclosures and moderate-duty heat spreaders	Thermal conductivity and corrosion resistance balance fabrication needs

3A18 is most often chosen where a combination of good formability, satisfactory structural strength and strong corrosion resistance are required in a cost-efficient alloy. It is particularly well-suited to stamped and drawn components that demand good surface appearance and long-term exposure performance without the costs and processing complexity of heat-treatable high-strength alloys.

Selection Insights

When choosing 3A18, prioritize applications that need a middle ground between commercially pure aluminum and higher-strength, heat-treatable alloys: it offers significantly higher yield and tensile strength than 1100 while retaining much better formability and corrosion resistance than many high-strength alloys. Use 3A18 when forming complexity, surface finish and long-term atmospheric exposure are more important than maximum achievable strength.

Compared with 1100 (commercially pure): 3A18 trades some electrical/thermal conductivity and slightly reduced corrosion nobility for materially higher strength and lower springback, making it a better choice for structural stamped components. Compared with work-hardened alloys such as 3003 or 5052: 3A18 typically provides higher baseline strength while maintaining similar corrosion resistance; 5052 gives superior strength in marine environments but with different forming and joining considerations. Compared with common heat-treatable alloys such as 6061 or 6063: choose 3A18 when complex forming operations are required or when cost and corrosion resistance outweigh the need for peak precipitate-strengthened tensile/yield levels.

Closing Summary

3A18 occupies a pragmatic position in the aluminum alloy portfolio, delivering enhanced mechanical strength over pure aluminum while preserving the formability and corrosion performance critical to many industrial applications. Its non-heat-treatable nature simplifies fabrication routes and makes it a cost-effective choice for stamped, drawn and welded components where moderate strength, good fatigue behavior and reliable long-term outdoor performance are required.