Aluminum A384: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

A384 is classified within the 3xxx series of aluminum alloys, a family characterized by manganese as the principal alloying element. It is a wrought Al‑Mn alloy engineered for a balance of moderate strength, excellent formability, and good corrosion resistance, and it is strengthened primarily through work‑hardening rather than by conventional heat treatment.

Typical major alloying elements in A384 include manganese as the deliberate strength and grain‑stability addition, with low levels of silicon, iron, copper and trace elements. The alloy delivers a predictable combination of moderate tensile strength, good ductility, favorable weldability and widespread cold‑forming capability suitable for sheet, plate and extruded products.

A384 finds use in industries that require easily formed aluminium parts with reasonable strength and corrosion resistance, such as building components, HVAC, light transport panels, and general architectural applications. Engineers select A384 when formability and weldability are priorities over maximum age‑hardening strength, and when a cost‑effective, readily available Al‑Mn alloy is appropriate.

The alloy is often chosen over purer aluminium grades for its higher mechanical strength and over certain 5xxx or heat‑treatable alloys when easier cold forming, lower cost and specific corrosion behavior are more important than the highest possible strength. Its predictable behavior in rolling, forming and joining makes it a pragmatic choice for high‑volume fabrication.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Annealed condition, maximum ductility and formability
H12	Low–Medium	Moderate	Very Good	Excellent	Partially strain‑hardened by limited cold work
H14	Medium	Moderate–Low	Good	Excellent	Common commercial temper for moderate strength
H16	Medium	Moderate	Good	Excellent	Strain‑hardened to higher strength than H14
H18	Medium–High	Low–Moderate	Fair–Good	Excellent	Heavier cold working, reduced elongation
H22	Medium	Moderate	Good	Excellent	Strain‑hardened and stabilized by stress relief
H24	Medium–High	Low–Moderate	Fair	Excellent	Strain‑hardened and partially annealed for formability
H32	Medium	Moderate	Good	Excellent	Strain‑hardened and stabilized by controlled thermal treatment

Temper has a direct and predictable influence on A384’s properties, because the alloy is non‑heat‑treatable and depends on dislocation density introduced by cold work. As tempers progress from O to H18/H24, tensile and yield strengths increase while elongation and formability decrease, with H‑tempers chosen to balance forming needs against required service strength.

In fabrication and selection, choosing a temper is a trade‑off: O or H12 is preferred for deep drawing and severe forming operations, while H14–H18 series are specified where higher as‑fabricated strength or improved dimensional stability is required without resorting to a different alloy class.

Chemical Composition

Element	% Range	Notes
Si	0.10–0.60	Silicon kept low; improves fluidity in cast alloys but here minimized to preserve ductility
Fe	0.20–0.70	Impurity element that can reduce ductility and increase intermetallics
Mn	0.60–1.50	Primary strengthening and recrystallization control element for 3xxx alloys
Mg	0.05–0.20	Minor; can contribute to strength when present but kept low to maintain formability
Cu	0.05–0.20	Limited; small amounts raise strength but may reduce corrosion resistance
Zn	0.05–0.20	Typically low; higher levels can promote strength but risk stress‑corrosion susceptibility
Cr	0.01–0.10	Trace; improves grain structure and helps control recrystallization
Ti	0.01–0.10	Grain refiner in some production routes
Others	Balance to 100 (residuals)	Trace elements and residuals controlled to low levels for consistent properties

The chemistry of A384 centers on manganese for dislocation strengthening and grain stability, while low concentrations of silicon, iron and copper are tolerated as either residuals or minor performance modifiers. Small variations in Mn and Cu content materially affect yield strength, strain‑hardening behavior and corrosion resistance, so composition control is key for consistent sheet and extrusion performance.

Mechanical Properties

A384 exhibits a tensile behavior typical of Al‑Mn non‑heat‑treatable alloys: moderate ultimate tensile strength with relatively low yield in the annealed condition, and substantial increases in yield and tensile strength with cold work. The alloy’s elongation is high in O temper but falls significantly as H‑tempers increase dislocation density; designers should account for reduced forming reserve in H18/H24 states.

Hardness correlates with temper and cold work: annealed material shows low hardness and good chipless ductility, while hardened conditions reach substantially higher hardness values that influence wear and surface finishing. Fatigue performance is acceptable for moderate cyclic loads; fatigue life is sensitive to surface condition, work hardening, and residual stresses introduced by forming or welding.

Thickness and product form influence mechanical response: thin gauge sheet is easy to strain‑harden and can achieve higher as‑fabricated strength via cold rolling, while thicker plate or extrusions have coarser microstructures and lower attainable strain‑hardening per processing pass. Designers must specify temper and thickness together to ensure required static and fatigue margins.

Property	O/Annealed	Key Temper (H14)	Notes
Tensile Strength	~90–120 MPa	~160–200 MPa	H14 tensile depends on cold‑work level and gauge
Yield Strength	~30–50 MPa	~100–140 MPa	Yield increases more rapidly than UTS with cold work
Elongation	~30–40%	~8–18%	Elongation drops as strain‑hardening increases
Hardness (HB)	~25–40 HB	~55–75 HB	Hardness roughly tracks tensile properties with temper

Values are indicative ranges for common commercial gauges and production practices; vendors should be consulted for certified mill test data for specific product forms and tempers.

Physical Properties

Property	Value	Notes
Density	2.70 g/cm³	Typical for wrought aluminum alloys; useful for weight calculations
Melting Range	~640–660 °C	Practical working range, solidus close to pure Al melting point
Thermal Conductivity	~130–150 W/m·K	Alloying lowers thermal conductivity from pure Al but remains high for heat dissipation
Electrical Conductivity	~25–35 % IACS	Lower than pure Al; conductivity varies with cold work and composition
Specific Heat	~0.90 J/g·K	Approximate value for thermal‑mass calculations
Thermal Expansion	~23–24 µm/m·K	Linear coefficient suitable for joins with other structural metals if accommodated

A384’s physical properties make it a good candidate for applications requiring lightweight construction with reasonable thermal performance. Thermal conductivity is high compared with steels, making A384 preferable for heat‑dissipating components, and the coefficient of thermal expansion must be considered when assembling with materials that have significantly different expansion rates.

Electrical conductivity is moderate, so A384 is not a primary choice for high‑efficiency electrical bus bars but can be used where mechanical attributes are more important than maximum conductivity. Density and specific heat figures are used directly in stiffness and thermal mass calculations for structural and thermal systems.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.2–6.0 mm	Strength increases with cold rolling	O, H12, H14, H24	Widely produced; used for panels, envelopes and HVAC components
Plate	6–25 mm	Lower cold‑work per thickness; moderate strength	O, H22, H32	Heavier structural parts and brake/cover plates
Extrusion	Profile dependent	Strength varies with TEMPER, extrusion ratio	O, H14, H18	Profiles for architectural framing and channels
Tube	Ø6–200 mm	Cold drawing or extrusion impacts final strength	O, H14	Used for ducts, structural tubing and furniture
Bar/Rod	Ø3–60 mm	Less strain hardening achievable; depends on drawing	O, H12, H14	Fasteners, formed components and machined parts

Processing method and product form determine achievable properties: sheet benefits from rolling and post‑rolling cold work to reach H‑tempers, while extrusions and bars rely on extrusion cooling rates and subsequent cold work to develop strength. Plate thickness limits the rate of cold work and therefore the maximum H‑temper typically practical.

Applications should specify product form, temper, and surface finish together because forming, welding and fatigue performance are jointly determined by these parameters. For example, deep‑drawn panels will typically be supplied in O or H12 rather than H18 to preserve ductility.

Equivalent Grades

Standard	Grade	Region	Notes
AA	A384	USA	Designation in AA database for this wrought Al‑Mn composition
EN AW	AW‑3xxx (closest)	Europe	No one‑to‑one; AW‑3003/AW‑3004 are the closest commercial equivalents
JIS	A3003 (closest)	Japan	JIS A3003 series alloys are similar Al‑Mn wrought grades
GB/T	3xxx series (closest)	China	Chinese standards list Al‑Mn alloys comparable to 3003 family

There is often no exact one‑to‑one cross‑reference because temper, impurity limits and processing specifications vary among standards and vendors. Engineers should compare certified chemistry limits, mechanical property tables, and process certificates rather than relying solely on the nominal grade name when substituting materials.

When converting between standards, pay attention to allowable impurity levels (Fe, Si), mandated tempers, and testing practices; these differences can affect corrosion behavior and formability in critical applications.

Corrosion Resistance

A384 provides good general atmospheric corrosion resistance typical of aluminum alloys with modest copper and zinc content. In urban and industrial atmospheres it forms a protective oxide film that limits generalized corrosion, and minor surface treatments or conversion coatings can significantly improve long‑term appearance and performance.

In marine or high‑chloride environments A384 performs adequately for sheltered or periodically exposed applications but is not as resistant as specialized 5xxx (Al‑Mg) or 6xxx series with controlled Cu. Localized pitting can occur on rough or damaged surfaces, so protective coatings, anodizing, or cathodic design measures are recommended for long service life in aggressive saltwater exposure.

Stress corrosion cracking (SCC) susceptibility is low for Al‑Mn alloys like A384 compared with high‑strength Al‑Cu or Al‑Zn‑Mg alloys, but high tensile residual stresses combined with corrosive media should still be avoided. Galvanic interactions with more noble metals such as stainless steel can accelerate local corrosion of A384; isolation and appropriate fastener selection are important design considerations.

Compared with other alloy families, A384 trades off some corrosion performance versus 5xxx alloys and the ability to age‑harden to high strengths in 6xxx/7xxx families. Its balanced resistance and formability make it a common choice for architectural and HVAC applications where frequent maintenance is undesirable.

Fabrication Properties

Weldability

A384 welds very well using common fusion processes such as TIG (GTAW) and MIG (GMAW) with conventional aluminium fillers like ER4043 (Al‑Si) or ER5356 (Al‑Mg) depending on required post‑weld properties. Heat‑affected zones (HAZ) do not experience dramatic softening since the alloy is non‑heat‑treatable, but careful control of distortion and filler compatibility is needed to avoid galvanic or corrosion issues at welds.

Hot‑cracking risk is low relative to high‑strength heat‑treatable alloys but can occur if inappropriate fillers or joint designs trap stresses and solidification shrinkage. Preheating is rarely required for thin gauge work, but restrained heavy sections may benefit from controlled interpass temperatures to minimize residual stresses.

Machinability

Machining A384 is straightforward with conventional carbide or high‑speed steel tooling. Its machinability index is lower than free‑cutting brass or some leaded aluminium alloys, but acceptable for most industrial applications. Recommended practices include moderate cutting speeds, positive rake tools, and good chip evacuation to avoid built‑up edge and surface work‑hardening.

Surface finish and dimensional accuracy are achievable with standard machining feeds, but allowances for spring back and ductile chip formation must be made. Where higher hardness H‑tempers are used, tool wear rates increase and coolant strategies should be adjusted.

Formability

Formability of A384 is excellent in O and lightly strain‑hardened tempers, enabling deep drawing, hemming and complex bending operations. Minimum bend radii depend on temper and thickness but are typically 1–3× thickness for O temper and increase for H‑tempers; empirical trials or finite element forming simulations should be used for complex parts.

Cold‑work increases strength but reduces forming reserve; intermediate annealing is available to restore ductility if multiple forming steps are needed. Springback is predictable and manageable with appropriate die design and process control.

Heat Treatment Behavior

As a 3xxx series alloy, A384 is a non‑heat‑treatable alloy and does not respond to solution heat treatment and aging to significantly raise strength. Attempting to apply T‑type heat treatments will not produce the precipitation hardening seen in Al‑Mg‑Si or Al‑Cu families.

Strength is developed and controlled by mechanical work (cold rolling, drawing) and subsequent H‑tempers. Annealing (full softening to O) is achieved by heating above the recrystallization temperature (typically in the range of 330–420 °C depending on section size and alloy condition) followed by controlled cooling to obtain a fully recrystallized microstructure.

Stabilizing treatments such as slight thermal exposure (e.g., H32) can be used to relieve residual stresses without fully annealing the material. For critical dimension parts, stress relief cycles should be validated as they can shift mechanical properties subtly.

High-Temperature Performance

A384 maintains usable mechanical properties at modest elevated temperatures but experiences progressive strength loss as temperature increases. Above ~100–150 °C prolonged exposure produces measurable reductions in yield and tensile strength due to recovery and softening of the cold‑worked structure.

Oxidation is minimal compared with ferrous alloys because of the protective aluminum oxide film, but at higher temperatures surface scaling and embrittlement from surface reactions can occur if aggressive environments are present. For continuous service above 150 °C, designers should validate creep behavior and consider alloys specifically engineered for elevated‑temperature stability.

Welded joints exposed to elevated temperatures require attention to HAZ behavior; since the alloy is non‑heat‑treatable, HAZ softening is limited but thermal exposure can relax cold work and reduce localized strength, impacting load paths.

Applications

Industry	Example Component	Why A384 Is Used
Automotive	Interior panels, heat shields	Good formability, weldability, cost efficiency
Marine	Ducts, non‑structural enclosures	Corrosion resistance in atmospheric marine environments
Aerospace	Non‑critical fittings, fairings	Strength‑to‑weight and easy forming for secondary structures
Electronics	Chassis, heat spreaders	Thermal conductivity and good manufacturability
Building & Construction	Roofing, cladding, gutters	Weather resistance, formability, and finishability

A384’s combination of formability, weldability and moderate strength make it suited to a broad range of non‑high‑stress components across multiple industries. It is most commonly used where complex shaping, surface finish and corrosion resistance are required at reasonable cost.

Selection Insights

Choose A384 when your design prioritizes high cold‑formability, good weldability and moderate strength with broad availability and low cost. It is ideal for stamped or drawn components, architectural elements and general fabrication where extreme tensile strength is not required.

Compared with commercially pure aluminium (1100), A384 trades some electrical and thermal conductivity and slightly reduced pure‑metal ductility for a meaningful increase in strength and better dimensional stability during forming. Compared with other work‑hardened alloys like 3003 or 5052, A384 sits in a similar bracket of formability and corrosion resistance but is typically selected when a specific combination of Mn‑based strengthening and vendor availability aligns with design needs.

Against heat‑treatable alloys such as 6061 or 6063, A384 is chosen when ease of forming and welding, and lower material cost outweigh the need for higher peak age‑hardening strength. If higher long‑term static or fatigue strength is mandatory, a heat‑treatable family may be preferred despite increased fabrication complexity.

Closing Summary

A384 remains a relevant and widely used Al‑Mn wrought alloy because it reliably delivers an