Aluminum 384: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

Alloy 384 is a wrought aluminum alloy that falls into the 3xxx series family, where manganese is the principal alloying addition that distinguishes the series from 1xxx (commercially pure) and 6xxx (Mg-Si heat-treatable) families. It is formulated to provide a balance of moderate strength, excellent formability, and good corrosion performance while remaining non-heat-treatable; strengthening is accomplished primarily via solid-solution effects and cold working rather than precipitation hardening. Key alloying constituents beyond manganese often include modest concentrations of iron and magnesium with trace additions of chromium or titanium to control grain structure and recrystallization behavior. Typical end-users come from automotive body and trim, appliance and consumer goods stampings, architectural components, and certain marine and heat-exchanger applications where a combination of formability, weldability, and adequate strength is required.

The alloy is chosen over many alternatives when designers need better strength than commercially pure aluminum without sacrificing deep-drawability and bend performance; 384 sits above 1100 in strength yet retains superior forming compared with many 5xxx and 6xxx alloys in comparable conditions. Corrosion resistance is good in atmospheric and mildly corrosive environments because of the alloy’s low copper content and controlled manganese/iron ratios that limit intermetallic cathodic sites. Weldability is generally excellent in common fusion processes, and annealed/soft tempers permit tight-radius forming operations that would be difficult with cold-worked high-strength alloys.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High (30–45%)	Excellent	Excellent	Fully annealed, maximum ductility for drawing
H14	Moderate-High	Moderate (8–18%)	Good	Excellent	Single-step strain-hardened, commonly used for moderate-strength stampings
H18	Moderate	Moderate-High (12–25%)	Very Good	Excellent	More work-hardened than H14 with retained formability
H22	Moderate	Moderate (10–20%)	Good	Excellent	Strain-hardened and stabilized by partial anneal for consistent properties
H24	Moderate-High	Moderate (8–15%)	Good	Excellent	Strain-hardened and slightly softened for balancing strength and formability
H111	Low-Moderate	High (20–35%)	Very Good	Excellent	Essentially annealed but with slight cold work, used for sheet with controlled properties

Temper choice strongly affects the alloy’s mechanical envelope and forming window; annealed O-temper maximizes stretch and deep-draw performance but yields the lowest strength, while H-series tempers trade ductility for higher yield and tensile strength via controlled cold work. Weldability remains favorable across most tempers because the alloy is non-heat-treatable and has low susceptibility to softening in the heat-affected zone; designers should select temper to match forming route and post-fabrication performance targets.

Chemical Composition

Element	% Range	Notes
Si	0.10–0.60	Controlled to limit brittleness and to influence fluidity in cast derivatives; low Si in wrought 384 preserves ductility.
Fe	0.20–0.90	Iron is an unavoidable impurity; managed to minimize coarse intermetallics that reduce formability.
Mn	0.80–1.50	Primary strengthener for 3xxx series; refines grain and reduces recrystallization during processing.
Mg	0.10–0.60	Small Mg additions raise strength without moving alloy into 5xxx-class corrosion sensitivity.
Cu	0.05–0.20	Kept low to preserve corrosion resistance and reduce SCC susceptibility.
Zn	≤0.20	Low levels to avoid significant increases in environmental embrittlement risk.
Cr	0.02–0.15	Microalloying to stabilize grain structure and improve surface finish after processing.
Ti	≤0.05	Minor addition for grain refinement in some product forms.
Others	Balance Al, trace impurities	Residuals and deliberate trace elements controlled to maintain consistency and surface quality.

Compositional control in 384 is tuned to deliver a favorable combination of strength, formability and corrosion resistance; manganese provides the principal strengthening and recrystallization control while modest magnesium increases strength without pushing the alloy into the more corrosion-prone 5xxx domain. Iron and silicon levels are kept low to limit coarse intermetallic particle formation that would otherwise reduce elongation and impair ductility during severe forming operations.

Mechanical Properties

In tensile behavior, 384 displays significant variation with temper and amount of cold work; annealed sheet exhibits relatively low yield strength but high elongation and stable necking characteristics, while H‑series tempers show substantially higher yield and tensile strengths at the expense of uniform elongation. Yield strength in cold-worked conditions increases roughly in proportion to the amount of pre-strain, and the strain-hardening exponent (n-value) falls as temper becomes harder, affecting springback and stretch forming outcomes. Hardness correlates with yield; Brinell or Vickers numbers are frequently used as a quick shop-floor check to estimate tensile properties, and fatigue resistance follows the alloy’s tensile strength and surface condition — polished or shot-peened surfaces substantially improve fatigue life.

Thickness has a pronounced effect: thinner gauges typically achieve higher effective strain-hardening during rolling and exhibit somewhat higher measured strengths in H‑tempers, while thicker plate can contain more coarse intermetallics and show slightly reduced elongation. Fatigue crack initiation is commonly controlled by surface condition, residual stress and mid‑range loading; 384 alloys generally perform well under moderate cyclic loads but require design attention for high-cycle, high-stress applications. Thermal exposure near 200 °C and above progressively relaxes cold work and reduces strength because 384 is non-heat-treatable and lacks stable precipitates to retain strengthened states.

Property	O/Annealed	Key Temper (e.g., H14)	Notes
Tensile Strength	90–140 MPa	160–240 MPa	Values vary with gauge and percent cold work; typical shop ranges shown.
Yield Strength	30–80 MPa	120–200 MPa	Yield increases strongly with H-temper level and prestrain.
Elongation	30–45%	8–18%	Annealed affords deep drawing; H tempers trade ductility for strength.
Hardness	20–35 HB	45–85 HB	Brinell hardness scales roughly with yield strength; used for quick QC checks.

Physical Properties

Property	Value	Notes
Density	2.70 g/cm³	Typical for Al alloys; useful for mass and stiffness calculations.
Melting Range	~555–650 °C	Alloying broadens the melting interval vs pure Al (660 °C solidus for pure Al).
Thermal Conductivity	120–160 W/m·K	Slightly lower than pure Al; good for heat transfer applications.
Electrical Conductivity	~30–42 %IACS	Lower than 1xxx series due to alloying; adequate for many electrical chassis uses.
Specific Heat	~900 J/kg·K	Near that of pure Al; important for transient thermal design.
Thermal Expansion	23–24 µm/m·K	Typical coefficient for Al alloys used in thermal mismatch calculations.

The physical properties make 384 attractive for components that require both structural function and thermal management because its thermal conductivity remains relatively high compared to steels and many non‑ferrous alternatives. Electrical conductivity is reduced relative to pure aluminum, so designers should account for higher resistive losses if the alloy is considered for conductor applications; the alloy’s low density contributes to beneficial strength-to-weight ratios in transport and aerospace-related components.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.3–6.0 mm	Thin gauges show higher effective strength after cold rolling	O, H14, H24, H111	Most common form for body panels, appliances, and architectural cladding.
Plate	6–50 mm	Lower work-hardening in thick gauges; reduced elongation	O, H22	Used where stamping is not required but structural stiffness is needed.
Extrusion	Cross-sections to >200 mm	Mechanical behavior depends on billet processing and aging of surface layers	O, H18	Extrusions allow complex shapes with consistent wall thickness for frames and rails.
Tube	ø6–200 mm	Cold drawing and welding affect properties; good weldability	O, H14	Used for condenser tubing, lightweight structural members and furniture.
Bar/Rod	ø3–50 mm	Drawn or extruded stock with work-hardened surfaces	O, H14	Used for machined fittings, fasteners, and small structural parts.

Processing route dictates microstructure and therefore final properties: rolling and subsequent cold work set the H‑tempers used for sheet and strip, while extrusion promotes elongated grain structures that influence directional strength and bend performance. Plate and thicker products often require homogenization or controlled cooling to minimize segregation and intermetallic growth, and extruded profiles are frequently solution-treated in production of complex shapes to optimize surface finish and dimensional stability.

Equivalent Grades

Standard	Grade	Region	Notes
AA	384	USA	Wrought 3xxx-series alloy used in specialty sheet and extruded forms.
EN AW	No direct equivalent	Europe	Closest functional equivalents: AW‑3003 / AW‑3004 for formability and composition.
JIS	No direct equivalent	Japan	Similar performance to JIS-series Al‑Mn sheet alloys used for stampings.
GB/T	No direct equivalent	China	Often substituted with 3003‑class or 3004‑class alloys depending on property requirements.

There is no single one-to-one conversion to major international specifications for 384 because regional standards emphasize slightly different chemistries and processing histories; in practice engineers select the nearest commercial family (3003/3004) and then validate through mechanical testing and corrosion trials. Where interchangeability is required, buyers should request specific chemistry and mechanical certificates and, if necessary, run qualification testing for critical applications.

Corrosion Resistance

384 exhibits good atmospheric corrosion resistance owing to its low copper content and manganese-dominated alloying, which reduces the electrochemical potential of intermetallic particles that can act as cathodic sites. In urban and industrial atmospheres the alloy forms a stable alumina film that limits general corrosion, and performance in cyclic wet-dry conditions is acceptable for architectural and automotive exterior applications. Chloride environments (marine) are more aggressive; although 384 performs better than many copper-containing alloys, localized pitting can occur on roughened surfaces or where contaminant salts concentrate.

Stress corrosion cracking (SCC) susceptibility is low relative to high-copper or high‑zinc alloys, but SCC risk increases with elevated tensile residual stresses, aggressive chloride exposure, and raised temperatures; designers should avoid combinations of those conditions for long-term underwater or splash-zone service. Galvanic interaction with dissimilar metals should be managed: when mated to steels or copper alloys, electrical continuity and area ratios drive galvanic rates — bonding to more noble materials can accelerate attack on 384 unless insulating barriers or sacrificial anodes are used. Compared with 5xxx (Al‑Mg) alloys, 384 is less prone to strain‑induced SCC but may offer slightly lower baseline corrosion resistance in some marine bulkhead or weld-heavy applications.

Fabrication Properties

Weldability

Alloy 384 is highly weldable with common fusion processes such as TIG (GTAW) and MIG (GMAW), and it displays low hot-cracking tendency when proper joint fit-up and cleanliness are maintained. Recommended filler wires include Al‑4043 or Al‑5356 depending on desired post‑weld corrosion and mechanical performance; Al‑4043 provides improved flow and lower cracking sensitivity whereas Al‑5356 delivers higher weld strength but requires consideration for corrosion in chloride environments. Heat-affected-zone (HAZ) softening is limited due to the non-heat-treatable nature of the alloy, but excessive heat input can reduce local strength due to recovery of cold work and should be controlled for critical dimensions.

Machinability

Machinability of 384 is moderate; it machines easier than many high-strength aluminum alloys but is not as free-cutting as some leaded or high-silicon alloys. Carbide tooling with polished geometries and positive rake angles is recommended to minimize built-up edge and improve surface finish, and conventional spindle speeds for aluminum alloys (high speed, low feed per tooth) apply. Chip control can be managed with chip breakers and high-volume coolant or compressed air to prevent re-cutting; burr formation is generally modest but requires attention when producing tight-tolerance features.

Formability

Formability is one of 384’s strong points in annealed and lightly worked tempers, showing excellent stretch and deep-draw performance with tight bend radii achievable when the O temper is used. Recommended minimum inside bend radii typically fall in the range of 0.5–1.0× material thickness for O temper and increase to 1.0–2.5× thickness for H‑tempers depending on gauge and tooling, with lubrication and die design key to avoiding wrinkling and cracking. Cold working is an effective method to reach desired strength levels, and when extensive forming is required it is common to form in O temper then perform controlled work-hardening operations or select H111/H18 to balance formability and strength.

Heat Treatment Behavior

Because 384 is a non‑heat‑treatable alloy, conventional solution treatment and artificial aging cycles used for 6xxx and 7xxx families do not produce the same precipitation-strengthening effects. Attempts to heat-treat 384 will primarily influence recovery and grain growth; elevated-temperature exposure will soften the alloy through annealing effects rather than creating new strengthening precipitates. Practical property control relies on the cold-work path: varying the degree of rolling, drawing, or bending allows designers to tune yield and tensile strength.

Annealing to O temper is accomplished by heating into the recrystallization range (typically in the range of 350–420 °C for sufficient time depending on section thickness) and then controlled cooling to retain a fine-grained, ductile microstructure; care must be taken to avoid excessive thermal exposure that could coarsen grain and reduce toughness. Stabilizing operations such as slight anneals and stress-relief can be used to reduce springback and improve dimensional control prior to final forming or fabrication operations.

High-Temperature Performance

At elevated temperatures the mechanical strength of 384 degrades progressively because its primary strengthening is from work-hardening and solid solution effects that relax with heat. Service temperatures above ~150 °C will begin to produce measurable reductions in yield strength and hardness, and extended exposure above ~200 °C can lead to significant softening and microstructural coarsening. Oxidation is minimal compared to ferrous alloys, but surface scaling and grain-boundary changes can influence fatigue and creep behavior in long-term high-temperature use.

Weld heat-affected zones may show localized softening if post-weld thermal cycles overlap with annealing ranges, although substantial re-precipitation is not a factor; for components that must retain mechanical properties at moderately elevated temperatures, alternate heat-resistant aluminum alloys or design adjustments are recommended. For short-duration thermal excursions such as welding or painting cure cycles, 384 maintains functional performance, but designers should validate critical dimensions and tolerances after thermal processing.

Applications

Industry	Example Component	Why 384 Is Used
Automotive	Exterior trim and body-panel reinforcements	Good drawability plus higher strength than pure Al for functional panels
Marine	Interior structural members and trim	Balanced corrosion resistance and formability for splash and bilge zones
Aerospace	Secondary fittings and fairings	High specific strength and ease of fabrication for non-primary structures
Electronics	Chassis and moderate-duty heat sinks	Good thermal conductivity combined with structural function

The alloy is widely used where forming operations and welding are required alongside moderate strength and light weight, delivering a cost-effective alternative to both pure aluminum and higher-strength heat-treatable alloys. Typical production runs leverage sheet rolling and controlled tempering to deliver consistent, repeatable performance in stamped, bent and welded assemblies.

Selection Insights

For design selection, 384 is a logical choice when engineers require a step up in strength from commercially pure aluminum (1100) while preserving the excellent formability and weldability that facilitate deep drawing and brazing. Compared with 1100, 384 trades off some electrical and thermal conductivity for higher yield and tensile strength, making it better for structural elements that need forming.

Against common work-hardened alloys such as 3003 or 5052, 384 typically sits between 3003 and 5052 in terms of strength and corrosion resistance: it offers higher strength than 3003 with comparable formability, and it is less corrosion-sensitive than many high-magnesium 5xxx alloys. When compared to heat-treatable alloys like 6061 or 6063, 384 lacks the same peak strength but is often preferred for complex forming operations and where weldability and post‑form dimensional stability are more critical than maximum strength.

Choose 384 when the design priority list is: moderate structural performance, excellent forming and welding characteristics, and solid atmospheric corrosion resistance at competitive material cost and broad availability; validate via prototype testing for marine or high‑cycle fatigue applications.

Closing Summary

Alloy 384 remains relevant as a practical engineering aluminum that bridges the gap between pure aluminum and higher‑strength families, delivering a pragmatic balance of formability, weldability, corrosion resistance and moderate strength for a wide range of industrial applications. Its processing flexibility and stable performance in common fabrication routes make it a dependable option for designers seeking lightweight components that are economical to manufacture and service.