Aluminum 4004: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

Alloy 4004 is a member of the 4xxx series of aluminum alloys, which are silicon-bearing wrought compositions in the Al-Si family. The 4xxx series is characterized by silicon as the principal alloying element, typically combined with trace levels of iron, copper, manganese and other impurities to tailor castability and thermal properties.

The nominal strengthening mechanism for 4004 is primarily solid-solution strengthening from silicon and dispersion of intermetallic Si-rich phases; it is largely non-heat-treatable and relies on strain hardening (H-temper operations) and controlled cooling to adjust properties. Key traits of 4004 include moderate-to-good strength for a non-heat-treatable alloy, improved wear and thermal stability compared with very pure grades, good corrosion resistance in many atmospheres, and generally favorable weldability and formability.

Industries that commonly use 4xxx-series alloys such as 4004 include automotive (body components and filler wires), consumer appliances, heat exchange and electronics (where thermal conductivity and castability matter), and transport where a balance of formability and elevated thermal performance is required. Engineers select 4004 when they need better elevated-temperature dimensional stability or thermal properties than commercially pure aluminum, but without the cost or processing complexity of higher-strength heat-treatable alloys.

4004 is often chosen over lower-alloyed grades because it offers a pragmatic trade-off: enhanced silicon content improves high-temperature stability and reduces thermal expansion while retaining good cold-forming behavior and weldability. It is preferred when design drivers are moderate strength combined with thermal conductivity, reduced hot-shortness during welding or brazing, and consistent performance across forming and joining operations.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed condition for max ductility
H12	Low-Medium	Medium	Very Good	Very Good	Light strain hardened, limited forming recovery
H14	Medium	Medium-Low	Good	Very Good	Common cold-work temper for sheet applications
H18	High	Low	Poor	Good	Fully hard, used when spring properties are required
T4*	Low-Medium	Medium	Very Good	Very Good	Limited solutionized condition; applicability depends on exact chemistry
T5*	Medium	Medium-Low	Good	Good	Artificially aged from cooled-from-casting; limited hardening potential
T6*	Medium	Medium-Low	Moderate	Moderate	Some 4xxx alloys show limited precipitation response; benefits are modest

After the table, temper selection for 4004 primarily revolves around work hardening versus anneal states, with O providing maximum ductility and the H-temper series incrementally increasing yield and tensile levels. Where minor heat treatment (T-types) is specified, the achievable hardening is limited relative to 2xxx or 6xxx heat-treatable alloys and is used mainly to stabilize microstructure or relieve residual stresses rather than to create large strength gains.

Chemical Composition

Element	% Range	Notes
Si	0.7–1.6	Primary alloying element; controls solid-solution strengthening and thermal behavior
Fe	0.2–0.8	Impurity element; forms intermetallics that influence strength and machinability
Mn	0.05–0.5	Grain structure modifier; improves strength and corrosion performance marginally
Mg	0.02–0.25	Low levels can enhance work-hardening response; limited precipitation strengthening
Cu	0.02–0.25	Small additions increase strength but can reduce corrosion resistance if high
Zn	0.02–0.15	Generally low; kept limited to avoid embrittlement and SCC susceptibility
Cr	0.01–0.10	Trace element to control grain structure and recrystallization in tempers
Ti	0.01–0.10	Grain refiner added in small quantities, especially in cast or billet processing
Others	Balance Al	Residuals and tramp elements controlled to meet mechanical and corrosion specs

The combination of silicon with modest levels of iron and manganese defines the 4004 alloy's mechanical and thermal behavior; silicon primarily lowers the melting range locally and increases strength via solid solution and intermetallic formation. Trace elements like Ti and Cr are used to refine grain size, improving toughness and formability, while higher copper or zinc contents are kept intentionally low to preserve corrosion resistance and to avoid sacrificing weldability.

Mechanical Properties

Tensile behavior of 4004 is consistent with a non-heat-treatable Al-Si alloy: it provides moderate ultimate and yield strengths that can be increased through cold working but do not approach the peak strengths of age-hardenable alloys. Elongation in the annealed state is high, allowing complex forming, and it decreases predictably with increasing H-temper. Hardness and tensile values are influenced by thickness, processing history and the presence of silicon-rich intermetallics which can either strengthen or act as crack initiation sites under cyclic loading.

Fatigue performance is adequate for many structural applications, but engineers should be cautious with high-cycle fatigue in the presence of machining notches or weld defects, as silicon intermetallics can localize stress. Thickness effects are significant: thinner gauges cold-work more uniformly and reach higher relative strengths for a given temper, while thicker sections may retain softer cores and show reduced ductility in bending or deep drawing.

Property	O/Annealed	Key Temper (e.g., H14)	Notes
Tensile Strength (MPa)	90–140	140–220	Tensile ranges depend on cold work and gauge; values approximate for sheet forms
Yield Strength (MPa)	40–80	80–160	Yield increases markedly with H-temper; H14 typical for structural sheet
Elongation (%)	20–35	6–18	Annealed condition yields max ductility; H-temper lowers ductility for strength
Hardness (HB)	20–40	40–90	Brinell/Vickers rises with cold work; hardness correlates with tensile properties

Physical Properties

Property	Value	Notes
Density	2.68–2.71 g/cm³	Typical aluminum alloy density, slightly dependent on alloying content
Melting Range	~577–652 °C	Silicon lowers localized melting points relative to pure Al; solidus-liquidus range varies with Si
Thermal Conductivity	120–165 W/m·K	Lower than pure Al but still high compared to steels; favorable for heat-sinking
Electrical Conductivity	30–45 %IACS	Reduced relative to pure Al (60%+ IACS) due to alloying additions
Specific Heat	~0.88–0.90 J/g·K	Comparable to other Al alloys; useful for thermal mass calculations
Thermal Expansion	22–24 µm/m·K	Slightly lower than pure Al in Al-Si alloys, improving dimensional stability with temperature

These physical properties make 4004 attractive for applications requiring a balance between light weight, thermal conduction and reasonable electrical conductivity. The thermal conductivity remains high enough for many heat sink and heat spreader applications, while the lowered thermal expansion and improved solidification characteristics make the alloy well-suited to welded or brazed assemblies where distortion must be controlled.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.3–6.0 mm	Shows strong thickness-dependent properties; sheet work-hardens predictably	O, H14, H18	Primary form for body panels, heat exchangers and appliance skins
Plate	6–50+ mm	Thicker sections retain softer cores unless heavily worked	O, H12, H14	Used where added stiffness is required; limited deep drawability
Extrusion	2–80+ mm cross-section	Extruded sections can be age-stabilized and cold worked post-extrusion	O, H11, H22	Common for structural profiles and frames
Tube	Ø 6–300 mm	Welded or seamless tubes; strength depends on wall thickness and temper	O, H14, H18	Used in fluid handling and lightweight framing
Bar/Rod	Ø 3–100+ mm	Bars can be cold-drawn to increase strength; machinability is good	O, H12, H14	Used for machined components and fastener blanks

Sheet and extrusion products are the most common delivery forms for 4004, and their processing routes—rolling, annealing, cold reduction and stretch leveling—dictate final mechanical responses. Plate and heavier sections are less formable and often require pre-machining or staged forming, while extrusions take advantage of controllable cooling and billet conditioning to manage grain flow and surface finish.

Equivalent Grades

Standard	Grade	Region	Notes
AA	4004	USA	Aluminum Association designation; used in some regional catalogs
EN AW	4xxx (approx)	Europe	EN designations group Al-Si alloys broadly; specific numbering may vary
JIS	A4xxx (approx)	Japan	Japanese standards list Al-Si family members with similar chemistries
GB/T	4xxx (approx)	China	Chinese standards include several Al-Si wrought alloys with overlapping properties

Equivalency across standards should be treated with caution because the 4xxx family covers a range of silicon contents and minor additions that shift performance. Cross-referencing must consider exact chemical ranges and temper definitions; direct substitution without property verification can lead to unexpected differences in formability, weldability and corrosion resistance.

Corrosion Resistance

Atmospheric resistance of 4004 is generally good for typical indoor and mildly polluted outdoor environments; the relatively low copper and zinc contents limit galvanic acceleration of corrosion. The presence of silicon and iron intermetallics can create local cathodic sites under aggressive conditions, but overall the alloy forms a stable passive oxide layer that protects against uniform corrosion.

In marine and chloride-containing environments, 4004 performs better than some copper-bearing alloys but is still more susceptible to pitting at sites of mechanical damage or weld discontinuities compared with high-magnesium 5xxx series alloys. Appropriate surface treatments, sealants and design for drainage are recommended to mitigate crevice and pitting corrosion in exposed marine applications.

Stress corrosion cracking (SCC) susceptibility for 4004 is low relative to high-strength heat-treatable alloys; however, localized residual stresses from welding or cold work, combined with a corrosive environment, can increase risk. When designing assemblies in contact with dissimilar metals, galvanic considerations must be addressed—aluminum 4004 is anodic to stainless steels and noble metals and may require isolation or sacrificial protection to prevent accelerated attack.

Fabrication Properties

Weldability

4004 exhibits good fusion weldability with standard processes such as MIG, TIG and resistance welding due to its silicon content which reduces hot-cracking tendency. Filler selection typically favors matching Al-Si compositions (e.g., Al-5Si filler types) to control solidification and minimize porosity; preheat and controlled heat input improve joint integrity. The heat-affected zone can show softening if the parent material was strain hardened, so post-weld mechanical treatment or design compensation is often necessary.

Machinability

Machinability of 4004 is rated as fair to good compared with softer commercially pure aluminum; silicon and small intermetallic particles improve chip breakage but can increase tool wear relative to very pure grades. Carbide tooling with positive rake and high-speed capable geometries yields the best productivity, and moderate to high cutting speeds with abundant coolant reduce built-up edge. Drilling and tapping require attention to feeds to avoid tool chatter, and finishing passes help manage surface integrity where fatigue performance is critical.

Formability

Formability in O and light H-tempers is good, supporting deep drawing and complex bending with appropriate springback control. Minimum bend radii are a function of temper and thickness; annealed sheet can take tighter radii (≈1–2× thickness) while H18 or heavily worked tempers require larger radii (≥3–6× thickness). For severe forming operations, use of O or H12 followed by age-stabilization and stress-relief cycles will optimize dimensional control and reduce tear risk.

Heat Treatment Behavior

As a representative 4xxx alloy, 4004 is classified as largely non-heat-treatable; it does not respond to conventional solution heat treatment and artificial aging with the same magnitude of strength increase as 2xxx or 6xxx alloys. Attempts to apply T6-style treatments produce only modest improvements, so thermal treatments are mainly used to homogenize cast microstructures, relieve stresses, or slightly modify ductility rather than to generate large strength gains.

Work hardening is the principal strengthening pathway: controlled cold reduction and strain paths (H1x/H2x/H3x) allow predictable incremental increases in yield and tensile strength. Full anneal cycles return the material to a ductile condition and are often specified prior to forming operations; stabilization heat treatments (e.g., low-temperature aging) can be used to minimize property drift after forming or welding.

High-Temperature Performance

At elevated temperatures, 4004 shows a gradual reduction in yield and tensile strength as silicon-rich phases coarsen and solid-solution strengthening diminishes; useful structural capability typically extends to moderately elevated service temperatures (roughly up to ~150–200 °C) depending on loading and environment. Oxidation is minimal compared with ferrous alloys, but long-term exposure at higher temperatures can cause softening and dimensional drift; designers should account for creep under sustained loads.

Welded joints can be sensitive to high-temperature exposure where residual stresses and local microstructural changes create zones of reduced mechanical capability; post-weld heat treatments or design for load redistribution are common mitigations. For thermal cycling applications, 4004’s relatively stable thermal expansion and good conductivity reduce thermal gradients, but attention to thermal fatigue initiation at stress concentrators is required.

Applications

Industry	Example Component	Why 4004 Is Used
Automotive	Body inner panels, heat shields	Balanced formability, thermal stability and weldability
Marine	Non-critical structural components, trim	Good corrosion resistance and fabricability for marine atmospheres
Aerospace	Secondary fittings, fairings	Favorable strength-to-weight and thermal dimensional stability
Electronics	Heat spreaders, housings	High thermal conductivity with easier forming than cast Al-Si alloys

4004 is commonly specified where the design needs a combination of formability, reasonable strength and improved thermal behavior compared with very pure or high-copper alloys. Its use in automotive and electronics reflects the need for manufacturability (forming, joining) together with thermal and corrosion performance.

Selection Insights

For a quick selection note: choose 4004 when you need moderate strength with superior formability and thermal properties compared with commercially pure aluminum, and where weldability and low hot-crack susceptibility are important. It is particularly attractive when thermal conductivity and dimensional stability under thermal cycling are design drivers.

Compared with 1100 (commercially pure Al), 4004 trades some electrical conductivity and slightly better formability for meaningful increases in strength and thermal stability. Compared with work-hardened alloys like 3003 or 5052, 4004 generally offers comparable or somewhat higher thermal performance and similar formability, but slightly lower ultimate corrosion resistance in high-chloride environments than 5xxx magnesium-bearing grades. Compared with heat-treatable alloys such as 6061 or 6063, 4004 will usually have lower peak strength but better weldability and thermal behavior; select it when peak age-hardening strength is not required and when ease of joining and forming outweigh the need for maximum tensile properties.

Closing Summary

Alloy 4004 remains relevant because it fills a practical niche: a silicon-strengthened, non-heat-treatable aluminum that combines good formability, reliable weldability and favorable thermal performance for a wide range of industrial applications. Its balanced property set and predictable processing behavior make it a robust choice for designers seeking manufacturable, thermally stable aluminum solutions.