Aluminum 4043: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

4043 is a member of the 4xxx series of aluminum alloys, which are silicon-containing alloys designed primarily for welding applications and improved fluidity in molten state. The 4xxx family is not a heat-treatable series; strengthening comes from solid-solution effects of alloying elements and from work‑hardening when cold‑worked.

The principal alloying element in 4043 is silicon (Si), typically in the 4.5–6.0 wt% range, with low levels of iron and trace additions of Ti and other elements as grain refiners. Silicon lowers the melting range, improves castability and weld metal fluidity, and reduces hot-cracking susceptibility during fusion welding.

Key traits of 4043 include moderate tensile strength, excellent weldability, good corrosion resistance, and reasonable formability in annealed conditions. It is widely used as a filler alloy for MIG/TIG welding of aluminum and also supplied as wrought product for non-structural components where weldability and corrosion resistance are prioritized over peak strength.

Industries that commonly use 4043 include automotive fabrication (weld wire and brazing), appliance manufacturing, general fabrication, and electrical/electronic assemblies where good conductivity and clean welds are required. Engineers choose 4043 over alternatives when fluidity, low hot-cracking tendency, and compatibility with aluminum oxide-controlled weld pools are the primary drivers rather than maximum mechanical properties.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High (15–30%)	Excellent	Excellent	Fully annealed, best formability and ductility
H14	Moderate	Low–Moderate (3–10%)	Fair	Excellent	Cold-worked to a quarter-hard condition, increases yield
H18	Moderate–High	Low (≈3%)	Limited	Excellent	Full hard cold-worked condition for higher strength
T4	Low–Moderate	Moderate	Good	Excellent	Solution heat-treated and naturally aged; not common for 4043 but seen in some wrought products
T5 / T6 / T651	N/A / Variable	N/A	N/A	Excellent	Typical T5/T6 tempers are not standard for 4043 because it is not a classic age-hardenable alloy; listings indicate limited or specialized processing

Temper has a primary influence on ductility, yield and formability for 4043. Annealed (O) provides the highest elongation and easiest forming, while H- and cold-worked tempers trade ductility for higher yield and hardness.

Processing tempers also affect welding behavior and residual stress sensitivity; softer tempers reduce cracking drive in welded assemblies and are preferred for complex forming prior to welding.

Chemical Composition

Element	% Range	Notes
Si	4.5–6.0	Primary alloying element; improves fluidity and reduces melting range
Fe	≤0.8	Common impurity; forms intermetallics that can affect surface finish and mechanical scatter
Mn	≤0.05	Typically minimal; little strengthening contribution
Mg	≤0.05	Low; 4043 is not designed for Mg-based precipitation strengthening
Cu	≤0.2	Kept low to maintain corrosion resistance and weldability
Zn	≤0.25	Minor impurity level; inertia on properties at these concentrations
Cr	≤0.05	Trace; may be used for impurity control
Ti	≤0.20	Often added as grain-refiner in cast/weld filler forms
Others / Al balance	Balance	Aluminum constitutes the balance with trace elements controlled per specification

Silicon dominates performance in 4043: it reduces the liquidus temperature and increases fluidity of molten metal, which improves fusion welding and decreases solidification cracking. Minor elements are controlled to limit deleterious intermetallics and to retain corrosion resistance; Ti and small additions are used deliberately as grain refiners to improve microstructure in cast and weld deposits.

Mechanical Properties

4043 exhibits tensile behavior typical of non-heat-treatable Al-Si alloys: modest ultimate tensile and yield strengths with relatively high ductility in the annealed condition. Yield behavior is influenced strongly by temper and cold work; cold‑worked (H‑temper) material can reach useful yields for structural non-critical applications, while annealed product is used where forming is required.

Elongation values are high in O temper and drop substantially with increased cold work. Hardness correlates with temper—annealed hardness is low; H‑tempers show higher hardness and accompanying reductions in elongation. Fatigue performance is moderate and strongly dependent on surface condition, heat-affected zones from welding, and the presence of casting or weld-related porosity.

Thickness has a measurable impact: thinner gauges can exhibit slightly higher measured tensile strengths due to cold rolling and processing histories, while thick sections and weld deposits can show lower properties and larger microstructural heterogeneity. Surface condition and residual stress from forming/welding will strongly influence fatigue life and crack initiation.

Property	O/Annealed	Key Temper (e.g., H14/H18)	Notes
Tensile Strength	≈80–140 MPa	≈120–200 MPa (depending on cold work)	Wide range due to processing route; weld metal tensile strength may differ
Yield Strength	≈30–80 MPa	≈90–160 MPa	Yield increases markedly with cold work
Elongation	≈15–30%	≈3–10%	Ductility drops with cold working
Hardness (HB)	≈25–50 HB	≈50–85 HB	Hardness varies with temper and previous cold work

Physical Properties

Property	Value	Notes
Density	2.68 g/cm3	Typical for aluminum alloys; useful for mass calculations
Melting Range	≈577–613 °C (solidus–liquidus)	Si lowers solidus compared with pure Al; actual range varies with exact Si content
Thermal Conductivity	≈120–160 W/m·K	Lower than pure Al due to alloying; still good for thermal management
Electrical Conductivity	≈30–45 %IACS	Reduced vs. pure Al; weld deposits and microstructure further influence conductivity
Specific Heat	≈0.9 J/g·K (900 J/kg·K)	Typical aluminum specific heat; depends weakly on alloying
Thermal Expansion	≈23–24 µm/m·K (20–100 °C)	Typical linear coefficient for aluminum alloys; important for thermal stress calculations

The physical-property set of 4043 positions it for thermal and electrical applications where modest conductivity and low density are advantages. Thermal conductivity is sufficient for many heat-sink and heat-transmission uses, but designers should account for the reduction compared with pure Al when precise thermal modeling is required.

The reduced melting range and improved fluidity imparted by Si are key enablers for welding and casting, and these thermophysical traits influence solidification kinetics and susceptibility to hot cracking in fusion processes.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.3–6.0 mm	Lower strength in O; can be work‑hardened	O, H14	Used for panels, housings, and applications requiring formability
Plate	6–50 mm	Modest strength; thick sections show microstructural gradients	O, as-rolled	Less common for structural plate due to limited peak strength
Extrusion	Complex profiles, 1–50 mm cross-sections	Varies with profile and cold work	O, H-processes	Extrusions used where weldability and shape definition matter
Tube	Ø few mm to large diameters	Strength varies with wall thickness and temper	O, H	Used for fluid delivery, structural non-critical tubing
Bar/Rod	2–50 mm	Generally moderate strength; often used as filler wire	O, drawn	Common form for welding wire and brazing rods */

Wrought forms of 4043 are processed to emphasize weldability and formability; sheet and extrusions are frequently annealed to facilitate forming and subsequent welding. Cold work can be applied to increase strength for non-critical structural members, but operators must balance reduction in ductility.

Welding-grade and rod/wire products of 4043 are produced with controlled chemistry and grain refinement to maximize molten fluidity, reduce porosity, and manage solidification cracking in fusion welds and brazed joints.

Equivalent Grades

Standard	Grade	Region	Notes
AA	4043	USA	Aluminum Association designation; commonly referenced in specifications
EN AW	4043	Europe	Often referenced as EN AW-4043 or AlSi5 for similar chemical range
JIS	A4043 / AlSi5	Japan	Japanese industrial standards use similar Al–Si descriptions; exact designation may vary
GB/T	4043	China	Chinese GB/T designations map closely to AA/EN chemistries for Al–Si welding alloys

Equivalency is approximate because manufacturing practices, impurity limits and permitted trace additions can vary by regional standard. Engineers should verify supplier certificates of analysis for critical applications and be aware of small allowed variations in Fe, Ti and trace elements that can influence welding and casting behavior.

Corrosion Resistance

4043 exhibits good general atmospheric corrosion resistance typical of aluminum alloys when the alloy is in contact with air or mildly corrosive environments. The alloy forms a stable aluminum oxide film that provides passivation, and the presence of silicon does not significantly degrade the passive layer under normal conditions.

In marine or chloride-bearing environments, 4043 is moderately resistant but still susceptible to localized attack if galvanic coupling exists with more noble metals or if coatings are compromised. Pitting resistance is better than some high-strength alloys due to the low copper content, but it is not as robust as specialized marine alloys under active salt spray conditions.

Stress corrosion cracking susceptibility for 4043 is low compared with high-strength heat-treatable aluminum alloys; however, weld heat-affected zones and tensile residual stresses can localize corrosion-assisted cracking. Designers should consider coatings, cathodic protection, and isolation strategies when dissimilar metals are present to reduce galvanic attack.

Compared with 2xxx and 7xxx series alloys, 4043 offers superior general corrosion resistance owing to its low Cu and high Si content; compared with 5xxx series, its performance is similar for many atmospheric conditions but 5xxx alloys with higher Mg typically have better seawater resistance in structural service.

Fabrication Properties

Weldability

4043 is one of the preferred filler alloys for welding aluminum due to its high silicon content providing excellent fluidity and low hot-cracking tendency. It performs well with MIG (GMAW) and TIG (GTAW) processes and is the standard choice for aluminum-to-aluminum welding where a softer, more ductile weld metal is acceptable. Hot-cracking risk is low in 4043 weld deposits relative to many other filler or base alloy combinations, but weld porosity and hydrogen pickup must still be controlled.

Machinability

Wrought 4043 has moderate machinability; it machines more easily than higher-strength heat-treated alloys but slightly harder than pure Al due to silicon-induced abrasiveness. Carbide tooling with positive rake geometries and rigid tooling setups are recommended for predictable chip control. Cut speeds and feed rates should be optimized to avoid built-up edge and to handle the abrasive silicon particles in the microstructure.

Formability

Formability is excellent in annealed O condition with tight bend radii achievable for thin gauges; typical minimum inside bend radii are on the order of 1–3× thickness depending on tooling and temper. Cold working raises strength but reduces formability, so forming is usually performed in O temper or with intermediate anneals. For severe forming, attention should be paid to springback and to the potential formation of surface cracks in heavily cold-worked H-tempers.

Heat Treatment Behavior

4043 is nominally a non-heat-treatable alloy; it does not respond to conventional solution-treatment plus artificial aging sequences in the way that 6xxx or 7xxx series alloys do. Attempts to pursue T6-style aging yield limited precipitation strengthening because Mg and Cu levels are too low for significant age-hardening.

Solution treatment can homogenize microstructure and dissolve segregations in cast forms, but any subsequent aging produces only modest property changes. Annealing (O temper) is the standard thermal process to restore ductility and relieve residual stresses; typical annealing cycles are in the 300–400 °C range depending on product form and desired softness.

Cold work (H tempers) is the primary route to additional strength for 4043 after forming. Work-hardening increases yield and hardness but must be balanced against reductions in elongation and increased susceptibility to fracture under cyclic loads.

High-Temperature Performance

Like most aluminum alloys, 4043 experiences substantial strength loss as service temperature increases above ambient. Useful structural properties diminish noticeably above ~150–200 °C, and long-term exposure near the melting range will degrade mechanical integrity. Oxidation at elevated temperatures is limited to the formation of the stable alumina layer, but scaling and embrittlement mechanisms can occur in aggressive atmospheres.

The heat-affected zone around welds sees metallurgical changes and localized softening or coarsening of microstructure; while 4043 weld metal itself is ductile, the HAZ may have reduced properties that limit high-temperature load-bearing capability. For continuous elevated-temperature service, alloys specifically developed for creep resistance should be selected.

Applications

Industry	Example Component	Why 4043 Is Used
Automotive	Decorative trim and welded assemblies	Excellent weldability and good surface finish after welding
Marine	Non-structural housings, weld filler for assemblies	Good corrosion resistance and low hot-cracking in welds
Aerospace	Filler for aluminum welding, repair rods	Compatibility with aluminum base metals and controllable weld metallurgy
Electronics	Busbars, housings, heat-spreader components	Useful balance of conductivity and low density
Consumer Appliances	Cookware and cabinet components	Formability, weldability, and corrosion resistance

4043 is heavily used as welding wire and rod rather than the primary structural alloy; its role in assemblies is often to enable reliable fusion joints and to supply a ductile weld metal that tolerates thermal cycling. The combination of fluidity, low crack sensitivity and reasonable corrosion resistance sustains its broad applicability across non-critical structural and enclosure parts.

Selection Insights

Choose 4043 when welding compatibility, fluidity of molten metal, and corrosion resistance are higher priorities than peak strength. It is an excellent filler for general-purpose aluminum welding and for components where formability and a ductile weld deposit are required.

Compared with commercially pure aluminum (e.g., 1100), 4043 trades a bit of electrical conductivity and formability for increased strength and much better weld pool fluidity. Compared with work-hardened alloys such as 3003 or 5052, 4043 generally offers similar or slightly lower strength but improved weldability and lower hot‑cracking tendency; corrosion performance is comparable to slightly better depending on environment. Compared with heat-treatable alloys such as 6061/6063, 4043 is selected when peak strength is not required but where weldability, filler compatibility and reduced cracking risk are dominant concerns.

In procurement and design trade-offs, consider availability of filler forms, cost advantages for welding operations, and whether post-weld mechanical requirements necessitate a higher-strength alternative or engineered joint design.

Closing Summary

4043 remains relevant in modern engineering because it provides a predictable, low-cracking weld metal with good corrosion resistance and adequate mechanical behavior for a wide range of non-critical structural and enclosure applications, making it a staple alloy for welding, fabrication, and general-purpose aluminum components.