Aluminum 4049: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

Alloy 4049 sits within the 4xxx series of aluminum alloys, a family characterized by silicon as the principal alloying element. The 4xxx designation denotes Al-Si compositions where silicon is added primarily to lower melting temperature, improve fluidity for casting and welding, and reduce thermal expansion in some applications. Typical uses of the 4xxx family include filler metals for welding and brazing, extrusions, and applications where enhanced wear or reduced melting range is helpful.

The major alloying element in 4049 is silicon, typically present at elevated levels relative to pure aluminum; small controlled amounts of iron, copper, manganese, titanium, and trace elements may also be present. Strength in 4049 is obtained through solid-solution strengthening and, where cold worked, by strain hardening; it is essentially a non-heat-treatable alloy and does not develop significant precipitation hardening like 6xxx or 7xxx series alloys. This behavior yields moderate static strength combined with good ductility and very good weldability.

Key traits of 4049 include good fluidity and low melting range beneficial for welding and brazing, reasonable atmospheric corrosion resistance comparable to many commercial aluminum alloys, and good formability in the annealed condition. Weldability is a particular strength: silicon lowers the melting range and reduces hot-cracking susceptibility in fusion welding, which is why 4049 and related fillers are widely used for joining aluminium components. Typical industries include automotive (weld filler and brazed assemblies), marine (fittings and repair rod), consumer goods (extrusions and trim), and fabrication shops that require reliable weld filler metal.

Engineers choose 4049 over other alloys when the design requires a filler or base alloy with excellent weldability and fluidity, tolerance for modest strength, and superior feeding into joints during fusion welding. It is often preferred over higher-strength heat-treatable alloys when avoiding post-weld heat treatment is important, and over pure aluminum when improved molten behavior and reduced cracking risk are needed.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed; best formability and ductility
H12	Moderate	Moderate	Good	Very Good	Lightly strain-hardened; commonly used for extrusions
H14	Moderate	Moderate	Fair	Very Good	Strain-hardened to a controlled yield level
H18	Higher	Lower	Limited	Very Good	Heavily cold-worked for higher strength where needed
F (as fabricated)	Variable	Variable	Variable	Excellent	Typical condition for filler/wire products
T5 (limited)	Moderate	Moderate	Fair	Excellent	Artificially aged after cooling from elevated temperature (rare for 4049)

Temper has a direct effect on mechanical behavior and forming response. The annealed (O) temper offers the highest ductility and deepest drawing capabilities, while H-series tempers introduce strain hardening to increase yield and tensile strength at the expense of elongation and some formability.

Weldability remains strong across common tempers because silicon lowers solidification cracking susceptibility; however, H‑tempers will typically require more forming force and are less tolerant of tight bend radii. For filler and welding wire applications, the F and O conditions dominate manufacturing and application practice.

Chemical Composition

Element	% Range	Notes
Si	6.0–12.0	Primary alloying element; improves fluidity and reduces melting range
Fe	0.2–1.0	Common impurity; forms intermetallics that can affect ductility
Mn	0.05–0.5	Minor addition; can refine grain and influence toughness
Mg	0.01–0.3	Low levels; can slightly increase strength but limited in 4xxx alloys
Cu	0.01–0.4	Small amounts may be present; increases strength and decreases corrosion resistance
Zn	0.05–0.3	Trace to low levels; generally not a purposeful additive in 4049
Cr	0.01–0.2	Trace addition for grain control in some heats
Ti	0.01–0.2	Used as grain refiner in cast/weld products
Others	Balance to 100%	Trace elements and residuals controlled per specification

Silicon dominates the alloy chemistry and directly controls melting range, solidification characteristics, and weldability. Iron and other impurities form intermetallic phases that can embrittle the microstructure if present in excess; controlled levels and proper processing keep these phases fine and dispersed. Small additions of Mn, Ti, or Cr are used to refine grain structure and stabilize mechanical properties during thermal cycles.

Mechanical Properties

Alloy 4049 typically demonstrates moderate tensile and yield strengths with reasonably high ductility in the annealed condition. Tensile behavior is characterized by a relatively flat strain-hardening response: after yielding, the material elongates appreciably before ultimate tensile failure, making it forgiving in forming and welding situations. Elongation in annealed product is often sufficient for deep drawing and many sheet-forming operations.

Hardness values are low to moderate in annealed conditions and rise predictably with cold work; hardness correlates with yield increase in H tempers. Fatigue strength in 4049 is generally lower than high-strength heat-treatable alloys because of its lower static strength and the presence of Si-rich phases that can act as crack initiation sites; design for cyclic loading should include conservative safety factors and attention to surface finish and welding quality. Thickness effects are important: thinner sections cool faster during welding and may be more susceptible to solidification features; thicker sections retain heat and may develop coarser microstructures.

Property	O/Annealed	Key Temper (e.g., H14/T5)	Notes
Tensile Strength	90–140 MPa	120–180 MPa	Wide ranges reflect product form and degree of cold work
Yield Strength	40–70 MPa	70–140 MPa	H tempers show marked increases via strain hardening
Elongation	10–25%	5–15%	Annealed condition shows the highest ductility
Hardness	25–45 HB	35–70 HB	Hardness rises with cold work; T5 effect modest if present

Values above are indicative ranges for wrought or filler forms; exact properties depend on product form, processing history, and precise chemistry. For critical designs, verify properties from supplier certificates and conduct application-specific testing such as fatigue or fracture toughness evaluation.

Physical Properties

Property	Value	Notes
Density	2.68 g/cm³	Typical for aluminium alloys; useful for mass calculations
Melting Range	~570–615 °C	Reduced from pure Al due to elevated Si; eutectic influences solidus-liquidus interval
Thermal Conductivity	120–160 W/m·K	Lower than pure Al; Si reduces conductivity but remains good for heat dissipation
Electrical Conductivity	30–45 %IACS	Reduced vs. pure aluminium; conductivity adequate for some conductors but not optimized
Specific Heat	~0.90 J/g·K (900 J/kg·K)	Typical value near room temperature for aluminium alloys
Thermal Expansion	22–24 µm/m·K	Slightly reduced by Si; important for thermal cycling and joint design

The reduced melting range versus pure aluminium is a central physical trait that makes 4049 attractive as a welding filler and for castings where controlled solidification is required. Thermal conductivity and electrical conductivity are lower than commercially pure aluminium but remain useful for thermal management in housings and heat spreaders where mechanical and joining performance matter.

Density and thermal expansion remain similar to many Al alloys, allowing for predictable weight and thermal strain calculations in assemblies. Engineers must account for the altered melting behavior when welding dissimilar alloys or designing joints to control solidification and residual stress.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.3–6.0 mm	Modest; thickness-dependent	O, H12, H14	Common for trim, housings, and welded structures
Plate	6–25 mm	Lower strength with increasing thickness due to casting-like microstructure	O, H18	Less common; used when welding thermal mass is acceptable
Extrusion	Up to 200 mm cross-section	Good dimensional stability; strength depends on section and temper	O, H12	Used for profiles requiring good weldability and surface quality
Tube	0.5–10 mm wall	Good formability in thin-wall tube; welded tube uses filler alloys	O, H14	Tube production often relies on welding/filler alloys compatible with 4049
Bar/Rod	Ø2–25 mm	Solid bar strength varies with cold work	F, O	Common form for filler rods and welding wire; sizes tailored for hand or automated welding

Sheet and extrusion products of 4049 are favored where weldability and forming are priorities rather than maximum strength. Extrusions benefit from silicon’s effect on flow during hot extrusion and on surface finish, while plate-grade products are less typical due to the alloy’s intended use cases.

Filler rods and welding wire are a significant product form for 4049 chemistry; these are produced to tight composition and melting-range controls to ensure consistent weld pool behavior and minimal hot cracking.

Equivalent Grades

Standard	Grade	Region	Notes
AA	4049	USA	Common designation in American standards and filler classifications
EN AW	4049	Europe	Often listed under EN for filler and cast/wrought forms with local spec variations
JIS	A4049	Japan	Regional implementations may control impurity levels differently
GB/T	4049	China	Chinese standard grades approximate international 4049 but require verification

Subtle differences between equivalent designations typically relate to permitted impurity limits, exact silicon ranges, and certification/test requirements. Regional standards may adjust Fe and Cu maximums or require additional controls for hydrogen and porosity when 4049 is produced as welding wire or filler rod. Always cross-check the exact standard sheet and supplier certification when substituting between regional grades.

Corrosion Resistance

In atmospheric environments, 4049 exhibits corrosion resistance comparable to many general-purpose aluminium alloys; the passive oxide film reforms readily and provides protection in most urban and industrial atmospheres. The presence of silicon does not inherently degrade general corrosion resistance, although coarse intermetallics from iron or other impurities can act as local cathodic sites and promote pitting in aggressive environments.

Marine behavior is generally acceptable for short- to mid-term exposure, but prolonged immersion in chloride-containing environments demands careful design and surface protection measures. 4049 is not among the most highly corrosion-resistant aluminium alloys for long-term marine structural use; anodizing, coatings, or sacrificial protection may be required for extended service life.

Stress corrosion cracking susceptibility is low relative to high-strength 2xxx and 7xxx series alloys because 4049’s nominal strength and alloy chemistry do not promote the same SCC mechanisms. However, weld zones must be managed for residual stresses and potential galvanic couples, especially when joined to stainless steels or copper-rich alloys. In galvanic interactions, 4049 behaves similarly to other Al-Si alloys and will act anodically to more noble metals; insulating joints and careful material pairing minimize accelerated corrosion.

Fabrication Properties

Weldability

4049 is highly weldable with both TIG and MIG/GMAW processes and is widely used as a filler alloy for welding aluminium because its silicon content reduces hot-cracking tendency and improves molten flow. ER4049 filler wire is commonly recommended when welding 6xxx-series base alloys or similar chemistries to improve fluidity and prevent cracking in aluminum castings and wrought sections. Hot-cracking risk is low compared with low-silicon welds, but good joint fit-up, proper cleaning, and control of heat input remain essential to avoid porosity and defects.

Machinability

Machinability of 4049 is moderate; silicon-rich alloys can form abrasive intermetallics that accelerate tool wear relative to soft commercial-purity aluminium. Carbide tooling with positive rake geometry and robust chip evacuation is recommended. Higher cutting speeds are possible due to the alloy’s softness compared with high-strength Al alloys, but feed and depth of cut should balance surface finish and tool life. Coolants or air blast help reduce built-up edge and improve surface integrity.

Formability

Formability in the annealed condition is very good, enabling bending, deep drawing, and stretching operations with modest springback. Typical minimum bend radii for sheet in O temper are in the range of 1–2× thickness for simple bends, increasing for H tempers. Cold working (H tempers) increases strength but reduces elongation and may necessitate intermediate anneals for complex forming. For deep draw operations, O temper is preferred to minimize tearing and thinning.

Heat Treatment Behavior

As a member of the non-heat-treatable 4xxx series, 4049 does not respond to solution heat treatment and aging in the same way as 2xxx, 6xxx, or 7xxx alloys. Attempts at conventional solution treatment and artificial aging produce minimal precipitation strengthening because silicon does not form the same strengthening precipitates as magnesium or copper-based systems. For this reason, mechanical properties are controlled primarily by chemistry and cold work.

Annealing is the primary thermal treatment used to soften 4049, restore ductility, and homogenize microstructure; typical anneal cycles involve heating into the 300–400 °C range and slow cooling to relieve residual stress. Work hardening (H tempers) is the routine method to increase strength; tensile and yield strengths are raised predictably by cold deformation. Some manufacturers supply artificially aged (T5) products for dimensional stability after extrusion, but the T‑temper effect on strength is limited relative to truly heat-treatable alloys.

High-Temperature Performance

4049 experiences progressive strength loss with increasing temperature; usable mechanical properties decrease notably above 150 °C and the alloy is generally not recommended for sustained structural service above ~200 °C. Oxidation is controlled by the protective aluminium oxide scale, but at elevated temperatures scaling and intermetallic coarsening accelerate, leading to degradation in mechanical behavior.

The heat-affected zone (HAZ) in welded assemblies tends to remain ductile because there is no precipitation-hardened matrix to overage, but coarsening of silicon-rich phases can locally change mechanical and fatigue behavior. For cyclic high-temperature conditions, expect reduced fatigue life and design conservatively, or consider heat-treatable aluminum alloys or high-temperature materials as alternatives.

Applications

Industry	Example Component	Why 4049 Is Used
Automotive	Weld filler for body assemblies and repair rods	Excellent weldability and fluidity; low hot-cracking risk
Marine	Small fittings, repairs, brazed assemblies	Good corrosion resistance and joining performance
Aerospace	Non-primary fittings and brackets	Favorable formability and weldability for secondary structures
Electronics	Housings and heat sinks for low-power devices	Adequate thermal conductivity with easy forming and joining

4049 is particularly valuable where joining quality and molten behavior take precedence over peak structural strength. Its role as a filler alloy for welding and brazing is a primary application, but wrought forms are used for extruded profiles and formed parts where good surface finish, weldability, and moderate strength are required.

Selection Insights

Choose 4049 when weldability and molten fluidity are critical design drivers, when designers need a filler or base alloy that minimizes hot cracking and promotes clean fusion without post-weld heat treatment. The alloy is a pragmatic choice for repair rods, welding wire, and formed components that will not be heavily loaded in structural service.

Compared with commercially pure aluminum (e.g., 1100), 4049 sacrifices some electrical and thermal conductivity and slightly higher formability for improved molten behavior and modest strength increases. Compared with common work-hardened alloys such as 3003 or 5052, 4049 typically offers better weld filler compatibility and fluidity but can be similar or slightly lower in corrosion resistance depending on environment and temper. Compared with heat-treatable alloys like 6061 or 6063, 4049 provides superior weldability without the need for post-weld solutionizing, making it preferred where ease of joining and minimal thermal distortion outweigh the need for maximum peak strength.

Closing Summary

Aluminum 4049 remains a relevant and widely used alloy where its silicon-rich chemistry delivers exceptional weldability, controlled melting behavior, and good formability, making it a first choice for filler metal applications and welded or extruded components that demand reliable joining and practical mechanical performance.