Aluminum 4045: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

Alloy 4045 is a member of the 4xxx series of aluminium alloys, which are silicic alloys primarily alloyed with silicon as the principal alloying element. The 4xxx series is characterized by silicon additions that lower the melting range, improve fluidity, and influence weldability and brazing performance; 4045 sits within this family with silicon content significantly higher than near-pure alloys and often higher than the common 4043 filler alloys.

The major alloying constituent in 4045 is silicon, typically complemented by low levels of iron, manganese and trace elements such as titanium and chromium. 4045 is essentially a non-heat-treatable alloy; its primary strengthening mechanisms are solid-solution effects from silicon and strain hardening introduced by cold working when processed into H-temper conditions.

Key traits of 4045 include good weldability, enhanced fluidity for welding/brazing applications, moderate strength, and acceptable corrosion resistance in many atmospheric and mildly corrosive environments. It exhibits good formability in annealed conditions but loses ductility with work hardening; machinability is moderate relative to pure aluminium because silicon promotes chip formation control.

Typical industries using 4045 are automotive (as filler or clad applications), HVAC and heat exchanger manufacturing, general fabrication where weld/braze filler compatibility is needed, and certain consumer appliance components. Engineers select 4045 where improved weldability, lower melting behavior and silicon’s effect on wetting/flowability are required over higher-strength heat-treatable alloys or very pure, highly conductive aluminium.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed, maximum ductility for forming
H12	Low-Medium	Moderate	Good	Good	Lightly strain-hardened; limited bendability
H14	Medium	Moderate-Low	Fair	Good	Common commercial work-hardened sheet temper
H16	Medium-High	Lower	Limited	Good	Heavier strain hardening for stiffness
H18	High	Low	Poor	Good	Maximum cold work strengthening, minimal elongation
T4 (if applicable)	N/A	N/A	Variable	Variable	Not typically heat-treatable; T4-like states due to solutionizing in some processing
T6/T651 (rare)	N/A	N/A	N/A	N/A	4xxx alloys are not classically precipitation-hardening; these tempers are atypical

Temper has a major influence on mechanical behavior and forming capability for 4045. Annealed (O) tempers maximize elongation and formability, permitting deep drawing and severe bends, while increasing H-number cold work progressively raises strength at the expense of ductility and bendability.

Because 4045 is not a precipitation-strengthened alloy, “T” tempers associated with age-hardening do not produce the same responses as in 6xxx or 7xxx alloys; process control of cold work and annealing schedules is therefore the primary route to tailor final properties for production parts.

Chemical Composition

Element	% Range	Notes
Si	9.0–12.5	Primary alloying element; controls melting range, fluidity and weldability
Fe	0.2–0.7	Common impurity; influences intermetallic formation and strength
Mn	0.1–0.5	Minor addition; refines structure and can improve strength slightly
Mg	≤0.10	Typically very low; limits solid-solution strengthening from Mg
Cu	≤0.10	Usually minimal; limits susceptibility to localized corrosion and SCC
Zn	≤0.10	Trace levels only; not a strengthening contributor here
Cr	≤0.10	Trace element for grain control if present
Ti	≤0.10	Grain refiner in cast or wrought processing when used intentionally
Others (each)	≤0.05	Other controlled impurities; balance Al

Silicon dominates performance by lowering the solidus and liquidus temperatures and increasing fluidity of the melt, which improves weld pool flow and reduces hot-cracking sensitivity. Trace elements like Fe and Mn influence the formation of intermetallic particles which affect strength, machinability and localized corrosion tendencies.

Exact chemical limits are product- and standard-dependent; purchasers should reference the controlling specification (AA, EN, JIS, or GB/T) for certified composition limits for a given lot or mill product.

Mechanical Properties

In tensile behavior, 4045 in annealed condition typically shows moderate ultimate tensile strength and relatively high elongation, reflecting its alloying and lack of precipitation hardening. As cold work increases (H-tempers), tensile and yield strengths rise while elongation and toughness decrease, following the classic work-hardening response of non-heat-treatable alloys.

Yield strength in O-temper is modest and sufficient for many formed components, while H14–H18 tempers are used when higher static stiffness or dimensional control is required. Hardness values scale with cold work; the alloy maintains reasonable fatigue resistance in lower tempers but fatigue life can fall with increased cold work due to reduced ductility and microstructural defect sites.

Thickness plays a role: thin gage sheet tends to be stronger in equivalent temper because of increased cold work from rolling; very thick sections may exhibit lower, more isotropic strengths and different bendability. Welded joints typically show a softened HAZ versus base metal depending on processing; design must account for HAZ behavior for fatigue-critical components.

Property	O/Annealed	Key Temper (e.g., H14/H16)	Notes
Tensile Strength	90–150 MPa (typical)	140–220 MPa (typical)	Values vary with thickness, cold work, and product form; verify mill data
Yield Strength	30–70 MPa (typical)	80–160 MPa (typical)	Yield defined by 0.2% offset; cold work significantly raises yield
Elongation	20–35%	6–18%	Anneal has high ductility; H18 has low elongation suitable for stiff parts
Hardness	HB ~25–45	HB ~40–80	Brinell ranges approximate; correlate with tensile via standard conversions

Physical Properties

Property	Value	Notes
Density	2.68–2.70 g/cm³	Typical density for Al-Si wrought alloys; slight increase with Si
Melting Range	~577–615 °C	Silicon lowers eutectic solidus near 577 °C for Al–Si alloys; range depends on Si%
Thermal Conductivity	120–160 W/m·K	Lower than pure Al due to alloying; still high for heat-spreading parts
Electrical Conductivity	~30–45 % IACS	Reduced relative to pure aluminium due to Si and impurities
Specific Heat	~900 J/kg·K	Approximate near room temperature, varies slightly with alloying
Thermal Expansion	22–24 µm/m·K	Typical linear thermal expansion coefficient for Al-Si alloys

4045’s density and thermal properties make it attractive for components where weight savings and thermal management are important, such as heat exchangers and housings. Thermal conductivity is reduced relative to pure aluminium but remains high enough for many heat-transfer applications; designers should account for the alloy’s reduced conductivity when specifying finned or thin-section thermal components.

Electrical conductivity is not a primary asset of 4045; if high conductivity is required, purer alloys (1xxx series) should be considered. The lowered melting range compared with pure aluminium is a key processing attribute for welding and brazing applications.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.3–6.0 mm	Strength increases with cold rolling	O, H12, H14, H16	Dominant form for HVAC, appliance panels and filler clad sheets
Plate	>6.0 mm	Lower work-hardening than thin sheet	O, H14	Less common as 4045 is optimized for thinner products
Extrusion	Profiles up to several meters	Strength depends on post-extrusion strain	O, light H tempers	Extrusions used for trim and small structural members
Tube	Ø few mm to 100+ mm	Similar to sheet; cold-worked options	O, H14	Used for heat exchangers and HVAC tubing
Bar/Rod	3–100 mm	Higher cross-section reduces cold-work strengthening	O	Rod often used as filler or brazing wire

Sheets and coils are the most common mill forms for 4045 because its main strengths are in welding/brazing behavior and formability in thin gages. Extrusion and rod forms appear where custom profiles or filler rods are needed, but the alloy is rarely used for heavy plate where strength-to-weight demands favor other families.

Processing differences govern final properties: rolling and controlled anneals for sheet produce good surface finish and formability, while extrusion requires careful thermal control to avoid segregation of silicon-rich phases; filler wire manufacture emphasizes consistent chemistry and low inclusions for welding reliability.

Equivalent Grades

Standard	Grade	Region	Notes
AA	4045	USA	Primary designation under Aluminum Association; consult AA spec for limits
EN AW	AlSi9–12 (approx)	Europe	No single direct EN AW exact equivalent; AlSi9 or AlSi11 families are approximate matches
JIS	A4045 (approx)	Japan	Local standards may use similar 4xxx designations; confirm JIS spec for composition
GB/T	AlSi10–12 (approx)	China	Chinese casting/wrought designations may map to AlSi series; check GB/T tables

Direct, drop-in equivalents for 4045 are not always exact across regional standards because of differing tolerances and intended use cases (wrought sheet vs filler wire vs casting grades). Engineers should compare certified composition ranges, mechanical tests, and product form (sheet, rod, filler) rather than relying solely on nominal grade names to ensure interchangeability.

Corrosion Resistance

4045 exhibits good general atmospheric corrosion resistance typical of aluminium alloys, with silicon additions not markedly degrading naturally forming oxide protection. In typical outdoor and indoor environments, properly finished 4045 components show long service life without specific active corrosion control measures.

In marine exposures, 4045 performs reasonably but is not as resistant as the best marine-grade aluminium alloys (e.g., 5xxx magnesium-bearing series). Chloride-driven pitting can occur especially where impurities or galvanic couples are present; designers should specify protective coatings or sacrificial barriers for prolonged salt-water immersion use.

Stress corrosion cracking susceptibility is generally low for low-copper 4xxx alloys; the primary SCC drivers—significant tensile stresses, corrosive chlorides, and certain microstructural features—are less pronounced in 4045 than in some high-strength, heat-treatable alloys. Galvanic interactions should be considered: aluminium is anodic to many common metals including copper and steel; when in contact, aluminium will corrode preferentially unless insulated or cathodically protected.

Compared with 5xxx series alloys, 4045 gives up some resistance to localized corrosion under marine chloride attack but often offers better weldability and lower susceptibility to hot-cracking; compared with 6xxx or 7xxx, 4045 has lower peak strength but can be less sensitive to certain weld-related corrosion phenomena due to its silicon content.

Fabrication Properties

Weldability

4045 is highly regarded for fusion welding and is often used in filler wire form for GTAW and GMAW applications. Silicon lowers the melting range and improves wetting and fluidity of the weld pool, reducing hot-cracking risk versus many other aluminium alloys. Recommended filler rods for general aluminium-to-aluminium welding include alloys similar to 4043/4045 depending on required silicon content; for joining to dissimilar metals, brazing or use of specifically formulated filler materials may be required.

Welded joints can show HAZ softening relative to heavily cold-worked base metal; however, because 4045 is non-heat-treatable, the loss is typically from annealing of work hardening rather than precipitation dissolution. Pre- and post-weld considerations include controlling distortion, avoiding contamination (oxides, oils), and specification of filler chemistry to match corrosion and mechanical requirements.

Machinability

Machinability of 4045 is moderate and often better than lower-alloyed, near-pure aluminium because silicon improves chip control and reduces gummy behavior. Typical machining uses high-positive rake carbide tooling, modest cutting speeds, and flood cooling to manage heat and prevent built-up edge. Chips tend to be continuous and need good evacuation; feed and depth should be chosen to avoid chatter and to maintain surface finish.

Turning and milling can achieve good surface finishes in O-temper; harder H-tempers will increase tool forces and accelerate wear. Drilling into thick sections should account for silicon particles that can abrade tooling; use of coated carbide and proper peck-drilling cycles is recommended.

Formability

Formability is excellent in annealed O condition; 4045 can be deep drawn, bent and stretch formed with small bend radii relative to thickness. As cold work progresses (H14–H18), formability drops and springback increases, necessitating tighter process control and larger bend radii. Recommended minimum inside bend radii in O-temper commonly start at 1–2× thickness for simple bends and increase with complexity or thicker gauges.

Cold working increases strength but reduces elongation and increases the risk of edge cracking; for severe forming operations, specify O-temper or perform intermediate anneals as needed. Hot-forming is rarely used for 4045 but can be employed in specialized extrusion or bending operations to avoid fracture when large deformations are required.

Heat Treatment Behavior

4045 is classified as a non-heat-treatable alloy; conventional solution treating and precipitation aging do not yield the significant strength increases seen in 6xxx or 7xxx series. Attempts at classical T6-style treatments do not produce appreciable age-hardening because the alloy lacks the required major Mg and/or Cu solute content.

Control of mechanical properties is achieved predominantly through cold work (strain hardening) and annealing cycles. Annealing (recrystallization) is performed by heating into the appropriate temperature range (commonly 300–415 °C depending on product and mill practice) to restore ductility. Careful thermal exposure during welding can locally anneal cold work and must be considered in design to avoid soft zones.

Where thermal processing is used as a means of stress relief or to homogenize formed parts, time-at-temperature and cooling rate are controlled to prevent coarsening of silicon-rich phases which may impair ductility and surface finish.

High-Temperature Performance

At elevated temperatures, 4045 experiences progressive strength loss typical of aluminium alloys; above roughly 150–200 °C, mechanical properties decline significantly and long-term creep can become a design concern. The low-temperature eutectic and silicon-rich phases limit use at sustained high temperatures compared with certain heat-resistant aluminium or iron-based alloys.

Oxidation is modest and typically limited to a thin aluminium oxide layer; however, prolonged high-temperature exposure in aggressive atmospheres can cause scale formation and affect surface appearance. The HAZ in welded parts will show altered microstructures when exposed to elevated temperatures during service, potentially reducing fatigue life and changing dimensional stability.

For applications requiring continuous service above 150 °C or cyclic thermomechanical loads, alternative alloys specifically designed for elevated temperature performance or metallic systems other than aluminium may be required.

Applications

Industry	Example Component	Why 4045 Is Used
Automotive	Filler wires for body and trim welding	Good weld pool fluidity and reduced hot-cracking; compatibility with Al sheet
Marine/HVAC	Heat exchanger fins and tubing	Good thermal conductivity and formability for thin gages
Aerospace (non-primary)	Secondary fittings, fairings	Moderate strength-to-weight and good corrosion behavior for non-critical parts
Electronics	Heat sinks and housings	Thermal performance combined with ease of forming and joining
General Fabrication	Appliance panels, trim, brazed assemblies	Cost-effective weld/filler alloy combining formability and flowability

4045’s utility is often more about joining and fabrication behavior than being the highest-strength structural alloy. It is chosen where a balance between good weldability, flow in the molten state, and adequate mechanical performance is necessary for manufacturable, serviceable components.

Selection Insights

Choose 4045 when weldability and molten-metal fluidity are priorities and when a silicon-rich, non-heat-treatable alloy’s characteristics match part requirements. It is particularly appropriate for filler-wire applications and for thin-section formed parts that require good flow and wetting in joining operations.

Compared with commercially pure aluminium (1100), 4045 trades some electrical conductivity and ultimate formability for greater weld/braze behavior and slightly higher strength in cold-worked tempers. Compared with work-hardened alloys like 3003 or 5052, 4045 typically provides comparable or slightly lower ductility but improved weld pool fluidity and resistance to certain hot-cracking modes. Compared with heat-treatable alloys such as 6061 or 6063, 4045 has lower achievable peak strength but is often preferred where excellent weldability and lower melting behavior are essential, or where precipitation hardening compatibility is not required.

Use selection logic centered on manufacturing needs (welding/brazing vs. structural strength), corrosion environment, and post-processing capability (can you anneal or rely on cold work?), and always confirm availability and cost from suppliers, as some 4xxx variants are produced primarily for filler or specialty uses and may have limited stock forms.

Closing Summary

Aluminium 4045 remains a practical engineering alloy where silicon-driven weldability, controlled melting characteristics, and good formability in annealed conditions are required. Its non-heat-treatable nature channels designers toward cold-work and process control to meet strength targets, making it a go-to choice for filler metals, HVAC components and fabricated assemblies where manufacturability and corrosion-compatible performance outweigh the need for high-temperature strength.