Aluminum 4048: Composition, Properties, Temper Guide & Applications

Comprehensive Overview

Alloy 4048 is a member of the 4xxx series of aluminum alloys, a silicon-rich family primarily characterized by silicon as the principal alloying element. The alloy is usually classified with other Al-Si alloys used for welding filler, brazing, and certain extruded shapes where fluidity, low melting range, and good wear characteristics are required.

The major alloying elements in 4048 are silicon (Si) in the high single- to low double-digit percent range, with minor additions of manganese, magnesium, copper and trace elements that tailor castability and mechanical response. Because silicon is the dominant alloyant, strengthening is largely non-heat-treatable and relies on microstructural control, solid-solution effects and, in wrought forms, work hardening; age-hardening (precipitation) is limited compared with 6xxx and 7xxx series.

Key traits of 4048 include good fluidity and low melting range (useful for filler and brazing), good corrosion resistance in many atmospheric and industrial environments, reasonable weldability when matched with appropriate filler alloys, and moderate formability when in softer tempers. Industrial applications include automotive welding filler and clad layers, brazing alloys, certain extruded components, and applications where a silicon-rich surface or brazeable chemistry is advantageous.

Engineers select 4048 when a silicon-enhanced alloy is needed to improve weld pool fluidity, reduce hot cracking, or provide a silicon-rich surface for brazing or joining. It is chosen over higher-strength, heat-treatable alloys when service demands fluidity, compatibility with Al-Si fillers, or enhanced wear resistance rather than peak strength.

Temper Variants

Temper	Strength Level	Elongation	Formability	Weldability	Notes
O	Low	High	Excellent	Excellent	Fully annealed condition for forming and brazing
H12 / H14	Medium	Moderate	Good	Good	Light to moderate strain hardening; common for extrusions
H18 / H22	High	Low	Fair	Fair	Higher work-hardening, used where extra strength is needed
T4 (if used)	Medium	Moderate	Good	Good	Natural aged after solutionizing; limited response in 4xxx series
T6 (rare)	Limited gain	Moderate	Moderate	Moderate	Artificial aging shows limited effect; not primary strengthening route

Temper has a major influence on ductility, strength and formability for 4048. Softer O temper maximizes elongation and cold-forming capability, while H tempers produced by cold working raise yield and tensile strength at the expense of elongation and bendability.

Because 4048 is principally non-heat-treatable, T-tempers produce only modest changes compared with 6xxx series alloys; practical property tailoring is usually achieved through mechanical deformation and annealing cycles rather than classical solution-and-age treatments.

Chemical Composition

Element	% Range	Notes
Si	8.0 – 12.0	Primary alloying element controlling melting range, fluidity and wear; high Si lowers melting point and improves brazing behavior
Fe	0.3 – 1.0	Impurity element that can form iron-rich intermetallics affecting ductility and machinability
Mn	0.1 – 0.8	Small additions refine grain structure and improve strength and corrosion resistance marginally
Mg	0.05 – 0.6	Small Mg can modify strength and precipitation behavior; excessive Mg can reduce silicon eutectic modification
Cu	0.05 – 0.5	Minor amounts increase strength and may reduce corrosion resistance; controlled to limit hot-cracking sensitivity
Zn	≤ 0.2	Kept low; zinc has limited role in 4xxx alloys
Cr	≤ 0.1	Trace addition for grain structure control and recrystallization suppression
Ti	≤ 0.15	Grain refiner in castings and extrusions when added in controlled amounts
Others (including Sn, B, Ni)	Balance to 0.15 total	Residuals and trace elements kept low to avoid detrimental intermetallics

The chemistry of 4048 drives its behavior: silicon governs the eutectic characteristics, lowering the solidus and liquidus temperatures and enhancing fluidity for welding and brazing; manganese and minor transition elements refine microstructure and increase resistance to localized corrosion; magnesium and copper, kept low, are used to tweak strength but are limited to avoid deleterious phases.

Mechanical Properties

In tensile behavior 4048 shows moderate ultimate tensile strength and good ductility in the annealed condition. Tensile and yield values increase substantially with cold work (H-tempers) while elongation drops. Hardness follows the same trend; annealed material is relatively soft and easy to form, while work-hardened tempers show increased Brinell or Vickers readings.

Fatigue performance in 4048 is typical of Al-Si alloys: fatigue strength improves with cold work and decreased surface roughness, but the presence of silicon-rich phases and intermetallic particles can act as initiation sites for cracks. Thickness has a strong effect on mechanical response and formability; thin gauges are easier to draw and bend and respond more uniformly to strain-hardening, while thicker sections retain higher as-cast intermetallic populations and can be stiffer but less ductile.

For design work, engineers should base static strength on measured data from the specific temper and product form and apply appropriate safety factors for fatigue and environmental exposure. Welding and brazing processes can locally soften or embrittle the material depending on heat input and filler compatibility, so post-process mechanical testing is recommended for critical components.

Property	O/Annealed	Key Temper (H14)	Notes
Tensile Strength	80 – 130 MPa	160 – 260 MPa	Range depends on gauge, processing and degree of strain hardening
Yield Strength	30 – 70 MPa	110 – 200 MPa	Yield rises significantly with H-tempers
Elongation	18 – 30 %	6 – 18 %	Annealed alloys provide high ductility; cold work lowers elongation
Hardness (HB)	20 – 35 HB	45 – 90 HB	Hardness correlates with temper and cold work level

Physical Properties

Property	Value	Notes
Density	2.68 – 2.72 g/cm3	Typical for aluminum-silicon alloys; slightly dependent on Si content
Melting Range	~565 – 620 °C	Silicon-rich composition lowers solidus/liquidus compared with pure Al
Thermal Conductivity	110 – 140 W/m·K	Lower than pure aluminum but still good for thermal management
Electrical Conductivity	~28 – 40 % IACS	Reduced from pure aluminum due to alloying; conductivity decreases with Si
Specific Heat	~0.90 J/g·K	Typical aluminum specific heat at ambient temperatures
Thermal Expansion	22 – 24 µm/m·K (20–100 °C)	CTE similar to other Al alloys; silicon content slightly lowers expansion coefficient

The physical properties reflect the silicon-rich chemistry: melting range reduction and good thermal conductivity make 4048 useful in joining and thermal applications. Electrical conductivity is reduced relative to 1xxx series alloys and should be accounted for in electrical or thermal path design.

Product Forms

Form	Typical Thickness/Size	Strength Behavior	Common Tempers	Notes
Sheet	0.3 – 6.0 mm	Responsive to cold work; thin gauges form well	O, H14	Common for clad or brazing sheet and heat-exchange fins
Plate	6 – 50+ mm	Thicker plates show higher as-cast intermetallic content	O, H22	Used where mass and wear resistance are required
Extrusion	Profiles up to several meters	Strength controlled by work-hardening and extrusion strain	O, H12/H14	Good for complex cross-sections benefiting from Si-enhanced surface
Tube	0.5 – 10 mm wall	Geometry affects cold work response and burst strength	O, H18	Used for low-pressure fluid systems and brazed assemblies
Bar/Rod	3 – 100 mm	Typically supplied in softer tempers for machining or drawing	O, H14	Straight bars for machining or secondary forming operations

Different product forms are processed to exploit 4048’s silicon-driven characteristics: thin sheet for brazing and heat-transfer surfaces, extrusions for complex cross-sections, and bars/rods for machining. Processing parameters such as extrusion temperature, cooling rate and post-extrusion cold work strongly affect final mechanical properties and microstructure.

Equivalent Grades

Standard	Grade	Region	Notes
AA	4048	USA	Recognized in supplier literature as a silicon-rich 4xxx variant
EN AW	AlSi9Cu (approx.)	Europe	No direct one-to-one; some EN alloys have similar Si but differ in Cu/Mg
JIS	A4048 (informal)	Japan	Local designations vary; confirm chemistry with mill certs
GB/T	4048	China	Local standard grades may exist; check national spec for exact ranges

Equivalency between regional standards is approximate because 4xxx alloys have wide compositional windows and small variations in Mg, Cu or Mn can change properties. Engineers should always verify chemical and mechanical certificates from mills before declaring interchangeability for critical parts.

Corrosion Resistance

4048 exhibits good atmospheric corrosion resistance typical of Al-Si alloys because the passive aluminum oxide film is maintained and silicon does not significantly depassivate the surface. In industrial and urban atmospheres the alloy performs well, and surface treatments such as anodizing or protective coatings further improve lifetime.

In marine environments 4048 has moderate performance; chloride-induced pitting is a concern on unprotected surfaces, particularly at stressed locations or crevices. Proper design to avoid crevices, application of coatings and cathodic protection can mitigate marine corrosion. Cladding with purer aluminum layers or paint systems is common where long-term seawater exposure is expected.

Stress corrosion cracking is not a primary failure mode for 4048 compared with high-strength heat-treatable alloys, but localized embrittlement can occur adjacent to welds or brazed joints if microstructural heterogeneity and residual stresses are high. Galvanic interactions with dissimilar metals should be assessed: 4048 is anodic to stainless steels and cathodic to more noble metals, so isolation materials and fastener selection are important.

Compared to other alloy families, 4048 generally outperforms high-strength Cu-rich alloys in corrosion resistance but is slightly less resistant than high-purity 1xxx series alloys. Its silicon content provides a beneficial effect for certain surface treatments and brazing processes, which influences corrosion performance positively in assemblies.

Fabrication Properties

Weldability

4048 is widely used as a filler alloy for TIG and MIG processes due to its high silicon content, which improves fluidity and reduces hot-cracking in the weld pool. When used as a base alloy, conventional GTAW/GMAW can be applied with matched wire or ER4043-type fillers to control silicon dilution and mechanical properties. Heat-affected zones can soften or undergo microstructural changes depending on the base temper and heat input, so control of interpass temperatures and pre/post-heat is recommended for critical joints.

Machinability

Machining 4048 is moderate; silicon-rich alloys tend to produce abrasive, discontinuous chips and can be harder on cutting tools than pure aluminum. Carbide tooling with appropriate coatings (TiN, TiAlN) and rigid setups delivering moderate to high cutting speeds with ample coolant produce the best results. Chip control strategies and conservative feed rates reduce tool wear; surface finishes depend on temper and silicon particle distribution.

Formability

Formability is best in annealed (O) tempers where bend radii can be small and deep drawing is feasible. With increasing H-temper cold work, bend radii must be enlarged and forming steps introduced to avoid cracking. For severe forming operations, intermediate anneals are commonly used to restore ductility, and designers should target minimum bend radii tied to sheet thickness and intended temper.

Heat Treatment Behavior

As a 4xxx-series alloy, 4048 is essentially non-heat-treatable in the conventional precipitation-hardening sense. Solution treatment and artificial aging produce only limited improvements because silicon does not precipitate the strengthening phases exploited in 6xxx or 7xxx series alloys. Attempts to apply T6-style treatments yield marginal gains and are seldom cost-effective for bulk property changes.

Work hardening is the primary means of increasing strength: controlled cold deformation (H-tempers) raises yield and tensile strength at the expense of ductility. Annealing is used to restore ductility and relieve residual stresses; typical annealing cycles are performed just below the eutectic temperature for wrought material to avoid grain coarsening and preserve surface finish. For brazing or filler applications, localized heating and controlled cooling are used instead of full-scale solution treatments.

High-Temperature Performance

4048 loses strength progressively with increasing temperature, with significant reductions above approximately 150–200 °C; service temperatures approaching or exceeding 300 °C will markedly decrease mechanical performance and dimensional stability. Oxidation at elevated temperatures is generally limited to the formation of aluminum oxide; thick scale is uncommon at typical service exposures but should be considered for long-term high-temperature duty.

Heat-affected zones from welding can introduce localized softening and embrittlement; high-temperature exposure accelerates any diffusion-driven changes in silicon distribution and can coarsen brittle intermetallic particles. For components requiring stability at elevated temperatures, select alloys specifically designed for creep resistance rather than 4048.

Applications

Industry	Example Component	Why 4048 Is Used
Automotive	Welding filler for body and structural seams	High Si content improves weld pool fluidity and reduces hot cracking
Marine	Brazed heat exchangers and fittings	Good brazeability and corrosion resistance with appropriate coatings
Aerospace	Non-critical fittings, sealants, and clad layers	Compatibility with Al-Si brazing and moderate strength-to-weight
Electronics	Heat sink fins and brazed assemblies	Thermal conductivity and brazeability suitable for thermal management

4048 is frequently selected where joining and brazing performance or weld filler compatibility is critical. Its balance of formability in soft tempers and strengthened performance in cold-worked tempers allows it to fill a niche between pure aluminum and higher-strength heat-treatable alloys.

Selection Insights

Choose 4048 when your primary requirements emphasize weld/braze fluidity, resistance to hot-cracking, and good service corrosion resistance without the need for peak precipitation-strength. The alloy is particularly effective as a filler or clad material and where a silicon-rich surface or brazeable chemistry is required.

Compared with commercially pure aluminum (1100), 4048 trades some electrical and thermal conductivity and formability for higher strength and superior brazing/welding behavior. Compared with work-hardened alloys like 3003 or 5052, 4048 typically offers similar or slightly lower ductility but improved weld/braze fluidity and comparable corrosion resistance in many atmospheres. Compared with heat-treatable alloys such as 6061 or 6063, 4048 provides lower peak strength but is preferred when joining compatibility, reduced hot-cracking and silicon-enhanced surface properties matter more than maximum tensile properties.

When selecting between materials, weigh the trade-offs: if you require high strength after heat treatment, choose a 6xxx alloy; if you need exceptional formability and conductivity, choose 1xxx series; for joining and brazing performance with solid corrosion resistance, 4048 is often the pragmatic choice.

Closing Summary

Aluminum 4048 remains relevant where silicon-driven properties—improved weld and braze fluidity, reduced hot cracking, and good environmental resistance—are required alongside moderate strength and formability. Its role as a filler, clad, and specialized wrought alloy makes it a practical solution in assemblies that prioritize joining performance and reliable corrosion behavior over peak heat-treatable strength.