4145 Aluminum

Representative aluminum raw/semi-finished material photo; exact grade not verified

4145 aluminum is a registered wrought aluminum–silicon–copper alloy primarily associated with welding filler wire. Its high silicon content promotes fluidity and lowers the melting range relative to many base aluminum alloys, while copper contributes to the deposited metal chemistry. It is particularly intended where low weld-cracking susceptibility is needed with 2xxx-series aluminum alloys and aluminum–copper or aluminum–copper–silicon castings. Material selection should be based on the filler-wire specification and the qualified welding procedure, rather than on generic wrought-product temper properties.

Chemical Composition (wt.%)
Chemical Composition wt.%
Element	Min	Max
Silicon	9.3	10.7
Iron	—	0.80
Copper	3.3	4.7
Manganese	—	0.15
Magnesium	—	0.15
Chromium	—	0.15
Nickel	—	0.20
Others, each	—	0.05
Others, total	—	0.15
Aluminum	Remainder

Registered composition limits are mass percent for wrought alloy 4145. Aluminum is the remainder. The registered table lists nickel at 0.20% maximum; unlisted elements are not reported as zero. “Others” limits apply as 0.05% maximum each and 0.15% maximum total.

The reported density is a calculated nominal value for active wrought alloy 4145. The melting range is reported by AZoM for 4145; it is useful for filler-metal selection but is not a welding-parameter recommendation. No tensile or yield data are listed because mechanical performance depends on filler-wire condition, deposited weld metal, dilution, and the qualified welding procedure.

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Table of 4145 Aluminum Properties

Table of 4145 Aluminum Properties
Physical Properties	Metric
Density (calculated nominal)	2.74 g/cm³2.74 g/cm³
Thermal Properties	Metric
Melting Range	521–585 °C
Melting Range	970–1085 °F

Test conditions & data notes

Density (calculated nominal): Active wrought alloy designation 4145; calculated nominal density.
Melting Range: Reported physical-property range for aluminum alloy 4145.
Melting Range: Reported physical-property range for aluminum alloy 4145.

Advantages & Limitations

Advantages	Limitations
High silicon content supports good molten-metal fluidity, an important characteristic for aluminum filler metal. Its relatively low melting range is beneficial when joining compatible aluminum alloys and castings. The alloy is identified for low susceptibility to weld cracking with 2xxx-series alloys and aluminum–copper or aluminum–copper–silicon castings. The copper-containing chemistry can provide a weld-metal composition better matched to certain copper-bearing aluminum substrates than silicon-only filler alloys. Nominal density remains low at approximately 2.74 g/cm³.	4145 is not a general-purpose structural wrought alloy; published bulk mechanical properties cannot be assumed for wire or for deposited weld metal. Copper-bearing aluminum weld deposits may have different corrosion behavior from the base material; service-environment compatibility should be evaluated. Weld properties are strongly affected by dilution from the base metals, welding process, shielding, heat input, and post-weld condition. The high silicon content can influence deposit appearance, anodizing response, and color matching. Use only within a qualified procedure for the specific joint design and base-alloy combination.

Advantages

Limitations

High silicon content supports good molten-metal fluidity, an important characteristic for aluminum filler metal.
Its relatively low melting range is beneficial when joining compatible aluminum alloys and castings.
The alloy is identified for low susceptibility to weld cracking with 2xxx-series alloys and aluminum–copper or aluminum–copper–silicon castings.
The copper-containing chemistry can provide a weld-metal composition better matched to certain copper-bearing aluminum substrates than silicon-only filler alloys.
Nominal density remains low at approximately 2.74 g/cm³.

4145 is not a general-purpose structural wrought alloy; published bulk mechanical properties cannot be assumed for wire or for deposited weld metal.
Copper-bearing aluminum weld deposits may have different corrosion behavior from the base material; service-environment compatibility should be evaluated.
Weld properties are strongly affected by dilution from the base metals, welding process, shielding, heat input, and post-weld condition.
The high silicon content can influence deposit appearance, anodizing response, and color matching.
Use only within a qualified procedure for the specific joint design and base-alloy combination.

Processing & Fabrication

Process	Description
Welding filler selection	Use 4145 as a filler-metal option for compatible 2xxx-series aluminum and aluminum–copper or aluminum–copper–silicon castings where resistance to hot cracking is a principal consideration. Confirm compatibility through the governing filler-metal specification and procedure qualification.
Gas metal arc welding and gas tungsten arc welding	Maintain clean joint faces and filler wire, appropriate shielding-gas coverage, and controlled heat input. The final weld chemistry is a combination of the 4145 deposit and base-metal dilution, not the nominal filler composition alone.
Pre-weld preparation	Remove moisture, oil, oxide, and other contaminants immediately before welding. Aluminum’s persistent oxide film and hydrogen sensitivity make surface preparation important for reducing porosity risk.
Post-weld finishing	If appearance, corrosion performance, or subsequent coating is critical, evaluate a representative weld. Silicon- and copper-bearing deposits can respond differently from the parent alloy during finishing or anodizing.

Applications

4145 is selected principally as a consumable for aluminum joining rather than as a stand-alone structural product. Its composition is useful where fluid filler metal and crack-resistant weld-metal behavior are needed in joints involving copper-bearing aluminum alloys or castings.

Joining of 2xxx-series aluminum alloys: The alloy is identified as a filler metal with very low susceptibility to weld cracking for 2xxx-series aluminum applications.
Aluminum–copper castings: Its silicon- and copper-containing filler chemistry is intended for joining aluminum–copper casting compositions where weldability must be controlled.
Aluminum–copper–silicon castings: 4145 is specifically cited for low weld-cracking susceptibility with these castings and offers fluid filler-metal behavior.
Repair welding of compatible copper-bearing aluminum components: When supported by an approved repair procedure, the alloy can provide a compositionally suitable filler for crack-sensitive casting repairs.

Standards & Designations

Designation	Value	Description
Aluminum Association registered wrought designation	4145	Active registered wrought aluminum alloy designation; composition limits are published by the Aluminum Association.
Aluminum Association designation	AA 4145	Common designation for the registered 4145 alloy.
UNS	UNS A94145	Designation reported for aluminum 4145 by AZoM.

Frequently Asked Questions

What is 4145 aluminum mainly used for?

4145 is mainly used as aluminum welding filler wire. It is intended for crack-sensitive welds involving 2xxx-series aluminum and aluminum–copper or aluminum–copper–silicon castings, subject to a qualified welding procedure.

Why does 4145 contain both silicon and copper?

The registered composition contains 9.3–10.7% silicon and 3.3–4.7% copper. The high silicon level supports filler-metal fluidity and a comparatively low melting range, while copper makes the filler chemistry relevant to copper-bearing aluminum alloys and castings.

Can 4145 mechanical properties be specified using a T temper?

Not without a product-specific source and qualification. For 4145 filler wire, useful mechanical values are generally those of the qualified deposited weld metal, which vary with base-metal dilution, welding process, joint design, shielding gas, and any post-weld treatment.

References & Data Notes

(n.d.). International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys, December 2025 — Aluminum Association. https://www.aluminum.org/sites/default/files/2026-01/Teal%20Sheets%20December%202025.pdf
(n.d.). Aluminum 4145 Alloy (UNS A94145) — AZoM. https://www.azom.com/article.aspx?ArticleID=8688
(n.d.). ALCOTEC Weld Filler Wire 4145 — Alloy Digest. https://dl.asminternational.org/alloy-digest/article/51/12/Al-383/6554/ALCOTEC-WELD-FILLER-WIRE-4145Aluminum-Welding-and

Composition values are registered wrought-alloy limits from the Aluminum Association. Density is a calculated nominal value from the same publication. The melting range and qualitative filler-metal application information are separately reported by AZoM. Mechanical values are intentionally omitted because the available evidence does not provide reliable values for a defined 4145 wire condition or deposited-weld-metal condition.