# ER4043 aluminum filler

Aluminum–silicon ER4043 wire and rod: base-metal selection, weld behavior, anodizing, service limits, and process preparation.

Reviewed: 2026-11-01

Tags: consumables, welding, aluminum, er4043, filler-metal

SAF warns that **4043 can turn very dark after anodizing** and recommends 5356 for a closer match. For sustained exposure above **150°F (about 65.6°C)**, Hobart instead points to suitable **4043/4943 or 5554** selections. Verify the exact alloy pair, service exposure and representative anodized appearance. [SAF anodizing guidance](https://www.saf.com/faqs/can-i-weld-anodized-aluminum/) [Hobart elevated-temperature selection note](https://www.hobartbrothers.com/resources/technical-guides/aluminum-welding-guide/filler-metal-guidelines-for-selecting-the-most-appropriate-filler-metal-4043-4943-or-5356/)

## Identity and specification

ER4043 is a bare aluminum–silicon filler, supplied as GMAW wire or GTAW rod. Its approximately 5% silicon improves weld-pool fluidity. [Hobart aluminum welding basics](https://www.hobartbrothers.com/resources/technical-articles/aluminum-welding-getting-to-the-basics/)

The published classification standard is **AWS A5.10/A5.10M:2023**, **13th edition**, approved by ANSI on **19 May 2023**, with **ISO 18273:2015 modified** identification. Its scope addresses classification of solid aluminum electrodes and rods through composition, operability, and mechanical testing where required. Classification does not establish the strength, corrosion performance, or service approval of every joint made with that filler. Confirm the applicable edition and supplied product documentation when a specification governs the work. [AWS 2023 preview, title page and scope](https://pubs.aws.org/Download_PDFS/AWS_A5.10M_Final_PV.pdf)

A named example is **Lincoln SuperGlaze 4043**. Its product brochure lists **4.50–6.00% silicon** as the ER4043 requirement and **5.26%** as its reported test result, with aluminum the remainder. The distinction between a specified range and a reported value matters: the nominal alloy name is not a batch analysis. Lincoln describes this product for heat-treatable alloys, especially the 6xxx series, with greater fluidity and lower melting point than 5xxx filler alloys. [Lincoln SuperGlaze brochure, printed p. 7](https://ch-delivery.lincolnelectric.com/api/public/content/19ceefbf1e6a4576ba5a3aa1c95e6fbe?v=eae2421e)

## Base-metal compatibility comes first

Identify **both parent alloys and their tempers**, then use a supplier's filler-selection chart for that combination and service. A family number such as “5xxx” is too broad to settle the choice. Hobart's guide permits 4043/4943 or 5356 for 6xxx alloys and 5xxx alloys containing up to **2.5% nominal magnesium**, but directs users **not to use 4043/4943 above that magnesium level**. This is a selection boundary in that guide, not permission to estimate composition from appearance. [Hobart aluminum filler-selection guidance](https://www.hobartbrothers.com/resources/technical-guides/aluminum-welding-guide/filler-metal-guidelines-for-selecting-the-most-appropriate-filler-metal-4043-4943-or-5356/)

For **6061**, ESAB permits considering 4043 or 5356 according to finished-part requirements. Castings still need alloy identification: Lincoln's listed casting applications do not approve every unknown casting or repair. [ESAB selection guide](https://esab.com/us/nam_en/esab-university/blogs/how-to-choose-between-4043-and-5356-filler-alloy/); [Lincoln SuperGlaze 4043, p. 7](https://ch-delivery.lincolnelectric.com/api/public/content/19ceefbf1e6a4576ba5a3aa1c95e6fbe?v=eae2421e)

## What silicon changes—and what it does not

Silicon promotes a **fluid weld pool and wetting action**. Hobart describes 4043 as offering clean welds and reduced cracking tendency, while 5356's magnesium contributes greater strength and toughness but more smut. These are comparative filler characteristics, not a guarantee against lack of fusion, porosity, or cracking in an improperly prepared or restrained joint. Filler selection remains one part of process development. [Hobart aluminum welding basics](https://www.hobartbrothers.com/resources/technical-articles/aluminum-welding-getting-to-the-basics/)

| Finished-part requirement | Selection implication |
| --- | --- |
| Anodized color match | 4043 commonly darkens after anodizing; 5356 usually matches common compatible base alloys more closely. |
| Higher weld ductility or shear capacity | Evaluate alternatives such as 5356 where the base-metal and service chart permits them. |
| Smooth wetting and low crack sensitivity | 4043 is often attractive on compatible alloys. |
| Sustained elevated temperature | Reassess filler choice; the usual 5356 alternative has a service limitation. |

Sources: [ESAB comparative guidance](https://esab.com/us/nam_en/esab-university/blogs/how-to-choose-between-4043-and-5356-filler-alloy/); [Hobart selection guide](https://www.hobartbrothers.com/resources/technical-guides/aluminum-welding-guide/filler-metal-guidelines-for-selecting-the-most-appropriate-filler-metal-4043-4943-or-5356/).

SAF notes discoloration can remain with 5356. Verify appearance on representative anodized parts. [SAF anodizing guidance](https://www.saf.com/faqs/can-i-weld-anodized-aluminum/)

Confirm service temperature, duration, load, parent alloy and design rules before applying the supplier’s elevated-temperature selection guidance. [Hobart elevated-temperature selection note](https://www.hobartbrothers.com/resources/technical-guides/aluminum-welding-guide/filler-metal-guidelines-for-selecting-the-most-appropriate-filler-metal-4043-4943-or-5356/)

## Strength and post-weld heat treatment

**Filler strength is not the strength of the welded assembly.** Hobart explains that welding heat-treatable aluminum reduces mechanical properties in the heat-affected zone. Base-metal temper, dilution, joint design, and the intended post-weld condition therefore matter alongside filler choice. A weld in 6061-T6 should not be assigned the original parent-material properties merely because a familiar filler was used. [Hobart post-weld heat-treatment guidance](https://www.hobartbrothers.com/resources/technical-guides/aluminum-welding-guide/weld-preparation-treatments-post-weld-heat-treatment-and-age/)

Post-weld aging or solution treatment is a separate metallurgical procedure. Hobart warns that a filler may not respond to the thermal cycle in the same way as the parent alloy, leaving the joint with lower properties. Establish the complete cycle and required final properties with the material/filler supplier and governing procedure. Do not improvise a heat-treatment schedule from the ER4043 designation or transfer a 5356 fillet-weld design unchanged. [Hobart heat-treatment discussion](https://www.hobartbrothers.com/resources/technical-guides/aluminum-welding-guide/weld-preparation-treatments-post-weld-heat-treatment-and-age/)

## Shielding, feeding, and preparation

Lincoln lists **100% argon or argon–helium mixtures** for SuperGlaze 4043 MIG wire. Gas composition and delivery must suit the actual process, current, nozzle, and joint; a catalog flow range is not a universal prescription. Hobart identifies argon as the common aluminum MIG/TIG shielding gas and discusses helium additions as a tradeoff involving heat transfer, starting behavior, and consumption. [Lincoln SuperGlaze 4043](https://ch-delivery.lincolnelectric.com/api/public/content/19ceefbf1e6a4576ba5a3aa1c95e6fbe?v=eae2421e); [Hobart aluminum shielding gases](https://www.hobartbrothers.com/resources/technical-guides/aluminum-welding-guide/welding-procedures-shielding-gases-used-for-mig-and-tig-welding/)

ER4043 wire is softer than 5356, so feeding deserves attention. Use the equipment supplier's approved wire size and feeding components rather than compensating for an unsuitable path with higher drive pressure. [ESAB wire-feed comparison](https://esab.com/us/nam_en/esab-university/blogs/how-to-choose-between-4043-and-5356-filler-alloy/)

Cleanliness is especially important for aluminum. Miller directs **degreasing first, then oxide removal** with a clean stainless-steel brush; brushing an oily surface first embeds contamination. Use dedicated clean tools, remove contamination from both sides of the joint, and choose a residue-free cleaning method compatible with welding. The article warns against chlorinated solvents in the welding area. Keep these preparation controls separate from any arc-cleaning function. [Miller aluminum preparation guidance, 6 February 2023](https://www.millerwelds.com/en-us/resources/knowledge-hub/aluminum-welding/welding-basics/what-you-need-to-know-about-cleaning-and-preparing-aluminum-filler-and-base-metals-before-welding?hmsr=www.afiparts.com)

## Practical selection example

For a **6061-to-6061 assembly**, ER4043 is a candidate. Check anodizing, sustained heat, post-weld forming, and heat treatment before comparing allowable fillers. Identical parent alloys can require different filler choices because their service and finishing differ. [ESAB 6061 comparison](https://esab.com/us/nam_en/esab-university/blogs/how-to-choose-between-4043-and-5356-filler-alloy/)

Select an identified wire or rod and develop the welding procedure specification on representative material, including joint fit, shielding, process settings, and final condition. Verify fusion, porosity, cracking, dimensions, and the specified mechanical or leak performance. A clean bead and an ER4043 label are useful observations, but neither replaces the assembly's acceptance criteria. [Hobart aluminum welding basics](https://www.hobartbrothers.com/resources/technical-articles/aluminum-welding-getting-to-the-basics/); [Hobart heat-treatment guidance](https://www.hobartbrothers.com/resources/technical-guides/aluminum-welding-guide/weld-preparation-treatments-post-weld-heat-treatment-and-age/)

## Related reference

[Welding methods](../../processes/welding-methods/index.md)