ESAB offers a complete line of welding and cutting products and solutions. Explore our equipment offering with ease based on product line and industry.
ESAB is a world leader in welding and cutting equipment and consumables. Explore our complete line of welding & cutting products for virtually every application.
ESAB University is your online learning destination for welding and fabrication technology. Make personalized playlists of your favorite resources including videos, blogs, articles, webinars and more.
ESAB Courses are structured learning paths designed to take your welding knowledge and skills to the next level.
Articles cover industry topics more in-depth and are created in partnership with ESAB engineers and master welders. Click the links to see the latest.
ESAB blogs include information and tips from ESAB Experts to improve your welding and fabrication knowledge.
ESAB University videos are curated with tips and best practices from top fabricators around the world. Learn new techniques or improve your current skills with ESAB University videos.
ESAB is a world leader in welding and cutting equipment and consumables. We offer a complete line of fabrication solutions for virtually every application.
ESAB Newsroom - Stay up to date with the latest news from ESAB. View press releases, product announcements, corporate news, and more here.
ESAB EHS (Environment, Health & Safety) initiatives are monitored with the highest degree of importance and commitment to safety is ingrained in our culture.
The history of ESAB is the History of Welding. Go here to view an interactive look at ESAB's history in shaping the future of innovation in welding, cutting, and fabrication.
View available job openings and more on the ESAB Careers page.
ESAB offers a wealth of product support resources, including a range of technical and service publications, from Safety Data Sheets and downloadable product manuals to product certifications.
Visit ESAB's global manual search engine to access the items below and more.
Global User Manuals
Spare Parts List
Product Storage Instructions
View Main Contact Page
View ESAB Location Information
No Playlist Found ! Please Create Your PlayList Here
The majority of aluminum base alloys can be successfully arc welded when using the correct welding procedures. However, there are some aluminum base alloys that are sometimes referred to as unweldable. These groups of alloys, which we will further discuss, are typically well known as being unsuitable for arc welding. For this reason, they are joined mechanically by riveting or bolting.
Before we start examining the various reasons for the poor weldability of these alloys, we should start by considering the term unweldable. This is a nonstandard term that is sometimes used to describe aluminum alloys that can be difficult to arc weld without encountering problems during and/or after welding. These problems are usually associated with cracking, most often hot cracking, and on occasion, stress corrosion cracking (SCC).
When we consider the aluminum alloys that fall into this difficult-to-weld category, we can divide them into different groups.
We will first consider the small selection of aluminum alloys that were designed for machineability, not weldability. Alloys such as 2011 and 6262 which contain 0.20-0.6 Bi, 0.20-0.6 Pb, and 0.40-0.7 Bi, 0.40-.7 Pb, respectively. The addition of these elements (Bismuth and Lead) to these materials greatly assist in chip formation in these free machining alloys. However, because of the low solidification temperatures of these elements, they can seriously reduce the ability to successfully produce sound welds in these materials.
There are a number of aluminum alloys that are quite susceptible to hot cracking if arc welded. These alloys are usually heat-treatable alloys and are most commonly found in the 2xxx series (Al-Cu) and 7xxx series (Al-Zn) groups of materials.
In order to understand why some of these alloys are unsuitable for arc welding (unweldable), we need to consider the reasons why some aluminum alloys can be more susceptible to hot cracking.
Hot cracking, or solidification cracking, occurs in aluminum welds when high levels of thermal stress and solidification shrinkage are present while the weld is undergoing various degrees of solidification. The hot cracking sensitivity of any aluminum alloy is influenced by a combination of mechanical, thermal, and metallurgical factors.
Many high-performance, heat treatable aluminum alloys have been developed by combining various alloying elements to improve the materials’ mechanical properties. In some cases, the combination of the required alloying elements has produced materials with high hot cracking sensitivity.
Perhaps the most crucial factor affecting the hot crack sensitivity of aluminum welds is the temperature range of dendrite coherence and the type and amount of liquid available during the freezing process. Coherence is when the dendrites begin to interlock with one another to the point that the melted material begins to form a mushy stage.
The coherence range is the temperature between the formation of coherent interlocking dendrites and the solidus temperature. This could be referred to as the mushy range during solidification. The wider the coherence range, the more likely hot cracking will occur because of the accumulating strain of solidification between the interlocking dendrites.
Hot cracking sensitivity in the Al-Cu alloys increases as we add Cu up to approximately 3% Cu and then decreases to a relatively low level at 4.5% Cu and above. Alloy 2219 with 6.3% Cu shows good resistance to hot cracking because of its relatively narrow coherence range. Alloy 2024 contains approximately 4.5% Cu which may initially encourage us to suppose that it would have relatively low crack sensitivity.
However, alloy 2024 also contains a small amount of Magnesium (Mg). The small amount of Mg in this alloy depresses the solidus temperature, but it does not affect the coherence temperature; therefore, the coherence range is extended, and the hot cracking tendency is increased. The problem to be considered when welding 2024 is that the heat of the welding operation will allow segregation of the alloying constituents at the grain boundaries. The presence of Mg, as stated above, will depress the solidus temperature. Because these alloying constituents have lower melting phases, the stress of solidification may cause cracking at the grain boundaries and/or establish the condition within the material conducive to stress corrosion cracking later. High heat input during welding, repeated weld passes, and larger weld sizes can all increase the grain boundary segregation problem (segregation is a time-temperature relationship) and subsequent cracking tendency.
The 7xxx series of alloys can also be separated into two groups as far as weldability is concerned. These are the Al-Zn-Mg and the Al-Zn-Mg-Cu types.
Al-Zn-Mg Alloys such as 7005 will resist hot cracking better and exhibit better joint performance than the Al-Zn-Mg-Cu alloys such as 7075. The Mg content in this group (Al-Zn-Mg) of alloys would generally increase the cracking sensitivity. However, Zr is added to refine grain size and this effectively reduces the cracking tendency. This alloy group is easily welded with the high magnesium filler alloys such as 5356 which ensures the weld contains sufficient magnesium to prevent cracking. Silicon-based filler alloys such as 4043 are not generally recommended for these alloys. This is because the excess Si introduced by the filler alloy can result in the formation of excessive amounts of brittle Mg2Si particles in the weld.
Al-Zn-Mg-Cu Alloys such as 7075 have small amounts of Cu added. The small amounts of Cu, along with the Mg, extend the coherence range and, therefore, increase the crack sensitivity. A similar situation can occur with these materials as with the 2024 type alloys. The stress of solidification may cause cracking at the grain boundaries and/or establish the condition within the material conducive to stress corrosion cracking later.
It should be stressed that the problem of higher susceptibility to hot cracking from increasing the coherence range is not only confined to the welding of these more susceptible base alloys such as 2024 and 7075. Crack sensitivity can be substantially increased when welding incompatible dissimilar base alloys (which are normally easily welded to themselves) and/or through the selection of an incompatible filler alloy.
For example, by joining a perfectly weldable 2xxx series base alloy to a perfectly weldable 5xxx series base alloy, or by using a 5xxx series filler alloy to weld a 2xxx series base alloy, or a 2xxx series filler alloy on a 5xxx series base alloy, we can create the same scenario. If we mix high Cu and high Mg, we can extend the coherence range and, therefore, increase the crack sensitivity.