Aluminum GTAW Crater Prevention

Aluminum TIG welding (GTAW) is known for producing clean, high-quality welds, but it also presents unique challenges. One of the most common is crater formation at the end of your weld. While these craters might appear cosmetic, unfortunately, it's deeper than that. These craters act as stress concentrators and can lead to cracking with time. Preventing them is essential for producing structurally sound aluminum welds, so let's talk about why it happens and the steps you can take to avoid it. 

​Craters can form for various reasons, and understanding them is important for troubleshooting. Aluminum’s high thermal conductivity and rapid solidification make it particularly susceptible to this issue. Craters tend to form when your arc is terminated too abruptly or when your weld pool cools unevenly. Without enough filler metal to compensate for the shrinkage that happens during cooling, your weld is left vulnerable to cracking.

Now, let's go over the steps you can take to prevent this issue from happening in your shop!

First things first is surface prep. This step is critical because aluminum quickly forms a natural oxide layer on its surface. Aluminum oxide melts at about 3700 °F, while aluminum itself melts at roughly 1200 °F. Because of that difference, the oxide does not melt along with the base metal. Instead, it can float to the surface of the weld puddle, leading to porosity, incomplete fusion, cracking, or craters. 

Proper surface prep includes:

• ​Chemical cleaning with an aluminum prep solution containing hydrofluoric acid to remove oils and residues
• A stainless steel wire brush dedicated to aluminum can be used as an alternative for non-critical repairs, but it often just moves oxides around rather than fully removing them. ​

The choice of filler metal is another factor that plays a key role in crater prevention. For many aluminum applications, 4043 filler alloy is a reliable option due to its good flow characteristics, lower melting point, and crack resistance. 5356 offers higher strength and is used when color match or anodizing is important. 
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Continuing the trend of cleanliness we started with our surface prep, it's just as important to keep your chosen filler rods clean! Clean TIG rods by hand with Scotch-Brite or use a suitable chemical prep if needed. Since contaminated filler can compromise your weld puddle, always store your rods in a dry environment and don't handle them with dirty gloves. 

The last factor to consider when trying to avoid crater formation is how you end your weld. A commonly made mistake here is abruptly breaking your arc.

What you should do instead is:

• Slow your travel speed
• Add more filler metal to keep your weld puddle full at the end, which compensates for shrinkage. 
• And gradually taper down your amperage, gradually backing off the foot pedal over 2 to 4 seconds.
• Keep the torch in place after extinguishing the arc to maintain shielding gas coverage while it cools.
  

These steps allow you to control the cooling, which lets your weld pool solidify more evenly and reduces internal stresses. Some machines conveniently have a crater fill function, but if yours doesn't, manual control is essential and well worth the extra attention.

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Focus on the fundamentals

To summarize, preventing craters in aluminum TIG (GTAW) welding comes down to these three simple fundamentals:

• Start with a recently cleaned base material
• Choose the proper filler metal and treat it with care
• Finish strong with gradual, controlled cooling at the end of your weld, and add filler metal.

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Looking for hands-on help mastering TIG techniques?
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Earlbeck Technical Center is here to help. Check out our complete line-up of classes, including Intermediate and Advanced TIG classes, and enroll in a session that works with your schedule!

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Need help dialing in a process at your shop?

Our team can help! With our FREE Welding Productivity Analysis,  we'll take a look at your weld procedures and processes, review joint design, prep, and code compliance. We'll help you figure out the best way to reduce defects, improve weld consistency, and save you money in the long run!