How It Works: How does porosity form in welds?

How does porosity form in welds?

Porosity in welds results from only one thing – gas absorbed by the liquid metal in excess of what it can retain in solution when solidified. The classic example is nitrogen and oxygen from air absorbed by steel weld metal.  The steel weld pool easily absorbs large amounts of both gases which is rejected as the weld solidifies – forming bubbles.  

Which gas or gases that cause porosity change with different metal types. For example: nitrogen and oxygen do not produce porosity in aluminum.  Neither of these gases are “soluble” in aluminum – both form solid compounds with aluminum at much higher temperatures than the solidification temperature of aluminum.

In trying to determine the source of porosity one must first recognize which gases produce porosity in a given material type.

 

Bruce James


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