The four common type of solid inclusions usually found in welding are;
- Slag inclusions
- Flux inclusions
- Oxide inclusions
- Metallic inclusions
Let us go through these inclusions one by one.
1. Slag Inclusions
Slag inclusions are slag that is trapped during welding. They have an irregular shape so the appearance is different from a gas pore.
Slag inclusion is caused by an incomplete slag removal from the underlying surface of a multi-pass weld.
Sometimes the technique used can also cause slag inclusion. For example, when one is welding, the slag flood ahead of the arc.
Some slag can also be entrapment in the work surface. That is why the work surface must be clean and smooth before start welding.
A fine dispersion of inclusions may be present within the weld metal in the MMA process. Although these become a problem only when large or sharp-edged inclusions are produced.
2. Flux Inclusions
Also differs in appearance from a gas pore, flux inclusions only appear in flux related welding processes (i.e. MMA, SAW, and FCAW).
Flux inclusions are caused by unfused flux due to damaged coating. Sometimes, flux fails to melt and becomes trapped in the weld, particularly in SAW or FCAW process. To overcome this, flux or wire change is recommended.
Furthermore, welding parameters like current and voltage should be adjusted to produce satisfactory welding conditions.
3. Oxide inclusions
Cause by oxides trapped during welding, they also have an irregular shape which differs in appearance from a gas pore.
To prevent oxide inclusions, properly grind and cleaned the work surface from heavy mill scale or rust prior to welding.
There is a type of oxide inclusion which is puckering and occurs especially in aluminum alloys. You will find a gross oxide film enfoldment in these alloys due to a combination of unsatisfactory protection from atmospheric contamination and turbulence in the weld pool.
4. Tungsten Inclusions
During TIG welding, particles of tungsten can become embedded in the weldment.
They appear as a light area on radio-graphs as tungsten is denser than the surrounding metal and absorbs larger amounts of X-ray or gamma radiation.
Obviously keeping the tungsten out of the weld pool is the main prevention for Tungsten inclusions but sometimes the filler wire touches the tungsten tip which also contaminates the weld pool.
Spatter could also contaminate the tip but this can be avoided by reducing the current and adjusting the shielding gas flow rate.
An overheated electrode due to its extension beyond the normal distance from the collet can also cause tungsten inclusion. If this is the case, reduce the electrode extension and/or the welding current.
Speaking about collet, before you start welding, make sure the tightening is adequate. So, check your collet and tighten it.
Insufficient shielding gas flow rate or excessive droughts can result in oxidation of the electrode tip. Thus, adjust the shielding gas flow rate, protect the weld area and ensure that the post gas flow after stopping the arc continues for at least five seconds.
Sometimes, Splits or cracks can appear in the electrode. Therefore, to avoid tungsten inclusions, you should change the electrode and ensure the correct tungsten size selected to match the welding current.
Due to the use of argon-oxygen or argon-carbon dioxide mixtures in MAG welding, the shielding gas sometimes becomes insufficient. Therefore, correct the gas composition.