The entrapment of unwanted solid particles impairs weld metal strength. Such weld imperfections are developed by the inclusion of solid substances like slag, flux, foreign metal or oxide. These inclusions are appeared singly or in clustered form. On the basis of shape they are categorized in linear and rounded forms. Common causes are defected consumables, welder’s negligence, inadequate shielding gas flow and joint contamination. They are liable to occur in multi-pass welding method when proper slag removal is not exercised prior to new weld bead. Unlike cracks the solid inclusion have no wedge shape spots for crack propagation. These imperfections are primarily linked with flux using welding processes like Stick welding, submerged arc welding and Flux cored arc welding. So proper joint cleaning, gas shield, well maintained consumables and welder’s proficiency are foremost elements in order to avoid unwanted inclusions in weldment. Below is the brief description about possible causes of solid inclusions and their practicable prevention.
The entrapment of flux in weld metal due to incomplete fusion and melting of flux, primarily in manual metal arc welding, SAW and FCAW. Common causes are defected consumables (damage electrode coatings, flux core wires and spoiled SAW flux) and incorrect welding parameters voltage, arc length, current etc. To fix flux inclusion problems, trained welder must;
- Use well maintained consumables
- Deposit good profile weld by correct configuration of welding parameters.
The entrapment of slag appears in linear form along the weld metal length when spotted with the help of radiography. Slag is the product produced by the de-oxidation reaction of flux during the weld bead deposition and must be removed before the next weld bead. In worst situation poor overlapping of beads allows cavities to develop. On the other hand rough surface of previous beads can also cause cavity formation. These cavities are the primary source of slag inclusions in your weld. Moreover, incorrect electrode angle creates slag overflow, impairing the arc characteristics. In order to prevent this; well maintained flux coated consumables must be used and welder must have good experience to tackle slag inclusion problems. Moreover correct current, voltage and good arc characteristics are essential elements, to produce smooth and quality welds with complete fusion among multi-pass runs.
The absorption of other metals in liquid weld, is referred to as metal inclusion. This problem frequently occurs in Tungsten Inert Gas welding where tungsten metal may entrap due to a slight negligence in welding. Tungsten inclusion looks white when observed on radiography film. (where the procedure and identification is same as the X-ray examination of a broken bone). Besides tungsten, other metals like copper can also be captured in weld deposits. Tungsten inclusion is primarily caused by welder’s incompetency, inappropriate welding parameters, improper gas shield and defected consumables. In order to fix it, one must prevent above mentioned causes. TIG welder must use accurate welding variables and ensure the proper gas shield during bead deposition.
The entrapment of oxides in weld metal (especially in case of welding aluminum alloys). Oxide inclusion occurs due to the presence of mill scale and rust on the joint surface. Such imperfection can harm the mechanical characteristics of weldment. To prevent this, welder must prepare rust and scale free joint surface by suitable procedures like grinding, chipping and brushing.
Solid inclusions genesis is mainly promoted by inept welders. Only the qualified welder must be authorized for specific arc process. Pre-cleaning and post cleaning must be employed. On the other hand consumables must be stored in good condition to avoid any damage.