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.
Flux Inclusion
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.
Slag inclusion
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.
Metallic Inclusion
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.
Oxide Inclusion
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.
Last Comments
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.