What is "incomplete fusion" in welding?

Incomplete fusion in welding refers to a defect that occurs when the filler metal does not fully bond with the base material. This can happen due to various reasons, such as insufficient heat during the welding process, the presence of contaminants on the metal surfaces, or improper technique. The result is a weak joint that may not have the necessary strength and integrity required for the welded structure.

Understanding this concept is crucial because it highlights the importance of achieving proper heat and technique to ensure the filler metal flows and adheres adequately to the base materials. Incomplete fusion can compromise the overall reliability and performance of the weld, making it essential for welders to be aware of this defect and take precautions to prevent it.

The other options present different concepts related to welding but do not define what incomplete fusion actually is. Misalignment of weld joints, methods of applying heat, and surface preparation are all important aspects of welding but do not specifically address the bonding issue that is central to the definition of incomplete fusion.