What does the term "incomplete fusion" refer to in welding?

The term "incomplete fusion" specifically refers to the condition where the weld metal does not adequately join to the base material. This phenomenon occurs when there is insufficient heat or improper technique during the welding process, preventing a complete bonding of the weld metal to the base metal. This results in a weak joint, which can lead to failures under stress or load. Proper fusion is crucial for structural integrity; therefore, achieving complete fusion is a fundamental aspect of effective welding practices.

In contrast, the other options represent different issues or phenomena that can occur in welding but do not accurately define incomplete fusion. For instance, the option discussing the fusion of different metals pertains to a separate topic related to metallurgical compatibility, while thickness or overlap issues relate to different weld defects impacting the quality and performance of the weld. Understanding incomplete fusion helps in identifying potential weaknesses in welded joints and underscores the importance of proper welding techniques for ensuring strong, reliable connections.