What is the term used for a weld characterized by incomplete fusion?

• A. Lack of penetration
• B. Lack of fusion
• C. Porosity
• D. Underfill

Answer: (B)

The term used for a weld characterized by incomplete fusion is known as lack of fusion. This occurs when the molten weld metal does not adequately bond to the base material or to the preceding layers of weld metal, leading to a weakness in the weld joint. This type of defect can compromise the integrity of the weld, making it essential to identify and address it to ensure structural reliability.

Lack of penetration, while related to weld quality, refers specifically to situations where the weld does not extend deep enough into the base materials, affecting the strength and load-bearing capacity at the joint. Porosity refers to the presence of gas pockets trapped within the weld metal, which can lead to similar weaknesses but does not directly pertain to the bonding process between materials. Underfill describes a condition where the weld metal is insufficient to completely fill the joint or groove, creating a profile that is lower than required but is distinct from the fusion quality issues. Each of these defects disrupts the weld's intended purpose, but lack of fusion is the precise terminology for incomplete bonding.