Incomplete fusion can be caused by:

Incomplete fusion occurs when the weld metal does not fully fuse with the base metal or the preceding layer of weld metal, resulting in a weak connection. This condition can significantly affect the integrity of the weld and the overall strength of the welded structure.

Factors leading to incomplete fusion include poor fit-up and weld joint contamination. Poor fit-up refers to the alignment and contact of the base materials before welding. If the materials are not properly aligned or if there are gaps, it can hinder the welding process and prevent adequate fusion.

Weld joint contamination involves any unwanted materials present in the weld area, such as dirt, oil, rust, or moisture, which can create barriers that prevent the molten weld metal from merging with the base materials effectively.

As both poor fit-up and weld joint contamination can independently contribute to the risk of incomplete fusion, the correct choice is that both factors can lead to this welding issue. Recognizing the impact of these variables is crucial in preventing incomplete fusion and ensuring high-quality welds.