What can excessive joint clearance cause in filler metal?

Excessive joint clearance can significantly impact the integrity of the weld. When there is too much space between the pieces being joined, the filler metal may not flow properly into the joint, reducing the quality of the weld. This improper filling can lead to voids or weaknesses in the weld, which increases the likelihood of cracking, especially when exposed to stress or vibration. These cracks can compromise the joint's strength and durability, leading to potential failure in the system.

While other choices might seem plausible, they do not directly relate to the consequences of excessive joint clearance as accurately as the potential for cracking. For instance, rusting generally occurs due to environmental factors, and while melting could happen, it is not a direct consequence of excessive clearance but more about temperature and material properties. Expandability refers to a material's ability to expand, which is not influenced directly by joint clearance in the context of welding or joining processes. Thus, the focus on cracking under stress or vibration clearly highlights the critical reason why maintaining appropriate joint clearance is essential for structural integrity.