Why is it essential to remove all flux from the metal after welding magnesium?

Removing all flux from the metal after welding magnesium is essential primarily to prevent severe corrosion. Magnesium is a highly reactive metal that can undergo corrosion quickly if contaminants such as flux residues are left on its surface. Flux is often made up of chemical compounds that can attract moisture and create a corrosive environment. If these residues are not removed, they can lead to localized corrosion or even pitting, which can compromise the structural integrity of the welded joint over time.

Thus, ensuring that all flux is cleaned off effectively protects the magnesium from environmental exposure, enhancing the longevity and safety of the weld. While aspects like surface smoothness for painting and aesthetic appearance may also be addressed through cleaning, the pivotal reason tied to the performance and durability of the weld lies in corrosion prevention.