What type of weld joint is required for welding magnesium?

The correct choice identifies that butt welds are typically required for welding magnesium due to the specific characteristics and requirements of magnesium as a material. Butt welds provide a continuous, strong joint that allows for the best potential for full penetration and fusion, which is essential given magnesium's properties.

Welding magnesium requires careful control to prevent issues such as cracking or the introduction of impurities, which can happen more easily with joints that allow for more space for gaps or misalignment, like fillet or lap welds. Butt welds minimize the edge preparation and help in creating a tighter joint, making it suitable for magnesium applications where strength and uniformity are critical.

Additionally, because magnesium is more reactive than many other metals, the protection against atmospheric contamination and maintaining joint integrity during the welding process is vital, which the configuration of a butt joint helps achieve effectively.