In welding, what does the term "base metal" refer to?

The term "base metal" refers specifically to the metal that is being welded. It is the primary material on which welding is performed, and it can be composed of various metals such as steel, aluminum, or other alloys. Understanding this term is crucial in welding, as effective welds necessitate proper preparation and understanding of the base metal's properties. This includes its composition, thickness, and the specific welding process that should be utilized to ensure a strong and durable joint.

In contrast, the other terms in the question refer to different aspects of welding. Filler material is used to add extra material to the weld but does not define the base metal itself. The protective layer generally refers to coatings that might be applied for corrosion resistance or to protect the weld area, not the metal being welded. The heat-affected zone describes the area adjacent to the weld that has undergone changes in microstructure due to the heat of the welding process, which is also not the base metal itself. Therefore, recognizing the base metal is fundamental to successful welding practice.