What is the purpose of a filler rod in welding?

The purpose of a filler rod in welding is to provide additional material that enhances the weld joint by filling the gap between the base metals being joined. In the correct answer, the filler rod is specified as having a different composition than the base metals. This is significant because using a filler rod that is compatible with the base metals can help achieve a strong and reliable bond, particularly in situations where the base metals may not be weldable without additional material.

Filler rods are often selected based on their ability to contribute to the strength and properties of the weld or to improve the metallurgical qualities of the joint. They can be made from materials that have different melting points or properties, which allows for adaptability in various welding applications, particularly when joining dissimilar metals or in specialized processes.

The other options do not correctly identify the role of the filler rod. Using a rod with the same composition as the base would limit the versatility of the weld. Stating that a filler rod serves only for decoration undermines its structural importance, and noting that it is used only for non-metal processes misrepresents the applications of filler rods, which are widely used in metal welding.