In welding, the function of filler metal is to:

• A. Strengthen the weld by filling the gap between joined pieces
• B. Decrease the weld temperature
• C. Change the color of the weld
• D. Protect the weld from corrosion without filling gaps

Answer: (A)

Filler metal is used to fill the space between joined pieces and become part of the weld metal, creating the final cross-section that carries the load. By bridging the gap, it ensures proper fusion with the base metals and provides the material needed to form a strong, continuous joint. The filler also introduces alloying elements that tailor the weld’s strength, toughness, and sometimes corrosion resistance to suit the base metals. It isn’t meant to decrease heat, change the weld color, or provide corrosion protection on its own without filling the joint—those outcomes are either controlled by welding parameters, incidental heat effects, or other protective measures. So the main purpose is to fill the gap and build the weld metal for a strong, credible joint.