Definition
The primary metal being joined, cut, plated, or worked on in a manufacturing or repair process such as welding, soldering, brazing, or electroplating. It is the parent material to which filler metal, solder, or a plated coating is applied.
Plain English
The main piece of metal you are working on. When you weld, solder, or plate something, the base metal is the actual part — not the filler or coating you add to it.
Context Anchor
Seen in aircraft maintenance, especially in welding, brazing, soldering, sheet-metal repair, and structural repair instructions.
Derivation
From Latin basis, meaning foundation or support. The base metal is the foundation material — everything else (filler, solder, plating) is added onto it.
Why Pilots Care
Proper identification of the base metal ensures welds meet strength requirements and maintain airframe integrity.
Intuition Check
Base metal does not mean the metal is basic, cheap, or low quality. Here, base means the main original metal being worked on.
Example Sentence 1
Before welding the bracket, the technician cleaned the base metal to remove paint, oil, and corrosion.
Example Sentence 2
After welding, the inspector checked the base metal for any heat damage or distortion.