HAZ (Heat Affected Zone)
The Heat Affected Zone (aka HAZ) is the volume of material at or near the weld which properties have been altered due to the weld heat. Since the resistance welding process relies on heating two parts, some amount of HAZ is inevitable. The material within the HAZ undergoes a change, which may or may not be beneficial to the welded joint. In general, the goal in good resistance welding is to minimize the HAZ.
For more information, read our Fundamentals of Resistance Welding