Abstract: The research on the theory and quality control techniques of spot welding nugget formation is the main hotspot and frontier in material science. In this article the new techniques-spot welding nugget inoculation proposed by the authors is applied to 65Mn and LY12CZ. Systematic procedure experimentation and micro-structure analysis have been carried out. It gives a preferable explanation and evaluation to the inoculation mechanism and effect that inoculation can enhance the mechanical properties of spot welding joint, producing and enlarging equiaxed grains structure area, diminishing and eliminating weak area and restraining the occurence of macro flaw etc.

Key words: resistance spot welding, inoculation, spot welding nugget, solidification structure