en گروه سرامیک Ceramic Materials and Engineering Research Paper Research Paper In this study, the effects of the second pulse resistance spot welding on the microstructure and mechanical properties of TRIP1100 steel were evaluated. The thermal process after welding was designed to improve metallurgical properties with pulse currents of 6kA, 9kA and 12kA after initial welding with 10kA current. The effect of the second pulse on mechanical and microstructural properties was investigated. The fracture of the welds was for pulsed samples of 6kA and 9kA PO with CTS test. Due to existence of the microstructure including the equaxial dendritic and finer in FZ in the pulsed current 9kA, the maximum fracture energy and maximum force were observed. A significant decrease in the FZ hardness in 6kA current was observed in the nanohardness results, which was attributed to existence martensitic and ferrite temper. The highest ratio of CTS / TSS was obtained for 6kA and 9kA, respectively, and force displacement rate was maximum in 9kA. The fracture surfaces included dendrites and dimples. The results of partial fracture revealed separation in the coherent boundaries of the coarse grain of the annealed region. resistance spot welding, second pulse current, fracture surface, shear tensile, dendritic microstructure 79 88 http://ijmse.iust.ac.ir/browse.php?a_code=A-10-1824-1&slc_lang=en&sid=1 I. Hajiannia i.hajiannia@ma.iut.ac.ir 1800319475328460010432 1800319475328460010432 Yes Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran M. Shamanian 1800319475328460010433 1800319475328460010433 No Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran M. Atapour 1800319475328460010434 1800319475328460010434 No Department of Materials Engineering, Isfahan University of Technology, Isfahan, Iran R. Ashiri 1800319475328460010435 1800319475328460010435 No Department of Materials Science and Engineering, Dezful Branch, Islamic Azad University, Dezful,Iran. E. Ghassemali 1800319475328460010436 1800319475328460010436 No School of Engineering, Jo ̈nko ̈ping University, Jo ̈nko ̈ping, Sweden.