Effects of preheating and slow cooling stages in small-scale resistance spot welding of the Ti-2Al-1Mn alloy

The aim of the study was to improve the stability of the quality of joints of two Ti-2%Al-1%Mn alloy plates with a thickness of 0.5 mm, obtained by resistance spot welding. The determined range of the optimal energy parameters (within the current amplitudes of 3.3–4.8 kA and the pulse durations of 8–16 ms) made it possible to form nuggets of sufficient diameters without expulsions in most cases. The implemented preheating stage (the pulse with the amplitude of ~ 1 kA and the duration of ~ 3 ms) reduced the dispersions of both nugget diameters (by 60%) and peak loads (by a factor of 2), while it increased the average fracture energy by 30% and the mean peak load by 8%. The simultaneously applied both preheating and slow cooling stages decreased the dispersion of the nugget diameters by 160% and enhanced the average both fracture energy by 48% and peak load by 15% in comparison with those for the rectangular pulse. Since no fundamental differences in the microstructure and phase composition were observed in the nuggets, lowering residual stresses was suggested as the most probable reason for such results.