Optimization of Welding Parameters for Small-Scale Resistance Spot Welding of Zirconium Alloys

Abstract

This paper presents the results of optimization of parameters for resistance spot welding of parts made of E110 zirconium alloy with a thickness of 0.25 + 0.25 mm. Its purpose was to determine the influence of welding current profiles on nugget metal structure and mechanical properties of welds. The highest tensile strength comparable with base metal (380...440 MPa) was observed when the ratio of integral heat input to current pulse duration was about two. Formation of martensitic structure and coarsening of nugget metal was observed with larger ratios. A proper fusion zone was not formed with lower ratios. Annealing of welded joints at a pressure of ~ 10–4 Pa and a temperature of 580 °C for one hour was necessary to reduce residual stresses and transformation of metastable martensitic phase to a more stable state. This reduced microhardness of nugget metal by 30...35% and increased tensile strength of welds. It was also possible to increase tensile strength and reduce dispersion of its values by increasing duration of current down slope after formation of a nugget. An increase in duration from 1 to 14 ms caused rise in tensile strength by ~ 18% and dispersion of its values by ~ 3%.

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

“…Immediately before welding, the parts had been degreased with C 2 H 5 OH ethyl alcohol. A special welding facility [12][13][14][15][16][17] was used that included an 'IPTKM-10' power source and a modernized 'MTT-02' welding gun. The 'IPTKM-10' power source was a digital synthesizer of unipolar current pulses with required algorithms regardless of the load resistance.…”

“…After analyzing the data presented in Table 1 and welding several trial joints, the current and pulse duration ranges were set from 3.3 to 5.1 kA and from 4 to 16 ms, respectively. Based on the recommendations of early SSRSW studies [3,4] and the authors' own experience [12][13][14][15][16][17], the preheating stage, as shown for modes 2 and 3 in Fig. 2, was also implemented to stabilize heat generation in accordance with Eq.…”

“…For titanium alloys, very few recommended SSRSW parameters have been published to date (Table 1), all of which assume the use of typical current pro les of capacitor-based power sources [3][4][5][6] or rectangular-shaped pulses of conventional inverter ones [7][8][9][10][11]. At the same time, some advanced power sources enable to preset almost any algorithms of unipolar pulses with amplitudes of up to several kiloamperes and durations of tens of milliseconds [12][13][14][15][16][17], allowing to improve the quality of the SSRSW joints [12][13][14].…”

“…In the RSW process, heat generation (and the quality of the joints as a result) can be stabilized only by strict control over both preparation of the welded parts and maintenance of deployed equipment. As some previous investigations have shown, current pro les should include the optimal main pulse (within a current-time weld lobe) [10,[12][13][14][15][18][19][20][21][22], as well as both preheating [3, 12-14, 16, 17, 23, 24] and post-weld [13,14,[25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] stages. In this case, the preheating one stabilizes initial RBE values and, respectively, heat generation in the weld zone according to Eq.…”

“…For SSRSW, it has been recommended to combine all these pulses into single current pro les considering low thermal capacities of the joined parts [3,4]. However, they have been optimized only for the Zr-1%Nb alloy [12][13][14] and the 321 steel [12] to date.…”