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This study was carried out to evaluate the microstructural and mechanical properties of resistance spot-welded Inconel 625 alloy. The effects of welding current, applied force, and holding time of resistance spot welding (RSW) process were investigated by optical microscopy (OM) and scanning electron microscope (SEM) images, microhardness tests, and also tensile shear tests. Microstructural investigations showed that the nugget structure consisted of homogenous columnar dendrite structure, which epitaxially grew along the electrode direction, and the microstructure of the heat-affected zone (HAZ) included a fine-grain recrystallized zone (FRXZ), coarse-grain recrystallized zone (CRXZ), and recovery zone (REZ). The effects of welding parameters on the mechanical properties of the spot weld in terms of peak load, fracture energy, and failure mode were investigated.

A 2D axisymmetric electro-thermo-mechanical finite element (FE) model is developed to investigate the effect of current intensity, welding time, and electrode tip diameter on temperature distributions and nugget size in resistance spot welding (RSW) process of Inconel 625 superalloy sheets using ABAQUS commercial software package. The coupled electro-thermal analysis and uncoupled thermal–mechanical analysis are used for modeling process. In order to improve accuracy of simulation, material properties including physical, thermal, and mechanical properties have been considered to be temperature dependent. The thickness and diameter of computed weld nuggets are compared with experimental results and good agreement is observed. So, FE model developed in this paper provides prediction of quality and shape of the weld nuggets and temperature distributions with variation of each process parameter, suitably. Utilizing this FE model assists in adjusting RSW parameters, so that expensive experimental process can be avoided. The results show that increasing welding time and current intensity lead to an increase in the nugget size and electrode indentation, whereas increasing electrode tip diameter decreases nugget size and electrode indentation.