Mechanism of Ni/NiCr joint formation by parallel micro gap welding

Ni leads (diameter of 0.15 mm) were welded to NiCr alloy thin film (5 μm thick) with strong current and short duration by method of parallel micro gap welding.A two-dimensional thermal conduction model of welding was developed.It was calculated that the position of top temperature was related to electrode gap.When the gap of two electrodes is greater than a critical gap,the top temperature position is in the middle of the two electrodes.Results show that the temperature in the middle of electrodes reaches the melting point of Ni or NiCr alloy firstly,however there are no nuggets in this position during the welding process.With electrode force,the formation of joint depends on diffusion below the two electrodes.