An advanced gas metal arc welding technique with controlled short-circuiting mode of metal transfer and arcing at low power was employed for brazing of galvannealed steels using CuSi3 filler wire. The brazed joints showed the presence of an interface layer with Fe-Si intermetallic compounds (IMC). Increase in heat input resulted in an increase of the interface layer thickness. The maximum failure load of 2.5 kN was achieved for a heat input of 105 J mm −1 with the corresponding interface layer thickness of 2.7 µm. Heat inputs beyond 105 J mm −1 led to excessive spatter of zinc and increase in interface layer thickness with hard Si-rich IMC. In contrast, heat input values lower than 80 J mm −1 produced inadequate wetting of the steel surface by the molten filler wire deposit and resulted in low joint strength.
Gas metal arc (GMA) brazing of thin sheets requires active control of heat input, filler alloy deposition and temperature field on sheet surface. A novel attempt is presented here for a rapid synchronous real-time monitoring of current and voltage transients, filler alloy depositions and temperature field using, respectively, a high-frequency recorder, high-speed videography and two thermal infrared cameras during GMA brazing of galvanized steel sheets. For heat inputs from 100 to 200 J mm −1 , the peak temperature varied from 1500 to 1700 K. The high-speed videography showed consistent filler deposition and bead profile. The methodology and results presented here depict a promising resource for real-time monitoring and feedback control of GMA brazing.
Appropriate substrate surface wetting by a molten filler ensures a sound bead profile during brazing. A theory to estimate the wetting length considering gradual cooling of liquid filler and loss in its ability to spread is currently unavailable. We present here a methodology to estimate wetting length based on the minimisation of energy for spreading of a liquid filler considering its gradual cooling and tested the computed results in gas metal arc brazing of galvanised sheets for a wide range of conditions. The computed wetting lengths are used further to estimate bead height and toe angle of joint profile.
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