Welding parameters and the grain structure of weld metal — A thermodynamic consideration

The grain structure of the weld metal can significantly affect its resistance to solidification cracking during welding and its mechanical properties after welding. An experimental study was conducted to investigate the effect of two basic welding parameters,i.e., the heat input and the welding speed, on the grain structure of aluminum-alloy welds. Gas-tungsten arc welding was performed under various heat inputs and welding speeds, with thermal measurements in the weld pool being carried out during welding and the amounts and nuclei of equiaxed grains in the resultant welds being examined using optical and electron microscopy. The experimentally measuredG/R ratios and the clearly revealed heterogeneous nuclei together demonstrated the thermodynamic effect of the heat input and welding speed on the weld metal grain structure.