4 Results and discussion
4.1 Effect of average current I on morphology and
microstructure of T-joint
Average current I as a main parameter in the
welding process affects the heat input Q directly, which
would further determine the temperature distribution and
fusion condition of the welding joint. Figures 6(a), (b)
and (c) show the temperature fields and the transverse
section of weld pools at average currents of 80, 90 and
100 A, respectively. The corresponding bead width and
depth of the T-joints are presented in Table 1. It can be
seen that both the temperature and the dimension of weld
pools correspondingly increase with the increase of
average currents. As the average current increases, the
arc heating area of the workpiece is enlarged and the arc
force is enhanced, which results in the increase of bead
width and depth of T-joints, respectively [16]. In addition,
the isotherm corresponding to the melting of the base
metal at the DP-MIG current of 90 A is compared with
the weld pool shape obtained by the experiment with the
same parameters, as shown in Fig. 7, verifying the
accuracy of the result by simulation.