Surface bead formation of a mild steel by pulsed current TIG arc

Abstract

The influence of pulse frequency on the surface bead formation and the fusion boundary microstructure of a mild steel was investigated using a pulsed current TIG arc within low and middle frequency regions. The appearance of the beads formed on the surface shows a distinct ripple shape. However, in the middle frequency region and at faster travel speeds, humped beads are formed. The number of ripples on the surface bead increases and decreases with increasing pulsed frequency and travel speed, respectively. The bead width and depth both increase with increasing pulse frequency and travel speed. In particular, a large decrease in the melt penetration is observed at middle frequency, which is probably due to a lowering of arc gouging and a discontinuity of the bead. The minimum reduction in grain size is obtained at pulse frequencies of 2.5, 5.0, 50 and 100 Hz, which is an equiaxed structure in the fusion zone, and consists of acicular ferrite and fine pearlite in a heat-affected zone. The best bead formation occurred at pulse frequencies of 2.5 and 5.0 Hz, and a travel speed of 280 mm min−1.