A Study on the coating of Arc Welding Elctrode for Zinc Plate Steel

Abstract

It is generally admitted that the weld of zinc plated mild steel has poor mechanical properties due to inclusion of zinc compounds in the deposit metal.
At first, mechanical properties of zinc plated steel welds were investigated. Mild steel 3.2 mm in thickness and zinc plated steel with 0.018 mm thick zinc layer were used for base metal.
Various types of coated electrode for mild steel welding were used.
There was little difference between mild steel and zinc plated steel in tensile test and bending test on single bead or butt welded specimens.
Next, relation between types of electrodes and zinc contents in weld metal was investigated (shown in Fig. 1 to Fig. 7).
The electrode coatings were composed of several different elements such as silica, lime, iron oxide, rutile, ferro-silicon, and others.
Using those electrodes, the zinc plated steel plates were welded, and chemical analysis of zinc in deposit metals was made.
Zn-content in the deposit metal was higher in the coating with rich iron oxide than in one with rich lime or rich silica. And when ferro-silicon was added to the coating, Zn content decreased.
Analysis shows that Zn in deposit metal exists as zinc oxide. In this case, to decrease the Zn in deposit metal, a coating of which the dissociation pressure is lower than that of zinc oxide must be used.