Porosity in zinc-coated advanced high strength steels during gas metal arc welding

The behaviour of a galvanised advanced high strength steel while being welded using wires and shielding atmospheres of different chemical compositions was studied. The analyses included metallographic examination and digital X-ray radiography to detect the porosity within the weld beads. Metallographic examination of welded samples revealed that the porosity was of the wormhole type. The results showed that porosity, attributed to vaporising of the zinc coating, increased as welding heat input augmented due to its effect on the solidification and cooling rates of the weld pool, allowing for a higher rate of zinc evaporation. Porosity was found to increase as the CO2 content in the shield gas was reduced, as well as the amount of silicon of the wires augmented, as both factors contribute to reduce the surface tension of the molten metal, which affects the shape of the Marangoni’s currents within the weld pool that will reduce the capacity of zinc fumes to escape from the weld pool.