EFFECTS OF NITROGEN AND TITANIUM ON BLOW HOLE FORMATION AND MICROSTRUCTURE IN COPPER WELD METAL BY Ar-N//2 GAS METAL ARC WELDING.

OFHC copper plates were welded with Cu and Cu-Ti electrode wires using Ar-N//2 gas shielding. The effects of welding conditions, N//2% in the shielding gas and titanium content of the electrode wire on the porosity and the microstructure of the weld metal were systematically examined. The results are as follows: Using copper electrode wire, the weld metal shows better surface appearance, less porosity and deeper penetration with increase of the welding current. As N//2% in the shielding gas increases, the porosity of the weld metal increases. Using Cu-Ti electrode wire, a secondary phase is observed in the weld metal. The fractional area of the secondary phase in the weld metal increases with N//2% in the shielding gas and titanium content of the electrode wire. The electron diffraction patterns of the secondary phase are in good agreement with those of TiN. The temperature of molten copper pool was measured and the formation of TiN was discussed by using thermodynamic data.