Oxygen-free copper plates were welded with copper and copper-titanium alloy electrode wires using argon-nitrogen gas mixture shielding. The effects of the nitrogen percent (N2%) in the shielding gas and the titanium content (Ti%) of the electrode wire on mechanical properties and annealed structures of the weld metal were examined. The Vickers hardness increases with Ti% of the electrode wire. The yield stress and the tensile strength of the weld metal increase with Ti% of the electrode wire, while the elongation and the reduction of area show maximum at about 0.5%Ti in the wire. Those tensile properties of the weld metal are independent of N2% in the shielding gas. β' precipitates are observed in some of the weld metals annealed at 573—1173 K for 3.6 ks. The precipitation is the most remarkable after annealing at 700~800 K, and the amount of the precipitates increases with increase of Ti% in the wire and with decrease of N2% in the shielding gas. The Vickers hardness increases with the amount of the precipitates.
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