The synergistic effects of Nd and Ga on the microstructure and mechanical properties of ER4047 alloy wires and the resulting MIG(Melt inert-gas welding) joints were investigated. Experimental results show that the hydrogen content in the liquid and solid alloy decreases rapidly and then increases slowly with the addition of Nd in the range of 0–0.8 wt.%. Under the same conditions, the hydrogen content ratio in the solid and liquid is between 1.9 and 2.1. After adding 0.08–0.2 wt.% Nd, the α-Al

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... endrites and eutectic Si phases in the ER4047 alloys are refined and modified, respectively; the quality index of the cast rod increases and the weld percent porosity of the MIG joint significantly decreases. However, when 0.8 wt.% Nd is added, although the size of the eutectic Si phase reaches a minimum value, a large number of coarse needle-like Nd-rich phases precipitate in the structure. Moreover, Ga inhibits the precipitation of the Nd-rich phases, thus improving the mechanical properties, especially the elongation of the cast rod. When 0.2 wt.% Nd and 0.05 wt.% Ga are added into the alloy wire, the porosity of the MIG joint reaches the lowest value herein, and the tensile strength and face/back bending angles reach their maximum values.