在焊接热处理过程中，通过施加电流脉冲对熔池附加的振动效果可以有效改善焊缝成形差、晶粒粗大等问题。本工作通过对常规焊缝、传统脉冲电流焊缝以及复合脉冲电流焊缝的晶粒尺寸分析，探讨了脉冲电流对Al-Mg合金组织细化的影响及晶粒细化的机制。对于传统脉冲电流，当频率由0 Hz升高到100 Hz时，平均晶粒尺寸由78.2 μm降至53.3 μm，细化程度提高约30%。在传统脉冲电流波形上复合了低频脉冲电流后，晶粒尺寸最小可达到48.2 μm，细化效果达到近40%。对各焊缝区显微组织的EBSD结果表明，施加脉冲电流后小尺寸晶粒分布明显增加，且大角度晶界占比明显增加。热力学以及EDS分析结果表明晶粒细化的主要机制为枝晶破碎。

During welding, the vibration effect of applying a pulse current on the molten pool can effectively improve weld formation and refine grains. The effect of pulse current on grain refinement and its mechanism were studied for Al-Mg alloy welds fabricated by conventional plasma welding (PAW), PAW with conventional pulse current, and PAW with composite pulse current. The grain size produced by conventional PAW was 78.2 μm, whereas the average grain size was reduced from 78.2 μm to 53.3 μm with increasing conventional pulse current frequency from 0 Hz to 100 Hz; in addition, the degree of grain refinement increased by about 30%. However, the minimum grain size was 48.2 μm, and the grain refinement effect can reach nearly 40% by combining low-frequency pulse current with conventional pulse current. The proportion of small grains and high-angle grain boundaries increased significantly after applying the composite pulse current. The additional oscillation effect of the composite pulse current can effectively eliminate coarse grains during the solidification of the weld pool. The main mechanism of grain refinement is dendrite fragmentation, which is discussed through thermodynamics and composition.