In order to investigate the influence of ultrasonic on flow behavior of filler metal when the filler metal propagates on the solid/liquid surface in brazing process, the gap-filling behavior of the molten filler metal during ultrasonic-assisted brazing of magnesium alloy was in-situ observed by high-speed video camera. Besides, the gap-filling behavior in unparalleled gaps and brazed joint properties were investigated. When the filler metal fills the gap in the direction parallel to the ultrasonic energy propagation, the dynamic curve of filling-gap distance appears linear relation with the ultrasonic time. And it shows that at the same ultrasonic time, good pre-clearance results in low filling velocity. Along the filler flow direction, the thickness of brazed joint decreases gradually. The filling-gap distance decreases as ultrasonic time increases when filler metal is placed at large gap side. The compactness of the joint is general. The filling-gap distance increases firstly and then decreases with the ultrasonic time increasing when the filler metal is placed at small gap side. In this case, the defects appear in the whole joint. The analysis indicates that the flow behavior of filler metal in unparalleled clearance is influenced by the combined effect of ultrasonic induced gap-filling action and capillary action.%采用高速摄影对超声波辅助钎焊镁合金过程熔态钎料的填缝行为进行了实时观察,并研究了不等间隙中钎料的填缝行为及接头性能.结果表明,超声波在钎焊固/液界面传播对钎料填缝行为有显著的影响.钎料在平行于超声波能量传播方向上填缝,填缝长度和超声时间的动力学曲线呈直线型.超声时间相同时,预留间隙越大,钎料的填缝速度越低.在大间隙端加钎料,随超声时间增加,填缝长度减小,钎缝致密性较好；小间隙端加钎料,随超声时间增加,填缝长度先增大后减小,整个钎缝均存在缺陷.认为钎料在不等间隙的流动行为受超声诱导填缝和毛细填缝共同作用的影响.
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