一脉一滴的熔滴过渡被广泛认为是脉冲熔化极惰性气体保护焊中最好的过渡形式，通过在方波脉冲的峰值后增加一个后中值脉冲能有效增强熔滴过渡的可控性，提高焊接过程稳定性和焊缝成形效果． 文中利用小波分析仪采集焊接过程瞬时电流电压信号，经过分析得到电流 －电压分布概率和 U-I 图，并将两者与焊缝外观相结合一起综合评定焊接效果．1．2 mm 铝合金 ER4303 焊丝焊接实验表明:在平均电流不变的情况下，采用后中值脉冲波形焊接能明显提高焊缝成形的质量，在焊缝表面形成规整的鱼鳞纹;中值电流取值太小，控制熔滴过渡的作用不明显，只是相当于增加了基值时间;取值太大，相当于增加了峰值时间，焊接过程不稳定;后中值时间太短，能量积累不够，不能控制熔滴过渡;时间太长容易造成熔滴过渡不规则，焊缝的鱼鳞纹消失;后中值电流时间取值在 6 ～10 ms 范围内，取值在强弱脉冲电流平均值左右时，焊接过程稳定，焊缝鱼鳞纹光亮、规整、美观．

“One droplet per pulse”is widely regarded as the best droplet transfer mode for pulsed metal inert gas welding． A peak pulse followed by median pulse in a square wave pulse can enhance the controllability of droplet transfer effectively and improve welding stability as well as seam appearance． In this paper，firstly，instantaneous current and voltage signals were acquired by using a wavelet analyzer． Secondly，current-voltage distribution proba-bility and U-I graphs were obtained by analysis，which were then combined with seam appearance to assess the welding efficiency． Experimental results on 1． 2-mm EＲ4043 aluminum alloy welding wire show that (1) at the same average current，the adoption of median waveform helps improve the welding quality significantly and form uniform scaly ripples on seam surface; (2) too small median current has no obvious effect on droplet transfer，and only an increase of base current is observed; (3) too large median current results in instability of welding process，and only an increase of peak current is observed; (4) if the median time is too short，the accumulated energy is not enough to control droplet transfer; if the median time is too long，irregular droplet transfer appears and scaly ripples disappear; and (5) a backward median time ranging from 6 to 10ms as well as a current value varying around the mean of peak current and base current may result in stable welding process and bright scaly ripples with excellent regularity and good appearance．