Abstract: Based on hybrid ultrahigh frequency pulse variable polarity gas tungsten arc welding process of 2219-T87 high strength aluminum alloy,the effect of pulse frequency on weld appearance was analyzed.Experimental results show that the pulse frequency has a great impact on arc characteristics and the molten pool flow behavior,which makes significant changes in the weld width,depth and penetration.When the pulse frequency f_H is less than 60 kHz,the weld width and depth increase with the increase of pulse frequency.The weld penetration is hardly changed with f_H< 35 kHz,while it is considerably improved by at least 34% compared with the conventional variable polarity GTAW process when f_H> 35 kHz.When the pulse frequency reached up to 60 kHz,the weld penetration significantly increases by 60% compared with the conventional variable polarity GTAW process.When the pulse frequency f_H> 65 kHz,the weld width,depth and penetration presented show the downward trend.