Abstract: The influence of pulse square-wave current frequency on the microstructure and mechanical properties of 2219 high strength aluminum alloy weld joints was investigated based on a novel ultrafast-convert hybrid pulse current variable polarity gas tungsten arc welding technique.The experimental results showed that comparing with no effect of pulse current,the coarse grains changed to fine equiaxed grains.A kind of finer equiaxed non-dentrites was observed distributing in the form of banding at the weld zone while the pulse current frequency was more than 20 kHz.Mechanical properties of weld joints were improved predominantly at the given pulse frequency of 60 kHz,tensile strength and percentage elongation of weld joints are increased by about 17.6% and 66%,respectively,compared to that of weld joints with no effect of pulse current.At the given pulse current amplitude and pulse duty cycle,with the pulse current frequency in certain range increased,the width of fusion zone obviously decreased and the ductility of welds was improved significantly.However,the variation in tensile strength of weld joints was relatively less sensitive with the increase of pulse current frequency.