Abstract: A novel arc welding technique with ultrafast-convert variable polarity square-waveform for aluminum alloys was developed.The influence of variable polarity current converting speed on the porosity and mechanical properties of 2219-T87 weld was studied based on the conventional and ultrafast-convert variable polarity tungsten inert gas(VPTIG) welding techniques,respectively.The experimental results show that compared with the conventional variable polarity welding,weld porosity is obviously improved in the case of the faster current converting speed and less zero-crossing time.The number of gas pore is reduced and eliminated indeed.The tensile strength and percentage elongation of the weld joints are respectively enhanced by 8.97% and 12.6% due to the softening of weld bond area.