Abstract: A novel ultrafast-convert hybrid-pulse square-wave variable polarity arc welding technology for aluminum alloy is developed.Based on the hybrid-pulse variable polarity TIG welding technique,the effect of hybrid-pulse square-wave current frequency on the microstructure and mechanical properties of 5A06 welds is researched.The experimental results show that,compared with no hybrid-pulse current,the weld mechanical properties are decreased when the pulse current frequency is less than 20 kHz.Under the condition of pulse current frequency up to 40 kHz,the size of crystal grains and degree of welds softening are decreased,tensile strength of weld joints is improved obviously.The rates of weld tensile strength and percentage elongation to base metal are 95.8% and 84.8%,respectively.