Abstract: The arc-ultrasonic can be excited by modulating the TIG arc through high frequency.The mechanism of arcultrasonic was analyzed,and the effect of excitation current on pores and tensile strength of the MGH956 alloy joint made with TIG welding process was investigated.Without arc-ultrasonic, when the excitation current was 5 A and 10 A,pores in the weld obviously grew up,although the amount of pores kept almost the same.When the excitation current increased to 20 A and 30 A, the amount of pores decreased.With arc-ultrasonic,the tensile strength of the resultant joint was improved and reached the optimum value 550 MPa,76% of that of base metal,when the excitation current was 20 A.The joints fractured with mixed brittleductile features.