Abstract: A double invert variable polarity plasma arc(VPPA) power source based on 16-bit MCU which is used for aluminum alloys is introduced. The mechanics characteristics of VPPA are analyzed. The arc stability, arc energy, the transferring characteristics of the arc pressure and the reliability of VPPA power source as well have been researched. It is found that during the VPPA welding procedure of aluminum alloy, the arc of EN has more effect on force; the arc of EP has more effect on thermal, and to keep the balance of the force and thermal is the sticking point of VPPA. This power source is used to weld aluminum alloy with 15 mm thickness successfully. The conclusions will make sense to the application of the variable polarity plasma arc welding technique in the aerospace industry.

Key words: Aluminum alloy, Arc pressure, VPPA