Abstract: Al-Mg-Si 6082 alloys with thickness of 3 mm and 10 mm were respectively welded by TIG welding and MIG welding,and the good welded joints without the superficial flaws were obtained.Through the metallographic test to the joints,the type and difference of blowhole in the joints were studied,and the reason for the blowhole difference was analyzed.Through the measurement of ingredient contents of Mg and Si alloying elements,the burning loss rule of Mg and Si by argon arc welding was discovered.The results show that the skin pores,under-shoulder pores,and heart stomal pores are easy to emerge in the weld by MIG welding.The nearer to heat-affected zone the lower the element burning loss is.The most serious burning loss of Mg and Si elements is in the middle of the weld,and the burning loss of Mg is obviously higher than that of Si.The burning rate of Mg and Si elements is inversely proportional to the arc length by MIG welding.