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Magnesium alloy has a wide application foreground in mechanical,chemical,traffic, aerospace,nuclear,industry,petroleum equipment and other fields because of good performance,which is honored as the green engineering materials of 21st century.The world attaches attention to the development of magnesium more and more.Recently,study of high efficiency and energy saving new welding processes has become one hot topic of the international welding fields.Activating TIG welding method as a high efficiency and energy saving new welding processes has used welding stainless steel,carbon steel,nickel-base alloy,titanium alloy and other metal materials.But the good surface and a significant increase in penetration can not be achieved when welding magnesium alloy by A-TIG welding method because of characteristics of magnesium alloy.FZ-TIG welding method is proposed by change the coating method of flux to solve this problem,In the method,a low melting point,low boiling point and low resistivity activating flux is coated on the weld surface center region and a high resistivity activating flux is coated on both sides before the TIG welding.Using AZ31B magnesium alloy as experiment material,using simple substance（Te, Ti,Si）,oxide（SiO2,TiO2,V2O5） and halide（MnCl2,CdCl2,ZnF2） as activating flux,welding the specimen by ac and straight polarity direct current A-TIG welding method.The effect of activating flux and welding method on the penetration,width and tissue of weld is analyzed.The results show that,the four activating flux（CdCl2,MnCl2,ZnF2,Te） are good in increasing the penetration of weld,and the effect of activating flux in increasing the penetration of weld is better with straight polarity direct current than ac A-TIG welding method.According to above results,obtained a better activating flux ingredient（M101） by using uniform design method.Welding magnesium alloy by straight polarity direct current FZ-TIG welding method using M101 and SiO2 as activating flux.The effect of parameters on penetration,width and forming of weld is analyzed.The effect of activating flux on tissue and chemical constituents of weld and welding arc is analyzed.The effect of activating flux on the voltage drop of arc polar region and potential gradient of arc column is analyzed by changing arc length.The effect of activating flux on temperature field is studied by measuring the workpiece surface temperature using thermo-couple. Based on this,the mechanism of activating flux in increasing the penetration of weld is primarily analyzed.
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