Welding joint with sound microstructure and perfect bonding between the weld and AZ91B Mg base alloy can be obtained with AZ61 and AZ91 welding wire by TIG.The microstructure of the weld is composed of snowy α Mg dendrite with developed branches and interdendrite eutectic （α+Mg 17 Al 12 ） with low melting point.The microstructure of bonding zone consists of fine equaixed α Mg and interdendrite eutectic

while the microstructure of heat affected zone is very similar to those of base materials

consisting of coarse α Mg dendrites and interdendrite eutectic （α+Mg 17 Al 12 ）.Due to the super heated vaporization of Mg atom during welding

the Al content and eutectic content in the weld increase

resulting in the increase of hot crack tendency in the weld.In the case of using ERAZ61 wire

the joint consistent with base materials in composition and microstructure exhibits high crack resistance

high tensile strength and elongation.Therefore

taking comprehensive consideration for welding technology and mechanical properties of the jiont

the ER AZ61 welding wire should be selected preferably.