Research On TIG-MIG Hybrid Welding Of Magnesium Alloy

In this paper,the TIG-MIG hybrid welding of AZ31 magnesium alloy profile was studied.The weld appearance and microstructure were observed and the mechanical properties were tested.Firstly,the TIG-MIG hybrid welding system which includes the control system and the clamping device for TIG welding torch and MIG welding torch was constructed.Secondly,the relative position of TIG welding torch and MIG welding torch was determined.The position relation of the two welding torches was suitable for this experiment:two welding troches in a straight line,and TIG welding torch in front and the MIG welding torch in rear.TIG welding torch perpendicular to the workpiece,MIG welding torch and TIG welding torch has an included angle of 45 degrees.Thirdly,the influence of process parameters on weld formation was studied.the process parameters include TIG welding current,MIG welding current,MIG welding voltage,welding speed,the center distance of between TIG welding arc and MIG welding arc.An excellent welded joint has been obtained.The tensile strength of welded joints reach 215MPa,which was about 79.63%of the strength of base metal.The fracture type of welded joint was mixed with dimple fracture and cleavage fracture.The hardness of the welded joint was investigated,the average hardness of the weld was 57.78HV,the average hardness of the heat affected zone was 52.81HV,and the average hardness of the base metal was 56.14HV.The microstructure of welded joint was studied.The results show that welded joint constitute of base metal zone,heat affected zone and weld zone.The microstructure of base metal is uniform and the grain is fine.The base metal is mainly composed of α-Mg phase.The microstructure of the heat affected zone is coarse and irregular,and there is a small amount of β-Mg17Al12 intermetallic compound.The weld is fine and uniform equiaxed crystal,which is mainly consists of two parts:a-Mg phase and β-Mg17Al12 intermetallic compound.The β-Mg17Al12 intermetallic compounds of strip and granular are mainly distributed among grain and grain boundaries.At fast,the welded joints of high-speed welding(800mm/min)and low-speed welding(340mm/min)of TIG-MIG hybrid welding were compared.From the comparison of macrostructure,the seam surface scales of high-speed welding was finer and weld width was wider.From the comparison of microstructure,the grain sizes in high-speed welding of the heat affected zone and weld was smaller than the corresponding area of low-speed welding.From the comparison of hardness,the hardness in high-speed welding of heat affected zone and weld was higher than the corresponding area of low-speed welding.