Microscopic Structure And Property Of TIG-MIG Welded Joint Of AZ31B Magnesium Alloy

The paper is focus on the research on TIG-MIG welding of AZ31 B magnesium alloy sheet with 2.3mm thickness. The effect of Main parameter( main current, bypass current and welding voltage) are studied in the paper. Yttrium(Y) and carborundum(SiC) are used as activating flux to improve the ability of welding joint. The experiment conducted in accordance with the following steps:First, in order to gain the best welding parameters, different welding experiments are done in different p arameters. Every four groups of experiments are set to research the effect of main current, bypass current and welding voltage. The appearance and size are studied to analyze the effect on morphology of weld layers of the parameters. Then microstructure, composition, microhardness and mechanical performance are researched quantificationally and qualitatively.Second, suspending liquid of yttrium and acetone is smeared on the surface for welding area. Welding experiment is conducted when all of acetone is volatilized. The effect caused by Y is studied by macro and micro analysis to the joints. The best dosage is determined in the end.Third, suspending liquid of silicon carbide and acetone is smeared on the surface for welding area. Welding experiment is conducted when all of acetone is volatilized. The effect caused by SiC is studied by macro and micro analysis to the joints.The results show that, TIG-MIG arc welding process is a suitable high-speed welding process for AZ31 B magnesium alloy sheet. The best parameters of main current(Itotal), bypass current(Ibp)and welding voltage(U) is: Itotal=220A, Ibp=160A, U=22V. Tensile strength of welded joints can be up to 92.5% to it of the base material. The burning of alloying elements occurs in weld zone.Adding Y can affect weld joints. Good shape, refined grains and preferable hardness and tensile strength are obtained in the joint, when the amount is not more than 3.46 mg /cm2. And if the amount continues is increased, there will be a lot of defects and weaken joint performance.SiC particles will play the role of pinning at grain boundaries, and it can become nucleus of bath metal. When the amount does not exceed 5.87 mg/cm2, the joint performance is greatly improved.