Analysis Of Microstructure And Properties Of Magnesium Alloys TIG Welding Technology With Filler Wire

Magnesium alloys have been used widely in structural applications due to their unique properties such as low density, high special strength and rigidity, good dimensional stability, good damping capacity and excellent recycle character et al. Magnesium alloys are also new style materials to be recognized and developed in domestic and foreign countries praised with vive environmental protection materials in 21th Centuries. Welding is an inevitable method with the application of magnesium alloys into structural parts. At present, tungsten inert gas (TIG) welding method is one of the most widely used methods for its advantages of economy and convenience.Because TIG welded joints without filler wire always hold low strength and poor formation, tungsten inert gas welding process with filler wire is inevitable. Focused on the application of magnesium alloy welding materials, this paper researched the preparation process of Mg welding wire and explored the tungsten inert gas welding process with filler wire of magnesium alloys butted plates. Furthermore, the microstructure feature and performance of TIG joint with filler wire and the effects of filler wires' ingredients on microstructure and performance of joints have been researched by modern analysis methods such as optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron probe microanalysis (EPMA) et al. The weldabilities of AZ31, AZ61, AZ91 plates have also been researched. In addition, the effects of microelements Sb, Y and Nd on the microstructure and performance of welded joints have been researched.The results showed that magnesium alloy welding wire can't be fabricated by drawing method as aluminum alloy wire for its poor plasticity, which results in magnesium alloy's close-packed hexagonal lattice and few slip system. In this study, hot-extruding process has been adopted with proper process parameters, and magnesium alloy welding wire has been fabricated successfully. As to welding method, well-formed welded joint has been obtained by determining proper TIG with filler wire process parameters. The microstructure and performance of TIG with filler wire joint revealed, contrasted to that of welded joint by TIG welding without filler wire, that the well-formed welded joints have been obtained, and the width and dimension of coarse grains in heat-affected zone (HAZ) have been reduced, thus the performance of welded joint has been improved. From the analysis of joint welded by different .filler wire, the effect of Al element on AZ31 joint's microstructure and performance is obvious. With the increase of Al content in welding wire, the eutectic phases ( α -Mg+ Mg₁₇Al₁₂) in joint increase and tend to distribute from graininess to discontinuous reticular structure. Strength analysis showed that the joint welded by AZ61 welding wire is the highest. As to AZ61 plates, the composition of welding wire takes less effect on strength of welded joints. And the strength of weldedjoint is only 85-87 % of base metal, which is lower than that of AZ31 joint. The strength of AZ91 joint welded by the similar AZ91 wire is 87.2% of base metal. It indicated that the weldability of AZ61 and AZ91 plates are lower than AZ31 plate.From the analysis of the effect of microelements Sb, Y and Nd on welded joint's microstructure and performance, the addition of Sb element has improved the strength of welded joint. The improvement of strength ascribed to the effects of refined grains and granulated eutectic phases by Sb. The addition of Y and Nd in welded joint took less action of strengthening.