The Experimental Research On TIG Welding Process And The Joint Properties Of Wrought Magnesium Alloys

The characteristics and industrial applications of magnesium alloys were summerized in this paper, and the main problems in the welding process of magnesium alloy were analyzed, some welding methods that may be used on magnesium alloys, its procedure factors as well as its updated research results were reviewed, including gas tungsten arc welding, metal inertia gas welding, laser beam welding, electron beam welding, friction welding, resistances pot welding, brazing and so on. Furthermore the forwarding problems to be researched were pointed out.The related issues of gas tungsten arc welding (GTAW / TIG) which is lower-costing and has good prospects for the applications in the manufacturing of magnesium alloy components were investigated. The TIG welding experiments for dissimilar magnesium alloys (ME20M and AZ31) and different thickness magnesium alloy plates were tested. The microstructure was investigated with optical microscopy. Mechanical properties were tested by standard tensile tests on small-scale specimens. Fractography characteristics were observed by scanning electron microscopy (SEM). Chemical components were analized by X-ray diffraction (XRD). Meanwhile, the reasons that causing macroscopical and microcosmic defects (cracks and porosity) , and the prevention measures in the welding process of magnesium alloys were discussed.The results show that: the joints with good surface can be gained under proper matching of TIG welding parameters. The grains in the heat-affected zone (HAZ) are coarse, while in the welded zone are finer. The hardness of welded zone increases due to the finer grains, but decreases in the HAZ. The tensile strength of welded jionts is lower than base metal, which can reach up to 75% of the strength of base metal. Tensile fracture of joints usually occurs in the HAZ, which shows that HAZ is the weak zone in the jionts. The morphology of fracture is ductile and brittle mode. The common welded defects in the joints are oxide slag, porosity, cracks, etc. The occurrence of weld porosity and cracks could be reduced by taking some measures, such as using high current with high welding speed, removing the oxide film, dirt and oil completely before welding, strengthening the protection for welding pool, etc.