| Magnesium alloys are used as the basis of the wide range of high quality industrial alloy materials, owing to their unique properties such as low density, high specific strength and specific stiffness, good castability and machinability, excellent thermal conductivity and electromagnetic shielding efficiency, and recyclable characteristics, and have recently attracted great attention at home and abroad and is actively developing a new type of environmentally-friendly materials. In aerospace, electronics, automotive, military and other fields of national defense magnesium alloys have wide application prospect and have been called as the most potential for the development and application of "green materials" in the 21st century. However, due to poor welding of magnesium alloy, in using the traditional welding methods, it is easy to produce thermal cracks, pores, alloying elements and the weld zone to soften burning issues, in addition, welding of magnesium alloy and welding technology research less, therefore, the problem of welding of magnesium alloy as a constraint on the wider use of magnesium alloy, one of the important obstacles, has attached great importance to material processing experts around the world. Based on the welding of magnesium alloy is not a long history of the development and still in the initial stage, some of magnesium alloy welding characteristics related issues arised welding are to be further revealed, therefore, to carry out the study has important theoretical and practical significance. In this paper, the weldability of magnesium alloys AZ31B is systematically researched using TIG . The main conclusions are given as follows:(1) The effects of welding parameters on welded joints were systemically analyzed, and have optimized the welding parameters for the 2mm thick AZ31B magnesium alloy, the best welding process parameters are: when no wire is filled, the welding electric current is 90A, welding speed is 8mm/s, argon gas flow is 10L/min, length of welding arc is 1.5mm; when wire is filled, the welding electric current is 100A, welding speed is 6mm / s, argon gas flow is 12L/min, the speed of filling wire is 13mm/s. after added 0.5wt% of the rare earth cerium into AZ31B magnesium alloys, in the cerium-free, the excellent welding parameters are: welding electric current is 95A, the welding speed is 6mm/s, the speed of filling wire is 13mm/s; when add rare earth cerium the excellent welding process parameters were: the welding electric current is 90A, the welding speed is 8mm/s, the speed of filling wire is 9mm/s. Welding slot that added Cerium formed best.(2) Structure feature mechanical properties of magnesium alloy welded joints were were systemically studied, the result is the welding seam structure of magnesium alloy (AZ31B) is small equiaxed grains, and there are some intermittent structures distributing along the grain boundaries which was mainlyα-Mg andβ-Al12Mg17.(3) Adding 0.5% Ce to AZ31B magnesium alloy, researched the weldability of AZ31B +0.5% Ce magnesium alloys, and found n the analysis of its welding seam structure that besides eutectic structure composed ofα-Mg andβ-Al12Mg17 in the AZ31B + 0.5% Ce magnesium alloy welded joints, there are traces of Al4Ce. The microstructure is mostly fine equiaxed grains in weld zone. The grains are bigger in heat affected zone.C ompared to microstructure of magnesium alloy AZ31B ,grains in both weld zone and heat affected zone, rare earth cerium have the role of grain refinement.(4) the best of non-filling wire of AZ31B magnesium alloy welding TIG welding of the maximum tensile strength in the vertical direction of welding joint is 193.33MPa, which account for 73% of that of the mother board(263.45MPa), the best tensile strength along the welding slot direction is 228.38MPa, which account for 83% of that of the mother board(274.17MPa) the best of filling wire of AZ31B magnesium alloy welding TIG welding of the maximum tensile strength in the vertical direction of welding joint is 234.48MPa, which account for 89% of that of the mother board(263.45MPa), the best tensile strength along the welding slot direction is 249.77MPa, which account for 91% of that of the mother board(274.17MPa) The tensile property of the joints of filling wire significantly better than non-filled wire.(5) for welding joint of the AZ31B non-added 0.5%Ce of the magnesium alloy wire-free rare-earth in the best process parameters, the maximum tensile strength under the vertical direction is 246.76MPa, which account for 88% of that of the mother board (279.84MPa), the maximum tensile strength along the direction of welding joint is 275.13MPa, which account for 97%.of that of the mother board(283.35MPa) for welding joint of the AZ31B non-added 0.5%Ce of the magnesium alloy added Ce of rare-earth in the best process parameters, the maximum tensile strength under the vertical direction is 254.65MPa, which account for 91% of that of the mother board (279.84 MPa), the maximum tensile strength along the direction of welding joint is 275.13 MPa, which account for 98%.of that of the mother board(283.35 MPa)(6) Corrosion resistance of AZ31B magnesium alloy TIG welding weld zone is better than base metal, but corrosion resistance of heat affected zone is worse than base metal. After micro-arc oxidation treatment for magnesium alloy AZ31B welded joint, corrosion resistance of weld zone, heat affected zone and base metal has been improved, this is attributed to the protective effect of micro-arc oxidation film . After micro-arc oxidation treatment for magnesium alloy AZ31B+0.5%Ce welded joint, its film organizations are similar to non-rare earth, however, the coating particles in all regsions are smaller. corrosion resistance of weld zone, heat affected zone and base metal is also improved remarkably.
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