| The application of magnesium alloy has been taken more attention, because country supported the application and industrialization of magnesium alloy. Welding is one of the most important forming methods for fabricating huge and complex magnesium alloy components. But statistics show that 70%～90% weld structure failure is caused by fatigue fracture. So it has important theory significance and reality significance to research the fatigue property of magnesium alloy welding joint and improvement method.AZ61 magnesium alloy was welded by TIG welding with applied longitudinal magnetic field. The effect of magnetic field parameters on the mechanical property and the fatigue endurance of weld joint were studied by the research of microstructure and the feature of fatigue fracture of welding joint. The acting mechanism of magnetic on fatigue endurance was analyzed. Following are the main results:1. According to analysis of experimental data, we found that introducing magnetic field in the welding process, through the effects of electromagnetic stirring making impurities get the ball pool and purification and inhibiting the emergence of the source of fatigue; and the role of electromagnetic stirring made the grain refine to create a large number of small refined grains, improving the whole carrying capacity of welded joints, so that magnesium alloy welded joints fatigue performance has been significantly improved. The average fatigue life in non-magnetic state is 11412 times, for 73 percent of the base casing, the fatigue life in magnetic state is 12983 times, reaching the 83.2 percent of the base casing. The fatigue life of base casing is the highest, reaching to 15614 times.2. Observing the fatigue fracture by scanning electron microscope, continuous clear fatigue striations were not found in the fractures of magnesium alloy welded joints, most areas are composed of small-intensive cleavage stage, fan-shaped fracture patterns, river-like pattern fracture, and dimples and tear prism in many areas. AZ61 magnesium alloy welded joint fatigue fracture is a brittle fracture that the mainly is quasi-cleavage.3. During the magnesium alloy welding process, there will be some defects such as cracks and pores. Hot crack is due to emerging low-melting-point in metal solidification process and controlling the heat input can prevent heat cracks. The most pores of AZ61 weld defects are hydrogen pore. Cutting sources through the material itself and argon adequate protection can prevent the emergence of pores. In addition magnesium alloy welding process is also prone to some defects such as lack of penetration, slag, joint softening.
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