The Research Of Weldability Of Magnesium Alloy Under Magnetic Field

With the development of industrial technology and urgent needness of energy, lots of countries and researchers pay more attention to the light metal. Magnesium alloy has low mass, high strength-to-weight ratio, high vibration absorptive property, high anti-interference electromagnetic, recyclabe, which adapt the needness of environment protection and energy conservation. Magnesium alloy have gained increasing interest in transportation industries, aerospace and electronics fields. The weld technology is one of most important forming technology. Magnesium alloy is one of new high performance structural material, which will been formed by weld technolgoy. The poor weldabity limit the application of mangesium alloy. Electromagnetic is applied to welding as a new welding technology in recent years. Electromagnetic exhibit the attractive combination of low cost,simple device and action effect explicit on the welded joint.In this paper, AZ31 magnesium alloy whose thickness is 5mm was welded using GTAW under longitudinal magnetic field. The parameters of weld current, magnetic field current and magnetic field frequency were varied during welding. After welding,tensile test,hardmeter,optical microscopy and scanning electron microscopy (SEM)were used to examine the mechnical properties,microstructure and fracture of AZ31 magnesium alloy welded joint. The compositions of phase were researched by XRD and the reason of hor cracking was discussed. More endeavors have been put on investigating the effect of magnetic field and weld current parameters on microstructure and performance of welded joint. The acting machnisum of magntic field on the crystal procedure of liquid welded pool was researched. The relationship between properties and the size, shape and distribution of grain was discovered. At the same time, the influence of electromagnetic stirring on the crack and gas cavity was researched. The main results are as following:1. The optimal value of AZ31 welded jiont using GTAW without magnetic field is obtained when I=70A,whichσb=201.7MPa,85% of base metal,δ=12.18%,ψ=8.4%,hardness is 62.3HV.2. The optimal value of AZ31 welded jiont using GTAW with magnetic field is obtained when IC=2A,f=20Hz,whichσb=213.4MPa,90% of base metal,δ=11.5%,ψ=14.8%,hardness is 76.2HV. 3. The welding arc and molten pool are affected by magnetic field throngh electromagntic stirring. The nucleation of molten bath and the process of crystalline growth will been affected. The temperature field and compnent will be uniform,dissolvability of alloying agent will been increased.The degree of crystallization will been refined,secend phase will been spheriodized and impurity will been purifed by machanical action. The strength and plastic property of welded joint will been improved.