| Electromagnetic stir welding technique is an efficient method to improve andoptimize the welding process. By adding a magnetic field during the welding process,electromagnetic stir welding can control arc shape, thereby affecting the heating andmelting of base metal, stirring the molten weld pool, and changing its crystallizationconditions, which will lead to the improvement of the welding quality. The presentstudy investigates the TIG welding process of magnesium alloy AZ91whose deeps is5mm under a longitudinal magnetic field, studys the revolution of weld pool under anapplied magnetic field by employing fluid mechanics, and analyzes the influence ofapplied magnetic field intensity, welding speed and welding current on the temperaturefield, velocity field and the evolution process of the weld pool.The numerical model of the weld pool in TIG welding under a longitudinalmagnetic field was developed. using. The temperature field and velocity field of theweld pool in the TIG welded AZ91magnesium alloy was calculated employing theFluent section in ANSYS software. The heat flux density and current density at theanode surface under different magnetic field intensity was fitted into expression andadded into the calculation of the weld pool as boundary conditions and source terms.Calculation results indicate that the maximum temperature decreases, the energydistribution on the welding pool surface become more uniform and the temperaturegradient diminish when the longitudinal magnetic field strength is0-0.05T. With thelongitudinal magnetic field strength increases, the length and width of the weld poolincreases first and then decreases. The maximum length of the weld pool is19.8mmwhen the longitudinal magnetic field strength is0.02T, and the maximum width of thepool is14.4mm when the longitudinal magnetic field strength is0.03T. Under thecondition of welding current200A, welding speed7mm/s and the longitudinal magneticfield strength ranging from0-0.05T, the workpiece can be full penetrated. With thewelding speed increasing, dragging effect of the weld pool is more and more evident,the maximum temperature, the length and width of the pool decreases, and the widthreduce the is more obvious than length reduce. When the weld speed is beyond7mm/s,the weld pool is incomplete penetration, and the depth decreases with the weld speedincreasing. The increase of welding current can improve the maximum temperature andweld pool size significantly, decreasing the temperature gradient behind weld pool and promoting the flowing in the pool. The workpiece is incomplete penetration when theweld current is below200A.Liquid metal in the pool has a high speed rotation on top surface due to attachingelectromagnetic force and surface tension when longitudinal magnetic field is applied,leading to asymmetric and y negative offset in the trail of weld pool. And the offsetdirection is concerned with the direction of applied magnetic field. The positive appliedmagnetic field drive liquid metal rotate clockwise. Plenty of liquid metal accumulate tothe section at positive semi axis y. When the direction of applied magnetic field isnegative, liquid metal will rotate anti-clockwise. And the trial of pool will lean tonegative semi axis y.Under different longitudinal magnetic field strength（B0=0，0.01T，0.02T，0.03T，0.04T，0.05T）, the flowing speed of the liquid metal in weld pool will change. With theincreasing of magnetic field strength, the rotating speed of liquid metal become higher,which promote from0.073mm/s under no magnetic field to0.798mm/s when themagnetic strength is0.05T. When the longitudinal magnetic field strength is0.02T, thearea of weld pool attains its maximum. The trail deflection angle increase with theincrease of magnetic strength. When the magnetic strength is0.05T, the trail deflectionangle could reached20.6°.It has obvious stir effect to the pool. |
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