The GTAW Of Magnesium Alloy In Longitudinal Magnetic Field

As the third-class metal structural material arising quickly after steel and aluminum, magnesium alloy has an extensive prospect in transport, aerospace and information industry field. Because welding technique is the most conventional method to form structure and the development of magnesium alloy is confined in its bad weldability, making good welding procedure is very important to improve the performance of welding joint on magnesium alloy.Electromagnetism is applied to welding as a new welding technology in recent years. People are very interested in electromagnetism because of its low cost and simple equipment. It is showed in experience that longitudinal magnetic field can give an effective intervention to the shape of arc, flowing of molten bath metal, crystalline and nucleation of molten bath and the process of crystalline growth in welding process. The texture of welding seam is refined, the degree of segregation is reduced, the gas cavity and hot crack is decreased, the quality of welding joint on magnesium alloy is increased.In this paper, AZ31 magnesium alloy is studied on TIG welding with applied longitudinal magnetic field. The effect of the longitudinal magnetic field on formability of welding seam and micro-structure in joint is studied and the relationship between mechanical property of joint and mechanical parameters in different type magnetic fields has been examined systematically. The mechanism for liquid metal in fused bath during solidification by applied longitudinal magnetic field has been discussed intentionally. It shows the relationship between quantities and shape of precipitated phase in welding seam and mechanical property of joint. The main result is obtained as followed:1 Heat input has an obvious effect on mechanical property of joint on magnesium, while the welding current 110A, speed of welding 70 cm/min, gas feed rate 9 I/min is adopt, both the formability and the mechanical property of joint are good for welding 5mm board. 2 At the same magnetic current, double inversion pulse magnetic field is better than constant current magnetic field on property of joint. In the double inversion pulse magnetic field, magnetic frequency has an obvious impact on mechanical property of joint. Tensile strength of joint can increase quickly with magnetic frequency is increased in low frequency, but the property of joint begins to decrease in high frequency because the elastic vibration in fused bath and bad stability on front edge of crystalline.3 In the constant current magnetic field, electromagnetic stirring and electromagnetic damping which magnetic field applied to liquid metal in fused bath make that the relationship between mechanical property of joint and magnetic current are extremals. When the magnetic current is 4A, the tensile strength can reach 215MPa, hardness in welding seam is HB77. The mechanical property of joint is optimum, but both the tensile strength and the hardness of joint decrease when the magnetic current surpasses 4A.