Study On MIG Welding Technology And Property Of Magnesium Alloys

Butt welding experiments on 4mm wrought magnesium alloy have been done by MIG welding process in this thesis. The experiment adopts the method of pulse MIG welding with single wire to analyse how the welding parameters such as current and voltage,frequency,background current,peak current and welding speed influence the size of welding seam. Experiments have been done by choosing proper welding parameters combination on pulse MIG welding with single wire, we can get good shape of welding seam. In the case of choosing square groove and no-gap welding, we can get one-side welding with back formation. On the best technical condition, the average strength of the joint can reach 237MPa,and it is 93% as hard as that of the base metal. On the basis of this, compared with pulse MIG welding with single wire, if adopting tandem MIG welding and increasing 90% average current, we can raise 143% welding speed and further improve the quality of welding. For example, we can get stable welding current, little spatter, good welding seam, average arranging root penetration, and small welding deformation. On the optimum technical condition, the average strength of the joint can reach 240MPa, and it is 93% as hard as that of the base metal. To the 4mm wrought magnesium alloy by MIG welding, the best welding techniques are the following:when adopting pulse MIG welding with single wire, the current is 160A,the voltage is 24.4V,and the welding speed is 70cm/min; when adopting tandem MIG welding, the current of the first wire is 159A and the voltage is 22.0V, the current of the second wire is 51A and the voltage is 23.6V, and the welding speed is 170cm/min.The experiment results show that within certain wire feed rate, the adjusting range of welding current and welding speed is very narrow and it has a great effect on the size of welding seam. The welding current has a direct effect on the stability of the welding process, but the welding speed has a little effect on the welding process and has an obvious effect on the quality of welding. The regulating range of frequency,background current and peak current is fairly wide and it produces a little impact on the size of welding seam and the stability of the welding course.It is mainly primary a (Mg) phase in the welding seam area and the precipitated y (Mg17Al12) phase is mainly distributed over the crystal boundary. The hardness of welding seam is a little higher than that of base metal, and the hardness of HAZ is a little lower than that of base metal. The near area of melting line is the weak part of welding join. There are obvious dimples which have tough broken feature in the fracture of welding join. In addition to welding parameters, stalling the joint and protecting welding seam area are also very important.