Effect Of AC Longitudinal Magnetic Field On Properties Of Welded Joint Of AZ91 Magnesium Alloy

Magnesium alloy is known as the green engineering material in twenty-first century, with a small proportion, specific strength and high specific rigidity, good thermal conductivity and cutting, high anti-interference electromagnetic, recyclabe, and a series of unique properties.At present, the research of magnesium alloy is focusing on the casting, especially die-casting technology has become the most mature and widely used technique. But as the material used, magnesium alloy is relative lag, so the welding of magnesium alloy is in-depth study yet. However, as the poor welding of magnesium alloy, such as easy to form pores, cracks, oxide slag, resulting in reduced mechanical properties of welded joints, which restricts the magnesium alloy widely used in structural parts. Electromagnetic is applied to welding as a new welding technology in recent years. Electromagnetic exhibit the attractive combination of action effect explicit on the welded joint.This paper analyses the influence of different technological parameters on the microstructure and mechanical properties of welded joint by orthogonal test. The AZ91 magnesium alloy was welded by introducing longitudinal magnetic field. In the experiment, welding current, magnetic current and magnetic field frequency are adjustable. After welding, the stretching, hardness experiments have been done for samples. optical microscopy and scanning electron microscopy (SEM) were used to examine the mechnical properties, microstructure of welded joint of AZ91 magnesium alloy.The results show that the welding current is one of the main parameter which affected the welding of AZ91 magnesium alloy. With the increase of welding current, penetration depth and width are both increasing. Without magnetic field, when the welding current is 110A, the mechanical properties of welded joint comes to its maximum, whichσb=236.8MPa,δ=5.5%,ψ=13.18%, hardness is 96.38HV. The optimum process parameters of welded joints by orthogonal: welding current is 100A, magnetic field current is 1.5A, magnetic field frequency is 15Hz. The mechanical performance of welded joints areσb=267.2MPa,δ=7.8%,ψ=16.54% and hardness is 109.32HV. The interaction between outside longitudinal magnetic-field, arc and molten pool produces electromagnetic stirring. The electromagnetic stirring can refine crystal grain and improve solubility of alloy element. Alloy elements is more well-distributed so that the weldability of magnesium alloy is improved significantly.