Study on butt fusion welding characteristics of AZ31B magnesium alloy to steel by hybrid laser-TIG welding with Ni interlayer

Investigations on butt fusion welding characteristics of AZ31B magnesium alloy to steel with Ni interlayer were carried out by utilizing the gradient energy density characteristic of laser-TIG heat source. The tensile strength and microstructure of the joint were examined by electronic tension machine, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results indicated that magnesium alloy can be butt joined to steel by hybrid laser-TIG welding with good Mg/Fe interface by using Ni foil as the interlayer. At the same time, tests showed that a distinct transition zone consisting of Fe, Ni and Al elements forms at the steel side nearby the interface; the microstructure of the joint is mainly composed of α-Mg and a large number of small white particles which are mainly composed of AlNi phase and dispersively distributed. The joint fractures nearby the Mg/Fe interface and the fracture surface shows a typical quasi-cleavage crack. The average of the joint tensile strength is 232 MPa, which is about 90% of the magnesium base metal.