Study On The Welding Of Dissimilar AZ31B Magnesium Alloy And 304 Steel

The joining of dissimilar magnesium alloys to steel is of great industrial significance as it allows design engineers to take advantages of the excellent property sets of both materials. To date, rare reports have been published on joining the two dissimilar metals. Moreover, no reports have been published on the fusion welding of the two dissimilar metals.The dissimilar materials are difficult to weld on their wide difference in physical and mechanical properties. The melting point of magnesium alloy is 650°C and the melting point of steel is 1539°C, so it is difficult for the two metals to melt at the same time and to form a joint. In this paper, dissimilar magnesium alloy and copper were lap welded by TIG welding. During the welding, the magnesium alloy melt but the steel do not, the liquid Mg wetting the solid steel and form the weld joint. The good weld appearance is not obtained because the Mg alloy is heavily oxidized during the process. Magnesium and steel do not mix in the liquid state, Mg atom and Fe atom do not join together with interatomic force at the interface of Mg-Fe and many metallic oxides produced. The shear strength is about 60 MPa.Dissimilar magnesium alloy and copper were lap welded by Laser-TIG hybrid welding, the over-lapped weld joint between Mg alloy and steel could be obtained. Good welding shape was formed, and the weld penetration which determines the mechanical properties of the welded joints is mainly influenced by the laser power. The shear strength is about 90 MPa. The depth of the weld penetration is mainly influenced by the welding parameters. The interface of Mg-Fe is different at the dissimilar welding parameters which are observed by the SEM and EPMA. Mg element diffused into the Fe matrix by form of oxides and reaction, and the two atoms join together with interatomic force when the laser energy density is large; Mg alloy and steel recrystallized separately at the interface of Mg-Fe when the laser energy density is small. The weld fractured at the interfacial region between iron plate and magnesium alloy. Metallic oxides were observed in the interfacial region between iron plate and magnesium alloy. It was the main reason influenced the strength of weld.