Research On Laser Welding Characeristics Of Mg-Fe With Al As Interlayer And Interface Reaction Mechanism

Mg alloys are widely applied in the fields of automobile and aerospace because oflow density and high specific strength. Laser welding is a welding method with highefficiency. If the Mg-Fe joint can be achieved by laser welding, this structure will beapplied widely in the future because of light weight. For Mg-Fe can’t dissolve in orreact with each other, how to achieve their effective joining is the key point of thisproject.In this paper, pure aluminum was used as the interlayer between Mg sheet and Fesheet. Mg and Fe were welded together through the stitch welding joint. Mg-Fe weldingcharacteristics were studied. The influences of Al interlayer shape and weldingparameters on the welds appearances were analyzed. And then, mechanical propertytests were taken. Finally, the best result was achieved in such conditions: Mg sheet asthe upper one, Fe sheet as the lower one; the thickness of Al interlayer added was2mm,the width was0.2mm; the laser power was set as800W and the welding speed was0.3m/min. In this way, the shear force of the joints could reach1.3kN/cm, which was2.6times that of joints without Al interlayers and the shear strength could be105percent that of AZ31B base materials.With the increase in width of Al interlayers, the shear forces firstly increased andthen decreased. Mg-Fe joints fractured in three modes below in turns: in the lap plane inthe Mg seam; near the melting line in the Mg seam; in the interface between Mg and Fe.More sheet-like Mg-Al phase and dispersive Al-Mn phase appeared in the weldseam with more Al added. Those led to the increase in hardness in the Mg seam, whichreflected the reinforcement effect of phased above. When the Al interlayer was too large,net-like Mg-Al phased appeared. At this time, the brittle fracture in joints would occur.The heat affected zone in the Fe side was a recrystallization region, the grain size ofwhich was finer than that of base materials.The effect of Al adding on the interface reaction was studied, which showed thatthe adding of Al interlayers could promote the reacting in the interface and sew thecrack up. When Al element was added les, the phenomenon of Al concentrationappeared in the interface. Al atoms entered into the crystal structure of Fe. Mg and Feare joined together by Al-Fe solid solution. When Al element was added more, Alatoms in the seam reacted with Fe atoms to form a kind of Al-Fe intermetalliccompound in the interface. With the increase in the width of Al interlayers, someregions in the Al-Fe reacting layer would fracture.