Effect of vertical and horizontal zinc interlayer on material flow, microstructure, and mechanical properties of dissimilar FSW of Al 7075 and Mg AZ31 alloys

The objective of present research work is to improve the joint strength of dissimilar FSW of Al and Mg alloy. The method used for joining Al and Mg alloys is the application of Zn interlayer in different orientations in FSW process. The horizontal orientation of Zn interlayer has been used first time and compared for material mixing and strength with that of without interlayer and vertical Zn interlayer. The result shows that the maximum tensile strength of 126 MPa has been achieved for horizontal Zn interlayer as compared to the 85 MPa in the case of vertical Zn interlayer. It has been observed that cracking occurs when no interlayer was used due to formation of hard and brittle intermetallic compound (IMC) Al12Mg17. The two different types of eutectic structures and one eutectoid structure have been observed in FSW while using vertical Zn interlayer, whereas only one eutectic structure has been observed in case of horizontal Zn interlayer. New major phases identified in these FSW welds are Al5Mg11Zn4, Mg-32(Al,Zn)(49), MgZn, and MgZn2 in place of Al3Mg2 and Al12Mg17 phases. It has been concluded that orientation of Zn interlayer in the horizontal position has improved material flow and better mixing, which provided less hard intermetallic compounds and resulted in improved tensile strength.