Strength-ductility synergic enhancement in friction stir welded AA2024 alloy and copper joints: Unravelling the role of Zn interlayer's thickness

This study aims to justify an appropriate condition for enhancement of strength and ductility trade off in dissimilar friction stir welded joints of AA2024/copper having Zn interlayer with various thicknesses. For this aim, friction stir welding (FSW) was conducted at a rotation rate of 950 rpm, traverse speed of 85 mm/min and with tilt angle of 2°, offset of +2 mm and shoulder plunge depth of 0.05 mm. After FSW, the microstructure and mechanical properties of the joints were examined in detail using optical microscopy, scanning electron microscopy equipped with energy dispersive spectroscopy, X-ray diffraction, and tensile test. The tensile results proved that addition of Zn interlayers results in improvement of strength besides ductility by changing the nature of intermetallic compounds in the joints. Furthermore, the accurate analysis indicated that the optimum thickness of Zn interlayers is 0.2 mm in order to obtain the best mechanical properties. The fracture appeared in the AA2024 part instead of the joint interface and more dimple type surface is appeared after fracture. The detail of different intermetallic compounds formed in the interfacial area of the joints is discussed throughly.