Influence of the Zn interlayer on the mechanical strength, corrosion and microstructural behavior of friction stir-welded 6061-T6 aluminium alloy and AZ61 magnesium alloy dissimilar joints

Abstract

To reduce structural weight, the transportation industry needs to join dissimilar Al and Mg alloys. However, due to their different properties, joining dissimilar materials is much harder than joining identical ones. Brittle intermetallic compounds (IMCs) make it difficult to produce strong Al/Mg joints even with friction stir welding (FSW). Mechanical and corrosion properties are important for joint protection over time. Mg-based alloys corrode preferentially in dissimilar Al/Mg joints due to their lower corrosion potential. Consequently, this study introduces a novel interlayer-based strategy to address this issue. Therefore, this study explored the influence of Zn interlayers on the mechanical properties, microstructure, and corrosion behaviors of Al6061-T6 and AZ61 Mg alloy FSW butt joints. A scanning electron microscope, a transmission electron microscope, X-ray photoelectron spectroscopy, X-Ray diffraction, and an energy dispersive spectrometer were used to observe and characterise the microstructures and IMCs formation at the interface of Al/Mg welded joints. In Zn-added FSW joints, finer and better-distributed Mg-Zn IMCs form in place of the brittle Al-Mg IMCs (multilayered structure) observed in Zn free Al/Mg joints. Moreover, the addition of Zn significantly improved the joints' tensile strength through the proper dispersion and distribution of the zinc interlayer in the weld zone. In this way, a tensile strength of 198.85 MPa was attained, 34.17% greater than a Zn free Al/Mg joint. Furthermore, immersion tests revealed that the weld joints of Al/Mg with Zn are more resistant to corrosion than the joints of Al/Mg, resulting in a 12.78% lessening in weight loss compared with a Zn free joint. The reason for that is the Zn interlayer's ability to reduce the dissimilar metal corrosion amid the base materials.