Influence of Variation Ambient System on Dissimilar Friction Stir Welding of Al Alloy to Mg Alloy by the Addition of Nanoparticles and Interlayer

In the current study, conventional and underwater friction stir welded aluminum-magnesium joints to decrease heat input and control the formation and morphological properties of brittle intermetallic compounds (IMC) were investigated. The joining was incorporated by Zn interlayer and TiC nanoparticles to the interface of joints by providing a novel groove design on the adjacent side of magnesium to hinder nanoparticle dissipation during the welding process. The implemented rotation speeds were varied within 850-950 rpm under a constant traverse speed of 45 mm/min to achieve optimized joining parameters and sound joints with acceptable metallurgical bonding and mechanical interlocking. It was found that the changing of heat input plays the most significant effect on microstructure evolution, wettability, nanoparticle distribution, and IMC formation (Al3Mg2 and Al12Mg17). The joined sample produced at 950 rpm and 45 mm/min underwater friction stir welding (UWFSW) process reached the best microstructure evolution and mechanical properties. It was shown that the TiC particles play a significant role in the microstructure modification and enhanced mechanical properties of weld samples while the Zn foil interlayer plays a vital on avoiding the formation of Al-Mg IMC phases. Mg-Zn and Mg-Al-Zn IMCs, residual Zn, Al and Mg solid solution were observed as the most common phases in the boarded interfaces instead of the formation of the hard and brittle Al-Mg IMCs. The refinement microstructure, presence of thin IMCs, uniform distribution of nanoparticles, and controlled heat input in the stir zone (SZ) were shown as the fundamental reasons for a noticeable improvement in the mechanical properties of dissimilar weld samples by UWFSW. Also, brittle fracture mode was detected for most joint samples, while relative ductile fracture mode was also observed.