Investigation of microstructure and mechanical characteristic of underwater friction stir welding for Aluminum 6061 alloy – Silicon carbide (SiC) metal matrix composite

Abstract

Demand for metal matrix composites (MMCs) is expected to increase in these applications, such as ‎in the aerospace and automotive sectors.  Adequate joining techniques, which are important for ‎structural materials, have not yet been developed for Metal Matrix Composite (MMCs), however.  ‎This work aimed to demonstrate the feasibility of ‎friction stir welding (FSW) and ‎underwater friction stir welding (UFSW) for joining Al 6061/5, Al 6061/10, and Al ‎‎6061/18 wt. %SiC composites have been produced by utilizing reinforce stir casting technique. Two ‎rotational ‎speeds,1000and 1800 rpm, and traverse speed 10mm \ min were examined. Specimen ‎composite plates 10 mm thick have been successfully welded by FSW. For FSW and UFSW, a tool ‎made of high-speed steel (HSS) with a conical pin shape was used. The result revealed that the ‎ultimate tensile strength of the welded joint by FSW and UFSW at rotation speed 1800 rpm for (Al ‎‎6061/18 wt. ‎‎% SiC composites) was 195 MPa and 230 MPa respectively. The ultimate ‎tensile ‎strength of the welded joint by FSW  and UFSW (Al 6061/18 wt.% SiCe composites) was 165 MPa ‎and 180 MPa at rotation speed ‎‎1000 rpm respectively. The microstructural assessment showed that due ‎to larger grain sizes at FSW and UFSW, most of the fractures are located in the thermal ‎mechanically affected zone (TMAZ) adjacent to the weld nugget zone (WNZ). It is observed that in ‎failure, most of the joints show ductile features. As the volume fraction of SiC (18 wt.%) increases, ‎the friction stir welded and underwater friction stir welded efficiency decreases.