Role of Mg₂Si particles on mechanical, wear, and corrosion behaviors of friction stir welding of AA6061-T6 and Al-Mg₂Si composite

Abstract

This paper investigates the effect of different tool pin morphologies on the inter-mixing capability, microstructure, mechanical properties, corrosion, fracture, and wear behaviors of the dissimilar friction stir welded AA6061-T6 alloy--Al 20wt% Mg 2 Si composite. Grooved shoulder tools with varying pin profiles such as tapered cylindrical, threaded tapered cylindrical, and triangular tapered pins were used for joining the base materials. The parameter combination of 80 mm/min travel speed and 1000 r/min rotation speed (at which no visible flow-induced defect was obtained) was used for this study. Among the pin profiles, the triangular tapered pin produced significantly improved intermingling/inter-material flow, fragmentation, and dispersion of the primary Mg 2 Si particles in the AA6061-T6/Al-Mg 2 Si joint. The triangular tapered tool reduced the average grain sizes of the AA6061 alloy and the Mg 2 Si particles from 18.4 to 4.6 µm and from 115 to 7.5 µm, respectively. Intermetallic phases of Mg 2 Si, AlFe, Al 3.21 Si 0.47 , and Al 0.7 Fe 3 Si 0.3 are formed in the weld nugget of all the AA6061/Al-Mg 2 Si joints. The tensile strengths of the joints fabricated with tapered cylindrical, threaded tapered cylindrical, and triangular tapered tools are 108, 139, and 141 MPa, respectively. Abrasive wear is promoted in the joints fabricated with triangular tapered tool due to the homogeneous dispersion and fragmentation of the inherent hard Mg 2 Si particles. The corrosion attack is dependent on the fragmentation level of the Mg 2 Si phase. Triangular tapered pin tool is recommended for dissimilar Al/composite welding due to favorable tool-induced material flow, dispersion, and fragmentation of reinforcement.