Effect of friction stir processing on microstructural evolution and mechanical properties of nanosized SiC reinforced AA5083 nanocomposites developed by stir casting

Abstract

AA5xxx alloys are widely used for different parts of marine appliances of low to moderate level of strength. However, these alloys are not suitable for high-strength marine parts because of its low mechanical strength, elastic modulus, and weld yield strength. Hence, with an aim to improve performance of these alloys for various high-strength marine components, the present study efforts to develop fine grained AA5083 alloy-based nanocomposites with uniform dispersion of nanosize SiC particles through stir casting followed by microstructural modification using friction stir processing (FSP). AA5083-SiC nanocomposites (1, 2 & 3 wt%) were produced by an indigenously designed bottom pouring stir casting setup reinforced with nanosize SiC (n-SiC, ∼80 nm) particles. Then, FSP was performed with the optimized parameters (1216 rpm rotational speed and 41 mm/min traverse speed) to modify as-cast interdendritic structures of the nanocomposites. Microstructural investigation through optical and electron microscopy (SEM-EBSD, TEM-EDS) confirmed the evolution of fine recrystallized grains with a uniform distribution of n-SiC within the matrix after the FSP. The FSP is found more advantageous to attain better grain refinement (∼50 % more) for the n-SiC reinforced composites as compared to that of the FSPed pure AA5083 alloy. The mechanical properties were found to improve up to 2 wt% reinforcement significantly as compared to the as-cast counterparts. However, because of huge agglomeration of n-SiC particles in the 3 % reinforced composite, it showed inferior mechanical properties. Tensile yield strength (YS) and average hardness were recorded to be 224 MPa and 84 HV, respectively, for the FSPed AA5083–2 wt% n-SiC nanocomposite as compared to the YS-152 MPa, hardness-75 HV for the FSPed AA5083 alloy without any reinforcement. The enhancement in the mechanical performance is attributed to the breakdown of interdendritic microstructure to evolve dynamically recrystallized fine grains (grain boundary strengthening) with uniform distribution of n-SiC particles (dispersion strengthening) and other secondary precipitate phases. Analysis of strengthening mechanisms’ contribution found to be in good agreement with the experimental YS up to 2 % reinforced nanocomposites. Fractography analysis of the tensile samples is found to correlate well in accordance with the tensile properties.