Fabrication of Surface Metal Matrix Composites Using Friction Stir Processing
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Friction stir processing has been employed to produce metal matrix composites by incorporating reinforcement particles in an Al 5059 matrix. Various particles with sizes from 130 nm to 4.3 um, and different process parameters, were examined to obtain a uniform distribution of particles within the processed region. Mechanical properties (i.e. tensile and microhardness) of the Al 5059 matrix metal matrix composites reinforced with Al2O3, SiC, and B4C were tested and compared. Tensile tests demonstrated increases in yield strength by 20, 32, and 38 percent compared to the matrix alloy for composites containing Al2O3, SiC, and B4C, respectively. The average microhardness value within the stir zone increased from 85 HV in the base material to a maximum of 170 HV in the B4C-reinforced composite. Particle refinement during friction stir processing was more pronounced with micron-sized particles, and virtually insignificant for nano-sized particles. Nano-scale particles seem to be more efficient in increasing the hardness when a similar fraction is used compared to micro-sized particles.