Fabrication of metal matrix composites by friction stir processing with different Particles and processing parameters

Friction stir processing has been employed to produce metal matrix composites by incorporating reinforcement particles in an Al 5059 matrix. The fabrication method involved repeated friction stir passes on a groove which contained powder reinforcements, with different processing parameters and tool geometries used for each pass. Various particles with sizes from 130 nm to 4.3 μm, and different process parameters were examined to obtain a uniform distribution of particles within the stir zone. Mechanical properties (i.e. tensile and microhardness) of the Al 5059 matrix MMCs reinforced with Al2O3, SiC, and B4C with particle sizes of 130, 250, and 35 nm respectively were compared. Tensile tests showed 11%, 20%, and 38% increases in yield strength compared to the matrix alloy for composites containing nano-scale Al2O3, SiC, and B4C, respectively. When 4.3 μm Al2O3 particles were employed, higher volume fractions could be achieved which resulted in a 32% increase in yield strength compared to the base metal. 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. Nano-scale particles seem to be more effective to increase hardness by increasing the particle fraction in the produced composites.