Modification of a cold sprayed SiC_p/Al5056 composite coating by friction stir processing

The SiC particles reinforced Al5056 composite coating was deposited onto a pure Al substrate by cold spraying (CS) of a powder mixture having 45 vol.% SiC, and then modified by friction stir processing (FSP) with a threaded stir tool probe aiming to study the changes in microstructure and tribological behavior of the composite coating before and after the FSP treatment. Results showed that the coatings consisted of two phases of Al and SiC, and no other diffraction peaks were detected in FSPed coating. The sizes of reinforcement particles in the FSPed composite coating were substantially refined from 12.2 μm to 4.4 μm due to the severe stir effect of the tool at a rotating speed of 1400 rpm. The refined SiC particles exhibited a homogenous distribution in the FSPed coating. A dramatic increase in microhardness from 92.5 HV to 185.7 HV was observed due to the redistribution and refinement of reinforcements in the FSPed coating. The average coefficients of friction (COF) of the as-sprayed and FSPed coatings were 0.25 and 0.39, respectively. The higher COF of the FSPed coating was the effect of increased microhardness and friction force which originated from the uniformly dispersed SiC particles embedding the matrix.