Effect of Tool Rotation Speed on Microstructure and Microhardness of Friction-Stir-Processed Cold-Sprayed SiCp/Al5056 Composite Coating

SiC-particle-reinforced Al5056-matrix composite coatings were deposited onto Al2024 substrates by cold spraying using a powder mixture having 15 vol.% SiC. To investigate the effects of friction stir processing (FSP) parameters on the microstructure and microhardness of the as-sprayed coating, the as-sprayed composite coating was then subjected to FSP using a stir tool having a threaded pin with rotation speed of 600 rpm and 1400 rpm. Results showed that the coatings presented Al and SiC phases before and after FSP treatment, and no other diffraction peaks were detected. Fine grains were produced in the Al5056 matrix due to severe plastic deformation during FSP, and the refined SiC particles exhibited a homogeneous distribution in the FSPed coating. In addition, an evident reduction of porosity (from 0.36% to 0.08% at 600 rpm or 0.09% at 1400 rpm) occurred, and a dramatic size reduction of the reinforcement from 12.5 A mu m to 6.5 A mu m at 600 rpm or 7.0 A mu m at 1400 rpm was achieved. Nevertheless, the microhardness profile presented general softening and a decrease from 143.9 HV to about 110 HV.