Wear characteristics of surface-hybrid-MMCs layer fabricated on aluminum plate by friction stir processing

Aluminum-base hybrid composites reinforced with mixtures of SiC and Al₂O₃ particles 1.25 μm in average size have been fabricated on an A 1050-H24 aluminum plate by friction stir processing (FSP) and their wear resistance has been investigated as a function of relative weight ratios of the particles. A mixture of SiC and Al₂O₃ powders of different weight ratios was packed into a groove of 3 mm width and 1.5 mm depth cut on the aluminum plate, and covered with an aluminum sheet 2 mm thick. A FSP tool of square probe shape, rotated at a speed of 1500 rpm, was plunged into the plate through the cover sheet and the groove, and moved along the groove at a travelling speed of 1.66 mm/s. After the hybrid composite was fabricated on the Al plate, the homogeneity of the particles distribution inside the Al matrix has been evaluated from the macro/microstructure and hardness distribution. Moreover, the wear characteristics of the resulted hybrid composites were evaluated using a ball-on-disc wear tester at room temperatures at normal loads of 2, 5, and 10 N. As a result, it was found that the reinforcement particles were distributed homogenously inside the nugget zone without any defects except some voids that appeared around the Al₂O₃ particles. The average hardness decreased with increasing the relative content of Al₂O₃ particles. Regarding the wear characteristics, the wear volume losses of the hybrid composites depended on the applied load and the relative ratio of SiC and Al₂O₃ particles. The hybrid composite of 80% SiC + 20% Al₂O₃ showed superior wear resistance to 100% SiC and Al₂O₃ or any other hybrid ratios at a normal load of 5 N, while the wear resistance was insensitive to the reinforcement ceramic type and was very close to the unreinforced FSP sample at a normal load of 10 N.