Effect of mono and hybrid ceramic reinforcement particles on the tribological behavior of the AZ31 matrix surface composites developed by friction stir processing

The effects of the size and morphology of the reinforcement particles on hardness and tribological behaviors of the AZ31 Mg alloy matrix composites were studied. Different ceramic compounds, including boron carbide (B4C), tungsten carbide (WC), and Zirconia (ZrO2) were selected as the reinforcement materials for developing mono composites. The average sizes of the B4C, WC, and ZrO(2 )particles were about 150 mu m 5 mu m and 35 nm, respectively. Besides, hybrid reinforcements composed of the B4C + ZrO2 and WC + ZrO2 powders were employed to develop hybrid composites. All the composite were fabricated using the friction stir processing (FSP) technique. Investigating the microstructure of the composites by secondary electron microscopy (SEM) analysis showed a homogenous distribution of the reinforcement particles in the AZ31 Mg alloy matrix. Microhardness measurements revealed that the hardness of AZ31/ZrO2 nanocomposite is about 120% higher than that of AZ31 base metal. According to the results of the dry sliding wear tests, the AZ31/B4C and AZ31/ZrO(2 )composites had a maximum wear resistance and a minimum friction coefficient average, respectively. Combining the B4C and WC reinforcements with the ZrO2 nanoparticles caused an improvement in wear resistance and friction performances of the hybrid composites. SEM observations of the worn surfaces and debris resulted from wearing of the samples after 500 m sliding distance under the normal load of 10 N, revealed that the severe and mild abrasive mechanisms are dominant.