Fabrication of Hybrid Surface Composites AA6061/(B4C + MoS2) via Friction Stir Processing

Poor tribological properties restrict structural applications of aluminum alloys and surface composites of aluminum alloys have gained more attention in material processing. The addition of solid lubricant reinforcement particles along with abrasive ceramics contributes to the enhancement of tribological performance of surface composites. In the present study, the solid-state technique, friction stir processing (FSP) was used to develop mono (B4C) and hybrid (B4C+ MoS2) surface composites in the AA6061-T651 aluminum alloy. The hybrid surface composites were produced by varying an amount of MoS2. Multipass FSP with different direction strategies was adopted for achieving uniform distribution of reinforcement powders in the aluminum matrix. Microstructure analysis showed a uniform dispersal of reinforcement particles without any clustering or agglomeration in the processing zone. Microhardness and wear performance of mono and hybrid composites improved in comparison with the base metal. The mono surface composite exhibited the highest hardness while the hybrid surface composite (75%B4C+ 25%MoS2) achieved the highest wear resistance. This was attributed to the solid lubricant nature of MoS2. Furthermore, dissolution of the strengthening precipitate condition during multipass FSP without reinforcement particles resulted in the reduction of hardness and wear resistance.