Effect of tool design on synergistic improvement of tribological and mechanical properties of AA5083/CeO₂ + hBN hybrid surface composites fabricated via friction stir processing (FSP)

This paper assessed and compared the effect of shoulder shape on microstructural, mechanical and tribological characteristics of AA5083/CeO₂ + hBN hybrid surface composites fabricated via friction stir processing (FSP). For this purpose, a novel tool defined as double step shoulder (DSS) tool was designed. It was found that the dissemination of CeO₂ + hBN particles within the matrix is one of the main reasons for the increment of hardness and thereby the improvement of wear and shear resistance. Results also showed that using the DSS tool during FSP not only can improve surface quality but also increase the material's plastic flow ability, thereby diminishing the chance of the formation of defects in the stirred zone. Attained data also revealed that DSS tool can also lead to better plasticization and further dissemination of CeO₂ and hBN particles within the matrix. An increase in the flowability of materials via a DSS tool also resulted in an improvement in the shear strength of the AA5083/CeO₂ + hBN hybrid surface composite from 159 MPa to about 193 MPa. The combined effect of the DSS tool on reducing the reinforcing particles and grain size not only remarkably improved the friction coefficient of the composites from 0.42 to 0.36 but also enhanced the wear resistance of the composite by eradicating large agglomerations of particles in the matrix.