Investigation on Modification of NiCrBSi Coatings Deposited on 6061 Aluminum Alloy via Plasma Spraying Using Novel Reverse Friction Stir Processing

In this study, a novel reverse friction stir processing (FSP) was adopted to investigate the effects of multi-pass reverse FSP on the microstructure, microhardness, bonding strength, and tribological properties of NiCrBSi coatings deposited on 6061-T6 aluminum alloy via atmospheric plasma spraying (APS). The results demonstrate that reverse FSP effectively eliminates pores, unmelted particles, and interlamellar defects in the as-sprayed coating without causing mechanical damage to the coating surface inside the processed zone. With an increase in processing passes, a micron-scale diffusion zone forms at the coating/substrate interface, transforming the bonding mechanism from mechanical interlocking to metallurgical bonding. Mechanical property tests reveal that compared with the as-sprayed state, the microhardness and tensile bonding strength of the three-pass FSPed coating are increased by 26.0% and 171.1%, respectively, indicating significantly improved mechanical properties. Tribological tests demonstrate that the main wear mechanism of the as-sprayed coating is severe abrasive wear. After multi-pass FSP, the wear mechanism of the coating transforms into a mixed wear mechanism. Among them, the FSP3 coating exhibits mild abrasive wear accompanied by local adhesive wear.