Synergistic Effect of Ex Situ and In Situ Reinforcements on the Dry Reciprocating Wear Behavior of AA6061-B4C Composite Fabricated Using Varying K2TiF6 Flux Content

This study aims to examine the dry reciprocating wear behavior of stir–squeeze cast AA6061-B₄C composites under the synergistic effect of ex situ B₄C particles and in situ formed Al-Ti intermetallic phases due to the use of K₂TiF₆ salt as flux and Mg₂Si precipitates formed after T6 heat treatment process. The K₂TiF₆ flux content in the composites varied between 40 and 100% of a constant B₄C content (6 wt.%). The heat treatment consisted of solutionizing at 540 °C for 8 h, followed by water quenching and then artificially aging at 180 °C for 4 h. While at any applied load, the wear rate decreased with increasing ex situ B₄C particle retention, at applied loads more than 20 N, the wear performance deteriorated due to increased fracture and dislodgement of B₄C particles. In situ Al-Ti intermetallics were more effective in lowering the wear rate at high applied loads. A mechanically mixed layer (MML) consisting of self-lubricating boron oxide and boric acid was formed in composites with high B₄C particle retention, lowering the friction coefficient up to 20 N applied load. However, the friction coefficient increased at a higher applied load of 30 N due to increased peeling off the MML and three-body wear.