Effect of La on Microstructure, Mechanical Properties and Friction Behavior of In Situ Synthesized TiB2/6061 Composites

In situ synthesized 3 wt.%TiB2/6061 composites with different La contents were fabricated by an Al-K2TiF6-KBF4 system at 850 °C with ball milling and stirring casting. The effects of La content (0 wt.%, 0.1 wt.%, 0.3 wt.%, 0.5 wt.%) on the microstructures and mechanical properties of the composites at room temperature were investigated. The results showed that the addition of La could refine α-Al grains and modify the morphology of TiB2 particles significantly. In 0.3 wt.%La-3 wt.%TiB2/6061 composites, there are chamfering planes on the surface of TiB2 particles, which are caused by the adsorption of La on the {112¯0}, {12¯12} and {101¯1} crystal planes. The values of YS, UTS and EL of the composites with 0.3 wt.% La were 216.8 MPa, 273.0 MPa and 11.2%, which were 69.2%, 34.8% and 5.7% higher than those of the 3 wt.%TiB2/6061 composites. The improvement of mechanical properties was mainly attributed to the grain refinement, distributed particles and transformation of particle morphology. In friction behavior, 0.3 wt.%La-3 wt.%TiB2/6061 composites have the best wear resistance properties with the smallest and shallowest grooves on the surface after wearing. The main mechanisms of the composites are adhesive wear and abrasive wear. In summary, the best content of La addition in 3 wt.%TiB2/6061 composites is 0.3 wt.%.