Effects of ZrB2 on substructure and wear properties of laser melted in situ ZrB2p/6061Al composites

Abstract

Aluminum matrix composites reinforced by in situ ZrB2 particles were successfully fabricated from an Al-KBF4-K2ZrF6 system via a direct melt reaction. A laser surface melting strategy is used to improve the surface strength of the in situ ZrB2p/6061Al composite, which includes a series of laser-melted composites with different laser power processed by a 2kW YAG laser generator. XRD and EDS results demonstrated the existence of ZrB2 nanoparticles in the composite. After laser melting, the penetration depth of the molten pool increases with increasing power density. OM and SEM analysis indicate that the laser melting process yields narrower cellular spacing of the matrix and partly disperses the ZrB2 particle clusters. Compared with laser-melted matrix alloys, the crystal orientations near the melted layers edge of the composite are almost random due to heterogeneous nucleation in the melt and the pinning effect of laser-dispersed ZrB2 nanoparticles at the solidification front. Wear test results show that the laser melted layer performs better at wear resistance than both the substrate and the matrix AA6061 by measuring wear mass loss. Compared with composite samples prepared without laser melting, the wear mass loss of the laser melted composites decreased from 61 to 56mg under a load of 98N for 60min.