Effects of ZrB₂ on substructure and wear properties of laser melted in situ ZrB_2p/6061Al composites

Graphical abstract: - Highlights: • Laser beam partly disperses ZrB₂ particle clusters and showing dispersed particles state after matrix solidification. • Laser melting process narrower cellular spacing in composites than AA6061 matrix. • Compared with matrix alloy, crystal orientation near melted layer edge of the composites is almost random duo to heterogeneous nucleation in melt and pinning effect of laser dispersed ZrB₂ nanoparticles at solidification front. • Laser melted layer shows better wear properties than matrix and composite without laser melting. - 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 ZrB_2p/6061Al composite, which includes a series of laser-melted composites with different laser power processed by a 2 kW 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 56 mg under a load of 98 N for 60 min.