Microstructure and fluidity evolution during recycling of Al–B 4 C metal matrix composites

Abstract

Fluidity of metal matrix composites can greatly influence the recyclability of the material in the conventional ingot metallurgy process. The fluidity evolution of the AA6063–10% B₄C composite in the form of cast billets and extruded plates, as well as the AA1100–16% B₄C composite of cast ingots and rolled sheets was investigated by the vacuum fluidity test. The results showed that the fluidity decline of cast billets was much faster than that of extruded plates. However, the fluidity of both the cast ingots and rolled sheets decreased at the same rate with the holding time. To understand the flow behavior and recyclability of different composites, the microstructure of process materials before and after remelting was examined. The distribution of B₄C particles and their reaction products, as well as the effective volume fraction, were quantitatively characterized. It was found that the fluidity of the extruded material, hence its recyclability, was better than that of the cast material due to a more uniform particle distribution and less particle agglomerates. Contrary to the extruded material, the rolled material did not show any fluidity improvement to the cast material due to damage of the TiB₂ protective layer around the B₄C surfaces during severe rolling deformation.