Fabrication and characterization of hybrid structured Al alloy matrix composites reinforced by high volume fraction of B₄C particles

In the present paper, hybrid structured B₄C particles reinforced Al2024 matrix composites were prepared by the powder metallurgy method. The composites made from 100% mechanical milled composite powders have fracture strength of 670MPa. With the addition of un-milled Al2024 powder increased from 10vol% to 40vol%, the room temperature compression strength decreased from 1115MPa to 739MPa, without any visible plastic deformation. However, when the fraction of un-milled Al2024 powder increased to 50vol%, the compression strength was decreased to 580MPa, while retaining a remarkable fracture strain up to 10%. The microstructures of the composites with different composition were examined by a scanning electron microscope and a transmission electron microscope. The contribution from different strengthening mechanisms was discussed. The hybrid structures are proved to account for the dramatic change of the fracture mechanism of the composites.