| In this work, as an armor material, B4C/2024 Al composite with 45 vol.% and 55 vol.% B4 C were fabricated through pressure infiltration process, which would reduce the cost and improve the fracture toughness of B4 C armor. The interfacial microstructures of as cast B4C/2024 Al composites were characterized, moreover, the aging hardness, bending strength, fracture toughness, compressive properties under high temperature and high strain rate, the relations between structures and properties under compressive condition were studied. The ballistic performance of B4C/2024 Al composites with two B4 C volume fractions was characterized by pierced remnant law. The effects of target thickness, hardness and fracture toughness of B4C/2024 Al composites on its ballistic performance were discussed. Moreover, the microstructures of composites at the edge and bottom of crater were observed by FIB and TEM.The phase structures of B4C/2024 Al composite were B4 C, Al3 BC, Al2 Cu and Al characterized by XRD. Incoherent interface between B4 C and Al was observed through TEM, and the micro-sized primary phase of Al2 Cu was produced on the surface of B4 C particles. Al3 BC, with rod-like morphology and approximate 500 nm length, was grown towards the Al matrix along the B4C-Al interface [100] Al3 BC.The results of aging hardness test of B4C/2024 Al composites showed that the aging peak was not transparent, and the aging time that reached the highest hardness reduced as the aging temperature increasing: when the aging temperatures were 130℃, 160℃ and 190℃, the aging times were 100 h, 10 h and 3h, respectively. The results observed by TEM showed that the part enrichment of Cu element, resulted from the partial re-dissolution of interfacial precipitation phase Al2 Cu, changed the kinds of precipitated phases: S′ phase and θ′phase precipitated together. The hardness, three point bending strength and fracture toughness of B4C/2024 Al composites after aging treatment were 315, 887 MPa and 21MPa·m1/2。In this work, the optimal aging process was 10 h at temperature of 160℃。The study results of compression test under high temperature and high strain rate showed that B4C/2024 Al composites with 45 vol.% and 55 vol.% B4 C exhibited the same compressive performance: the compressive flow stress at high temperature decreased as the increasing temperature, moreover, the strain rate showed insensitivity or negative sensitivity below 275℃, and positive strain rate showed positive sensitivity up 275℃。Through TEM observation, the microstructures of B4C/2024 Al composites after compression at high temperature showed that: the dynamic recovery and dynamic recrystallization were successively produced in the matrix after static compression at 400 ℃, however, sub-grain structures with large deformation dynamic recovery were produced in matrix, when the compression of composites was carried at high temperature and the strain rate was 1S-1。The protection factors of B4C/2024 Al composites with 45 vol.% and 55 vol.% B4 C were tested using 7.62 mm armor-piercing incendiary and the armored steel was used as backplane, and the values were 3.61 and 3.25 respectively, which would be equivalent to that of B4C+6061Al(backplane). Furthermore, the protective ability of B4C/2024 Al composites with 45 vol.% and 55 vol.% B4 C was tested by armor piercing bullets. The results showed that the crater was produced on the surface of semi-infinite target with 55 vol.% composite, and no broken was emerged, which could resist multi-bullets. Moreover, the TEM observation results showed that micro-deformations were dislocations, micro-cracks and crazing produced in B4 C particles at the bullet hole border, and the deformation laws of composite were the deformation of B4C(polycrystal of B4C) and ultra-fine grains of Al matrix.The observation results of warhead and crater by SEM showed that severe abrasion was produced between the warhead and composites target, which would result in the transfer of B4 C particles to the surface of warhead. The protection factor of composites showed a trend of decline first, and then rise as the increasing of target thickness. The bulletproof mechanisms of B4C/2024 Al composites would be three forms: warhead passivation, elastomer abrasion and energy absorption through plastic deformation. The warhead passivation could take effect for all target thicknesses. The effects of elastomer abrasion on the bulletproof were obvious as the target thickness exceeded 3mm, and increased as the increasing of target thickness between 3-5mm, and the tending towards stability when the thickness exceeded 5mm. The energy absorption through plastic deformation accounted for approximate 10% of bulletproof mechanisms of composites. |
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