Analysis of morphology and microstructure of B4C/2024Al composites after 7.62 mm ballistic impact

• Dislocations and microcrack were found in B4C after impact.
• The protection mechanism was varied with penetration states during impact.
• High density of dislocations were generated in the aluminum matrix.
• Three morphologies were observed: brittle spallings, abrasion and melted areas.

The effects of ballistic impact on morphology and microstructure of B4C/2024Al composites were studied. B4C/2024Al composites with 55% volume fraction of B4C particles were prepared by pressure infiltration method, and the experimental test of ballistic performance of composites was carried out by 7.62 mm armor piercing projectiles. The obvious upsetting of bullet and furrows on bullet tip are generated after bullet impact. Moreover, bared B4C particle distributes uniformly on the bullet surface, indicating that the composites target plays roles of passivation and abrasion on bullet. The protection coefficient of B4C/2024Al composites shows trends of falling, then an upward trend, at last keeping constant as the increasing thicknesses of targets, and could reach up to 2.8. For the composites target with semi-infinite thickness, three kinds of failure morphology are presented at the bullet crater: caving, erosion and melted areas, spreading successively as the increasing depth, which indicates that the interaction between bullets and targets is different at different stage of bullet penetration. Interestingly, the interface bonding of composites keeps well after bullet impact; moreover, no interface de-bonding was observed. High density of dislocation is generated in Al matrix around the interfaces, meanwhile, dislocations and micro-cracks were found in some B4C particles.