In the present study, the mechanical and ballistic properties of friction stir welded(FSW) aluminum alloy(AA5754) samples were investigated, both untreated and cryogenically treated, when impacted by a7.62 mm armour-piercing(AP) bullet at an impact velocity of 682±20 m/s. The FSW technique was used to prepare the welded samples for AA5754, with an axial force of 7 k N, a feed rate of 20 mm/min, and a speed of 1200 rpm. The cryogenic treatments performed after welding, including deep cryogenic treatment(DCT) at-196.C and shallow cryogenic treatment(SCT) at-80.C, for 6 and 72 h, respectively.The microstructure and mechanical characteristics of cryogenically treated and untreated joints were examined. The cryogenic treatment refined the grain size(1.05 μm) and enhanced the microhardness(93Hv). Moreover, DCT-FSW significantly improved the tensile strength(13.93%) and impact strength(8.45%) compared to untreated FSW sample. Additionally, in untreated FSW samples, the fracture behaviour varied: the impact fracture mode primarily exhibited ductile failure, while the tensile fracture exhibited a mixed fracture mode. In contrast, the tensile and impact fracture modes of the DCT-FSW were dominated by a ductile failure mode. The DCT-FSW target demonstrated a lower depth of penetration(DOP) of 31 mm compared to the SCT-FSW and untreated FSW targets. Post-ballistic SEM analysis in the crater region of all three zones revealed the formation of frictional grooves, small cracks, and adiabatic shear bands(ASBs).