Ballistic behaviour of spray formed AA7055 aluminum alloy against tungsten core projectile impact

Abstract

AA7055 aluminum alloy has been widely used in aerospace and aircraft industry. The ballistic behaviour of single layered spray formed 7055 aluminum alloy was investigated under two different heat treatment (T6 & T74) against deformable 6 mm tungsten alloy (W-Ni-Fe) core projectile impact (1250 m/s). The effect of ballistic impact on structure and morphology of aluminum alloy substrate was investigated through optical microscopy (OM), scanning electron microscopy (SEM) and x-ray diffraction (XRD). Among interesting results, hard metastable intermetallic compounds (Al12W, Al3Ni2, Cu0.4W0.6) and pores were observed after ballistic impact. These hard metastable intermetallic compounds increase the hardness (above 654 HV) in some effected zones (deformed channels) because of reaction between the bullet particles and target aluminum alloy. Moreover, modification in microstructure and hardness of aluminum alloy target was observed within 2 mm distance from the crater hole. In addition, T74 target material was perforated completely, however, bullet stopped inside the target material at T6 condition resulted in localized material softening effect subsequent to the formation of ASB. Furthermore, before ballistic test, mechanical properties of 7055 aluminium alloy were examined and combination of higher strength (UTS: 723 ± 10 MPa), ductility (14.3%) and hardness (245 HV) were attained at peak aging treatment due to MgZn2 strengthening phase particles. Spray formed target material with hot forging followed by T6 heat treatment showed improved ballistic and mechanical properties as compared to T74 and other conventional forming methods.