Effect of heat treatment on the behavior of an AA7055 aluminum alloy during ballistic impact

Effect of heat treatment on mechanical properties and ballistic resistance of AA 7055 aluminum alloy plates has been studied. Large differences in the static mechanical properties are observed in the plates subjected to three different heat treatment schedules namely under-aging, peak aging and over-aging. The peak-aged plate shows the maximum strength and hardness followed by the under-aged and over-aged plates. The ballistic resistance of these heat treated plates of thicknesses 5 and 10 mm are evaluated by impacting deformable projectiles at a velocity of 820 ± 10 m/s and at a normal angle of attack, by using a thick backing technique. The under-aged and peak-aged materials exhibit similar ballistic penetration resistances which are superior to the over-aged material. Metallographic examination of the impacted plates shows formation of adiabatic shear band (ASB) induced cracks and few transformed ASBs. Peak-aged 7055 aluminum alloy plate shows much improved ballistic properties compared to commercially available 7017 aluminum alloy plate in terms of the depth of penetration.