The ballistic properties of the aluminium alloy AA6070 in different tempers are studied, using target plates of 20 mm thickness in tempers O (annealed), T4 (naturally aged), T6 (peak strength) and T7 (overaged). The stressstrain behaviour of the different tempers was characterised by quasi-static tension tests and was found to vary considerably with temper in regards to strength, strain hardening and ductility. Ballistic impact tests using 7.62 mm APM2 bullets were then carried out, and the ballistic limit velocities were obtained for all tempers. In the material tests it was shown that the O-temper was most ductile and almost no fragmentation took place during the ballistic impact tests. The T6-temper proved to be least ductile, and fragmentation was commonly seen. The experiments show that despite fragmentation, strength is a more important feature than ductility in ballistic impact for this alloy, at least for the given projectile and within the velocity range investigated. A thermoelasticthermoviscoplastic constitutive relation and a ductile fracture criterion were determined for each temper, and finite element analyses were performed using the IMPETUS Afea Solver with fully integrated 3 rd -order 64-node hexahedrons. The numerical simulations predicted the same variation in ballistic limit velocity with respect to temper condition as found in the experiments, but the results were consistently to the conservative side. In addition, analytical calculations using the cylindrical cavity expansion theory (CCET) were carried out. The ballistic limit velocities resulting from these calculations were found to be in good agreement with the experimental data.

A mathematical model to predict the through thickness temperature, strain and strain rate distributions during hot rolling and the subsequent microstructure evolution was developed using the commercial nite element package ABAQUS. Microstructure evolution predictions included the amount of recrystallisation through the thickness of the sheet based on its thermomechanical history during rolling and thermal history after rolling. The equations used to predict the microstructure evolution were based on semiempirical relationships found in the literature for a 5083 aluminium alloy. Validation of the model predictions was done using comprehensive experimental measurements which were conducted using the Corus research multimill, a pilot scale experimental rolling facility, in Ijmuiden, The Netherlands. The results indicate that the through thickness temperature and strain distribution predictions for the rolling operation are reasonable. Hence, the boundary conditions used in the nite element model adequately represent the interface heat transfer and friction conditions. Microstructure predictions using the literature based equations signi cantly underestimate the amount of recrystallisation occurring in the sheet. A sensitivity analysis indicates that the recrystallisation kinetics are extremely sensitive to the tting parameters used in the microstructure equation, and that the gradient in the recrystallisation kinetics is the result of the temperature gradient experienced by the specimen during deformation.A material constant in Garafolo law B constant in Avrami equation C, a, b, c material constants in t 0 . 5 equation C p speci c heat, J K 2 1 d 0 initial grain size, mm h heat transfer coef cient, kW m 2 2 K 2 1 k thermal conductivity, W m 2 1 K 2 1 m material constant in Garafolo law n Avrami exponent P interface pressure, Pa q heat ux, W m 2 2 q . heat released owing to plastic work, W Q activation energy, J mol 2 1 r radial position through work roll, mm R universal gas constant, J mol 2 1 K 2 1 t time, s dt time increment, s T temperature,°C, K W temperature compensated time parameter, s x position along length of strip, mm X V fraction transformed, % y position through thickness of strip, mm Y(t) thickness of strip at time t, mm Z Zener -Hollomon parameter, s 2 1 a material constant in Garafolo law e strain e . strain rate, s 2 1 g ef ciency of conversion of deformationenergy to heat m coef cient of friction r density, kg m 2 3 s ow stress, MPa t shear stress, Pa

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