The impact toughness of a few selected precipitation hardening aluminium alloys that have potential for vehicle armour applications is reported for the first time. It is observed that although the impact toughness is considerably higher in the solution heat-treated condition, it degrades with artificial ageing. The formation of weak grain boundaries in the artificially aged tempers is the major cause of poor impact toughness in these alloys. The impact toughness of commercially purity aluminium is reported for the first time within the context of the present work.

The changes in texture and microstructure that occur during superplastic deformation (SPD) of a suitably thermo-mechanically processed (TMP) Al alloy AA7010 containing Sc at a temperature and strain rate combination of 475°C, 1.9x10-2s-1 have been examined. It is observed that during the early stages of SPD, there is a significant increase in the Brass {110}<112> component as well as a considerable increase in the S {123}<634> component. Whilst, these components gradually decrease leading to the randomization of texture as the SPD process progresses to larger strains. These results are discussed in terms of the nature of the TMP together with significant variations in the number density of Al3ScxZr1-x dispersoids and percentage recrystallization with strain.

Recent studies have shown that a suitably thermomechanically processed Al-Zn-Mg-Cu-Zr-Sc alloy having an essentially unrecrystallized grain structure may be subjected to superplastic deformation at a temperature and strain rate combination of 475 degrees C, 1.9 x 10(-2) s(-1) to obtain a total elongation of 650%. The present work demonstrates that the utilization of two-step strain rate at 425 degrees C during superplastic deformation of a similarly thermomechanically processed alloy increases the total elongation value to as high as 916%. The beneficial effect of two-step strain rate could further be realized at 350 degrees C to obtain a total elongation of 438%. Using electron backscattered diffraction, the present work provides a systematic assessment of the changes in (i) percentage recrystallization and (ii) recrystallized grain size with percentage elongation in the material superplastically deformed using both one- and two-step strain rates. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The present study examines the superplastic potential of Al-Zn-Mg-Cu-Zr alloy AA 7449. It is demonstrated that the use of a suitable thermomechanical process (TMP) prior to superplastic deformation, together with the use of appropriate combinations of strain rate and temperature during the tensile test, enabled development of grain structures amenable (having an average grain size of <10 μm) to superplastic deformation in this alloy. This yielded as high as 460 pct elongation.

A procedure to estimate the effective elastic moduli and coefficient of thermal expansion (CTE) of particulate-reinforced metal matrix composites (MMCs) using a two-dimensional finite element method is presented. The actual microstructural geometry of the composites with randomly distributed second-phase particles is incorporated in the model. A generalized plane strain technique, realistically to describe the three-dimensional behaviour, is also incorporated in the model. The elastic moduli and the CTE, estimated using this model, agree favourably with the experimental data. The technique is shown to be superior compared to the conventional two-dimensional plane stress and plane strain approximations. Also, the results indicate that the effect of the shape of the randomly distributed second-phase particles on the effective elastic moduli is insignificant. Although the procedure is demonstrated for particulate MMCs, it can be easily extended to many other materials as well.