Papers by Author: Maurizio Ferrante

Abstract: It is well known that the low ductility of nanostructured materials seriously impairs their commercial development. In its turn that mechanical property is associated to the work-hardening behaviour and the vast literature on this relationship is a measure of its importance. This paper presents a short review of the basic models of work-hardening, dealing initially with conventional “coarse” grain metals and alloys, then moving to the behaviour of sub-microcrystalline materials within the bounds of Al alloys and Equal Channel Angular Pressing. Finally, the interrelations of tensile properties, work-hardening behaviour and microstructure are illustrated by data obtained on a precipitation and a non-precipitation hardening Al alloys, namely Al-4%Cu and AA3004. Results show that low temperature aging results in higher strength and high work hardening rate, besides high ductility. The effects of precipitation and of annealing heat treatments are discussed.

Abstract: The present study is an assessment of the effects of precipitation heat treatments on tensile behaviour, work hardening (WH) characteristics and microstructural evolution of an Al-4%Cu alloy deformed by equal channel angular pressing (ECAP). Two ageing temperatures were employed (170 and 100oC) and their effect on strength and WH behaviour was compared with that exerted on the same alloy, but in two different initial conditions: quenched from solution temperature and slowly cooled before anneal. Grain and precipitate sizes of samples deformed by one and four ECAP passes and heat treated as described were measured employing transmission electron microscopy (TEM). It was concluded that the lower ageing temperature gives the best combination of strength and ductility, a high WH rate and, possibly, the smaller grain and precipitate sizes. The relative participation of the various hardening mechanisms to total strength was estimated from tensile tests and hardness measurements.

Abstract: The present work was performed in order to analyze the influence of the outer corner radius (R) of ECAP die channels on the strain field of billets subjected to ECAP deformation in a Φ = 120o die, employing three different methods: (i) physical simulation, consisting of the direct measurement of deformations of a grid inscribed in longitudinally cut mid-planes of ECAPed billets; (ii) numerical simulation employing an explicit finite element code for large displacements and large plastic deformations, and (iii) calculation by the Iwahashi formula. Materials employed were Al-4%Cu and an eutectic Pb-62Sn alloy, and the dependence of shear strain with R was satisfactorily described using the three methods. The experimental method showed a small deviation from the other two, which was explained making use of the corner die formation concept. Similarly, this concept helped to understand the increase of strain heterogeneity with R. Also, it was shown that large corner radii decrease ECAP pressing loads, facilitating deformation of high strength materials. Finally, the data show that the deformation characteristics of the materials here studied do not exert a measurable influence on the shear strain magnitude and distribution.