Acta Metallurgica Slovaca

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Year 2008

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Year 2008 No 3

Fujda M., Kvačkaj T., Vojtko M., Milkovič O.

MECHANICAL PROPERTIES AND FRACTURE SURFACE MORPHOLOGY OF EN AW 2024 ALUMINIUM ALLOY PREPARED BY ECAP

Abstract
The mechanical properties, microstructure and fracture morphology of EN AW 2024 aluminium alloy subjected to heat treatment (solution annealing at 520°C + water quenching or annealing at 400°C + slow cooling), severe plastic deformation (ECAP) and post-ECAP treatment (natural or artificial ageing after ECAP of quenched state) are compared with those of the industrially processed alloy rods in T3 temper (initial state). The heat treated states of alloy were severely deformed at ambient temperature by equal channel angular pressing (ECAP). The ECAP pass of quenched alloy state caused a non-uniform plastic deformation throughout the ECAPed specimens and slip bands with different amount of deformation in microstructure were formed. On the contrary, homogeneous severe plastic deformation was obtained using the double ECAP of annealed alloy state. Formation of ultra-fine subgrains with high dislocation density in intensive deformed microstructure, high strain hardening of alloy and thus an improvement in strength, but degradation of the ductility and notch toughness of analyzed alloy was a result of severe plastic deformation in the ECAP die. Application of the post-ECAP artificial ageing instead of natural ageing slightly improved ductility, strength and notch toughness of ECAPed and aged alloy. Specimens of initial and heat treated alloy states were fractured in ductile manner during tensile or impact test and shows dimple morphology of their fracture surfaces. Fracture surfaces of ECAPed alloy states with a stage character were a result of deformation and fracture process in shear planes. Specimens of alloy states ECAPed after quenching showed a mixed morphology of fracture surfaces which consists of transgranular cleavage facets in the vicinity of irregular multiphase intermetallic particles and dimples of transgranular ductile fracture nucleated at matrix/Mn-rich phase particles interfaces. Specimens fracture surface of alloy states ECAPed after annealing had dimple morphology. It was a result of the voids nucleation at intermetallic particles/matrix interfaces or by irregular multiphase intermetallic particles cracking and its coalescence by deformation and fracture process on the shear plane.

No 3 (2008), p. 331-341