Effect of equal channel angular pressing on microstructural and mechanical properties of as cast Al–20 wt-Zn alloy

Abstract

The microstructural and mechanical properties, mainly the hardness, tensile properties and impact toughness of two phase Al–20 wt-Zn alloy subjected to severe plastic deformation via equal channel angular pressing (ECAP) up to two passes, were studied. High cycle fatigue behaviour of ECAP processed alloy was investigated for the first time. The ECAP almost completely eliminated the as cast dendritic microstructure including casting defects such as microporosities and formed a refined microstructure consisting of elongated microconstituents, aluminium rich α and zinc rich α+η eutectoid phases. As a result of this microstructural change, the tensile response, impact toughness and fatigue performance of the alloy improved significantly. The rates of increase in endurance limit and impact toughness after ECAP are 89 and 122 respectively. In addition, a relationship represented by an equation between the stress amplitude σ_a and number of cycles to failure N values was determined to express the fatigue behaviour of the alloy in all states. It was also observed that the nature of fatigue fracture characteristics of the as cast Al–20 wt-Zn alloy changed after ECAP.