Flow response of a severe plastically deformed two-phase zinc-aluminum alloy

A two-phase zinc-aluminum alloy (Zn-8 wt.% Al) has been subjected to severe plastic deformation via equal channel angular extrusion (ECAE). The alloy was successfully extruded at homologous temperatures around 0.5 T-m through various strain paths and magnitudes. Multi-pass ECAE processing following different routes led to the elimination of the as-cast dendritic microstructure and formed a structure of elongated, ribbon-shaped phases. Monotonic tensile tests were conducted at room temperature along the longitudinal axis of the ECAE samples in addition to the directions parallel and perpendicular to the long axis of the elongated hard eutectoid phase particles in order to reveal the effect of microstuctural morphology on the anisotropic flow response. The flow strength levels increased significantly after the first ECAE pass, and then saturated at a slightly higher value after the subsequent passes in route B-C. An average increase of about 50% in ultimate tensile strength and about 100 times increase in elongation to failure were achieved after eight ECAE passes following route B-C, as compared to the as-cast values. Despite the relative chemical homogenization between the hard and soft phases, the size and distribution of the hard phase in the matrix are found to be the dominant factor controlling the flow response of the present two-phase zinc-aluminum alloy after ECAE. The hard phase size, morphology, and distribution were also found to control the anisotropy in the flow strength and elongation to failure of the ECAE processed samples. Notable flow softening with increasing number of ECAE passes, a general observation for the ECAE processed Zn-Al alloys with Al content more than 12%, was lacking in the present alloy which was attributed to the hardening effect of the fine eutectoid particles in the eutectic matrix overcoming the softening effect of deformation-induced chemical homogenization. (C) 2009 Elsevier B.V. All rights reserved.