Effect of equal channel angular extrusion on fatigue properties of Zn-60Al and Zn-80Al alloys

Aluminium-rich binary Zn-60Al ve Zn-80Al alloys were produced by permanent mould casting. The as-cast alloys were subjected to equal-channel angular extrusion (ECAE) which is one of the severe plastic deformation techniques. The hardness, strength and ductility values of the alloys in as-cast and ECAE processed conditions were measured. The stress amplitude versus number of cycles to failure (S-N) curves of the alloys in all states were determined by using the rotating bending fatigue machine which is designed and manufactured for this work. In addition, the effects of ECAE parameters such as pass number and processing routes on the mechanical properties especially the fatigue performance of the alloys were investigated. The ECAE almost completely eliminated as-cast dendritic microstructure including casting defects such as micro porosities. A refined microstructure consisting of elongated micro constituents in route A and, more equiaxed and mixed micro-constituents in route-BC formed after multi-pass ECAE. As a result of this microstructural change, the significant improvement was obtained in fatigue performance, strength and ductility of the ECAP processed alloys. While the rate of increase in fatigue endurance limit of the ECAE processed Zn-60Al alloy is approximately 82.5%, in Zn-80Al alloy the rates of increase in endurance limit are approximately 74 % after one pass and 89 % after two passes. It was also observed that the ECAE relatively changed the nature of fatigue fracture characteristics of the as-cast Zn-60Al and Zn-80Al alloys from brittle to a ductile fracture mode.Key Words: Equal-channel angular extrusion (ECAE), Zn-Al alloys, fatigue.