Enhancement of the Fatigue Properties in a Weldable High-Strength Al-Zn-Mg-Mn Alloy by means of Mn-Dispersoid

Abstract

This present research was undertaken to investigate the effects of Mn dispersoids on low cycle fatigue (LCF) and high cycle fatigue (HCF) in the peak aged Al-Zn-Mg-Mn alloy. The Mn addition in an Al-Zn-Mg-Mn alloy was found to form Mn dispersoids in sizes ranging from 0.05 to 0.5 mu m. Mn dispersoids in an Al-Zn-Mg-Mn alloy results in increasing strength without sacrificing ductility by its dispersion hardening effects but at the same time homogeneous deformation. The homogeneous deformation is caused by the cross-slip of dislocations at Mn dispersoids and prevents stress and/or strain concentrations. In this Mn dispersoid containing alloy, both LCF and HCF lives are found to be significantly extended compared with that without any Mn dispersoids. This phenomenon is very interesting and is considered to be due to the simultaneous improvement of strength and ductility by Mn dispersoids. In this investigation, the reason why these excellent properties are observed is discussed in terms of the interaction between Mn dispersoids and the dislocation. (C) 1999 Elsevier Science Ltd. All rights reserved.