Influence of Elevated Temperature and Stress Ratio on the Fatigue Response of AM60B Magnesium Alloy Md. Nur-Hossain and Farid Taheri (Submitted May 3, 2011; in revised form June 23, 2011) The fatigue response of a high pressure die-cast AM60B Mg alloy is studied at room and elevated tem- peratures. The fatigue tests are conducted with stress ratio of R = 0.1 and frequency of 30 Hz. The main objective is to determine whether elevated temperature would affect the fatigue response of the alloy. In addition, fatigue crack growth characteristics of the alloy is investigated at room temperature. The purpose of this test is to ascertain the capability and accuracy of a finite element approach coupled with the Walker model in assessing the life cycle of the alloy, in consideration of the influence of stress ratio. Keywords AM60B magnesium alloy, fatigue crack growth rate, finite element method, linear elastic fracture mechan- ics, scanning electron microscope, single edge notch tension 1. Introduction Magnesium alloys are increasingly being used in the automobile and light truck industries. Among all other magnesium alloys, cast magnesium alloys are finding incre- mental use in the automotive industry due to their high-specific strength, lower density and excellent castability and machin- ability in comparison to the commonly used metallic materials. As a result, ongoing interest in the use of cast magnesium alloys in the automotive industry has recently triggered substantial research efforts to be focused on characterization of the structural properties of the metals (Ref 1). The increased use of the alloy in various fields demands knowledge about the fatigue properties and fracture response of the alloy. Therefore, before utilization of magnesium alloys in structural applica- tions, the determination of their fatigue lives and crack propagation characteristics at different stress ratios is necessary. Moreover, depending on the application, the environment might play a vital role on the fatigue life cycle of these alloys, since it is well-established that metals fatigue life cycles are markedly affected by changes in their environment (Ref 2). Assessment of fatigue performance, at room or elevated temperatures, is an integral part of the life assessment of any component, especially those employed in automobiles. As the uses of cast magnesium alloys is gaining higher demand in structural and high-temperature applications, the understanding of fatigue response of such cast alloys at elevated temperature becomes more imperative. In this study, AM60B magnesium alloy, which has been characterized as an alloy with outstanding ductility and energy absorbing properties, combined with good strength, light weight, and castability, is considered. Materials, especially those with relatively low fracture toughness, might fail even below their ultimate strength. The failure can be analyzed on the basis of linear elasticity concepts, through the use of the linear elastic fracture mechanics (LEFM) (Ref 3). High strength, light weight metallic alloys, such as those used in aerospace industry, are examples of such materials (Ref 3). By using LEFM, it is possible to make a direct comparison of fatigue crack growth behavior of the engineering components or structures and their counterpart laboratory specimens, using the stress intensity factor (SIF) range, DK (Ref 4). In recent years, some research works have been carried out on characterizing the fatigue response of various die-cast magne- sium alloys (Ref 1, 5). However, the work on high pressure die- cast (HPDC) magnesium alloys has been quite limited. Koch (Ref 6) investigated the fatigue limit of HPDC AM60 magne- sium alloy. Later, Lu et al. (Ref 7, 8) reported the fatigue characterization of HPDC AM60B magnesium alloy at room temperature. However, the above authors did not investigate the fatigue response of the alloy at elevated temperature. Md. Nur-Hossain and Farid Taheri, Department of Civil and Resource Engineering, Dalhousie University, 1360 Barrington Street, Halifax, NS B3J 1Z1, Canada. Contact email: farid.taheri@dal.ca. Nomenclature C P Paris model constant da/dN Crack growth rate K Stress intensity factor DK Stress intensity factor range DK eq Effective stress intensity factor range m p Paris model exponent R Stress ratio c Material parameter r y Yield stress a Ratio between crack length and width of the specimen JMEPEG (2012) 21:1395–1404 ÓASM International DOI: 10.1007/s11665-011-0019-9 1059-9495/$19.00 Journal of Materials Engineering and Performance Volume 21(7) July 2012—1395