Materials Science and Engineering A 427 (2006) 255–262 Quantitative fractographic analysis of variability in the tensile ductility of high-pressure die-cast AE44 Mg-alloy S.G. Lee a , G.R. Patel a , A.M. Gokhale a,∗ , A. Sreeranganathan a , M.F. Horstemeyer b a School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0245, USA b Department of Mechanical Engineering, Mississippi State University, Mississippi State, MS 39762, USA Received 4 August 2005; received in revised form 14 April 2006; accepted 24 April 2006 Abstract Cast magnesium alloys often exhibit large variability in fracture related mechanical properties such as ductility and strength. In this contribution, the variability in the tensile ductility of individually cast tensile test specimens of high-pressure die-cast AE44 Mg-alloy is examined at room temperature and at 394 K. Significant specimen-to-specimen variations in the ductility are observed at both temperatures. The variability in the ductility does not quantitatively correlate to the average volume fraction of porosity (or any other microstructural parameters) in the bulk three- dimensional microstructure. The area fraction of porosity measured in the fracture surfaces of the tensile test specimens is much larger than the average volume fraction of the porosity in the corresponding bulk microstructure. Therefore, the fracture path preferentially goes through the regions of highly localized clusters of gas and shrinkage pores. Interestingly, at both test temperatures, the percent tensile ductility e shows a quantitative correlation with the area fraction of the porosity f in the corresponding fracture surfaces, which can be represented by the following simple equation e = e 0 [1 - f] m , where e 0 and m are empirical constants. © 2006 Elsevier B.V. All rights reserved. Keywords: AE44; High-pressure die-cast magnesium alloys; Quantitative fractography 1. Introduction There has been an increasing thrust lately on the development of lightweight cast magnesium alloy components for structural automotive and other applications. Majority of the Mg-alloy castings are made from Mg–Al base (AM series) and Mg–Al–Zn base (AZ series) alloys. AM and AZ series alloys exhibit superior die-castability and a good combination of strength and ductility [1]. These cast Mg-alloys are suitable for structural automotive components such as steering wheels, instruments panels, seat frames, and doorframes that do not experience elevated tem- peratures in service [2,3]. As AM and AZ series alloys do not have adequate high temperature strength and creep resistance above 400 K [4,5], they are not suitable for automotive com- ponents such as gearbox housing, oil pump housing, oil pans, and intake manifolds that operate at elevated temperatures. Con- sequently, cast Mg-alloys that have improved creep resistance and bolt load retention properties are required for such appli- ∗ Corresponding author. Tel.: +1 404 894 2887; fax: +1 404 894 9140. E-mail address: arun.gokhale@mse.gatech.edu (A.M. Gokhale). cations. Addition of rare earth elements (RE) such as Ce and La are known to improve creep resistance and corrosion resis- tance of Mg–Al base alloys [6]. As mischmetal (MM) 1 is an economical way of adding such beneficial alloying elements, AE series of Mg–Al–RE base casting alloys such as AE42 were developed in the 1990s [7]. Recently, Hydro Magnesium devel- oped a new high-pressure die-casting alloy, AE44, which has attractive high temperature mechanical properties, as well as die- castability, and corrosion resistance [8]. The alloy contains 4% Al and 4% MM. AE44 also has good fracture sensitive mechan- ical properties such as ductility and strength. High-pressure die-casting (HPDC) is the preferred manufacturing process for cast Mg-alloy components. Consequently, HPDC AE44 alloy is being considered for structural components such as auto- motive front engine cradle [9]. However, the HPDC Mg-alloys contain considerable amount of micro-porosity [10–12]. Micro- porosity and other casting defects appear to adversely affect the mechanical properties of the HPDC Mg-alloys and may lead 1 A typical MM is a standard grade cerium-based alloy (>50% cerium) with lanthanum (20–35%), neodymium (10–20%), and proesodymium (4–10%). 0921-5093/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2006.04.108