Effects of Cellular Growth on Fatigue Life of Directionally Solidified Hypoeutectic Al-Fe Alloys

Al-Fe hypoeutectic alloys are a family of casting alloys characterized by cell growth, low cost and appreciable formability. It is well known that fatigue strength is a requirement of prime importance considering the nature of load typically observed during operations involving the risers used in oil extraction. The aim of this study is to examine the influence of cell size and its intercellular phase distribution on the fatigue life (N-f) of the directionally solidified Al-0.5, 1.0 and 1.5wt% Fe alloys. A water-cooled vertical upward unidirectional solidification system was used to provide the castings. Microscopy light and SEM microscopy were used. It was found that fatigue life decreases as cell spacing (lambda(c)) increases. Smaller cell spacing allows a homogeneous distribution of Al-Fe fibers to happen within the intercellular regions, which tends to improve the mentioned fatigue property. Hall-Petch type correlations [N-f = N-f0+A(lambda(-1/2)(c))-B(lambda(-1)(c)); where A and B are constants] seems to be able to encompass the fatigue life variation along the Al-Fe alloys.