Microstructure-Property Relations in Fatigue of a Cast A356-T6 Aluminum Alloy

Abstract

The work in this report was a five year effort to foster fundamental advances in microstructureproperty fatigue relations of a cast A356-T6 aluminum alloy. We identified and quantified microstructure-property relations and then developed a mathematical tool for fatigue analysis of a cast A356-T6 aluminum alloy that is used in automotive structural components. We focused on three main areas of research: a wide variety of cyclic experiments in which specimens were examined with scanning electron microscopic imaging, finite element micromechanical modeling, and the development of a macroscale microstructure-property model for fatigue. Collaborations with Lawrence Livermore National Laboratory (LLNL) and Oak Ridge National Laboratory (ORNL) were important to this work. LLNL provided quantitative data for casting pore size, distribution, volume fraction, and nearest neighbor distance using nondestructive methods. ORNL performed solidification modeling of the casting process and provided insight into the silicon particle size, distribution, and volume fraction; the pore size, distribution, volume fraction, and nearest neighbor distance; and the dendrite cell size. EXECUTIVE SUMMARYThe work in this report, performed by Sandia National Laboratories (SNL) in collaboration with Georgia Institute of Technology, was a five year effort to foster fundamental advances in microstructure-property fatigue relations of a cast A356-T6 aluminum alloy. The goal was to identify and quantify microstructure-property relations and then develop mathematical tools for fatigue analysis of a cast A356-T6 aluminum alloy that is used in automotive structural components. This comprehensive experimental-computational fatigue study was conducted in parallel with developing microstructure-property relations for monotonic loading conditions, covered in a companion report (Microstructure-Property Relations for a Cast A356 Aluminum Alloy). We focused on three main areas of research: a wide variety of cyclic experiments in which specimens were examined with scanning electron microscopic imaging, finite element micromechanical modeling, and the development of a macroscale microstructure-property model for fatigue. Collaborations with Lawrence Livermore National Laboratory (LLNL) and Oak Ridge National Laboratory (ORNL) were important to this work. LLNL provided quantitative data for casting pore size, distribution, volume fraction, and nearest neighbor distance using nondestructive methods. ORNL performed solidification modeling of the casting process and provided insight into the silicon particle size, distribution, and volume fraction; the pore size, distribution, volume fraction, and nearest neighbor distance; and the dendrite cell size.The mechanical, physical, and casting properties of this A356 aluminum alloy make it attractive for use in cheaper and lighter engineering components. However, to successfully use cast A356 in long life components, it is necessary to understand its resistance to fatigue. The standard method in determining fa...